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SUNY College of Environmental Science and Forestry SUNY College of Environmental Science and Forestry
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Dissertations and Theses
12-10-2019
Lignin Thermoplastic Blends: Biorefinery Willow Lignin and Lignin Thermoplastic Blends: Biorefinery Willow Lignin and
Poly(lactic acid) Poly(lactic acid)
Mathew J. Ovadias [email protected]
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Recommended Citation Recommended Citation Ovadias, Mathew J., "Lignin Thermoplastic Blends: Biorefinery Willow Lignin and Poly(lactic acid)" (2019). Dissertations and Theses. 119. https://digitalcommons.esf.edu/etds/119
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LIGNIN THERMOPLASTIC BLENDS:
BIOREFINERY WILLOW LIGNIN
AND POLY(LACTIC ACID)
by
Mathew J. Ovadias
A thesis submitted in partial fulfillment
of the requirements for the Master of Science Degree
State University of New York College of Environmental Science and Forestry
Syracuse, New York December 2019
Department of Paper and Bioprocess Engineering
Approved by:
Biljana Bujanović, Major Professor
Jill Weiss, Chair, Examining Committee
Bandaru Ramarao, Department Chair
S. Scott Shannon, Dean, The Graduate School
Gary M. Scott, Director, Division of Engineering
© 2019
Copyright
M. J. Ovadias
All rights reserved
iii
Acknowledgements First and foremost I must thank my advisor, Dr. Biljana Bujanović, as without her this research would not have come to fruition as her continuous guidance, persistence, and leadership has helped me grow as a researcher, student, and overall person. It is safe to say that I will miss you and our conversations on everything from lignocellulosic biomass to our cultures and those we have experienced to sports (as long as they involve Serbian athletes/teams). To Dr. Chang Geun Yoo – thank you as well for your guidance in this research and in general as your input has played an intricate role, as well as the tremendous amount of work you have put into growing our department. I would also like to thank Dr. Art Stipanovic for help with thermal analysis as well as the subtle sense of humor that is always appreciated. I would like acknowledge the other members of my committee (Dr. Jill Weiss – committee chair and Dr. Gyu Leem – examiner) and all other ESF/SU faculty and staff that I have had the pleasure of interacting with for not only their help with my work throughout this degree but also the seemingly infinite lessons learned. However, a particular thanks is needed for Debbie Dewitt and Lynn Mickinkle who have always been able to help me put things in perspective. I will always appreciate our conversations from over the years. As for my lab mates (Aditi Nagardeolekar, Autumn Elniski, and Prajakta Dongre), thank you for all of your direction and involvement in my research. I also appreciate the efforts of undergraduate researchers (Tristen Santiago, Bryan Gamble, Talon Mahay, and Nick Panico) that have assisted with my experiments. A special thanks to Yunxuan Wang and Dwyer Stuart for not only our friendship but your support as well, both have been invaluable to me. I would also like to recognize all my friends (the Seans, Weston, Cierra, the Colins, Zak, Ben, Chris and all the others from grade school, Walters, ESF, and all stops in between), as I have learned something from all of you and have always cherished our time spent together. Lastly I’d like to thank my family. My parents, for shaping me into the person I am today and their endless support, without which I would be nothing. I cannot even begin to express my gratitude. My girlfriend, Marisa, for sticking with me on this journey and being patient. I can’t wait to see what adventures we will stumble upon together. To my brothers, Mike and Luke, thanks for always staying true to yourselves and being a couple of the best friends I could ask for. Thank you to Nonni, Grampy, Uncle Dave and Aunt Deena for showing me the definition and value of hard work and passion while instilling them into who I am and pushing me to achieve what I am truly capable of. To the rest of my family (Aunt Meryl and Parmy, Uncle Ralph, Duke, Jimmy, Mike, Mark, and all the other Aunts, cousins, and Uncles that would make this list go onto the next page) thank you for doubling down on all the contributions already mentioned above, in addition to filling in any holes there could potentially be. I love you all and appreciate everything you have done for me. All of you make me feel truly blessed for who I am lucky enough to have around me, thank you. This work was funded by the USDA-McIntire-Stennis “Thermoplastic Blends on Biorefinery Lignin” Project.
iv
Table of Contents
List of Tables ............................................................................................................................................... vii
List of Figures ............................................................................................................................................. viii
List of Appendices ........................................................................................................................................ x
Abbreviation Index ...................................................................................................................................... xi
Abstract ......................................................................................................................................................xiii
Introduction .................................................................................................................................................. 1
Objectives .................................................................................................................................................. 4
Recalcitrance and an Overview of LCB Pretreatments ................................................................................ 5
Lignin Valorization: Thermoplastics .......................................................................................................... 14
Experimental .............................................................................................................................................. 28
Materials ................................................................................................................................................. 28
Chemical modification (Acylation) of Lignin .............................................................................................. 29
Acetylation (C2 chain addition) of Lignin ........................................................................................... 29
Acylation of Lignin with Lauroyl Chloride (C12 chain addition) ......................................................... 30
Lignin Purification Processes .................................................................................................................... 31
Alkali Purification of Lignin ................................................................................................................ 31
Hexane Extraction of WFAE ............................................................................................................... 32
Lignin Characterization ............................................................................................................................ 32
Fourier Transform Infrared Spectroscopy (FT-IR) of Lignins ............................................................. 32
v
Hydroxyl Group Content of Lignins - 31P NMR Analysis .................................................................... 33
Differential Scanning Calorimetry (DSC) of Lignins ........................................................................... 34
Thermogravimetric Analysis (TGA) of Lignins ................................................................................... 35
Molecular Weight Distribution of Lignins – Size Exclusion Chromatography (SEC) ......................... 35
Antioxidant Activity (AOA) of Lignins ................................................................................................ 36
UV Absorbance of Lignins .................................................................................................................. 37
Theoretical Calculation of Lignin’s Hansen Solubility Parameters ................................................... 37
Polymer Blend Production ........................................................................................................................ 38
Solvent Casting of Lignin-PLA Blends ................................................................................................. 38
Melt Extrusion of Lignin-PLA Blends .................................................................................................. 39
Characterization of Lignin-PLA Thermoplastic Blends ............................................................................... 40
Light Microscopy – Image Analysis of Lignin-PLA Blends.................................................................. 40
Mechanical Properties of Lignin-PLA Blends – Elongation Tensile Testing ...................................... 40
Differential Scanning Calorimetry (DSC) of Lignin-PLA Blends ......................................................... 41
Thermogravimetric Analysis (TGA) of Lignin-PLA Blends ................................................................. 42
UV Absorbance of Lignin-PLA Blends ................................................................................................. 42
Results & Discussion ................................................................................................................................... 43
Lignin Characterization ............................................................................................................................ 43
Fourier Transform Infrared Spectroscopy (FT-IR) of Lignins ............................................................. 43
Hydroxyl Group Content of Lignins – 31P NMR Analysis ................................................................... 47
vi
Thermal Analysis of Lignins (DSC and TGA) ....................................................................................... 48
Molecular Weight Distribution of Lignins – Size Exclusion Chromatography (SEC) ......................... 52
Antioxidizing Activity (AOA) of Lignins .............................................................................................. 53
UV Absorbance of Lignins .................................................................................................................. 54
Theoretical Calculation of Lignin’s Hansen Solubility Parameters ................................................... 58
Characterization of Lignin-PLA Thermoplastic Blends ............................................................................... 59
Light Microscopy – Image Analysis of Lignin-PLA Blends.................................................................. 59
Thermal Properties of Lignin-PLA Blends (DSC and TGA) ................................................................. 60
Mechanical Properties of Lignin-PLA Blends ..................................................................................... 64
UV Absorbance of Lignin-PLA Blends ................................................................................................. 67
Conclusions ................................................................................................................................................. 68
Future Work................................................................................................................................................ 72
References .................................................................................................................................................. 75
Appendix ..................................................................................................................................................... 90
Curriculum Vitae (CV) ............................................................................................................................... 122
vii
List of Tables
Table 1 - The main types of polysaccharides present in hemicelluloses .................................................... 6
Table 2 - Common lignin bonding structures .............................................................................................. 8
Table 3 - Overview of commonly selected pretreatments ....................................................................... 10
Table 4 - HWE degree of delignification based on species and reactor conditions ................................. 13
Table 5 - Hansen solubility parameters for lignin and commercially available polymers ....................... 23
Table 6 - Overview of lignin esterification from previous literature ........................................................ 25
Table 7 - Characterization of lignins recovered from HWE and standard technical lignins ..................... 27
Table 8 - Chemical compounds utilized during this study ........................................................................ 28
Table 9 - Summary of lignin-PLA blends evaluated ................................................................................... 41
Table 10 - Lignin FT-IR band assignment ................................................................................................... 44
Table 11 - Molecular weight distribution of acylated lignins ................................................................... 52
Table 12 - Hansen solubility parameters of lignins calculated by a group contribution method ........... 58
Table 13 - Summary of lignin-PLA blends thermal properties .................................................................. 61
viii
List of Figures
Figure 1 - Structure of cellulose ................................................................................................................... 5
Figure 2 - Hydroxycinnamyl alcohol precursors of H, G, and S lignin phenylpropanoid units .................. 7
Figure 3 - Typical LCC linkages in LCB........................................................................................................... 9
Figure 4 - Cleavage of LCC and lignin-lignin linkages by hydrothermal pretreatments ........................... 11
Figure 5 - Typical structure of hardwood glucuronoxylan ........................................................................ 12
Figure 6 - Lactic acid polymerization to produce high molecular weight PLA.......................................... 16
Figure 7 - Visual representation of an extruder ........................................................................................ 17
Figure 8 - Proposed mechanisms of PLA photodegradation ..................................................................... 18
Figure 9 - Benzophenone ........................................................................................................................... 19
Figure 10 - Benzotriazole ............................................................................................................................ 19
Figure 11 - Sketch of a typical Hansen solubility parameter sphere ........................................................ 22
Figure 12 - Proposed mechanism of complete acetylation of β-O-4 in lignin .......................................... 29
Figure 13 - Proposed mechanism of complete acylation with lauroyl chloride of β-O-4 in lignin .......... 31
Figure 14 - Phosphitylation mechanism of lignin hydroxyl groups with TMDP ....................................... 33
Figure 15 - Lignin 31P NMR spectrum with TMDP using NHND as the internal standard ........................ 34
Figure 16 - Proposed mechanism of lignin-DPPH reaction ....................................................................... 36
Figure 17 - Films of lignin-PLA blends produced by solvent casting ......................................................... 38
Figure 18 - Dynisco Lab-Mixing Extruder ................................................................................................... 39
Figure 19 - Extruded 1% lignin-PLA blends ................................................................................................ 39
Figure 20 - Load-extension curve of PLA ................................................................................................... 41
Figure 21 - FT-IR spectra of non-acylated lignins studied ......................................................................... 44
Figure 22 - FT-IR spectra of W before and after acylation reactions ........................................................ 45
ix
Figure 23 - Proposed mechanism of lauroyl chloride being converted to lauric acid .............................. 46
Figure 24 - Hydroxyl group content of W, WAc, WFAE, and WFAEH ........................................................ 47
Figure 25 - DSC thermogram of lignins ...................................................................................................... 49
Figure 26 - TGA thermogram of lignins ...................................................................................................... 50
Figure 27 - AOA (IC50) of selected lignins and standard antioxidants ....................................................... 53
Figure 28 - UV absorbance spectra of KL and W in dioxane:water (96:4) ................................................ 54
Figure 29 - Total UV absorbance of lignins from 200-400 nm .................................................................. 56
Figure 30 - Light microscopy images of PLA and 1% lignin-PLA blends .................................................... 59
Figure 31 - DSC thermogram of PLA ........................................................................................................... 62
Figure 32 - Mechanical properties of 1% lignin-PLA blends ...................................................................... 65
Figure 33 - Mechanical properties of lignin-PLA blends with more than 1% lignin ................................. 66
Figure 34 - Total UV absorbance of selected lignin-PLA blends from 200-400 nm .................................. 67
x
List of Appendices
A. Acylation yield data .................................................................................................................. 90
B. Yield from alkali purification of W ............................................................................................. 91
C. Additional FT-IR spectra ............................................................................................................ 92
D. DSC thermograms of lignins ...................................................................................................... 95
E. TGA thermograms of lignins ...................................................................................................... 96
F. UV absorbance spectra of lignins............................................................................................... 97
G. Stefanis group contribution values and examples of HSP calculation .......................................... 98
H. Additional light microscopy images of lignin-PLA blends .......................................................... 100
I. DSC thermograms of lignin-PLA blends .................................................................................... 101
J. TGA thermograms of lignin-PLA blends ................................................................................... 110
K. Raw mechanical properties data from elongation tensile testing ............................................. 116
L. UV absorbance spectra of lignin-PLA blends ............................................................................ 120
xi
Abbreviation Index
Abs: Absorbance units
AOA: Antioxidizing activity
AQ: Anthraquinone
BHT: 3,5-di-tert-butyl-4-hydroxytoluene
CoV: Coefficient of variation
DPPH: 1,1-diphenyl-2-picrylhydrazyl
DSC: Differential scanning calorimetry
δ: The Hildebrand solubility parameter
δd: Hansen solubility parameter representing dispersion forces
δh: Hansen solubility parameter representing hydrogen bonding forces
δp: Hansen solubility parameter representing polar forces
E: Cohesive energy density
Ed: Energies arising from dispersion forces
Eh: Energies arising from hydrogen bonding forces
Ep: Energies arising from polar forces
ESF: State University of New York College of Environmental Science and Forestry
FAC: Fatty acid chloride of lauric acid (lauroyl chloride)
FAE: Fatty acid esterification/esterified
FT-IR: Fourier transform infrared
G-unit: Guaiacyl unit
H-unit: p-hydroxyphenylpropanoid unit 1H NMR: 1Hydrogen nuclear magnetic resonance
HSP: Hansen solubility parameters
HSQC: Heteronuclear single quantum coherence
hv: Light
HWE: Hot-water extraction
HWE W MWL: Milled wood lignin of willow (Salix spp.; Family: Salicaceae) biomass after HWE
IC50: Concentration of antioxidant needed to decrease the initial DPPH• concentration to 50%
KL: Kraft (alkali) lignin purchased from Sigma-Aldrich
LC: Lignocellulosic(s)
LCB: Lignocellulosic biomass
LCC: Lignin-carbohydrate complex
Mn: Number average molecular weight
Mw: Weight average molecular weight
MWL: Milled wood lignin
xii
NHND: N-hydroxy-5-norbornene-2,3-dicarboximide
PBE: The Department of Paper and Bioprocess Engineering
PD: Polydispersity
PEO: Polyethylene oxide
PHA: Polyhydroxyalkanoate
PHB: Polyhydroxybutyrate
PhOH: Free phenolic hydroxyl group(s)
PLA: Polylactic acid
PP: Polypropylene
PS: Polystyrene 31P NMR: 31Phosphorous nuclear magnetic resonance
RA: The Hansen solubility parameter distance between two molecules
S-unit: Syringyl unit
SD: Standard deviation
SEC: Size exclusion chromatography
S/G ratio: Syringyl-to-Guaiacyl ratio
SUNY: State University of New York
Tc: Crystallization temperature
Td: Degradation temperature
Tg: Glass Transition temperature
TGA: Thermogravimetric analysis
THF: Tetrahydrofuran
Tm: Melting temperature
TMDP: 2-chloro-4,4,5,5-tetramethyl-1,3-2-dioxaphospholane
US: United States of America
UV: Ultraviolet light
UVA: Ultraviolet light from 320-400 nm
UVB: Ultraviolet light from 280-319 nm
UVC: Ultraviolet light from 100-279 nm
UV-vis: Ultraviolet and visible light
V: Molar volume of solvent
W: Lignin recovered from the HWE hydrolysate of shrub willow (Salix spp.; Family: Salicaceae)
WAc: Acetylated W
WAP: Alkali purified W
WFAE: Fatty acid esterified W by acylation with lauroyl chloride
WFAEH: WFAE after hexane extraction
3D: Three-dimensional
xiii
Abstract
M. J. Ovadias. Lignin Thermoplastic Blends: Biorefinery Willow Lignin and Poly(lactic acid), 124
pages, 13 tables, 34 figures, 2019. Nature style guide used.
Utilization of lignin for higher-value applications, rather than for energy, is essential in making
future lignocellulosic biorefineries economical. This research will focus on derivatization of
biorefinery lignin for use in thermoplastic blends with biorenewable polylactic acid, PLA. Lignin
was incorporated in PLA blends to improve PLA’s stability and functionality.
Biorefinery lignin recovered from the hot-water extract of shrub willow was subjected to
acetylation (C2) and acylation with lauroyl chloride, a fatty acid chloride (C12). The resulting
lignin esters were synthesized to improve lignin’s compatibility with PLA. Hexane extraction was
proposed to purify the lignin laurate. Lignin esters were characterized and blended with PLA (1-
12% w/w) via lab-scale melt extrusion. The physicochemical properties of lignin-PLA blends
were evaluated. Lignin-PLA blends exhibited an increase in UV absorbance that may be
leveraged in packaging to protect against decomposition of its contents and may also reduce
photodegradation of PLA in numerous applications.
Keywords: Biorefinery lignin, Polylactic acid, Acylation, Thermoplastic blends, Melt extrusion
M. J. Ovadias
Candidate for the degree of Masters of Science, December 2019
Biljana Bujanović, Ph.D.
Department of Paper and Bioprocess Engineering
State University of New York College of Environmental Science and Forestry,
Syracuse, New York
1
Introduction
Petroleum and natural gas are currently manufactured into many fuels, commodity
chemicals, and polymers. Drilling for and refining them, along with the use and disposal of their
products, have led to the pollution of our air, water, and land. Therefore, there is a growing need
to replace traditional petroleum refineries and petrochemicals. Biorefineries, which are
manufacturing facilities that produce a comparable array of bioproducts from biomass, are a
viable option1. Lignocellulosic biomass (LCB) represents a great opportunity to replace petroleum
and other fossil fuels while taking advantage of carbohydrates that do not affect the global food
supply. In addition, lignocellulosics tend to be less resource intensive than food crops like corn,
making LCB relatively low-cost feedstocks2.
Recent investments in infrastructure and related technologies have demonstrated the
efforts being made to replace petroleum refineries with lignocellulosic (LC) biorefineries.
Locally, in January of 2019, Attis Innovations announced their agreement to purchase the corn
ethanol plant in Volney, New York3. Attis has positioned itself to leverage underutilized LC
feedstocks through a patented process and agreement with Novozymes for cellulosic enzymes4.
LCB is a composite material, primarily made up of cellulose, hemicelluloses, and lignin.
While cellulose is the most utilized, Attis also plans to produce high-value products from the
other major components in LCB (hemicelluloses and lignin streams)3,4. Even though LCB has
appealing properties as a biorefinery feedstock, it also features some drawbacks. In addition to
being heterogeneous, this composite material is recalcitrant to chemical and physical
manipulation, making the separation of the constituting components challenging5. The
recalcitrant nature of LCB requires the employment of pretreatments to overcome these
2
challenges. The purpose of pretreatment is to specifically manipulate the “physical features and
chemical composition/structure” of LCB, making its individual components more accessible6.
Carbohydrates from LCB, cellulose and hemicelluloses, typically make up 31-52% w/w
and 11-34% w/w5,6, respectively. Cellulose and hemicelluloses can be converted into a wide
range of products7. However, the next largest constituent of LCB is lignin, 12-33% w/w, the
most abundant aromatic polymer on earth5,6. Currently, lignin is mainly produced as a
byproduct in pulp and integrated paper mills. More than 95% of this lignin is burned for low-
value energy during the chemical regeneration process in pulp mills; dominantly in the kraft
pulp industry8. With the potential growth of LC biorefineries, the amount of available processed
lignin will only grow. As a result, the development of value-added lignin-based products will
play a vital role in attempts to boost the economic viability of LC biorefineries9. Potential
applications and uses of lignin in biobased materials (e.g. plastics, composites, and carbon
fibers) aim to utilize lignin in its polymer form, or as it is recovered from various industrial
processes9. Chemical modification has been explored as a means to enhance lignin’s properties
when utilized in biobased materials10,11. Fuels and chemicals may also be produced from lignin.
However, this requires lignin depolymerization or upgrading which tend to be energy and
resource intensive9.
The goal of this research is to assess the use of lignin from a potential biorefinery as a
thermoplastic material, through chemical modification, in blends with commercially available
polymers. Lignin has been shown to have UV absorbing12 and radical quenching properties13–15.
In this research lignin recovered from the hydrolysate of a biorefinery pretreatment process,
known as hot-water extraction (HWE), was utilized. Lignin recovered from HWE of a commercial
3
mix of willow (Salix spp.; Family: Salicaceae) cultivars was selected as the starting material.
Details of the selection process will be explained as a part of the introductory work done on this
topic.
This research will focus on the properties of polymer blends composed of poly(lactic
acid) and lignin-ester derivatives. PLA, as one of the most prominent biorefinery products, was
specifically chosen in an effort to produce a 100% biobased polymer blend. The resulting blends
are intended to have equal or improved thermal and mechanical properties with expanded
functionality from the UV absorbing and antioxidant properties of lignin. This could reduce
photodegradation of PLA from UV irradiation and the subsequent generation of free radicals16.
In food packaging applications it is specifically important to protect the contents from UV-vis
light irradiation. Proteins, fats and vitamins are the main constituents of food susceptible to
photodegradation. This can lead to changes in flavor and color, in addition to nutritional loss17.
Currently utilized UV absorbers in plastic food packaging include benzophenones and
benzotriazoles18. These synthetic UV absorbers have been recognized as contaminants of
emerging concerns and are known to have adverse short and long-term effects on aquatic life19.
In an effort to address the problems that have, so far, been briefly introduced and to
guide this research a set of objectives have been laid out below. These objectives establish the
need to select a lignin source, evaluate the impact of lignin modification on the properties of
the lignin and lignin-PLA blends.
4
Objectives
Select lignin recovered from the hydrolysate of HWE (Willow, Miscanthus, and Wheat
straw) for use in the thermoplastics, based on previously determined molecular weight
distribution20 and hydroxyl group content measured by the Oak Ridge National
Laboratory, and preliminary acylation studies.
Produce lignin esters via two different acylation reactions that vary in chain length
addition (C2 and C12). Subsequently, analyze the hydroxyl group content (effectiveness
of acylation), thermal properties, molecular weight distribution, antioxidizing activity,
and UV absorbance of these lignin esters and of lignin prior to acylation, to assess the
impact of acylation. Additionally, compare the properties of the acetylated lignin and
the lignin laurate to determine the effect of chain length being added, C2 vs. C12 on
these properties.
Evaluate the impact of impurities and whether there is a need for purified lignin in
thermoplastic blends. PLA has been selected to be blended with lignin since it is the
most commonly used biorenewable polymer across a number of applications. PLA is also
known to be susceptible to UV photodegradation while also transmitting UV light.
Compare the effectiveness of different methods (solvent casting and melt extrusion) for
producing lignin-PLA thermoplastic blends.
Utilize lignin before and after acylation in lignin-PLA thermoplastic blends at 1% lignin
concentration.
Compare these blends under light microscopy and select the lignin, exhibiting the least
miscibility in PLA, to be utilized in blends with lignin concentrations greater than 1%.
5
Blends will be produced with the chosen lignin at higher concentrations (up to 12% due
to limitations of the method utilized to coat PLA pellets with lignin).
Characterize pure PLA and lignin-PLA thermoplastic blends (UV absorbance, thermal and
mechanical properties).
Identify future work with regard to chemical modification of lignin and lignin-
thermoplastic blends; as well as other potential applications of acylated lignins for other
higher-value lignin based products.
Recalcitrance and an Overview of LCB Pretreatments
LCB is made up of three major constituents; cellulose, hemicelluloses, and lignin.
Cellulose is a linear homopolysaccharide of β-D-glucopyranose units linked by 1→4 glycosidic
bonds with the structure shown in Figure 121. The homopolysaccharide nature of cellulose, the
most abundant biopolymer on earth, facilitates fermentation upon the release of a single
monosaccharide, glucose. This makes cellulose the preferred constituent of LCB for
fermentation processes to produce a variety of biofuels, bioplastics, and biochemicals. During
biosynthesis the individual chains of cellulose form bundles, elementary fibrils, through
intramolecular and intermolecular hydrogen bonding. In conjunction with the structural
homogeneity, the high level of hydrogen bonding also leads to the formation of crystalline
Figure 1 - Structure of cellulose
6
regions of cellulose that are particularly resilient to deconstruction. Elementary fibrils associate
with each other to form microfibrils which are the building blocks for LC fibers5.
Other types of polysaccharides in LCB, hemicelluloses, are branched
heteropolysaccharides that have varying monosaccharide composition. Within a single LC
species, there are multiple types of hemicelluloses present. However, the greatest variation is
typically observed between groups of LCs, gymnosperms, for instance softwoods, and
angiosperms, such as hardwoods and monocotyledons22. The specific hemicelluloses present in
each type of LCB are outlined in Table 1. Due to the branched and heterogeneous nature of
hemicelluloses no crystal regions are formed. While hemicelluloses represent an abundant
source of sugars but their heterogeneity is a drawback. The heterogeneity of hemicelluloses
present the need for more complex processes (than for cellulose) to completely hydrolyze and
utilize a majority of these sugars.
Table 1 - The main types of polysaccharides present in hemicelluloses22
Adapted from Peng et al. (2012)
Polysaccharide LCB of Origin
Amount in Dry LCB (%)
Units Degree of Polymerization Backbone Side Chains Linkages
Arabinogalactan Softwoods 5-35 β-D-Galp
β-D-Galp β-(16)
100-600 α-L-Araf α-(13)
β-L-Arap β-(13)
Galactoglucomannan Softwoods 10-25 β-D-Manp β-D-Galp α-(13)
40-100 β-D-Glcp Acetyl -
Glucomannan Hardwoods 2-5 β-D-Manp
- - 40-70 β-D-Glcp
Glucuronoxylan Hardwoods 15-30 β-D-Xylp 4-O-Me-
α-D-GlcpA α-(12)
100-200
Acetyl -
Arabinoglucuronoxylan Softwoods
and Grasses 5-10 β-D-Xylp
4-O-Me- α-D-GlcpA
α-(12)
50-185
α-L-Araf α-(13)
Glucuronoarabinoxylan Grasses 15-30 β-D-Xylp
α-L-Araf α-(12)
4-O-Me- α-D-GlcpA
α-(13)
Acetyl -
7
The most underutilized constituent of LCB is lignin, which is a polymer with a unique
amorphous phenolic structure. It is estimated that the annual global lignin production exceeds
70 million tons, while about 95% of this amount is burned11. Lignin is comprised of
phenylpropanoid units. The three main lignin units, p-hydroxyphenylpropanoid-units (H-units),
guaiacyl-units (G-units), and syringyl-units (S-units), vary in their degree of methoxylation23
(Figure 2). The ratio of these three units varies in different types of LCB. Phenylpropanoid units
are linked through multiple potential bonding structures in lignin (Table 2)24. The variation of H-
, G-, and S-units impacts the frequency of each bonding structure, which is mainly dependent
on the methoxylation state of C3 and C5 of the phenylpropanoid units. If these positions are not
methoxylated, they will be available for polymerization. Monocotyledons such as grasses (e.g.
Miscanthus spp.) and agricultural residues (e.g. Triticum spp., wheat straw) have lignin with a
relatively higher concentration of H-units (up to 15%) along with S- and the dominant G-units.
Lignin in hardwood species contains a negligible amount of H-units and is composed almost
exclusively of G- and S-units. Meanwhile, softwoods have lignin comprised of more than 90% G-
Figure 2 - Hydroxycinnamyl alcohol precursors of H, G, and S lignin phenylpropanoid units
8
units and some H-units, but rarely S-units25. Other more uncommon units, such as cinnamyl
alcohols (e.g. coniferyl, sinapyl, and p-coumaryl alcohols), benzaldehydes (e.g. p-
hydroxybenzaldehyde, vanillin, and syringaldehyde), and cinnamic acids (e.g. p-coumaric and
ferulic acids), may be present and vary between species. Willow lignin specifically is known to
also contain p-hydroxybenzoate units26.
Table 2 - Common lignin bonding structures5,24
Images adapted from Ralph et al. (2004) Major Structural Units of Lignin Name of Dimer Structure Linkage(s)
Arylglycerol-β-aryl ether β-O-4
Phenylcoumaran β-5
α-O-4
Resinol β-β
α-O-γ γ-O-α
Biphenyl 5-5
Diaryl ether 4-O-5
Dibenzodioxocin β-O-4 α-O-4
5-5
9
Lignin is part of a complicated matrix with carbohydrates, bridged to hemicelluloses
through covalent linkages which form a networking structure, known as a lignin-carbohydrate
complex (LCC) (Figure 3)27. The LCC has been considered as one of the critical contributors to
the recalcitrance of LCB5. The heterogeneity of lignin’s structure within various tissues in a
single plant (e.g. lignin in middle lamella vs primary wall vs secondary wall; fibers vs vessels)5 is
another contributing factor to the recalcitrance of LCs. Additionally, variation of lignin’s
structure between plants of the same species grown in varying conditions and between
different species makes processing in LC biorefineries even more difficult and complex.
The recalcitrance of LCB may be considered to result from the combined effects of its
composite structure formed by the three major constituents, reinforced by LCC linkages, and
the difficulties related to the crystallinity of cellulose and heterogeneity of lignin. In order to
overcome this intrinsic recalcitrance, LC biorefineries will need to employ pretreatments to aid
in the deconstruction and separation of the LCB constituents. In addition, it is important to note
that some methods may alter or damage the constituents6. While there are several types of
proposed pretreatments, this section will introduce selected pretreatments that have been
recognized in literature as the most promising methods being developed6. These include dilute
acid, alkaline (lime and ammonia fiber explosion), and hydrothermal (liquid hot water and
steam explosion) pretreatments (Table 3).
Figure 3 - Typical LCC linkages in LCB27
10
Table 3 - Overview of commonly selected pretreatments
Hydrothermal pretreatments are of particular interest for potential LC biorefineries
envisioned to utilize all constituents as high-value product streams. Hydrothermal
pretreatments (liquid hot water) based on autohydrolysis aid LCB deconstruction through a
substantial removal of hemicelluloses (e.g. xylans). Autohydrolysis in these processes is
performed without a strong impact on lignin’s structure and with limited production of
fermentation inhibitors, such as sugar degradation products (e.g. furfural and
hydroxymethylfurfural). This allows for more efficient and complete utilization of all
carbohydrates and lignin. Steam explosion, being more aggressive than liquid hot water, is
more likely to degrade hemicelluloses and form inhibitory compounds29. During autohydrolysis
xylans are deacetylated, releasing acetic acid and causing the pH to drop, producing mildly
acidic conditions30. Subsequently, xylans are depolymerized by cleavage of the glycosidic
linkages catalyzed by hydronium cations31. A similar, but slower31, attack is executed on ether
Pretreatment Hemicelluloses
Removed28
Lignin
Removed28
Alters Lignin
Structure28 Positives29 Negatives29
Alkaline Moderate
amounts Yes
Major
Impact
-Limited sugar degradation
compared with dilute acid -Lignin degradation
Dilute acid Yes No Major
Impact
-Hydrolyzes hemicelluloses
into fermentable sugars
-High saccharification yield
of cellulose
-May lead to the
production of
fermentation
inhibitors
Hydrothermal Yes Moderate
amounts
Minor
Impact
-Avoids formation of
fermentation inhibitors
-Limited impact to lignin
-Less aggressive
deconstruction
method
11
(benzyl ether) and phenyl glycosidic LCC linkages between lignin and xylans, as well as on the
ether linkages between lignin units, most readily benzyl aryl ether bonds, α-O-4 bonds,
followed by the cleavage of β-O-4 bonds (Figure 4). In Figure 4, displaying ether linkage
cleavage, routes 1 and 2 are results of acidolysis, which is common in more aggressive dilute
acid pretreatments, while autohydrolysis is almost exclusively represented by route 332.
Liquid hot water pretreatments are particularly attractive due to low corrosivity, leading
to moderate equipment costs compared to other pretreatments. Reduced concentration of
degradation products compared to other more aggressive pretreatments and the high
pentosan (i.e. xylan) removal are also benefits associated with liquid hot water pretreatments.
This pretreatment has been explored at temperatures ranging from 160-240 °C29. Studies
performed at the Department of Paper and Bioprocess Engineering (PBE) at SUNY College of
Figure 4 - Cleavage of LCC and lignin-lignin linkages by hydrothermal pretreatments32
Adapted from Li & Gellerstedt (2008)
12
Environmental Science and Forestry (ESF) have indicated that preferential liquid hot water
pretreatment conditions for a multi-product biorefinery based on xylan-rich angiosperms would
be 160-170 °C for 2 hours33. This process has been patented by Applied Biorefinery Sciences,
LLC as hot-water extraction (HWE) to remove a majority of hemicelluloses, specifically xylans in
angiosperms34 (Figure 5). A portion of lignin as a byproduct of this pretreatment may be
recovered from the hydrolysate after acidification of the hydrolysate35.
HWE has been employed on various angiosperms (hardwoods, agricultural residues, and
grasses) and experiments have been scaled-up from a benchtop scale 300 cm3 Parr reactor to a
pilot plant scale 65 ft3 digester (Table 4). Delignification was largely dependent on species but
also on the particle size and water:LCB ratio, which varied lignin removal from 10-40%, based
on the original amount of lignin present in LCB. Under similar conditions hardwoods were more
resistant to delignification than monocotyledons36. It was also found that species with a higher
S/G ratio have a greater degree of delignification in HWE37. The S/G ratio has been found to
have a positive relationship with ether linkages in lignin, such as β-O-4 linkages38. Since ether
linkages are specifically targeted during autohydrolysis32, it is expected that there would be a
greater degree of delignification with a higher S/G ratio. However, based on Table 4 it seems
that this trend is only valid amongst hardwood species (Paulownia spp. and sugar maple) or
Figure 5 - Typical structure of hardwood glucuronoxylan Note: Ac – Acetyl group
13
separately between monocotyledon species (Miscanthus spp. and wheat straw). This is
concluded based on the significantly lower S/G ratio but notably higher degree of delignification
in monocotyledons than hardwoods which suggests that other factors, such as heterogeneity
and molecular weight of native lignin, and porosity of biomass may play a role as well.
Table 4 - HWE degree of delignification based on species and reactor conditions
Species Reactor Size Water:LCB
Ratio
Particle
Size
Reaction
Time/Temperature
Delignification
(%-lignin removed)
S/G ratio of
native lignin*
Willow
(Salix spp.)39
65 ft3
Digester 4.5:1
~20 mm
wood chips 2 hours 160 °C 16.7 0.74-1.9826
Sugar Maple
(Acer saccharum)37
300 cm3
Parr Reactor 50:1 0.595 mm 2 hours 160 °C 30.4
1.9240 4 L
M/K Digester 4:1
≤23 mm
wood chips 2 hours 160 °C 9.4
Sugar Maple
(Acer saccharum)41
65 ft3
Digester 4:1 Wood chips 2 hours 160 °C 17.2
Aspen
(Populus tremuloides)42
6 L Recirc.
M/K Digester 4:1 Wood chips 1.5 hours 165 °C 27.4 -
Paulownia tomentosa37
300 cm3
Parr Reactor 50:1 0.595 mm 2 hours 160 °C 26.1
0.9837 4 L
M/K Digester 8:1 ≤6.5 mm 2 hours 160 °C 15.7
Paulownia elongata37 300 cm3
Parr Reactor 50:1 0.595 mm 2 hours 160 °C 20.9 0.8837
Miscanthus
(Miscanthus spp.)35
300 cm3
Parr Reactor 40:1 <0.595 mm 2 hours 160 °C 42.8
0.7043 4 L
M/K Digester 10:1
0.420-19.0
mm 2 hours 160 °C 32.5
65 ft3
Digester 8:1 ~19.0 mm 2 hours 160 °C 32.1
Apricot Pit Shells
(Prunus armeniaca) 36
300 cm3
Parr Reactor 20:1
30-mesh
Wiley mill 2 hours 160 °C 24.0 -
Wheat Straw
(Triticum spp.)44
65 ft3
Digester 8:1
~20 mm
wood chips 2 hours 160 °C 26.0 0.5045
*- Native lignin: MWL-milled wood lignin; all determined by nitrobenzene oxidation method except wheat straw (HSQC) 26-S/G ratio was determined separately on bark (0.74), inner bark (1.07), and wood (1.98) of willow
14
Lignin Valorization: Thermoplastics
It is estimated that 3% of total petroleum consumption in the US went to manufacturing
high-value chemical products, such as polymers. These high-value products are responsible for
more than 40% of the total value produced from a barrel of oil. Meanwhile, the remaining 97%
is used to produce low-value fuels46. For LC biorefineries to be economically competitive with
traditional petroleum refineries, it is imperative to manufacture high-value product streams.
Although, a majority of lignin is squandered as a low-value fuel, currently by the pulp and paper
industry, lignin carries tremendous potential to positively impact the viability of a LC
biorefinery9,11,34,47. As a result, higher-value applications of lignin, such as lignin-based
adhesives20,48, hydrogels39,49, and thermoplastics47,50–54, among others, have been explored and
are commonly referred to as “lignin valorization”. This research will focus on lignin-
thermoplastic blends.
Several thermoplastic polymers traditionally manufactured as byproducts of the fossil
fuel industry, such as polypropylene (PP), polyethylene oxide (PEO), and polystyrene (PS), have
been evaluated for their compatibility with lignin and lignin ester derivatives55–57. In order to
produce a 100% bio-based thermoplastic material with added functionality, bio-plastics like
polylactic acid (PLA) and polyhydroxybutyrate (PHB) have been blended with lignin as well58,59.
This research will focus on producing lignin-PLA blends in an effort to produce a 100%
bio-based polymer blend. PLA was specifically selected as a result of its wide range of
applications, specifically in bio-based packaging60. In addition to packaging, PLA has been used
in medical applications, such as implants and medical devices since the early 1960’s. Other
15
applications include textiles, service ware, parts for space exploration, agriculture,
environmental remediation, and 3D printing16.
The production of PLA begins by either bacterial fermentation of sugars or chemical
synthesis to produce lactic acid (2-hydroxy propionic acid); however, bacterial fermentation is
utilized in industry by the two largest producers of PLA (NatureWorks LLC and Corbion) as it is
the more economical option. Lactic acid, being a biorefinery product is typically produced from
carbohydrates present in food crops, like corn starch (first generation biorefineries). Research
in this area has shown that lactic acid can also be produced from LC feedstocks (second
generation biorefineries)61. Studies at ESF have even begun to model the fermentation of lactic
acid from hemicelluloses62. Specifically, chemical synthesis has been shown to be ineffective in
the production of 100% L-lactic acid over its counterpart, D-lactic16 (Figure 6). L-lactic acid is the
preferred monomer due to its ability to produce 100% crystalline PLA. A majority of commercial
PLA grades that are available are semi-crystalline, made up of chains of random copolymers of
L- and D-lactic acid. However, commercial PLA tends to only contain 1-2% D-lactic acid63 to
maintain some degree of crystallinity.
Lactic acid monomers are polymerized to produce high molecular weight PLA through
three potential methods. These include polymerization through lactide formation, direct
condensation polymerization, and azeotropic dehydration condensation (Figure 6)16. The most
common method utilized is polymerization through lactide formation which involves three
steps. First lactic acid is polymerized through condensation to produce low molecular weight
PLA that then forms a lactide ring through controlled depolymerization. Subsequently, the
lactide ring is purified by distillation to remove water, excess lactic acid, and low molecular
16
weight PLA. High molecular weight PLA is then produced through ring opening polymerization
of the lactide ring in the presence of a catalyst16. Common catalysts for ring opening
polymerization are typical Lewis acids, such as metals, metal halogenides, oxides, aryls, and
carboxylates, with the most common being stannous octoate (Tin(II) 2-ethylhexanoate)64,65. It is
important to note that low molecular weight PLA has a relatively smaller scope of uses
compared to high molecular weight PLA16.
Figure 6 - Lactic acid polymerization to produce high molecular weight PLA16
Reprinted from Castro-Aguirre et al. (2016)
17
High molecular weight PLA can be blended with lignin or processed into a large number
of products through several processing methods, specifically melt extrusion (Figure 7)16,59.
Polymer blends can also be produced through solvent casting59,66. Melt extrusion exposes PLA
resin to one or more heated screws that melt PLA and another polymer to be blended, in this
case lignin, producing a polymer blend59,67. Melt extrusion may also be employed as the first
step to process PLA for specific applications, often being followed by subsequent processes,
such as injection molding16. Solvent casting is an alternative to melt extrusion for producing
polymer blends that may contain thermally sensitive components and relies on the dissolution
and mixing of two polymers in a common solvent. Once the two polymers have been
sufficiently mixed, the solution is poured into a mold and the solvent evaporates, forming a
film59,66.
It is important to note that there are numerous crystal polymorphs of PLA; however,
only α’- and α-crystals are formed during typical industrial process like melt extrusion68. While
α’- and α-crystals are very similar in structure the main difference is that α’-crystals are slightly
disordered while α-crystals have a tighter, more organized structure63,69. It was determined that
Figure 7 - Visual representation of an extruder16
Adapted from Castro-Aguirre et al. (2016)
18
α’-crystals are formed at relatively low crystallization temperatures, below 110 °C upon a fast
cool. Meanwhile, α-crystals are formed at crystallization temperatures at or above 120 °C70.
Therefore, both α’- and α-crystals are commonly formed after PLA is melt extruded.
PLA has been shown to be highly susceptible to photodegradation and is especially
sensitive to UV light from 200-300 nm71. Photodegradation of PLA is initiated by the absorption
of light, exciting the molecule shown by mechanism 1 in Figure 872. Molecule excitation leads to
several PLA degradation reactions. Specifically, the Norrish type II reaction (mechanism 3 –
Figure 8) is believed to be the most common mechanism of PLA photodegradation72–75. Norrish
Figure 8 - Proposed mechanisms of PLA photodegradation72
Adapted from Mucha et al. (2014)
19
type I and main chain scission reactions (mechanisms 2 and 3, respectively – Figure 8) may also
occur during photodegradation of PLA in the presence of UV light72. PLA may be exposed to UV
irradiation by sunlight throughout its lifetime in many of the aforementioned applications.
However, biomedical and pharmaceutical products that include PLA are exposed to UV light
through sterilization that involves UV irradiation16. Lignin’s intrinsic UV absorbance with a
maximum around 280 nm indicates its potential to shield PLA from detrimental UV radiation
and therefore to prevent PLA photodegradation. Previous literature already showed mechanical
properties of PLA blends containing lignin were less impacted than just PLA following
accelerated weathering that included exposure to UV-vis light (200-700 nm)76.
Additionally, lignin-PLA blends may be able to provide protection in applications, such as
food packaging, where the contents are sensitive to photoreactions which can lead to off flavor,
loss of quality and even the formation of toxic byproducts77.
Currently utilized UV protectants in plastic food packaging include benzophenones and
benzotriazoles18. Both of which have been identified and recognized as contaminants of
emerging concerns and are known to have adverse short and long-term effects on aquatic life
(Figure 9 and Figure 10)19. Meanwhile, polyphenols have been shown to prevent
photooxidation18, paving the way for lignin through its
polyphenolic structure to be used as a UV protectant in active food
packaging.
Technical lignins recovered from various industrial processes
have been blended with several commercial polymers showing
favorable results, from increased radical scavenging capabilities in Figure 10 - Benzotriazole
Figure 9 - Benzophenone
20
PP blends to demonstrated use in applications like 3D printing with PLA. However, it was found
that technical lignins have limited compatibility with commercial polymers which negatively
impacted strength properties78,79. It is important to note that the added color of lignin
thermoplastic blends also poses an obstacle to overcome prior to commercialization in
applications where transparency is essential.
The overarching problem with technical lignins when being considered for blending with
commercial polymers is the presence of hydroxyl groups, while high molecular weight lignin is
also of concern80. The hydroxyl groups contribute to lignin’s comparatively strong hydrogen
bonding and polar structure55. These factors limit the compatibility of lignin with typically
hydrophobic polymers, which is explained well through the use of Hansen solubility theory.
There are three Hansen solubility parameters; δd, δp, and δh, describing dispersive,
polarity, and hydrogen bonding forces, respectively81. Cumulatively, these solubility parameters
are used as an approximation of the miscibility and can be applied to the compatibility of multi-
component systems (e.g. solute-solvent, polymer blends, and solvent-solvent)82. Miscibility in
polymer blends is defined as homogeneity down to the molecular level83. However, it is
important to consider that “homogeneity at a fairly fine level is necessary for optimum
performance but some degree of microheterogeneity is usually desirable to preserve the
individual properties of respective polymer components”84. Consequently, miscibility of
polymer blends may not necessarily be studied to obtain a completely homogenous blend, but
to evaluate methods that are aimed at improving compatibilization83.
Lignin-polymer blends have previously been analyzed by light microscopy to compare
miscibility of lignin with different polymers versus the Hildebrand solubility parameter of the
21
respective polymer to indicate the compatibility between the two57. Hansen solubility theory
builds on that of the Hildebrand solubility parameter. Hildebrand was the first to introduce the
idea of a solubility parameter, developing a relationship between surface tension and
properties of solvents through a single solubility parameter85. The Hildebrand solubility
parameter (δ) is calculated as the square root of the cohesive energy density, or square root of
the total cohesive energy (E) divided by the molar volume (V) of a solvent (Equation 1)86. A
solubility parameter may be assigned to a solute or polymer by testing its solubility in a set of
solvents with known solubility parameters. Group contribution methods have also been
developed for the theoretical calculation of solubility parameters, both Hildebrand and
Hansen87,88. However, the Hildebrand solubility parameter seems to oversimplify the complex
nature of solubility which Hansen attempted to address and enhance.
Research done by Professor Schuerch of ESF on lignin solubility considering the
Hildebrand solubility parameter began to shed a light on the flaws of the Hildebrand solubility
parameter89. It was shown that in addition to evident trends that were recognized between the
Hildebrand solubility parameters of different lignins and solvents, the strength of hydrogen
bonding was also required to indicate lignin solubility. Specifically, Schuerch noted that solvents
with a Hildebrand solubility parameter of ~11 cal1/2cm-3/2 (~22.5 MPa1/2) and strong hydrogen
bonding forces is required to solubilize lignin89. In this work, Schuerch identified good lignin
solvents and the corresponding Hildebrand solubility parameters. Furthermore, he recognized
that the Hildebrand solubility parameter on its own is an inadequate means of providing an
accurate indication of solubility.
δ = (E/V)1/2 1
22
Hansen assumed that E may be separated into contributions from dispersion (Ed),
permanent dipole-permanent dipole (Ep), and hydrogen bonding (Eh) forces86. While keeping in
mind the equation for the Hildebrand solubility parameter (Equation 1), this theory resulted in
Equation 2 that leads to the relationship between the Hildebrand solubility parameter and
Hansen solubility parameters (δd, δp, δh) in Equation 3.
The Hansen solubility parameters of each compound may be plotted three-
dimensionally, as the center of a hypothetical sphere (Figure 11). The radius of this sphere is an
approximation done through solubility studies86. If the coordinates of a different compound fell
within this sphere, the two compounds would be compatible to some extent. For example, in
consideration of a specific polymer and its solubility in different solvents, the following
scenarios are possible; a) if a solvent fell outside the polymer’s sphere, there would be little to
no solvent-polymer interaction; b) if a solvent fell near the edge of the polymer’s hypothetical
sphere, it would induce swelling of the polymer; c) if a solvent fell well within the bounds of the
polymer’s sphere, it should easily solubilize the polymer. Analogous concepts are guiding
E/V = (Ed/V) + (Ep/V) + (Eh/V) 2
δ2 = δd2 + δp
2 + δh2 3
Figure 11 - Sketch of a typical Hansen solubility parameter sphere86
Reprinted from Hansen (1969)
23
miscibility in polymer blends. A polymer with overlapping coordinates (center of their spheres)
should provide a 100% miscible blend. If the coordinates of one polymer fell within the sphere
of the other polymer, there will be varying levels of miscibility depending on the distance from
the center of the sphere. Conversely, if one polymer fell outside of the sphere of the other
polymer, the two should be completely immiscible82. Therefore, the smaller the difference in
Hansen solubility parameters between each of the compounds of interest, the greater the
compatibility between them is expected82,86. Literature values for the Hansen solubility
parameters of lignin and some commercially available thermoplastics are compared (Table 5).
Specifically δp and δh differ notably between lignin and these commercial polymers. Free
hydroxyl groups were even determined to be the greatest contributor to lignin’s relatively high
δp and δh90.
Table 5 - Hansen solubility parameters for lignin and commercially available polymers
Solubility Parameters Björkman Lignin-Spruce86 PLA82 PHB91 PEO82 PS82 PP82 Epoxy*82
δd (MPa1/2) 21.9 18.6 15.5 17 18.5 18 17.4
δp (MPa1/2) 14.1 9.9 9.0 10 4.5 0 10.5
δh (MPa1/2) 16.9 6 8.6 5 2.9 1 9
*Epoxy is an example of a thermoset
It was documented that technical lignins can resemble thermoset-like (in contrast to
thermoplastic) materials. At temperatures around or above the glass transition temperature
(Tg), condensation polymerization is induced, increasing molecular weight and Tg of lignin10,92.
This could negatively affect blending and thermal stability of lignin-thermoplastic blends,
specifically in the case of thermal processing (melt extrusion).
In lignin utilization, chemical modification has been explored to improve
thermoplasticity and compatibility with commercial polymers, among other purposes10,11,93.
Specifically esterification has been shown to have a substantial impact on lignin while being
24
relatively easy to carry out with regards to reagents and reaction parameters11. An overview of
the different lignin-ester derivatives that have been explored in previous literature is provided
in Table 6. It is interesting to note that esterification of lignins may be executed by using either
a carboxylic acid, acid chloride, or acid anhydride. However, esterification with the addition of a
hydrocarbon chain through an ester bond formed with available phenolic and aliphatic hydroxyl
groups of lignin and an acid chloride or acid anhydride is technically an acylation chemical
reaction. Esterification results in an increase in the hydrophobicity and thermal stability and
decrease in both hydrogen bonding and the Tg of lignin94–97. The degree of these changes may
be controlled by the extent of the acylation reaction and the size of the moiety added through
the ester linkage. For example, short chain acylation (acetylation) has shown the ability to
decrease the Tg of lignin by about 20 °C while acylation with long chain fatty acid chlorides is
able to reduce the Tg anywhere from 20-100 °C97. In attempt to determine the impact of chain
length on polymer blends, esterification was done with both short (acetic anhydride, C2
addition) and long (lauroyl chloride, C12 addition) chains in this work.
25
Table 6 - Overview of lignin esterification from previous literature
Reagent(s) Molecular Formula Technical Lignin Final Tg (°C) Application
Sebacoyl Chloride11,98 ClOC-(CH2)8-COCl Kraft 46 to 48 Lignin polyester synthesis
Dicarboxylic acids and Triethanolamine11,99
HOOC-(CH2)n-COOH and (CH2OHCH2)3N
Protobind 1000 -21 to 28 Lignin polyester amine for
elastomeric materials
Phthalic anhydride11,100
C6H4(CO)2O Kraft - Lignin-polyethylene blends
Dimer acid of predominantly steric
acid11,101 C36H68O4
Isolated from enzymatically
hydrolyzed steam-exploded
cornstalks
- Dimer acid-lignin copolymer as
an epoxy resin curing agent
Oleic acid10,102 C8H17CH=CH(CH2)7COOH Organosolv -24 Lignin oleate polyol for polyurethane synthesis
Acetic anhydride10,103 (CH₃CO)₂O Organosolv 120 Lignin-vinyl polymer blends
Propionic anhydride10,104
(CH₃CH₂CO)₂O
Organosolv
50
Lignin-poly(ε-caprolactone) blends
Butyric anhydride10,104,105
(CH₃CH₂CH₂CO)₂O 40
Valeric anhydride10,105 (CH₃CH₂ CH₂CH₂CO)₂O
Maleic anhydride56 C₂H₂(CO)₂O Kraft Eucalyptus - Lignin-recycled polystyrene
blends
Lauroyl chloride94 CH3(CH2)10COCl Organosolv
Spruce 38 Thermoplastic materials
Tall oil fatty acid chlorides (>50%
linoleic acid chloride)95 CH3(CH2)4(CH)2CH2(CH)2(CH2)7COCl
Indulin Kraft Softwood
- Lignin coating for paperboard
Acetyl chloride97 CH3COCl
Lignoboost Kraft Softwood
121
Thermoplastic applications (on its own or in polymer blends)
Octanoyl chloride97 CH3(CH2)6COCl 65
Lauroyl chloride97 CH3(CH2)10COCl 45
Palmitoyl chloride97 CH3(CH2)14COCl 45
Lignin recovered from the hydrolysate of autohydrolysis, specifically HWE (HWE lignin),
was utilized in this work. HWE lignin from multiple feedstocks (willow, wheat straw, or
miscanthus) available for this project has been collected from HWE hydrolysates produced in
the PBE pilot plant at ESF35,44. Lignin recovered from the HWE hydrolysate of sugar maple has
been included in Table 7 as an additional reference. The specific HWE lignin that would be
preferred for lignin-thermoplastic blends (willow) was determined based on the results of
26
earlier studies, which included the hydroxyl group content and molecular weight distribution
(Table 7). This data was compared to common technical lignins from literature as a
reference106,107. In comparison to organosolv lignins from literature, HWE lignins are
characterized by similar, but somewhat lower lignin content, and higher carbohydrate content.
However, lignin and carbohydrate contents of HWE lignins are more comparable and favorable
when compared to most of the other technical lignins considered.
HWE willow lignin was selected for this project as it displayed the most favorable
balance between a low hydroxyl group content and low molecular weight (of all HWE lignins
considered), two preferred traits of lignin for use in polymer blends80. In addition to having
favorable lignin properties for this application, willow as a LC feedstock is positioned to play a
large role in the future bioeconomy, leading to large amounts of available biorefinery willow
lignin.
The Department of Energy has initiated and conducted a study on the feasibility of
eliminating 30% of petroleum consumption in the US through the use of one billion tons of
renewable biomass. It was determined that about 20-25% of the required biomass would come
from short-rotation coppice systems108. An example of a short-rotation coppice system is shrub
willow, which has shown a great deal of promise as a LC biorefinery feedstock, specifically in
New York State. Shrub willow has shown the ability to grow on marginalized lands, be a carbon
neutral system with simplified propagation and a high biomass yields in short period of time,
while allowing for numerous harvests, and even pre-harvest utility109–112. Therefore, shrub
willow represents an attractive feedstock for potential LC biorefineries and corresponding
research.
27
Table 7 - Characterization of lignins recovered from HWE and standard technical lignins
Lignin
Recovered
from HWE at
ESF
Chemical Composition (%)a -OH content (mmol/g)b Molecular Weight
Distribution20 S/G
Ratio 20
Klason
Lignin
Acid
Soluble
Lignin
Total
Lignin
Lignin
Ash
Total
Carbohydrates Phenolic Aliphatic Total
COOH Mn
(Da)
Mw
(Da) PD
Willow 80.2 4.48 84.68 0.2 2.98 2.97 2.08 5.05 0.75 2186 5962 2.73 1.25
Miscanthus 76.3 4.96 81.26 0.5 8.68 2.95 3.28 6.24 0.46 2124 4672 2.2 2.86
Wheat straw 77.3 3.73 81.03 1.2 5.97 2.43 2.52 4.95 0.79 2850 12114 4.25 1.90
Sugar Maple 80.2 5.80 86.00 0.04 6.76 2.97 2.54 5.51 0.34 1825 3058 1.68 2.66
a – Data provided by USDA Forrest Products Lab, Madison, WI
b – Data provided by Oak Ridge National Laboratory, Oak Ridge, TN (31P NMR)
Technical
Lignin from
literature
Chemical Composition (%) -OH content Molecular Weight
Distribution S/G
Ratio Klason
Lignin
Acid
Soluble
Lignin
Total
Lignin
Lignin
Ash
Total
Carbohydrates Phenolic Aliphatic Total
COOH Mn
(Da)
Mw
(Da) PD
Kraft
Softwood106 61.2 4.9 66.1 27.10 3.28 4.10 10.09 14.19 - 545.2 1098.7 2.01 -
Ligno-
sulfonatec,106 - - 56.5c 9.30 - 2.00 - - - - - - -
Soda-AQ d,106 86.4 11.5 97.9 0.74 2.39 4.50 3.10 7.60 - 646.6 1300.6 2.01 -
Organosolv
Miscant.e,106 92.3 1.9 94.2 1.71 1.16 3.33 3.50 6.83 - 1123.4 2800.8 2.50 -
Ethanol
processedf,106 68.6 2.9 71.5 2.86 22.37 2.65 4.73 7.38 - 794.8 2106.7 2.65 -
Organosolv
Eucalyptus107 83.7 1.6 85.3 3.6 2.9 2.12 1.58 3.70 0.11 1567 5079 3.24 1.5
Kraft
Eucalyptus107 58.6 6.3 64.9 22.4 2.2 2.73 1.24 3.94 0.88 1059 2653 2.51 1.6
Organosolv
Spruce107 94.3 3.1 97.4 3.2 0.5 2.99 0.75 3.74 0.23 1065 3081 2.89 -
Kraft
Spruce107 88.5 2.3 90.8 2.5 1.0 4.04 1.75 5.79 0.40 1540 7195 4.67 -
106- Hydroxyl group content by 1H NMR (% w/w); Lignosulfonate phenolic OH by UV method (%w/w) 107- Hydroxyl group content by 31P NMR (mmol/g)
c- Lignosulfonate from unidentified feedstock; Total Lignin content = Lignosulfonate content by UV method
d- Soda-anthraquinone (AQ) from a mix of long fiber plants
e- Miscant. - Miscanthus sinesis
f- Ethanol process lignin after simultaneous saccharification and fermentation of poplar pretreated by steam explosion
28
Experimental
Materials
The hydrolysates of willow (Salix spp., Family: Salicaceae; a blend of commercial cultivars with
bark), miscanthus (Miscanthus spp.), and wheat straw (Triticum spp.) from HWE in a 65 ft3
digester were recovered by the PBE Pilot Plant crew. To recover the lignin in the hydrolysate,
the pH was dropped to 2 (using 20% H2SO4), and lignin was precipitated and collected through
centrifugation and vacuum filtration. Willow lignin recovered from the hydrolysate of HWE will
be referred to as W throughout this document. Kraft (alkali) lignin was obtained from Sigma-
Aldrich as a reference lignin, being the most abundant technical lignin, and may be referred to
as KL throughout this document. Ingeo PLA resin, extrusion grade (2003D), was purchased from
NatureWorks LLC. Other chemicals utilized, and their respective vendor are listed in Table 8.
Table 8 - Chemical compounds utilized during this study
Chemical Vendor Acetic Anhydride EMD Millipore
Acetone PHARMCO-AAPER
Chloroform J.T.Baker
Dioxane TCI
Ethanol PHARMCO-AAPER
Hexane PHARMCO-AAPER
Hydrochloric acid EMD Millipore
N, N-dimethylformamide VWR
Lauroyl Chloride Acros Organics
Pyridine EMD Millipore
Sodium Hydroxide Macron Fine Chemicals
Tetrahydrofuran (THF) PHARMCO-AAPER
Triethylamine TCI
29
Chemical modification (Acylation) of Lignin
Acetylation (C2 chain addition) of Lignin
Willow lignin recovered from the hydrolysate of HWE (W) was dissolved into 20 mL/g-lignin of
pyridine and acetic anhydride (1:1 v/v). The solution was allowed to mix on a stir plate for at
least 24 hours and up to 72 hours in order to ensure complete acetylation55. The acetylated
lignin was precipitated by pouring the solution into 300 mL of ice-cold water for one gram of
starting lignin. Once the acetylated lignin had completely precipitated the mixture was vacuum
filtered and washed with ice-cold water to remove excess pyridine, acetic anhydride and acetic
acid (a byproduct of the reaction). The acetylated lignin was dried overnight in a vacuum oven
(40 °C) prior to use in lignin characterization and lignin-PLA blends. When scaling this reaction
up to 5 grams, 70 mL of pyridine and acetic anhydride was utilized (0.4:1 v/v) in an effort to
reduce pyridine usage. Acetylated W will be referred to as WAc. The proposed mechanism of
this reaction can be observed in Figure 12.
Acetic Anhydride
β-O-4 Acetylated
β-O-4
Acetic Acid
Figure 12 - Proposed mechanism of complete acetylation of β-O-4 in lignin
30
Acylation of Lignin with Lauroyl Chloride (C12 chain addition)
W was subjected to acylation with lauroyl chloride, a chloride derivative of lauric acid, by
dissolving into 30 mL of N, N-dimethylformamide per gram of lignin in the presence of pyridine
(5.5 mL) and triethylamine (1.5 mL). Once the solution was homogenized, 1 mmol-lauroyl
chloride/mmol-OH was added to start the reaction. The reaction was allowed to proceed for 2
hours while mixing on a stir plate at room temperature (20-25 °C). The lignin acylated with
lauroyl chloride was precipitated by pouring the solution into 600 mL of ice-cold 2% HCl for one
gram of starting lignin. The mixture was vacuum filtered with nylon filters to make it easier to
recover the lignin laurate. The filter cake was then washed with ethanol and water (1:1 v/v) to
remove excess solvent, unreacted lauroyl chloride, and unbound fatty acid, lauric acid. The
lignin laurate was dried overnight in a vacuum oven (40 °C) prior to future use94. This laurate of
W will be referred to as WFAE. Acylation of miscanthus and wheat straw lignin recovered from
the hydrolysate of HWE was attempted initially but discontinued due to challenges with
handling and with purification. This was in addition to determining that W was best suited for
blending with PLA based on the data presented in Table 7. Yield data from preliminary acylation
studies on willow, miscanthus, and wheat straw lignins recovered from the respective
hydrolysates of HWE are included in Appendix A. The proposed mechanism of this reaction can
be observed in Figure 13.
31
Lignin Purification Processes
Alkali Purification of Lignin
W was dissolved in 125 mL 0.05 M NaOH and 25 mL dioxane per gram of lignin. Purification was
allowed to proceed under an N2 atmosphere. After 24 hours the solution was acidified with 0.1
M HCl to a pH of 2, ending the reaction. The solution was stored in the cold room (≤8 °C)
overnight and the resulting precipitate was vacuum filtered in a Buchner funnel. The filtrate
was returned to the cold room to ensure complete precipitation of lignin. Subsequently, the
lignin precipitate was washed with cold water until the filtrate reached a pH of 5. The filter cake
was placed in the vacuum oven (~40 °C) overnight and weighed the following day. The resulting
alkali purified willow lignin will be referred to as WAP.113
Lauroyl Chloride
β-O-4 β-O-4 Acylated with
Lauroyl Chloride
Figure 13 - Proposed mechanism of complete acylation with lauroyl chloride of β-O-4 in lignin
32
Hexane Extraction of WFAE
Hexane extraction was attempted to remove the unbound fatty acid, which was identified by
FT-IR, by soaking one gram of the WFAE (W acylated with lauroyl chloride) in 10 mL hexane for
30 minutes, decanting the solvent and repeating once more. Following extraction with hexane,
the insoluble lignin was allowed to air dry in the hood overnight, then it was placed in a vacuum
oven (~40 °C) for 24 hours prior to use in lignin-PLA blends. Following hexane extraction, this
lignin laurate, C12 acylated and hexane purified derivative of W will be referred to as WFAEH.
Lignin Characterization
Fourier Transform Infrared Spectroscopy (FT-IR) of Lignins
A PerkinElmer Frontier FT-IR/NIR Spectrometer was utilized in this analysis. The FT-IR spectra
were analyzed from 4,000-650 cm-1 in MIR mode, averaged over 16 scans and baseline
corrected. Values were obtained as % transmittance, %T, and were converted to absorbance,
Abs (Equation 4). All absorbance values were normalized based on the band from 515-505 cm-1,
which represents aromatic skeletal vibrations.
Abs = 2-log10(%T) 4
33
Hydroxyl Group Content of Lignins - 31P NMR Analysis
These studies, testing and calculations, were performed by Yunxuan Wang in the lab of Dr.
Chang Geun Yoo from PBE at ESF in accordance with methodology from literature114. About 20-
30 mg of vacuum-dried samples were dissolved in 500 μL of the prepared NMR solution which
is composed of an internal standard (endo-N-Hydroxy-5-norbornene-2,3-dicarboximide
(NHND)), pyridine/CDCl3 (1.6/1, v/v), and relaxation reagent (Cr(acac)3). When the samples
were completely dissolved in the solution, 50 μL of phosphitylation reagent (2-chloro-4,4,5,5-
tetramethyl-1,3,2-dioxaphopholane (TMDP)) was added to derivatize the samples (Figure
14114). The phosphitylated samples were analyzed using a Bruker AVANCE Ⅲ 600MHz NMR
spectrometer equipped with a 5mm liquid N2 cooled broad band observe with fluorine probe.
The acquisition parameters were as follows: spectra width 100 ppm, with 1.2 s acquisition time,
a 25 s delay, and 64 scans. The spectra of the samples was assigned (Figure 15) and calculated
with the known concentration of the internal standard115.
Figure 14 - Phosphitylation mechanism of lignin hydroxyl groups with TMDP114
Reprinted from Pu et al. (2011)
34
Differential Scanning Calorimetry (DSC) of Lignins
TA Instruments DSC Q200 was utilized using a heat/cool/heat cycle with a 2 °C/minute heating
rate and 10 °C/minute cooling rate in a N2 atmosphere. A 2 °C/minute heating rate was chosen
in these studies due to a subtle glass transition of lignins; it was found that a slower heating
rate made the transition more pronounced. The 10 °C/minute cooling rate was selected in
accordance with literature20. Lignins were analyzed on the first heat as it was also difficult to
identify the glass transition on the second heat. The glass transition temperature (Tg) of each
sample was determined to be the start of the endothermic event, while the melt temperature
(Tm) was determined to be the minimum of the corresponding peak. TA Universal Analysis
software, downloaded from tainstruments.com, was utilized to determine the value for each
transition.
Figure 15 - Lignin 31P NMR spectrum with TMDP using NHND as the internal standard115
Reprinted from Wang and Yoo (2019)
35
Thermogravimetric Analysis (TGA) of Lignins
TA Instruments TGA Q5000 was utilized with a 10 °C/minute heating rate in a N2 atmosphere in
accordance with literature20. Degradation temperature (Td) was determined to be the peak of
the curve that represents the weight derivative with respect to temperature. TA Universal
Analysis software, downloaded from tainstruments.com, was utilized to determine each
transition.
Molecular Weight Distribution of Lignins – Size Exclusion Chromatography (SEC)
These studies, testing and calculations, were performed by Aditi Nagardeolekar and Dr. Prajakta
Dongre from PBE at ESF. The molecular weight distribution was determined using size exclusion
chromatography (SEC). The columns used were Waters Styragel HR 0.5, HR 3, and HR 4E. The
solvent used was THF and the concentration of the sample was 1mg/mL. The dissolved samples
were then filtered through 45 μm polyvinylidene fluoride filters. The detection method used
was UV spectrophotometry with absorption at 280 nm. Polystyrene standards (molecular
weight range from 1,500-2,500,000 Da) were used for calibration and a third order polynomial
equation was used for quantification and the data was normalized. Only lignin derivatives
(WAc, WFAE, and WFAEH) can be analyzed due to limited solubility of crude lignin (W) in THF. W
after alkali purification, WAP, was acetylated and compared to WAc as an indication of how
alkali purification impacts molecular weight distribution of lignin. Acetylation is the
derivatization method consistent with literature20.
36
Antioxidant Activity (AOA) of Lignins
These studies, testing and calculations, were performed by Aditi Nagardeolekar from PBE at ESF
in conjunction with the method from literature15. The antioxidant activity of selected lignin
samples (W, WAc, and KL) and ascorbic acid, a natural antioxidant, were measured by
determining the amount of sample needed quench 50% of the free radicals present in the
solution. Free radicals in this case were of DPPH (2,2-diphenyl-1-picrylhydrazyl) as DPPH is
composed of a stable radical. A sample lignin solution in 500 μL of dioxane:water (9:1) with 4
mL of 6 x 10-5 mol/L DPPH• in methanol had its UV absorbance immediately measured at 517
nm using a Genesys 10 Series Spectrophotometer at room temperature. The decrease in DPPH•
content based on the change in UV absorbance at 517 nm was plotted at different
concentrations of each antioxidant, radical scavenger. The solutions were allowed to reach
steady-state (1-2 hours). The percentage of DPPH• remaining in solution at steady state was
plotted at different concentrations for each radical scavenger. The resulting function was
utilized to determine the concentration of the antioxidant that would be required to quench
50% of the free radicals from DPPH•, forming a lignin-DPPH• complex (Figure 16). This value
was recorded as the IC50 for each antioxidant. The lower the IC50 the greater the radical
scavenging capabilities of the antioxidant. A synthetic antioxidant, 3,5-di-tert-butyl-4-
hydroxytoluene (BHT), was also considered as an additional reference value, which was
obtained from Pan et al. (2006) based on the same method, just done at microplate scale14.
Figure 16 - Proposed mechanism of lignin-DPPH reaction
37
UV Absorbance of Lignins
A Genesys 10 Series Spectrophotometer was used in this experiment. 10 mL of dioxane:water
(96:4) was used to dissolve ~10 mg of material (lignin or PLA); the mass of sample was recorded
accurately to the nearest 0.0001 g. 30 minutes of sonication in a Branson Ultrasonicator Bath
with 5 minutes of degassing was done to assist in the dissolution of the solute when needed.
Lignins were diluted by a dilution factor of 31x to ensure that the absorbance of the maxima is
between 0.1-2.0 Abs. The solutions were scanned from 200-400 nm. The absorbance values
were standardized to an initial concentration of 1 mg/mL. The area under the curve was taken
over the entire range and UVA (320-400 nm), UVB (280-319 nm), and UVC (200-279 nm) were
also recorded.
Theoretical Calculation of Lignin’s Hansen Solubility Parameters
The group contribution method outlined in literature was followed87. Hydroxyl group and
carboxylic acid content from 31P NMR analysis and S/G ratio from Table 7 were utilized as inputs
for these calculations. Unknown values were varied to approximate the range of each solubility
parameter for the lignin being considered. These variables included the designation of aliphatic
(primary and secondary) hydroxyl groups, ester (LCC and acyl) and ether (LCC) linkages at Cα
and Cγ. The δp parameter was the most impacted by these variables. It was assumed that all
carboxyl groups were present at Cγ and all linkages involving aliphatic carbons were either
esters or ethers if no hydroxyl group was present. It was also assumed that lignin only
contained G- and S-units, with molar masses of 195 g/mol and 225 g/mol, respectively. An
example of calculations following this group contribution method developed by Stefanis et al.
38
(2008) can be seen in Appendix G. The difference in solubility parameters between two
compounds is quantified by RA (Equation 5)90.
Polymer Blend Production
Solvent Casting of Lignin-PLA Blends
1 gram of material (PLA or lignin and PLA) was dissolved into 10 mL of solvent (chloroform).
Solutions were in some cases exposed to 60 minutes of sonication and 5 minutes of degassing.
The solutions were allowed to mix for 24 hours or until completely dissolved. Once mixing was
completed, the solution was poured into a square silicone mold. The solvent was allowed to
evaporate and form a film. Once the films were air dried, they were placed in the vacuum oven
at 40 °C for at least 24 hours or until completely dry. Solvent casting was attempted; however,
due to poor film formation and a lack of lignin being evenly dispersed no properties could be
accurately measured (Figure 17). Therefore, solvent casting was not performed after these
trials.
RA2 = 4*(δd1 – δd2)2 + (δp1 – δp2)2 + (δh1 – δh2)2 5
Figure 17 - Films of lignin-PLA blends produced by solvent casting
From left to right: 1% WFAE, 10% WFAE, and 100% PLA
39
Melt Extrusion of Lignin-PLA Blends
A Dynisco Lab-Mixing Extruder was utilized in these experiments (Figure 18). Lignin was
dissolved in acetone (9:1 acetone-water utilized for underivatized lignins) and the solution was
used to coat the PLA pellets. PLA (coated or uncoated) was dried in a vacuum oven overnight.
The screw of the two-zone extruder was preheated to 170 °C and 180 °C at the dye/nozzle,
which was 1/8 inch in diameter. Prior to this, the cooling water was connected and turned on.
When extruding samples containing more than 1% lignin, the extruder was preheated to 190 °C
and 200 °C, respectively. The extruder was set to about 30 rpm
but minor adjustments were made on a case-by-case basis to
ensure proper filament formation of the melt. The pellets were
slowly fed into the hopper once the targeted temperature of the
extruder was reached and stabilized. The resulting filament was
collected and allowed to cool for 15-20 minutes before cutting
into 3 inch rods. All rods had a diameter between 2.7-4 mm. The
samples were then stored in conditions in accordance with ASTM standard D618116 for at least
72 hours prior to analysis. Examples of the resulting rods are pictured in Figure 19.
Figure 18 - Dynisco Lab-Mixing Extruder
Figure 19 - Extruded 1% lignin-PLA blends
From left to right: 1% KL, 1% W, 1% WFAEH, 1% WFAE, 1% WAc
40
Characterization of Lignin-PLA Thermoplastic Blends
Light Microscopy – Image Analysis of Lignin-PLA Blends
A Nikon Eclipse 600 Light Microscope at 4x magnification equipped with a Lumenara Infinity 1
camera was used to examine the compatibility between the commercial polymer and the
different types of lignin. Lignin aggregates indicated poor miscibility and compatibility with the
commercial polymer.
Mechanical Properties of Lignin-PLA Blends – Elongation Tensile Testing
An MTS Sintech 1/S Elongation Tensile Tester equipped with a load cell rated for up to 250 lbf
and serrated grips was utilized to determine tensile properties of the commercial PLA polymer
and the lignin-thermoplastic blends based on ASTM method D638116. At least seven samples
from each batch were tested. The diameter of each sample was determined utilizing an L&W
Micrometer accurate to +/- 0.01 mm. Measurements were made in 3 spots on each sample and
the average for each sample was used to calculate the tensile properties. TestWorks 4 software
was utilized to record the raw data and calculate the tensile properties. The initial rate of
separation between the two grips was 5 mm/min.
A typical stress vs strain curve for PLA and lignin-PLA blends may be observed in Figure 20. The
marker labeled as “M” represents the end of the linear region. The linear region is extended
and the slope is taken as the elastic modulus (Young’s Modulus). The yield point, which is
represented by marker labeled “Y”, was determined to be the point at which the angle of the
stress vs strain curve reached 35°. The peak is the point at which the highest level of stress was
41
recorded and the break point, marked by
“F”, is the point at which the sample
failed. Stress is calculated as the load per
cross-sectional area while strain is the
percent elongation relative to the initial
gage length, which was 2.54 cm. Raw data
was screened for outliers by ASTM E178,
using a critical T with an upper 5%
significance level117. Outliers were
removed from averages reported in the
results and discussion section. The
number of batches and replicates per batch for each sample is outlined in
Table 9.
Table 9 - Summary of lignin-PLA blends evaluated
Sample PLA 1% KL 1% W 1% WAc 6% WAc 12% WAc 1% WFAE 7% WFAE 1% WFAEH
Batches per sample
3 1 2 2 2 2 1 1 1
Replicates per batch
5 7 7 7 7 7 7 7 7
Differential Scanning Calorimetry (DSC) of Lignin-PLA Blends
The same instrument, data analysis software, and operating parameters were used as in the
DSC experiments for lignins. The Tg was determined to be the inflection point when using the
step/glass transition tool available in the data analysis software. Crystallization temperature (Tc)
and Tm were considered to be the peak maximum and minimum, respectively. Tc, Tg, and Tm of
Figure 20 - Load-extension curve of PLA
42
PLA and lignin-PLA blends were analyzed on the first heat while Tm was analyzed on the second
heat as well. It was deemed acceptable to analyze lignin-PLA blends on the first heat since they
all have similar thermal history from extrusion and the same thermal history following
extrusion. The operation of DSC at a 2 °C/minute heating rate allowed for the differentiation
between the Tm of different crystal polymorphs (α- and α’-crystals). DSC thermograms were
obtained for most lignin-PLA blends at a 10 °C/minute heating rate as well.
Thermogravimetric Analysis (TGA) of Lignin-PLA Blends
The same instrument, data analysis software, and operating parameters were used as in the
TGA experiments for lignins. The Td was determined to be the peak of the curve that represents
the weight derivative with respect to temperature.
UV Absorbance of Lignin-PLA Blends
10 mL of Dioxane:water (96:4) was used to dissolve ~10 mg of material (lignin or PLA); the mass
of sample was recorded accurately to the nearest 0.0001 g. 30 minutes of sonication in a
Branson Ultrasonicator Bath with 5 minutes of degassing was done to assist in the dissolution of
the solute when needed. The solutions were scanned from 200-400 nm and the absorbance
values were standardized to a concentration of 1 mg/mL. The area under the curve was taken
over the entire range but UVA (320-400 nm), UVB (280-319 nm), and UVC (200-279 nm) were
also recorded.
43
Results & Discussion
Lignin Characterization
Fourier Transform Infrared Spectroscopy (FT-IR) of Lignins
All FT-IR spectra of lignins were analyzed with specific consideration being given to the
bands and corresponding groups outlined in Table 10. When comparing the FT-IR spectra of W,
lignin recovered from HWE of willow, and W after alkali purification, WAP, to kraft lignin, KL,
there are some noticeable differences that should be mentioned (Figure 21). Lignin from willow
biomass is a typical SG lignin118. This is reflected by the presence of a band with a maximum at
1,322 cm-1, representing S units and condensed G units. However, this band is not observed in
KL, indicating a lack of S units. This suggests KL is sourced from softwood biomass that is known
to have mostly G units and very little to no S units. Additionally, the FT-IR spectrum of KL shows
a small, but clear and distinguished, band at 854 cm-1 specific to G-units. Following alkali
purification WAP, compared to W, maintains band intensity in regions representing aromatic
skeletal vibrations and S-units. Meanwhile, bands not representative of lignin structures, such
as 1,115-1,110 cm-1, are reduced. This may indicate that impurities were removed but to some
extent still remain.
44
Table 10 - Lignin FT-IR band assignment
Wavenumber (cm-1) Band Origin
3,600-3,000119,120 O-H stretch
3,000-2,800119,120 C-H stretch in alkanes and alkenes
1,760-1,73594,97 C=O stretch from ester formed by acylation reactions (~1760 – phenolic; ~1740 – aliphatic)
1,710-1,690119,120 C=O stretch in ketones, carbonyls, and esters (may originate from carbohydrates).
C=O stretch in carboxylic acids and aldehydes.
1,605-1,590119,120 Aromatic skeletal vibrations plus C=O stretch
1,515-1,505119,120 Aromatic skeletal vibrations
1,330-1,320119,120 S-units and condensed G-units
1,035-1,025119,120 Aromatic C-H in plane deformation; C-O deform in primary alcohols; C=O stretch
860-850119 C-H out-of-plane in position 2, 5, and 6 of G-units
To assess the impact of the acylation reactions, the FT-IR spectra of the lignin samples
were analyzed from 4,000-1,500 cm-1 (Figure 22; W-lignin recovered from HWE of willow, WAc-
W acetylated, WFAE-W acylated with lauroyl chloride, WFAEH-WFAE after hexane extraction). It
can be observed that the absorbance from 3,600-3,000 cm-1, which represents hydroxyl groups,
was diminished following both acetylation and acylation with lauroyl chloride. In addition, the
spectra of all acylated lignins display a band that may be assigned to the ester linkages formed
Figure 21 - FT-IR spectra of non-acylated lignins studied
45
with phenolic hydroxyl groups of lignin (1,760 cm-1), based on the band assignment from Table
10. Based on the FT-IR spectra it was found that WAc was the only acylated lignin sample with
aliphatic ester linkages at Cα and/or Cγ (1,740 cm-1). In addition, the two methods of acetylation,
with varying ratios of pyridine:acetic anhydride (1:1 and 0.4:1), did not have any observable
differences in the FT-IR spectra. The FT-IR spectral analysis suggests that acylation with lauroyl
chloride favored phenolic hydroxyl groups since the spectra of WFAE and WFAEH did not display
the band representing aliphatic ester linkages at 1,740 cm-1.
Unexpectedly, WFAE exhibits a strong band at about 1700 cm-1 that may be assigned to
carboxyl groups (Table 10), indicating the presence of the unbound fatty acid, lauric acid97. This
is supported by the presence of equally strong bands from 3000-2800 cm-1 that represent long
chain alkyl groups present in the free fatty acid (Table 10), in this case C12 saturated aliphatic
chains. It has been reported that acid chlorides may be hydrolyzed back to the free acid form in
the presence of water (Figure 23)121. In accordance with the acylation method used94,
unreacted lauroyl chloride is exposed to an aqueous solution during precipitation of the WFAE.
Figure 22 - FT-IR spectra of W before and after acylation reactions
H
46
It may be hypothesized that at this point lauroyl chloride is hydrolyzed back to lauric acid, which
is not easily removed by the washing procedure outlined in literature94. In similar studies on the
synthesis of lignin acylated with fatty acid chlorides, the reported FT-IR spectra contain a band
at around 1700 cm-1 as well94,95. However, the presence of the free fatty acid was not
mentioned94 or the free fatty acid was considered removed from the lignin sample95.
In an effort to remove the lauric acid contaminant from WFAE, hexane extraction was
explored in this research. After hexane extraction, WFAEH was obtained. FT-IR results (Figure
22) revealed that the carboxylic acid band (1,700 cm-1) and bands representing alkanes (3,000-
2,800 cm-1) were both notably reduced in WFAEH in comparison to those in WFAE. These results
suggest that hexane extraction was successful in removing the large amount of unbound fatty
acid from WFAE, the lignin laurate. There is still a noticeable increase in the bands from 3,000-
2,800 cm-1 following the removal of the free fatty acid by hexane extraction, when comparing
WFAEH to W. These bands may be assigned to C12 saturated chains in the sample (Table 10).
This, in addition to the presence of the band at ~1,760 cm-1 representing phenolic ester linkages
(Table 10), indicates that the lignin laurate is still intact in WFAEH. FT-IR spectra are shown
individually in Appendix C, along with spectra from preliminary studies on W, miscanthus, and
wheat straw lignins recovered from the respective hydrolysates of HWE.
Figure 23 - Proposed mechanism of lauroyl chloride being converted to lauric acid
47
Hydroxyl Group Content of Lignins – 31P NMR Analysis
The hydroxyl group content of the acylated willow lignins, WAc, WFAE, and WFAEH in
comparison with that of willow lignin, W was analyzed through 31P NMR (Figure 24). WAc was
observed to have 100% degree of substitution of the phenolic and aliphatic (primary and
secondary) hydroxyl groups, regardless of the pyridine:acetic anhydride ratio (1:1 or 0.4:1).
Acylation with lauroyl chloride was incomplete, as the presence of free aliphatic and phenolic
hydroxyl groups in WFAE was noticeable. It was calculated that the content of free aliphatic and
phenolic hydroxyl groups was reduced by ~73% and ~85%, respectively, compared to that of W.
Interestingly, 31P NMR analysis showed a reduction in the content of aliphatic hydroxyl groups
even though the FT-IR spectra (Figure 22) did not show the presence of aliphatic ester linkages
at ~1740 cm-1.
Due to the greater reduction of phenolic than aliphatic hydroxyl groups, it may be
concluded that acylation with lauroyl chloride was obstructed, most likely by steric hindrance,
specifically at the aliphatic hydroxyl groups. Previous research by Hult et al. (2013) on acylation
Figure 24 - Hydroxyl group content of W, WAc, WFAE, and WFAEH (from 31P NMR analysis)
48
of lignin with fatty acid chlorides (C16-C20 fatty acids present in tall oil) also showed a greater
reduction in phenolic hydroxyl groups, providing evidence that phenolic hydroxyl groups tend
to react more readily95. In contrast to these results, Koivu et al. (2016) observed that aliphatic
hydroxyl groups reacted faster than phenolic hydroxyl groups in similar reactions97. This may
indicate how slight structural differences between lignins, such as the degree of condensation,
could impact acylation reactions that specifically involve longer chain moieties.
Confirming the FT-IR results (Figure 22), WFAE experienced a large increase of carboxyl
groups (1.61 mmol/g) compared to W (0.41 mmol/g). Hexane extraction was again shown to be
successful in reducing levels of the free fatty acid, lauric acid. This was indicated by the
reduction in carboxyl groups in WFAEH (0.45 mmol/g) compared to before hexane extraction in
WFAE (~72% reduction in carboxyl groups). Analysis of hydroxyl group content also showed that
the aliphatic and phenolic hydroxyl group content in WFAEH was reduced by ~80% and ~70%,
respectively.
Thermal Analysis of Lignins (DSC and TGA)
Thermal analysis was conducted by TGA and DSC methods. Tg, Tm, and Td of studied
lignin samples were determined by these methods to assess the impact of the acylation
reactions. In addition, TGA and DSC results demonstrated the presence of the unbound fatty
acid, lauric acid, in WFAE corroborating the FT-IR and 31P NMR results.
49
As expected, based on DSC analysis, the Tg correlated to lignin decreased after the
acylation reactions, acetylation and acylation with lauroyl chloride (Figure 25). The anticipated
greater decrease in Tg in the case of lignin acylated with a longer chain was not observed97.
Incomplete acylation after the reaction with lauroyl chloride (C12) resulted in a smaller change
in Tg than in the case of a complete short-chain acylation, acetylation (C2), reaction. WFAE was
the only lignin detected to possess a Tm, which was observed at ~40 °C. This can be due to a
substantial amount of unbound fatty acid present in WFAE which is known to melt just below
40 °C122. Therefore, the unbound fatty acid, lauric acid is the likely source of the melt phase
observed as it is improbable lignin, being amorphous, melts. Based on our results, the Tg
reported in the study of different lignins acylated with lauroyl chloride94, a chloride derivative
of lauric acid, may be attributed to the Tm of the unbound lauric acid. Based on the results of
Figure 25 - DSC thermogram of lignins
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50
this research, it was proposed that unreacted lauroyl chloride is converted back into lauric acid
when exposed to water during precipitation in an aqueous solution (Figure 23) and remained in
the lignin laurate following filtration and washing.
In addition to providing the Tg and Tm (DSC - Figure 25), and Td (TGA - Figure 26), thermal
analysis revealed that during acylation, lignin may have undergone some purification. The DSC
thermogram of W displayed two Tg values, with the lower Tg (~105 °C) indicating the presence
of impurities. The higher Tg (~145 °C) may be attributed to lignin20. W following alkali
purification (WAP) no longer displays a lower Tg associated with impurities, demonstrating
removal of impurities by alkali purification. However, W following acylation (WAc, WFAE, and
WFAEH samples) and KL (kraft lignin) did not display more than one Tg either. The Tg of KL (~111
Figure 26 - TGA thermogram of lignins
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51
°C) is consistent with that of the literature which is 93 °C and 119 °C of hardwood and softwood
kraft lignin, respectively, while the same source lists the Tg of Alcell lignin as 70 °C123.
Prior to the lignin degradation peak above 350 °C, TGA of W exhibited a broad
degradation shoulder from 100-200 °C, which was missing in the thermograms of KL and WAP.
This demonstrates, similarly to the DSC thermogram, that alkali purification was able to remove
impurities, specifically those that degrade in the 100-200 °C range. Acylated W samples have a
narrower and stronger degradation peak just above 200 °C, but the broad shoulder from 100-
200 °C is no longer present. Following acylation, the lower Tg and the 100-200 °C degradation
shoulder observed in the DSC and TGA thermograms of W, respectively, were eliminated. These
results imply that there is a purification effect of acylation on lignin, resulting in at least partial
removal of impurities such as low molecular weight organic compounds, including
carbohydrates. However, further research such as HSQC analysis would be required to confirm
this hypothesis.
The TGA thermogram of all acylated W samples displayed a narrow peak around 200 °C.
This peak is the greatest in the WFAE sample. This sample was found to contain a large amount
of the unbound lauric acid from FT-IR and 31P NMR analysis (Figure 22 and Figure 24). It is
hypothesized that the 200 °C degradation peak is associated with the unbound fatty acid, lauric
acid. However, a smaller peak at 200 °C is still present in WFAEH and in WAc samples. In
addition, the degradation peak at ~200 °C may also be associated with the cleavage of the ester
linkages in acylated lignins. Subsequently, the resulting alkyl chain will degrade as well as the
unbound lauric acid. For clarity, individual thermograms of the lignins studied for DSC and TGA
may be found in Appendices D and E, respectively.
52
Molecular Weight Distribution of Lignins – Size Exclusion Chromatography (SEC)
Prior to testing by SEC, lignin should be functionalized, typically by acetylation, for
complete dissolution in the eluent (normally tetrahydrofuran - THF). Therefore, W was not
considered in this study. The SEC results show a minor variation between the samples produced
by the two methods of acetylation (varying amount of pyridine and time), and also between
lignin samples C12- acylated with lauroyl chloride, WFAE and WFAEH, before and after hexane
extraction, respectively (Table 11). It was found that C12-acylated lignins had a lower
polydispersity than the acetylated lignin, WAc. When considering alkali purified W, WAP,
acetylation of the sample was done to ensure dissolution in the eluent, THF (pyridine:acetic
anhydride ratio of 1:1 was used in acetylation for 24 hours). The results in Table 11 revealed
that the number average and weight average molecular weights of acetylated WAP increased
more than 2x and 10x, respectively, when compared to the WAc samples. However, increased
molecular weight of lignin is not desired for use in lignin-thermoplastic blends80. Previous
literature shows that lignins recovered from the kraft pulping process have a number average
and weight average molecular weight ranging from 500-1500 Da and 1,000-7,200 Da,
respectively (Table 7).
Table 11 - Molecular weight distribution of acylated lignins
WAP Acetylated WAc (1:1) WAc (0.4:1) WFAE WFAEH
Mn (Da) 4,200 1,500 1,600 2,200 2,200
Mw (Da) 17,000 3,300 3,800 3,900 3,900
Polydispersity 4.0 2.2 2.4 1.8 1.8
53
Antioxidizing Activity (AOA) of Lignins
As it was shown in previous literature, lignin can contribute its intrinsic antioxidizing
activity (AOA) to polymer blends78. This capability of lignin as a radical scavenger may provide
an additional avenue to prevent PLA degradation while also protecting the contents of the
packaging from free radicals, such as reactive oxygen species. AOA is measured as the amount
of a given radical scavenger (mg/mL) needed to quench 50% of the free radicals from a radical
producing compound (such as DPPH) in the solution, which is referred to as IC5015. A lower IC50
indicates a more potent radical scavenger. The antioxidant activity of W, WAc, and KL were
compared to that of 3,5-di-tert-butyl-4-hydroxytoluene (BHT) and ascorbic acid, as a relatively
weak and powerful radical scavenger, respectively (Figure 27). W and KL both proved to be
more effective radical scavengers than BHT; however neither was as effective as ascorbic acid.
Meanwhile WAc, which had no remaining phenolic or aliphatic hydroxyl groups, had more than
a 20x increase in IC50 (reduced radical scavenging ability) when compared to W. Even when
compared to BHT, the IC50 of WAc is more than 2x greater.
Figure 27 - AOA (IC50) of selected lignins and standard antioxidants (*-value obtained from Pan et al., 200614)
54
Dizhbite et al. (2004) emphasized that phenolic and aliphatic hydroxyl groups,
specifically primary aliphatic hydroxyl groups, are beneficial for AOA15. However Pan et al.
(2006) reported a negative effect of aliphatic hydroxyl groups on the radical scavenging
capabilities of lignin while they confirmed that phenolic hydroxyl groups are essential14. In
regard to our results, the low AOA of WAc demonstrated that free hydroxyl groups, specifically
phenolic hydroxyl groups, are imperative to lignin’s radical scavenging capabilities14,15. Further
studies would be required to determine the impact of aliphatic hydroxyl groups on lignin’s
radical scavenging capabilities through selective acylation of aliphatic hydroxyl groups.
UV Absorbance of Lignins
The UV absorbance spectra of willow lignin recovered from HWE, W, and kraft lignin, KL,
are shown in Figure 28. Spectra for other lignins studied are included in Appendix F. UV-light
can be split into three regions; UVC (100-279 nm), UVB (280-319 nm), and UVA (320-400
nm)124. The spectral areas in each of these regions were compared as well, with the UVC only
Figure 28 - UV absorbance spectra of KL and W in dioxane:water (96:4)
UVC (200-279 nm)
UVB (280-319 nm)
UVA (320-400 nm)
55
being considered from 200-279 nm (the Genesys 10 Series Spectrophotometer is only capable
of going down to 200 nm). An absorbance peak/shoulder at ~280 nm is present in all lignin
samples and is correlated to phenylpropanoid units125.
When comparing W to the widely available KL, it can be observed that KL has about a
33% greater UV absorbance (Figure 29). Additionally, the UV-absorbance spectra show that the
peak around 280 nm is more distinct in KL than W (Figure 28). The reason for this likely stems
from the differences in monomeric composition between these two lignins. As discussed in the
FT-IR analysis, KL is mainly comprised of G-units while W is made up of both S- and G-units. It is
known that the absorptivity of G-units at 280 nm is 3.5 times greater than that of S-units126.
Another study reported a similar trend, although only about a 2.3x difference between these
units was found127. It has also been shown that the absorptivity of hardwood lignin at ~280 nm
decreases with increasing the methoxyl group content, i.e. with increasing the S/G ratio125. A
high absorptivity at a specific wavelength may be translated to a higher overall UV absorbance.
In this case, KL is expected to have a greater overall UV absorbance as a result of being
comprised of mainly G-units. The UV absorbance spectra of KL may also be enhanced due to the
presence of stilbene, α-carbonyl, and conjugated groups formed during the kraft pulping
process125. The presence of these conjugated compounds may also lead to a bathochromic shift
(to higher wavelengths) of the peak at ~280 nm. Hardwood lignin, which is known to contain S-
and G-units, has been observed to have the peak at 280 nm shifted to shorter wavelengths125.
More specifically it has been reported that the absorbance maximum of 1-syringylpropane is
located at 272-273 nm while the absorbance maximum of 1-guaiacylpropane is located at 279-
280 nm127. These findings explain why the characteristic lignin peak ~280 nm is present at
56
slightly higher wavelengths in KL and slightly lower wavelengths in W. The presence of α-
carbonyl and conjugated compounds may also be responsible for the elevated UV absorbance
of KL between ~280 nm and ~340 nm (Figure 28). It has been reported than α-carbonyl
containing compounds have a UV absorbance maximum from 300-310 nm while that of lignin
end units, coniferyl alcohol and coniferyl aldehyde, bound by a β-O-4 linkage to lignin are at
295-298 nm and 340-343 nm, respectively127.
To evaluate the ability of lignin to block and absorb the UV light, preventing its effect on
the surrounding material, the total area under the spectral curves from 200-400 nm was
calculated (Figure 29). It is observed that acylation of lignin resulted in a decrease in the total
UV absorbance across this range with the effect lessening in the following order:
UVA>UVB>UVC (WAc and WFAEH vs. W). The decreased UV absorbance of acylated lignins may
Figure 29 - Total UV absorbance of lignins from 200-400 nm
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57
be attributed to the substitution of PhOH125, which were shown to significantly contribute to
the UV absorption128. When compared to W, the total UV absorbance of WFAEH and WAc was
reduced by ~20% and ~25%, respectively. It is worth noting that W has a greater total UV
absorbance than the lignin that remained in the biomass following HWE and was isolated as
milled wood lignin (HWE W MWL), which was included for comparison. The decrease in total
UV absorbance of HWE W MWL in comparison to that of W follows trends noticed for the
acylated lignins with a 19% decrease in the total UV absorbance. The decrease in UV
absorbance of HWE W MWL may also be the result of a lower content of PhOH. It is clear that
the acylated lignins would have a lower phenolic hydroxyl group content than W. However,
HWE W MWL is expected to be of higher molecular weight than W which would indicate a
lower PhOH content. Other factors must also be considered to accurately identify the reason
for reduced total UV absorbance of HWE W MWL, such as the lignin composition.
It was confirmed that lignin is intrinsically UV absorbent; in addition absorption at ~280
nm is due to the lignin phenylpropanoid units and at lower wavelengths (in this case ~240 nm)
is due to the aromatic rings126. Overall, lignin absorbs the most UV light in the UVB and UVC
ranges, proving lignin absorbs UV light from 200-300 nm. This range is significant because it is
the range of light where PLA was found to be the most susceptible to photodegradation71.
Therefore, it is expected that all lignins, when used in lignin-PLA blends, would serve as UV-light
blockers preventing photodegradation of PLA. The results from literature showing reduced
impact on mechanical properties from UV-assisted accelerated weathering when comparing
lignin-PLA blends to pure PLA support this hypothesis76.
58
Theoretical Calculation of Lignin’s Hansen Solubility Parameters
Expected values for each Hansen solubility parameter for the lignins utilized in this
research, and the difference between the solubility parameters for PLA and each lignin (RA)
were calculated (Table 12). It is known that the radii of PLA’s and Björkman lignin’s hypothetical
spheres are 10.782 and 13.786,90, respectively. Ideally, the distance between the solubility
parameters for lignin and PLA (RA) should be well below the radii of each of their spheres. This
would allow for greater overlap between the two spheres which is indicative of compatibility
between lignin and PLA82. The results from 31P NMR were factored into calculations of the
Hansen solubility parameters for W, WAc, and WFAEH lignins. While WFAEH had an incomplete
substitution of hydroxyl groups, a theoretical scenario was considered as if WFAEH had
complete substitution. When comparing solubility parameters of Björkman lignin from spruce86
and W it can be seen that there is a little difference between the two. Both δp and δh of
Björkman lignin fall within the range of the corresponding solubility parameter of W while δd is
slightly above the corresponding range of W. As expected, following acylation, the RA between
PLA and the given lignin decreases with chain length and degree of substitution. The δh
solubility parameter was the most influenced by the acylation reaction, being decreased by
more than 9 MPa1/2, which was observed for WFAEH with 100% degree of substitution.
Table 12 - Hansen solubility parameters of lignins calculated by a group contribution method
Solubility
Parameters PLA82
Björkman Lignin
-Spruce86 W* WAc*
WFAEH - 75% reduced
-OH by 31P NMR data*
WFAEH - complete
substitution (100%)*
δd (MPa1/2) 18.6 21.9 20.7-21.5 20.4-21.3 20.3-21.1 20.1-20.9
δp (MPa1/2) 9.9 14.1 12.5-16.1 11.3-14.7 11.5-14.8 10.9-14.3
δh (MPa1/2) 6 16.9 15.4-17.0 10.5-12.1 9.8-11.3 6.2-7.8
RA 0.0 13.4 10.6-13.9 5.9-9.4 5.4-8.8 3.2-6.7
* – values calculated by group contribution method outlined in experimental87
59
Characterization of Lignin-PLA Thermoplastic Blends
Light Microscopy – Image Analysis of Lignin-PLA Blends
Lignin-PLA blends produced with 1% lignin by mass were examined via light microscopy
to assess the homogeneity of blends and compatibility between PLA and the different lignins
(Figure 30). PLA blends with kraft lignin, KL and willow lignin, W (crude, not acylated) were
analyzed as a reference and to ensure improvement in compatibility following acylation
reactions, respectively. As previously discussed, while a completely homogenous (miscible)
polymer blend is not required, improved miscibility in polymer blends does indicate better
compatibility83,84.
W following alkali purification, WAP, seemed to have reduced miscibility in the polymer
blend when compared to W. WAP was not considered in subsequent experiments due to this
qualitative result, in conjunction with a low process yield from alkali purification (see Appendix
B), significantly higher molecular weight (Table 11). In addition, thermal analysis of lignins
A
F D
C B
E
Figure 30 - Light microscopy images of PLA and 1% lignin-PLA blends (A-1% KL; B-1% W; C-1% WAP; D-PLA; E-1% WFAEH; F-1% WAc)
60
(Figure 25 and Figure 26) that suggested there was a purification effect of acylation on its own,
accomplishing a similar goal.
Based on light microscopy results, blends with acetylated and hexane purified C12-
acylated W (1% WFAEH and 1% WAc) were observed to have improved miscibility compared to
blends with W and therefore, a better compatibility with PLA. The 1% WFAE blend also followed
this trend (as seen in Appendix H), but was not considered in this section due to the high levels
of the free fatty acid that are not observable by light microscopy. This demonstrated a need for
acylation, or in general for derivatization of lignin, to improve its compatibility with PLA. Due to
the low process yield following hexane extraction of WFAE (~50%) and approximately equal
compatibility achieved (compared to WAc), WFAEH was not selected to be blended with PLA at
concentrations greater than 1% by mass.
Thermal Properties of Lignin-PLA Blends (DSC and TGA)
Based on thermogravimetric analysis (TGA), the degradation temperature (Td) in lignin-
PLA blends when compared to pure PLA (Table 13) exhibited a slightly greater Td, with
exception to the 1% KL blend. The data also suggests that there is a slight increase in Td when
1% acylated lignins (WAc, WFAE, and WFAEH) are utilized as compared to the 1% W blend. This
indicates that improved miscibility may be beneficial for thermal properties because blends
that demonstrated improved miscibility also displayed improved thermal properties.
61
Table 13 - Summary of lignin-PLA blends thermal properties
Based on the DSC thermograms, all blends exhibited two different melt temperatures,
both of which fell within 145-160 °C (Figure 31). While there are numerous crystal polymorphs
of PLA, only α’- and α-crystals are formed during typical industrial processes like melt
extrusion68. The first Tm represents the melting of α’-crystals, while the second Tm represents
melting of α-crystals. While α’- and α-crystals are very similar in structure the main difference is
that α’-crystals are slightly disordered, while α-crystals have a tighter, more organized
Blend Tg (°C) Tc (°C) Tm1-α’ (°C) Tm2-α (°C) Tm1:Tm2* Td
PLA 55.8 105.7 150.5 158.7 1.85 356.5
1% KL 56.5 105.8 150.5 157.6 1.72 351.4
1% W 58.2 97.3 150.0 159.6 0.74 357.7
1% WAc 58.8 108.1 152.4 157.6 3.55 366.9
6% WAc 53.3 104.1 147.9 157.1 1.78 359.8
12% WAc 51.5 100.7 146.9 155.7 1.19 361.5
1% WFAE 54.6 98.0 146.8 155.9 0.43 365.4
7% WFAE 50.1 98.3 145.4 155.4 2.05 366.4
1% WFAEH 57.9 99.6 148.5 158.3 0.37 363.3
*Tm1:Tm2 is the ratio of the area within the melt phase transition on the second heat. The area within each melt
phase transition was calculated by TA Universal Analysis software and given in J/g.
62
structure63,69. It was determined that α’-crystals are formed at relatively low crystallization
temperatures, below 110 °C upon a fast cool. Meanwhile α-crystals are formed at crystallization
temperatures at or above 120 °C. However, upon heating the α’-crystals may be transformed
into α-crystals, irreversibly70. It is important to note that there are two potential avenues, when
executing DSC, in which α’-crystals will be transformed into α-crystals. One way this
transformation may occur is through solid-solid phase transition which is observed by the Tc68.
The alternative method is that at slow heating temperatures α’-crystals are melted and then
recrystallized as α-crystals prior to the second Tm63
.
The ratio between the first Tm, representing α’-crystals, and the second Tm, representing
α-crystals, is hypothesized to indicate each lignins ability to act as a nucleating agent for
crystallization and which crystal form is favored in each blend based on the lignin used. It is
Figure 31 - DSC thermogram of PLA
63
observed that this ratio is increased with blends containing 1% WAc, suggesting it favors the
formation of α’-crystals while perhaps disrupting the formation α-crystals due to its high
miscibility. Increasing lignin content in blends made with WAc brings about a reduced
miscibility and appears to be a more active nucleating agent in promoting the formation of α-
crystals. The lignin laurate and crude lignins seemed to promote the formation of α-crystals
more readily. However, elevated levels of lauric acid seem to disrupt α-crystals and favor
formation of α’-crystals.
The DSC results also revealed that the 1% WAc blend produced the highest Tg and Tc
(Table 13). The only blend to have higher Tm values than 1% WAc was 1% W, with both values
being greater than that of 100% PLA. It is largely accepted that if a polymer blend demonstrates
a single Tg, the blend components are miscible. However, this is typically only appropriate if all
components make up at least 10% w/w of the blend83. Therefore, while all blends displayed a
single Tg, only WAc can be considered miscible in the PLA blends produced since the 12% WAc
blend displayed a single Tg. It is also interesting to note that the Tc of blends containing KL was
maintained, while that of blends containing W was decreased. In the meantime, the Td of
blends containing KL was decreased, while that of blends containing W was increased. DSC
thermograms done with a 2 °C and 10 °C heating rate are shown in Appendix I, while TGA
thermograms are shown in Appendix J.
64
Mechanical Properties of Lignin-PLA Blends
Overall, mechanical properties of lignin-PLA blends (Figure 32) were negatively impacted
by the addition of kraft (KL) or willow lignin (W), even with just 1% lignin by mass. Blends
containing 1% of any of the acylated willow lignins (WAc, WFAE, WFAEH) better maintained the
mechanical properties of PLA with less than a 6% decrease in tensile strength (peak stress) as
compared to an 8.4% drop in 1% W blends. The greatest ability to maintain the tensile strength
of PLA was demonstrated by the 1% WFAEH blend, with only a 2.9% decrease in peak stress.
Furthermore, acylated lignins favorably reduced the impact of adding lignin on tensile strength
(peak stress) of PLA by 30-65% compared to crude lignin (W) in 1% lignin-PLA blends. Strain at
peak and elastic modulus of PLA were also better maintained in the blends containing 1% of any
of the acylated lignins compared to 1% W blend. However, the elastic modulus of the 1% WFAE
blend had a 28.7% change compared to pure PLA. Meanwhile, the other 1% acylated lignin
blends and 1% W had up to a 13.1% change and a 16.2% change compared to PLA, respectively.
65
Interestingly, the elastic modulus was
increased in blends containing lignin, with the
exception of blends containing WAc,
indicating increased stiffness in most lignin-
PLA blends. It was demonstrated that blends
with maintained or increased elasticity can be
produced with WAc lignin. These findings may
support observations from light microscopy
image analysis that showed increased
miscibility of lignin-PLA blends produced with
the use of WAc. It is hypothesized that lignin
with increased miscibility in PLA disrupts the
formation of more orderly crystalline PLA, α-
crystals, leading to a greater amount of the
slightly disordered α’-crystals. Meanwhile,
lignin that is immiscible in PLA blends, such as
crude lignin (W), may act as a nucleating
agent, promoting the formation of α-crystals.
It has been reported that PLA with a lower
fraction of α-crystals and higher fraction of α’-crystals displays a lower elastic modulus, or
greater elasticity69. On the other hand, the blend containing 1% WFAE had the highest elastic
H
H
H
Figure 32 - Mechanical properties of 1% lignin-PLA blends
66
modulus of all 1% lignin blends, which implies that the free lauric acid, remaining in lignin after
acylation with lauroyl chloride, increases the stiffness of blends.
At concentrations of more than 1% lignin by mass, mechanical properties decrease
further and differences between PLA blends
produced with different lignins become
greater (Figure 33). The higher concentrated
WAc blends still had improved strain and
elastic modulus when compared to the 1% W
blends. Meanwhile, peak stress declined even
below that of the 1% W blends in both the 6%
and 12% WAc blends, diminishing as much as
20.3% from that of pure PLA. On the other
hand, all mechanical properties of the 7%
WFAE blend were deteriorated more than
those of the 1% W blend, while the elastic
modulus displayed the greatest change.
Compared to pure PLA, peak stress and
elastic modulus of 7% WFAE were reduced by
31.5% and increased by 56.6%, respectively.
These results demonstrate the need to
remove the free fatty acid through hexane
extraction, as its presence is having a Figure 33 - Mechanical properties of lignin-PLA
blends with more than 1% lignin
67
significant negative impact on all mechanical properties. In each mechanical property
considered in this study, the 7% WFAE blend was inferior to other blends, even the 12% WAc
blend. The original data used can be seen in Appendix K.
UV Absorbance of Lignin-PLA Blends
Comparative analysis of the UV absorbance of lignin-PLA blends and of pure PLA showed
at least a 10x, and up to a 17.5x increase in total UV absorbance (200-400 nm) in lignin-PLA
blends (Figure 34). In packaging applications this will provide a significant increase in UV
protection for the contents of the package. This makes lignin-PLA blends specifically attractive
for food packaging or other applications where the contents of the packaging are sensitive to
UV light17. The overall trend between lignin-PLA blends is consistent with the trend observed
between the UV absorbance of each individual lignin. For example, 1% KL blends absorbed
~33% more UV light in this range than 1% W blends, the same difference as the respective
Figure 34 - Total UV absorbance of selected lignin-PLA blends from 200-400 nm
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68
lignins. Blends with increased lignin concentration had increased UV absorbance directly
correlated to the lignin content. All UV absorbance spectra of lignin-PLA blends measured can
be seen in the Appendix L.
Conclusions
These studies investigated the use of biorefinery lignin, specifically recovered from
hydrothermal pretreatment, hot-water extraction (HWE lignin) as a component in lignin-
thermoplastic blends with PLA. Throughout this research, numerous lignin and polymer blend
properties were analyzed and discussed. The subsequent conclusions, which have been made in
this work will be outlined in this section. Prior to experimentation, the type of HWE lignin,
differentiated by feedstock, was selected based on the lignin content, hydroxyl group content,
molecular weight, and S/G ratio. As a result, lignin recovered from the hydrolysate from the
HWE of willow, W, was chosen for its relatively low hydroxyl group content and molecular
weight. These properties were deemed to be favorable in previous literature on lignin-
thermoplastic blends80. When it comes to the production of lignin-PLA blends, melt extrusion
was selected over solvent casting. Melt-extrusion was capable of producing blends with lignin
more evenly dispersed throughout the PLA matrix.
When comparing the properties of the crude lignin (W) utilized in this work to those of
the industrial standard, kraft lignin (KL), numerous similarities may be noticed, but some
differences do stand out. Specifically, based on thermal analysis (DSC and TGA) KL was shown to
have less organic impurities of low molecular weight, which may include some carbohydrates.
69
However, more important for the objectives of this research, KL exhibited 33% higher total UV
absorbance from 200-400 nm than W, likely due to the higher concentration of G-units and the
presence of stilbenes, α-carbonyls and other conjugated groups in KL125. The same trend was
observed for the UV absorbance of the respective blends containing these lignins. Light
microscopy – image analysis and mechanical properties of lignin-PLA blends showed that KL had
similar compatibility with PLA as W. However, thermal properties of lignin-PLA blends
containing KL and W did not necessarily follow the same trends. For example, the Td of blends
containing KL decreased, while that of blends containing W favorably increased in comparison
to Td of PLA as a reference as seen in Appendix J.
Alkali purification was evaluated as a means to remove impurities that may negatively
impact lignin-PLA blends. Based on the thermal analysis of lignins, it was concluded that alkali
purification was not needed, as the acylation reactions may have a purification effect on their
own. In addition, light microscopy – image analysis and molecular weight determination studies
demonstrated negative effects of alkali purification on the blending capabilities of lignin with
PLA. They may be attributed to an increase in molecular weight of the purified lignin that
further reduces its miscibility in PLA.
The efficacy of acylation reactions on W was largely influenced by the specific type of
acylation (acetylation – C2 vs acylation with lauroyl chloride – C12). Based on 31P NMR analysis of
free hydroxyl groups in lignins, acetylation achieved 100% degree of substitution. Meanwhile,
acylation with lauroyl chloride, a chloride derivative of lauric acid, did not reach completion,
although a notable drop in hydroxyl group content was still observed.
70
FT-IR spectral analysis first indicated that during precipitation of the lignin laurate (in an
aqueous solution), the unreacted lauroyl chloride was hydrolyzed back to the free fatty acid,
lauric acid, and remained in the lignin laurate. This was later confirmed by 31P NMR hydroxyl
group analysis, due to the unusually high presence of carboxylic acids in the sample. Hexane
extraction was proposed in this research to remove the free lauric acid from the lignin laurate.
The FT-IR spectral and 31P NMR results, indicating a significant reduction in the carboxyl group
content, confirmed that hexane extraction resulted in a purer lignin laurate sample, with a
smaller amount of remaining free fatty acid, lauric acid. Mechanical properties of lignin-PLA
blends containing the lignin laurate demonstrated the need to remove lauric acid. Blends
containing 1% and 7% WFAE (lignin laurate prior to hexane extraction) had the most significant
changes in mechanical properties compared to PLA. Meanwhile, blends containing 1% WFAEH
(lignin laurate following hexane extraction) was the closest to maintaining the tensile strength
of PLA. This indicated that the presence of the free fatty acid, lauric acid, has a negative impact
on mechanical properties, specifically tensile strength. Additionally, unbound lauric acid may
introduce thermal instability to the blends due to its low Tm and Td.
Both acylation reactions demonstrated the ability to measurably impact lignin’s
physicochemical properties. As expected, thermal analysis by DSC indicated that both reactions
reduced the Tg of lignin94,95,97. However, when evaluating the TGA thermograms, it was
determined that all acylated lignins (WAc, WFAE, and WFAEH) developed a degradation peak
~200 °C. It is hypothesized that these degradation peaks correlate to the cleavage of the ester
linkage formed by acylation, but in the case of WFAE this degradation peak may also be
correlated to the degradation of the unbound fatty acid, lauric acid. The thermal sensitivity of
71
acylated lignins just above processing temperatures for extrusion is of concern when scaling up
the production of lignin-PLA blends. Another undesired outcome of acylation was the impact on
the UV absorbance and antioxidizing activity of lignins. Following acylation it was observed that
there was up to a 25% decrease in UV absorbance and a more than a 20x decrease in radical
scavenging capabilities of lignin. Both of these results were mainly the consequence of
substituting the PhOH during acylation14,15,125,128.
Nonetheless, lignin-PLA blends containing the acylated lignins showed improved
compatibility with PLA over the crude lignin, W, based on theoretical calculation of lignins
Hansen solubility parameters, with the hydrogen bonding parameter (δh) being the most
impacted by acylation. This was supported by the improved miscibility of acylated lignins in
lignin-PLA blends observed by light microscopy when compared to blends containing W. Even
though UV absorbance of lignin was reduced by up to 25% following acylation, acylated lignins
still demonstrated notable UV absorbing capabilities. Blends containing 1% of the acylated
lignins showed at least a 10x increase in UV absorbance when compared to pure PLA. These
results demonstrated the potential of providing substantial protection to UV-sensitive contents,
such as foods, in packaging applications, while also preventing UV photodegradation of PLA in
numerous other applications, in addition to packaging. In general, lignin-PLA blends containing
acylated lignins were able to better maintain the mechanical properties of pure PLA as
compared to those containing crude lignin (W). Specifically, the change in tensile strength of
PLA after 1% lignin addition was favorably reduced by 30-65% when using acylated lignins as
compared to crude lignin. An increase in the elastic modulus of lignin-PLA blends containing
crude lignin (W and KL) indicated increased stiffness. It is hypothesized that this is the result of
72
the crude lignins favored α-crystal formation over α’-crystals based on DSC analysis.
Meanwhile, with the addition of acetylated lignin (WAc) the elastic modulus was maintained or
even decreased. This correlates to the tendency of WAc lignin to favor the formation of α’-
crystals in lignin-PLA blends compared to crude lignins based on DSC analysis. Thermal analysis
by DSC and TGA showed that Tg, Tc and Td of lignin-PLA blends were increased in blends
containing WAc compared to pure PLA while the two Tm values were slightly decreased.
Overall lignin-PLA blends with WAc lignin are promising as an active packaging material
providing UV protection to its contents and potentially PLA while, for the most part, limiting
undesired changes in mechanical and thermal properties. W, WFAE, and WFAEH also showed
positive results that could be leveraged for value added applications of lignin. However, use of
KL seemed to be the best option for applications where UV absorbance and antioxidizing
activity are of the utmost importance.
Future Work
Exploration of other lignins (recovered from different feedstocks and/or processes) for
improving effectiveness of acylation and compatibility with PLA.
Determine compatibility of other biobased polymers, such as PHA, with C2 and C12
acylated lignins.
Refinement of acylation reaction of lignin with fatty acid chlorides, such as lauroyl
chloride, to reach completion. This could include exploration of reaction conditions such
as a different solvent, fatty acid chloride or variation in temperature.
73
Explore electro-spinning or solvent casting further while considering work done on
solvent evaporation from polymer films81. A potential solution to some issues observed
in solvent casting may be associated with the grade of PLA; other PLA grades may be
more compatible with the lignins than the PLA studied in this work.
Consideration of different types of chemical modification (as compared to acylation) to
mask hydroxyl groups of lignin for use in thermoplastic blends would be of value,
especially considering the thermal sensitivity of the ester linkage. Chemical modification
of lignin previously explored includes etherification such as oxypropylation or
phenolation11. However, these reactions will maintain or increase the number of
hydroxyl groups per lignin monomer, respectively, which is not desired in lignin-
thermoplastic blends80. Therefore, evaluation of more novel methods may be more
fruitful.
Another avenue that could be explored in acylation or any other chemical modification
would be the selective masking of primary and secondary free aliphatic hydroxyl groups.
Preserving the PhOH could allow the lignin derivative to better maintain its intrinsic
antioxidizing and UV absorbing properties14,15,125,127. Subsequent evaluation of how the
presence of phenolic versus aliphatic hydroxyl groups impacts compatibility with PLA, in
addition to the physicochemical properties of the resulting lignin and lignin-PLA blends
would also be of interest.
The lignin laurate that still contained the unbound lauric acid presented unique and
interesting properties. Specifically, the presence of the free lauric acid could be
74
leveraged in different applications, including in proposed lignin based sunscreens12 as a
“compatibilizer” with lotions and sprays.
Optimization of solvent extraction to obtain a higher yield by varying extraction time,
temperature, and solvent. Furthermore, use of a solvent or solvent blend based on the
Hansen solubility parameters of lauric acid and WFAE to enhance this process is
particularly promising.
Consider new method of recovering lignin from acylation with fatty acid chlorides rather
than precipitation in aqueous solution which is hypothesized to be the cause for forming
free fatty acid.
Experimental determination of lignin’s Hansen solubility parameters (testing solubility in
solvents with known Hansen solubility parameters). Compare experimental to
theoretical values obtained by group contribution methods proposed by Stefanis et al.
(2008) among others87.
Assess impact of UV irradiation on physicochemical properties of lignin-PLA blends
compared to pure PLA.
Evaluate impact of adding lignin on biodegradability (composting) of PLA blends.
75
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Appendix
A. Acylation yield data
In preliminary acylation studies the yield was recorded. In an attempt to achieve 100%
degree of substitution more than 1 fatty acid chloride (FAC) unit per free hydroxyl group (-OH)
unit. However, it was measured that more than the theoretical mass that could be added was
added to the final lignin laurate. This was the initial indicator that the free fatty acid, lauric acid,
was not being removed from the final lignin laurate. It was also observed that some lignin may
have been lost in the filtrate based on its color (to the right),
indicating that the yield measured is if anything low. The use of
FT-IR to detect the free fatty acid and the inaccuracy of the yield
values, subsequent (acetylation and acylation with lauroyl
chloride) experiments didn’t follow the yield, but it was valuable
in preliminary studies.
HWE Lignins
Date- 2018
Lignin crude
(g)
-OH content
(mmol/g)
FAC added/
-OH
Total FAC added to rxn (g)
Tare (g) Tare +
Sample (g)
Lignin laurate
(g)
Added mass
(g)
Ratio-mass added Experimental:
Theoretical
Willow Lignin (W)
5/22 0.500 5.05 1.70 0.94 100.488 101.649 1.161 0.661 1.44
9/6-A 0.513 5.05 2.00 1.13 42.294 43.675 1.381 0.868 1.84
9/6-B 0.519 5.05 2.00 1.15 39.455 40.725 1.270 0.751 1.57
Miscanthus Lignin
6/21 0.502 6.24 1.60 1.10 82.883 84.108 1.225 0.723 1.27
Wheat straw Lignin
6/26 0.501 4.96 1.62 0.88 42.250 43.304 1.054 0.553 1.22
7/18 0.497 4.96 1.62 0.87 46.704 47.721 1.017 0.520 1.16
7/20 0.515 4.96 1.62 0.91 46.702 47.849 1.147 0.632 1.36
FAC – Fatty acid chloride of lauric acid (lauroyl chloride)
91
B. Yield from alkali purification of W
Date Starting Lignin (g) Tare (g) Tare + Sample (g) Final Sample (g) Yield (%)
2/15/2018 1.009 152.289 152.772 0.483 47.9%
2/19/2018 1.000 123.211 123.685 0.474 47.4%
1.008 119.452 119.924 0.472 46.8%
2/22/2018 2.006 123.244 124.259 1.015 50.6%
2.007 119.420 120.464 1.044 52.0%
2/26/2018 2.005 123.213 124.284 1.071 53.4%
2.000 119.395 120.456 1.061 53.1%
3/5/2018 2.001 123.148 124.215 1.067 53.3%
2.005 119.379 120.405 1.026 51.2%
3/16/2018 4.012 123.245 125.463 2.218 55.3%
3/20/2018 2.026 119.508 120.598 1.090 53.8%
2.050 123.266 124.320 1.054 51.4%
Total Recovered (g) Average Yield (%) SD CoV
12.075 51.3% 0.0273 5.31%
92
C. Additional FT-IR spectra
93
94
95
D. DSC thermograms of lignins
KL W
WAP WAc
WFAE WFAEH
96
E. TGA thermograms of lignins
KL W
WAP WAc
WFAE WFAEH
97
F. UV absorbance spectra of lignins
98
G. Stefanis group contribution values and examples of HSP calculation
The number of each groups were
determined per lignin unit in the example
below.
First Order Group Contributions87
Group D P H
1 -CH3 -0.9714 -1.6448 -0.7813
2 -CH2 -0.0269 -0.3045 -0.4119
3 -CH< 0.6450 0.6491 -0.2018
4 >C< 1.2686 2.0838 0.0866
5 CH2=CH– -1.0585 -2.0035 -1.2985
6 -CH=CH– 0.0048 -0.2984 -0.0400
7 CH2=C< -0.4829 -0.7794 -0.8260
8 -CH=C< 0.5372 -0.9024 -1.8872
9 >C=C< 0.3592 1.0526 -15.4659
10 CH2=C=CH– -1.6518 *** -0.9980
11 ACH 0.1105 -0.5303 -0.4305
12 AC 0.8446 0.6187 0.0084
13 ACCH3 0.2174 -0.5705 -1.1473
14 ACCH2– 0.6933 0.6517 -0.1375
15 CH 3CO -0.3551 2.3192 -1.3078
16 CH 2CO 0.6527 3.7328 -0.5344
17 CHO (aldehydes) -0.4030 3.4734 0.1687
18 COOH -0.2910 0.9042 3.7391
19 CH3COO -0.5401 -0.3970 1.5826
20 CH2COO 0.2913 3.6462 1.2523
21 HCOO *** 1.9308 2.1202
22 COO 0.2039 3.4637 1.1389
23 OH -0.3462 1.1404 7.1908
24 ACOH 0.5288 1.1010 6.9580
25 CH3O -0.5828 0.1764 0.1460
26 CH2O 0.0310 0.8826 -0.1528
27 CHO (ethers) 0.8833 1.6853 0.4470
28 C2H5O2 -0.1249 3.6422 8.3579
29 CH2O (cyclic) 0.2753 0.1994 -0.1610
30 CH2NH2 -0.5828 1.4084 2.5920
31 CHNH2 0.0112 -1.1989 0.3818
32 CH3NH *** 0.6777 5.6646
33 CH2=C=C< -0.2804 *** -1.9167
34 O (except as above)
0.0472 3.3432 0.0256
35 >C=0 (except as above)
-0.4343 0.7905 1.8147
Second Order Group Contributions87
Group D P H
A (CH3)2–CH– 0.0460 0.0019 0.3149
B (CH3)3–C– -0.0738 1.1881 -0.2966
C ring of 5 carbons -0.6681 -2.3430 -0.3079
D ring of 6 carbons -0.3874 -3.6432 0.0000
E string in cyclic -0.1945 0.0000 0.0000
F CH3-C= -0.0785 0.3316 0.3875
G -CH2–C= -0.3236 -2.3179 -0.5836
H >C{H or C}–C= -0.2798 *** -1.1164
I CH3(CO)CH2– -0.0451 -0.3383 -0.4083
J ACCOOH -0.2293 -0.6349 -0.9030
K >C{H or C}–COOH 0.0000 -0.2187 1.1460
L CH3(CO)OC{H or C}< -0.5220 -0.0652 0.3085
M (CO)C{H2}COO *** -2.3792 0.8412
N (CO)O(CO) -0.2707 -1.0562 1.6335
O ACHO 0.3772 -1.8110 -1.0096
P >CHOH 0.1123 0.2564 -0.1928
Q >C<OH -0.0680 0.1075 1.2931
R Ccyclic–OH -0.0876 -3.5220 0.5914
S C–O–C=C 0.2063 0.6080 1.1344
T AC–O–C 0.2568 0.8153 0.6092
U ACCOO -0.1847 0.4059 -0.1921
V AC(ACHm)2AC(ACHn)2 -0.3751 -1.2980 0.6844
W AC–O–AC -0.5646 -3.4329 2.0830
X -O–CHm–O–CHn– 0.0839 0.3451 0.3767
Y C(=O)–C–C(=O) -0.4862 -0.4888 1.2482
Z Ccyclic=O -0.2981 0.4497 -0.4794
99
100
H. Additional light microscopy images of lignin-PLA blends
1% WFAE
101
I. DSC thermograms of lignin-PLA blends
PLA (2 °C heat rate)
PLA (10 °C heat rate)
102
1% W (2 °C heat rate)
1% W (10 °C heat rate)
103
1% WAc (2 °C heat rate)
1% WAc (10 °C heat rate)
104
3% WAc (2 °C heat rate)
3% WAc (10 °C heat rate)
105
6% WAc (2 °C heat rate)
6% WAc (10 °C heat rate)
106
12% WAc (2 °C heat rate)
12% WAc (10 °C heat rate)
107
1% KL (2 °C heat rate)
1% WFAEH (2 °C heat rate)
108
1% WFAE (2 °C heat rate)
7% WFAE (2 °C heat rate)
109
Overview of thermal properties from DSC (10 °C heat rate)
First heat Second heat
Sample Tg Tc Tm Tg Tc Tm PLA 62.94 132.38 157.93 62.46 132.99 154.87
1% W 61.86 117.82 163.33 60.53 125.41 154.93
1% WAc 62.25 131.89 157.91 61.35 132.09 154.04 3% WAc 60.4 133.43 158.55 61.77 134.8 155.07
6% WAc 60.08 135.25 157.29 61.06 134.4 153.95 12% WAc 57.33 124.87 153.97 59.5 130.1 152.04
110
J. TGA thermograms of lignin-PLA blends
PLA
111
1% W
1% WAc
112
3% WAc
6% WAc
113
12% WAc
1% KL
114
1% WFAEH
1% WFAE
115
7% WFAE
116
K. Raw mechanical properties data from elongation tensile testing
Peak stress (MPa) Strain at Peak (%) Young's Modulus (GPa)
Batch 1 61.354 7.2614 1.612
62.438 7.3526 1.554
62.342 6.904 1.724
59.042 7.558 1.67
63.074 7.0634 1.565
Batch 2 62.512 7.0737 1.706
62.762 7.382 1.615
62.377 7.2293 1.738
63.574 7.7335 1.684
59.612 7.3847 1.568
Batch 3 63.121 8.1004 1.475
59.667 8.0659 1.484
63.153 8.3282 1.346
60.366 7.841 1.504
60.472 8.7542 1.303
PLA
Peak stress (MPa) Strain at Peak (%) Young's Modulus (GPa)
Batch 1 56.938 5.3132 1.9
57.831 5.2743 1.909
58.798 5.6315 1.75
57.553 5.3159 1.756
55.92 5.3762 1.655
55.45 5.3669 1.768
57.06 5.6408 1.818
Batch 2 55.318 4.8794 1.925
55.977 5.4255 1.695
53.383 4.687 1.785
59.766 5.1244 1.852
57.201 5.0857 1.978
57.617 5.1968 1.934
54.613 5.172 1.81
1% W
117
Peak stress (Mpa) Strain at Peak (%) Young's Modulus (GPA)
Batch 1 56.9 7.9531 1.331
53.474 9.372 0.012
59.186 7.4294 1.336
58.224 7.9178 1.237
56.674 8.2477 1.367
57.784 8.257 1.322
59.729 7.6275 1.327
Batch 2 55.177 7.6116 1.472
57.581 7.5823 1.391
62.248 7.8022 1.483
56.41 7.4472 1.434
62.014 7.4402 1.397
58.447 7.6982 1.361
58.252 7.9164 1.291
1% WAc
Peak stress (Mpa) Strain at Peak (%) Young's Modulus (GPA)
Batch 1 53.282 6.4333 1.442
53.64 6.1482 1.593
49.104 6.71 1.564
54.166 6.6509 1.675
51.202 5.8103 1.499
52.105 5.9636 1.645
54.129 6.8735 1.618
Batch 2 55.767 6.2613 1.65
54.168 6.6398 1.491
55.626 6.4414 1.564
54.616 6.4198 1.59
55.706 6.4603 1.669
56.011 5.2242 1.707
57.697 6.606 1.46
6% WAc
118
Peak stress (Mpa) Strain at Peak (%) Young's Modulus (GPa)
Batch 1 48.407 5.5935 1.505
48.734 5.964 1.412
51.483 6.2847 1.648
49.182 6.3001 1.498
48.466 5.9194 1.565
48.081 6.3957 1.502
47.365 6.4577 1.471
Batch 2 50.132 5.9581 1.551
51.627 6.1411 1.522
53.562 6.1177 1.287
50.087 6.1044 1.605
50.36 5.6594 1.485
49.754 5.4232 1.588
49.109 5.6764 1.571
12% WAc
Peak stress (MPa) Strain at Peak (%) Young's Modulus (GPa)
53.253 6.5347 1.618
58.926 6.4116 1.534
60.171 6.0491 1.9
57.195 6.3089 1.698
48.76 6.2368 1.437
56.136 5.9121 1.706
1% KL
Peak stress (MPa) Strain at Peak (%) Young's Modulus (GPa)
59.341 6.6602 1.734
61.743 6.9157 1.77
54.885 6.9227 1.72
58.255 6.7669 1.63
61.269 6.9731 1.781
62.533 7.3075 1.769
62.577 6.8537 1.815
1% WFAEH
119
Peak stress (MPa) Strain at Peak (%) Young's Modulus (GPa)
58.754 7.2694 1.371
59.455 7.803 1.417
59.555 8.1194 1.342
58.133 7.4235 1.388
57.561 7.4937 1.423
57.671 7.6377 1.466
56.903 6.9838 1.353
1% WFAE
Peak stress (MPa) Strain at Peak (%) Young's Modulus (GPa)
42.663 5.0271 1.726
39.087 4.1893 1.54
44.955 5.0861 1.716
46.362 4.8246 1.684
41.133 4.7786 1.692
41.146 4.9095 1.66
41.275 4.2933 1.73
7% WFAE
120
L. UV absorbance spectra of lignin-PLA blends
121
122
Curriculum Vitae (CV)
M A T H E W J . O V A D I A S 113 Concord Place | Syracuse, NY 13210 | (315) 663 -7013 | movadias@ yahoo.co m
Experience with various bioprocesses such as cell culture, protein purification, genetic
engineering, pulping, fermentation and others relating to biomass valorization
Proficient in analytical techniques including FT-IR, DSC, TGA, enzymatic assays, antioxidizing
activity, and numerous biomass characterization methods
Adept at drawing and analyzing Process Flow Diagrams as well as Piping and Instrumentation
Designs
Extensive use of SuperPro Designer, Pi, MATLAB and Microsoft Office applications (Excel,
PowerPoint, Word)
SUNY College of Environmental Science and Forestry (ESF) - Syracuse, NY
M.S. Bioprocess Engineering (ABET Accredited Chemical Engineering) | GPA: 3.9
December 2019
Thesis Title: Lignin-Thermoplastic Blends
B.S. Bioprocess Engineering (ABET Accredited Chemical Engineering) | GPA: 3.6
December 2017
Paper Science Minor | Member of AXS (Honors Society) at ESF
Thesis Research: Lignin-Thermoplastic Blends, ESF | Research Project Assistant
January 2018 – December 2019
Development of lignin-thermoplastic blends through lignin modification and extrusion
Regeneron Pharmaceuticals, East Greenbush, NY | Process Sciences Intern
May – August 2019 Engaged scientists and engineers across multiple groups to document tacit knowledge of various
unit operations
Created technical documents that provide essential background information and justification for
expected effects in PFMEAs (Process Failure Mode and Effects Analysis)
International Paper, Campti, LA | Paper Mill Process Engineering Intern
May – July 2017 Performed cost and savings justification and initiated proposal of a project to install solids control
meters in the pulp mill with potential savings of more than $100,000 annually
Restructured Pi pages to properly reflect each unit operation and make utilization of the software
more intuitive
123
Ichor Therapeutics/Finger Lakes Biotechnology, Lafayette, NY | Biochemistry Intern
March – May 2017 Produced recombinant protein while following GLP (Good Laboratory Practice) through lab scale
cell-batch fermentation of E. coli and purified protein via column chromatography to test for
molecular activity
WestRock, Covington, VA | Paper Mill Process Engineering Co-Op
September – December 2016
Collaborated with full-time process engineers and operators in upstream processes on cost
savings projects
Organized and analyzed data from numerous sources to discover relationships and trends
Buckman Laboratories, Memphis, TN | Biotechnology R&D Intern
March – August 2016
Conducted a research project to improve enzymatic activity among other key attributes
Developed a new enzyme assay method, utilizing robotics, which aids efficiency and customer
support
SUNY Research Foundation, Syracuse, NY | Research Aide
June – November 2015
Independently researched lignin-based thermoplastics to produce a biodegradable alternative to
traditional plastics
Manny’s Syracuse University Apparel, Syracuse, NY | Supervisor
August 2013 – May 2019
Wegmans Food Markets, Dewitt, NY | Front End Associate & Cashier Trainer
June 2011 – August 2017
Graduate Teaching Assistant, ESF Dept. of Paper and Bioprocess Engineering
August 2018 – December 2019
Courses include: Fiber & Paper Properties, Introduction to Lignocellulosics, Process Control, and
Bioseperations
Senior Adviser of AIChE (American Institute of Chemical Engineers) Club, ESF
August 2018 – May 2019
Ovadias, M., & Bujanovic, B. (2019). Lignin-based thermoplastic blends: Biorefinery willow
lignin and polylactic acid (PLA). San Diego, California - August 25-29, 2019: American Chemical
Society (ACS) Fall National Meeting: Chemistry and Water
(Oral Presentation)
Nagardeolekar, A., Ovadias, M., Wang, K.-T., Wood, C., & Bujanovic, B. (2019). Valorization of
Willow Lignin in a Pilot-scale Biorefinery Based on Hot Water Extraction. St. Louis, Missouri -
October 27-30, 2019: International Bioenergy & Bioproducts Conference (IBBC)
(Oral Presentation and Manuscript published in Conference Proceedings)
Nagardeolekar, A., Ovadias, M., Wang, K.-T., Wood, C., & Bujanovic, B. (2019). Hydrogels and
Thermoplastic Blends from Willow Lignin Recovered from Pilot-Scale Hot-Water Extraction.
Saratoga, New York – June 23-26, 2019: American Chemical Society (ACS) Northeast Regional
(Oral Presentation)
124
Elniski, A., Nagardeolekar, A., Ovadias, M., Dongre, P., & Bujanovic, B. (2019). Valorization of
Hot Water Extracted Lignin from Different Angiosperms. Thunder Bay, Ontario - June 9-14,
2019: International Forest Biorefining Conference (IFBC)
(Oral Presentation)
Ovadias, M., & Bujanovic, B. (2018). Willow Lignin Recovered from Hot Water Extraction as a
Thermoplastic Material. Syracuse, New York - August 2, 2018: ESF - SCUT Student Workshop
and Poster Presentation (Poster Presentation)
Edwin C. Jahn Graduate Fellowship Fall 2019
H.P. Brown Memorial Scholarship
Spring 2019
Syracuse Pulp and Paper Foundation Paper Science Minor Scholarship
Fall 2014 – Fall 2017
Wegmans Employee Scholarship
Fall 2013 – Spring 2017
