Embed Size (px)
Citation preview
Ref. code: 25605822041702BJS
CHEMICAL RECYCLING OF DEGRADABLE
POLYLACTIC ACID EMPLOYING ALCOHOLYSIS
REACTION BY GLYCEROL
BY
SUWANIT KOONAWAT
A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF
THE REQUIREMENTS FOR THE DEGREE OF MASTER OF
ENGINEERING (ENGINEERING TECHNOLOGY)
SIRINDHORN INTERNATIONAL INSTITUTE OF TECHNOLOGY
THAMMASAT UNIVERSITY
ACADEMIC YEAR 2017
Ref. code: 25605822041702BJS
CHEMICAL RECYCLING OF DEGRADABLE
POLYLACTIC ACID EMPLOYING ALCOHOLYSIS
REACTION BY GLYCEROL
BY
SUWANIT KOONAWAT
A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF
THE REQUIREMENTS FOR THE DEGREE OF MASTER OF
ENGINEERING (ENGINEERING TECHNOLOGY)
SIRINDHORN INTERNATIONAL INSTITUTE OF TECHNOLOGY
THAMMASAT UNIVERSITY
ACADEMIC YEAR 2017
Ref. code: 25605822041702BJS
ii
Acknowledgements
I would like to express my special thanks of gratitude to my
advisor, Assoc.Prof.Dr. Pakorn Opaprakasit for his expert advice and encouragement
throughout this difficult project, as well as Dr. Atitsa Petchsuk for her kindly advice
about experiment and other committees, Asst.Prof.Dr. Paiboon Sreearunothai and
Prof.Dr. Teruoki Tago for their valuable comments and advices. I am also grateful to
Dr. Siwarutt Boonyarattanakalin and his advisee for their assistance on microwave
reaction for my experiment. Special thanks is given to MTEC’s staff, Mrs. Wilairat
Supmak, for experimental help and reserving the experimental machine for me. For
the help about the graduate process, I would like to thank staff of the Common and
Graduate Studies department namely; Mrs. Naree Chankeaw, Ms. Wilaiwan Siri-
umpai, and Ms. Mathawee Srisawas. I would like to recognize the support from my
research group members, the center of excellence in Materials and Plasma
Technology (M@P Tech). I am thankful for my classmates, TAIST Tokyo Tech
Batch 4, for the good memories and the help. Addition, this work is supported by
Sirindhorn International Institute of Technology (SIIT), the center of excellence in
Materials and Plasma Technology (M@P Tech), Thammasat University, and
Materials Technology center (MTEC), NSTDA. Appreciation is also expressed to the
scholarship support from the TAIST-Tokyo Tech program.
Finally, I must express my very profound gratitude to my parents, Mr.Surasak
Khunnawat and Mrs.Nittaya Khunnawat and to my godfather, Dr. Kampol
Nanthapong for providing me with unfailing support and continuous encouragement
throughout my years of study and through the process of researching and writing this
thesis. This accomplishment would not have been possible without them. Thank you.
Ref. code: 25605822041702BJS
iii
Abstract
CHEMICAL RECYCLING OF DEGRADABLE POLYLACTIC ACID
EMPLOYING ALCOHOLYSIS REACTION BY GLYCEROL
by
SUWANIT KOONAWAT
Bachelor of Science (Public Health), Thammasat University, 2015
Master of Engineering (Engineering Technology), Sirindhorn International Institute of
Technology, Thammasat University, 2017
Polylactic acid (PLA) is an attractive material to use instead of petroleum-
based polymers because of its good mechanical and physical properties similar with
petroleum-based polymers. PLA is widely used in many fields, such as biomedical,
agricultural, fibers, and packaging because of its environmental friendly and non-toxic
properties. However, this leads to a rapid increase in consumption rate. Mechanical
recycling is not suitable for post-consumer PLA products as this process made the
products have lower quality. In contrast, chemical recycling is an effective process to
convert polymeric waste to other valuable products. This work is aimed to develop a
chemical recycling process for post-consumer products of degradable PLA by
employing alcoholysis reaction with glycerol, and microwave irradiation as a heat
source. Effects of reaction conditions, in terms of PLA/glycerol feed ratios, reaction
temperature and time, on chemical structures and molecular weight of the resulting
products are investigated by GPC, 1
H-NMR, HPLC, and FTIR spectroscopy. The
product is then applied as additive for toughening of PLA resin. The optimal ratio of
additive contents are examined by tensile test, DSC, XRD and SEM. Furthermore,
effects of molecular weight of the alcoholysed products and the blend compositions
on miscibility, mechanical and thermal properties of the resulting blend are also
discussed.
Keywords: Poly(lactic acid), Chemical recycling, Alcoholysis, Microwave irradiation
Ref. code: 25605822041702BJS
iv
Table of Contents
Chapter Title Page
Signature Page i
Acknowledgements ii
Abstract iii
Table of Contents iv
1 Introduction 1
1.1 Statement of problems 1
1.2 Objectives 4
1.3 Scope of the study 4
2 Literature Review 6
2.1 Polylactic acid (PLA) 6
2.1.1 Backgroud of PLA 6
2.1.2 Properties 7
2.2 Microwave irradiation 8
2.3 Alcoholysis reaction 9
2.4 Blends of PLA 12
3 Experimental 14
3.1 Materials and Chemicals 14
3.2 Equipment and Instrumental 14
3.3 Analytical instruments 14
3.4 Experimental 15
Ref. code: 25605822041702BJS
v
3.4.1 Chemical recycling of PLA by alcoholysis reaction 15
3.4.1.1 Alcoholysis reaction 15
3.4.1.2 Removal of glycerol residues 17
3.4.2 Addition of alcoholysed products as additive reagent into
PLA resin 19
3.4.3 Characterization 20
4 Results and Discussion 23
4.1 Chemical recycling of PLA by alcoholysis reaction 23
4.1.1 Alcoholysis reaction of PLA under the microwave irradiation 23
4.1.1.1 Effect of alcoholysis conditions 23
4.1.2 Characterization of alcoholysed
products in the solid part (AlcPLAS) 25
4.1.2.1 Chemical stucture 25
4.1.2.2 Crytalinity of alcoholysis products 28
4.1.3 Characterization of alcoholysed
products in the liquid part (AlcPLAL) 29
4.1.3.1 Chemical stucture 29
4.1.3.2 Chemical composit of alcoholysed product
separated by HPLC 30
4.2 Enhancement of toughness of PLA resin by using
alcoholysed product 32
4.2.1 Characterization of flim blended with alcoholysed products 32
4.2.1.1 Thermal properties of flim blended 32
4.2.1.2 Mechanical properties of PLA composites 35
5 Conclusions and Further Works 39
5.1 Conclusions 39
5.2 Future works 40
References 41
Ref. code: 25605822041702BJS
1
Chapter 1
Introduction
1.1 Statement of problems
Plastic is widely used in many applications, due to its low cost, lightweight,
flexibility, and durability. Conventional plastics are made from petroleum-based or
non-renewable resources. Although conventional plastic is non-sustainable and
leading to depletion of fossil fuels, but it still have high consumption demand driven
by consumers. The total plastic demand in Europe for the year 2014 was 47.8 million
tons, as shown in figure 1.1. Packaging section has the highest demand, about 18.88
million tons, which is accounted for 39.5% of the entire end market segment. The
second highest demand is from building and construction segment, at 9.6 million tons,
which is 20.1% of the market share (PlasticEurope, 2016). The petroleum-based
polymer are widely used in packaging applications and distributed in several
household, which are daily from food packaging. It is reported that about 4 % of
petroleum production, is used as feedstock for polymers and a further 3-4% is
expended to provide energy for their manufacturing (Hopewell, Dvorak, & Kosior,
2009).
Figure 1.1 Total plastic demand in Europe for the year 2014(PlasticEurope, 2016).
Ref. code: 25605822041702BJS
2
Packaging is a major section that generates daily plastic waste. As a result of
this increasing post-consumer products derived from conventional plastics, it induced
serious environmental problems and global warming concern, as these take longtime
to break down into harmless substances. In order to decrease environment impact,
biodegradable polymers are used as alternative materials for petroleum-based
polymers, due to their attractive properties similar to conventional petroleum-based
polymers, especially strengths and toughness. Bio-polymers can be decomposed by
microorganisms and help decreasing the use petroleum-based resources and also
reducing carbon dioxide (CO2) emission(Madival & al., 2009). Biodegradable
polymers are not specifically used only in packaging applications, but also extensively
utilized in many fields, such as filament, bottles, and biomedical applications, because
of their compostability, non-toxicity, and environmental friendly(A., K., & K., 2011).
Recently, various types of biodegradable polymers are derived from variety of
renewable resources, such as biomass products, microorganisms, bio-technology, and
oil products. Example of biodegradable materials widely used in many fields, are
polyhydroxylbutyrate (PHB), polybutylenesuccinate (PBS), polycaprolactone (PCL)
and polylactic acid (PLA)(Chavhan, 2016).
Polylactic acidor PLA is a one of bio-based polymer and promising
biodegradable properties, which is derived from renewable resources, for instance,
corn starch, tapioca roots, sugarcane, sugar beets or rice. The commercial production
of PLA is mostly made from corn, due to it cheapest price and widely available raw
materials in many countries. In the first step of the process, a corn wet mill as the
starch without the other components of the corn kernel is converted to dextrose by
enzymatic hydrolysis. The dextrose is then fermented into lactic acid. Lactic acid is
purified by removal of water using condensation polymerization. After that, lactic
acid oligomer is converted to lactide dimer by using high vacuum and temperature.
Finally, lactide is employed in ring-opened polymerization (Erwin, Karl, David, &
Patrick, 2003).
Due to high consumption rate of polylactic acid, various management options
for handling of its post-consumer product have been employed, for example,
incineration for energy recovery, sanitary landfill, composting or anaerobic
digestions, and recycling (Song, Murphy, Narayan, & Davies, 2009). Recycling is an
Ref. code: 25605822041702BJS
3
effective process to reduce amount of post-consumer biodegradable, including
thermal recycling, biological recycling, and chemical recycling. Mechanical recycling
is a typical process to re-melt by heat and refabricated to products. However, this
leads to lower properties (Briassoulis, Hiskakis, & Babou, 2013). Biological
recycling takes a long time to convert post-consumer polymers into starting materials
or monomer by microbial, while chemical recycling is an effective process to convert
polymeric waste to other valuable products for specific applications, such as additives
or plasticizers for other resins. Effective reactions commonly used in chemical
recycling process of biopolymers include hydrolysis and alcoholysis. Alcoholysis
reaction provides high efficiency for conversion of poly(ethylene terephthalate) (PET)
to DPTP. This is conducted by using n-butanol as an alcohol agent (Shiwei Liu et al.,
2013). Moreover, alternative alcohol agent for alcoholysis reaction of polymers like a
glycerol was employed (Špitalský, Lacík, Lathová, Janigová, & Chodák, 2006).
Glycerol is one kind of polyols containing trihydroxyl, usually generated as
byproduct from biodiesel production. Biodiesel has received vast attention during the
past few decades because of the sharp decrease in fossil fuel reserves. Besides,
glycerol is a main byproduct from the tranesterification process. Due to its high
availability, researchers and industry are encouraged to utilize glycerol and convert it
to other high value products (e.g. chemical or material) (Xiaohu F. et al., 2010).
This work is aimed to develop a chemical recycling process for post-consumer
products of degradable Polylactic acid or PLA by employing alcoholysis reaction with
glycerol, and microwave irradiation as a heat source. Effects of reaction conditions, in
terms of PLA/glycerol feed compositions, reaction temperature and time, on chemical
structures and molecular weight of the resulting products are investigated by Proton
nuclear magnetic resonance(1H-NMR), Fourier Transform Infrared (FTIR), Gel
Permeation Chromatography (GPC), and High-performance liquid chromatography
(HPLC). Optimal conditions are determined to obtain products with specific structure
and properties. The main products of this chemical recycling are 3-branched
structures of lactate oligomers. The product is then used as additive for toughening of
PLA resin.
Ref. code: 25605822041702BJS
4
This technology has high potential to reduce waste post-consumer PLA for
sustainable management, and provide highly-efficient toughening agent for PLA
resin.
1.2 Objectives
The main objective of this work is to developing a chemical recycling process
for PLA waste by using glycerol and microwave irradiation. The specific objectives
of this research are as follows:
Reduce waste of post–consumered PLA products by 1.2.1
converting to its oligomers or monomer products utilizing a chemical
recycling process.
Develop a process to prepare chemical recycling products 1.2.2
from PLA waste and use as additive for toughening of virgin PLA resin.
Evaluate the use of glycerol, a by-product from biodiesel 1.2.3
production, as alcoholysis agent for of PLA chemical recycling process
using microwave irradiation.
Investigate effect of alcoholysis condition on chemical 1.2.4
structures and properties of the chemical recycling products.
1.3 Scope of the study
The major framework is to optimize reaction conditions to obtain chemical
recycling products of polylactic acid, with chemical structures and properties suitable
for use as additive in toughening of virgin PLA resin. To investigate effect of
conditions on chemical structures of the products, i.e. glycerol dosage, and reaction
temperature. The scope of this study is briefly summarized as follows:
1.3.1 The reaction is conducted using microwave irradiation as a heat
source. The reaction conditions are optimized by varying the reaction
times of 10, 15, and 30 min, at a temperature of 240 °C and a
PLA/glycerol ratio of 2:1.
1.3.2 FT-IR, 1
H-NMR, DSC and GPC are employed to examine chemical
structures and molecular weight of the alcoholysed products (solid
portion).
Ref. code: 25605822041702BJS
5
1.3.3 Molecular weight and chemical structures of alcoholysed products
(liquid portion) are investigated by 1H-NMR and HPLC.
1.3.4 The alcoholysed products of PLA are blended with virgin PLA resin as
toughening agent. Effect of blending ratio on properties of the blend is
examined.
1.3.5 Thermal and mechanical properties of blended film are investigated by
DSC, tensile test, and impact test.
1.3.6 Fractured surface morphology by employed by SEM to investigate
compatibility.
Ref. code: 25605822041702BJS
6
Chapter 2
Literature Review
2.1 Polylactic acid (PLA)
2.1.1 Backgroud of PLA
Polylactic acid or PLA is aliphatic polyester derived from agricultural
products, such as corn starch, tapioca roots, sugarcane, sugar beets, or rice, which are
renewable resources (Erwin et al., 2003). PLA’s life cycle starts with biomass which
is consumed by microorganisms. Lactic acid monomer is originated by fermentation
of sugar. PLA can be produced by two major routes from the lactic acid monomer.
The first route is a removal of water by condensation that is the direct
polycondensation. This process is simple and able to produce low-molecular-weight
PLA. The second route is a ring-opening polymerization through the lactide
intermediate. The first step of this route is removal water without solvent to produce
low molecular weight prepolymers. Then, this prepolymers is depolymerization as
lactide, and ring-opening polymerization is employed to produce to polylactic acid.
This route is possible to produce a wide range of molecular weights (Sin, Rahmat, &
Rahman, 2013). The overall production step of PLA is summarized in Figure 2.1
(Jamshidian et al., 2010).
2.1.1.1 Sub-heading 2
(1) Sub-heading 3
(2) Sub-heading 3
Corn starch
Figure 2.1 The overall production step of PLA. (Jamshidian, Tehrany, Imran,
Jacquot, & Desobry, 2010)
Ref. code: 25605822041702BJS
7
2.1.2 Properties
PLA is an attractive material to use instead of petroleum-based polymers,
which have appropriate properties for many fields, such as packaging, agriculture,
fibers, electric appliance, and electronics (Wolf, 2005). The stereochemistry of PLA
consists of two active configurations, poly(L-lactide) and poly(D-lactide). PLLA, with
L (+) stereoisomer contents of higher than 90%, trends to be crystalline, while those
consisting of L (+) lower than 90% is amorphous (Lasprilla, Martinez, Lunelli,
Jardini, & Filho, 2012). The degree crystallinity can be calculated from the ratio of
their enthalpy of fusion to enthalpy of fusion of polylactide crystal, ∆Hm (106 J/g)
(Sarasua, Prud'homme, Wisniewski, Le Borgne, & Spassky, 1998). For semi-
crystalline PLA, its glass transition temperature (Tg) and melting temperature (Tm)
are important thermal properties used to predict its behaviors (Bouapao, Tsuji,
Tashiro, Zhang, & Hanesaka, 2009). Physical characteristics, like heat capacity,
density, and mechanical properties are also dependent on glass transition temperature
(Buggy, 2006). Key properties of PLA are summarized in Table 2.1.
Table 2.1 Key properties of Polylactic acid (Lasprilla et al., 2012)
Lactic acid
polymer
Glass transition
temperature (Tg) (°C)
Melting temperature
(Tm) (°C)
Density
(g/cm3)
PLLA 55-80 173-178 1.290
PDLLA 43-53 120-170 1.250
PDLA 40-50 120-150 1.248
Ref. code: 25605822041702BJS
8
2.2 Microwave irradiation
Microwave irradiation is commonly employed in chemical synthesis (both
organic and inorganic) and also used for recycling of polymers. The common
frequency range of microwave irradiation in this application is 2.45 GHz. Interaction
between microwave irradiation and molecules can be described by quantum
equations. Polar molecules are moving in an electric field to produce kinetic energy,
which changed to heating source (K. Hirao & Ohara, 2011). The dielectric constant
decreases when solvent molecules are heated and the temperature increased. For
example, polar molecule of water has a dielectric constant which decreases from 78 at
25 °C to 20 at 300 °C (Lidstrom, Tierney, Wathey, & Westman, 2001). Bakibaev et al.
investigated two methods of polymerizations of lactic acid (LA) in a presence of
various catalysts and co-catalyst using conventional heating and microwave
irradiation as a heat source. The results showed that the process under microwave
irradiation is tens or hundreds times faster than the conventional heating (Bakibaev et
al., 2015).
In addition, microwave is also used for depolymerization of polymers. The
hydrolysis of poly(ethylene terephthalate) or PET using methanol, ethanol, 1-butanol,
1-pentanol, and 1-hexanol with various catalysts under microwave was reported by
Nikje et al. Depolymerization of PET produced terephthalic acid. Ethylene glycol
was used as a starting material without any side reactions and short-reaction time, in
comparison with conventional heating (Nikje & Nazari, 2006). Methanolysis of PET
from soft-drink bottles generated dimethyl-terephthalate. It was founded that
depolymerization of PET is preferred by increasing temperature, time and the
microwave power (Siddiqui, Redhwi, & Achilias, 2012).
In case of chemical recycling of PLA, Koichi Hirao et al. studied hydrolysis of
PLLA using microwave irradiation. The aim of this study was to compare yields of
lactic acid after depolymerization, between conventional heating and microwave
irradiation. Similar reaction conditions, i.e. temperature and PLA: water ratio were
introduced in both heating systems. The authors reported that similar yields of lactic
acid were obtained from both cases; around 45%. However the reaction time of
around 800 minutes was required in conventional heating, while microwave
Ref. code: 25605822041702BJS
9
irradiation technique could achieve the same yield within 120 minutes, as shown in
Figure, 2.2.
Figure 2.2 Results on lactic acid concentration (left axis) and yield (right axis) from
hydrolysis of PLLA under microwave irradiation (circles) and conventional heating
(squares) at 170°C, with a PLLA: water weight ratio of 3:1, as a function of time. The
line graph shows that the microwave irradiation is reach the high lactic acid
concentration in faster than using the conventional heating source (K. Hirao & Ohara,
2011).
2.3 Alcoholysis reaction
Solvolysis is a one of commonly-used chemical recycling process by
employing agent as solvent in reaction. Hirao et al. studied alcoholysis reaction and
compared its efficiency between conventional heating and microwave irradiation. The
molecular weight of PLLA decreased with increasing reaction time. The chemical
reactions were faster under microwave irradiation than conventional heating.
Esterification is normally used in industry with butanol for purification, because it can
be separated into two phase when combined with water. Ethanol and butanol are
employed in alcoholysis reaction for chemical recycling of PLA in the report. Figure
2.3 shows the changes in reciprocal of number average molecular weight of PLLA as
Ref. code: 25605822041702BJS
10
a function of reaction time, with different solutions and heating methods (H. Hirao,
Nakatsuchi, & Ohara, 2010).
Figure 2.3. Changes in reciprocal of number average molecular weight of PLLA, as a
function of reaction time, with different solutions and heating methods: (a) ethanol
under microwave irradiation; (b) ethanol under conventional heating; (c) butanol
under microwave irradiation; (d) butanol under conventional heating (H. Hirao et al.,
2010).
The results showed that the reaction rate in ethanol (140-180 °C) and butanol
(130-210 °C) were greater under microwave irradiation than under conventional
heating (H. Hirao et al., 2010). The alcoholysis reaction is also widely used for
chemical recycling of poly(ethylene terephthalate), or PET. Liu et al. investigated the
alcoholysis reaction of PET with n-butanol to produce dibutyl terephthalate (DBTP)
and ethylene glycol. Insights into effect of reaction conditions are very important for
the alcoholysis reaction. When the temperature was higher than 195 °C, the
conversion reached 100%, and the yields of products were higher than 95%. It is
indicated that the alcoholysis reaction has higher efficiency when the reaction
Ref. code: 25605822041702BJS
11
temperature increased. Figure 2.4 shows the PET conversion increased when the
reaction time is increased (Shiwei Liu et al., 2013).
Figure 2.4 Changes of PET conversion as a function of reaction time, at 205
°C ( ) and 195 °C ( ) (Shiwei Liu et al., 2013).
The reaction time is increased, the degradation rate of PET and the yield of
DOTP increase at relatively short time (Chen et al., 2014). Moreover, the dosage of n-
butanol also effect the conversion of PET because the conversion of PET decreased
with decreasing of n-butanol dosage (S. Liu et al., 2013). The degradation of
poly(hydroxybutyrate) or PHB is conducted by employing alcoholysis reaction. This
process is achieved by two types of alcohols for preparation of co-polymer
synthesized in the next step. Špitalský, Zdeno et. al. studied the alcoholysis reaction
with types of alcohol, namely ethylene glycol and glycerol. The alcoholysis products
with glycerol have higher molecular weight than those using ethylene glycol. In
addition, the degradation rate of ethylene glycol is significantly faster than with
glycerol (Špitalský et al., 2006).
Ref. code: 25605822041702BJS
12
2.4 Blends of PLA
Polymer blend is process to melt and mix more than one types of polymers
together. This process produces new material mixture with different physical
properties from original. Various types of blends can be produced, including
thermoplastic-thermoplastic blends, thermoplastic-thermosetting blends, rubber-
thermosetting blends, and polymer-filler blends (Parameswaranpillai, Thomas, &
Grohens, 2014). PLA blended with other polymers leads to enhancement in its quality
of and reduction the cost of production. Blends of PLA with polystyrene shows
improvements mechanical properties (tensile strength and elongation), as reported by
Hamad et al. The results of this report showed that PLA/PS blends presented good
compatibility, resulting from higher value of stress transfer and lower value of
interfacial tension, compared to other biodegradable polyesters/PS blends (Hamad,
Kaseem, Deri, & Ko, 2016) Other biodegradable polymers is also attractive for
blending with PLA to improve its mechanical properties and decreasing glass
transition temperature. Polycaprolactone (PCL) is biodegradable polyester with a low
melting point and glass transition temperature, Matta et al. reported that PLA/PCL
increased in the percentage of elongation, impact toughness, loss factor, and decrease
in strength and modulus compared to neat PLA. The ratio of 80/20% PLA/PCL blends
presented the highest elongation and impact strength. In order to estimate the glass
transition temperature (Tg) of polymer blends, The FOX equation (equation 2.1) was
used (Matta, Rao, Suman, & Rambabu, 2014)
…………..…………………Equation 2.1
Where Tg is the glass transition temperature of the polymer blends, and Tg1
and Tg2 are those of the blend components. W1 and W2 are the weight fractions of the
blend components (Matta et al., 2014)
Polybutylene succinate (PBS) is an alternative bio polymer used for blending
with PLA. Yakohara and Yamaguchi reported the structures and properties of binary
blends of PBS and PLA. This report showed that PBS and PLA blend is immiscible in
the molten phase and showed a phase-separated structure.
Ref. code: 25605822041702BJS
13
However, the blend of PBS can introduce the nucleating agent to promote
crystallization of PLA, which is examined by DSC and optical microscope
measurements (Yokohara & Yamaguchi, 2008)
To improve the miscibility of binary blends of PBS and PLA, Chirachanchai
et al. examined the blends of PLA/PBS by using random poly(butylene succinate-co-
lactic acid) as a multi-functional additive. The random copolymer of PLA and PBS
are prepared by polycondensation and esterification. The introduction of this
copolymer which consists of parts of PBS and PLA, results in improvements of
miscibility and toughness (Supthanyakul, Kaabbuathong, & Chirachanchai, 2016).
Ref. code: 25605822041702BJS
14
Chapter 3
Experimental
3.1 Materials and Chemicals
- Polylactic acid resin (Nature Work4043D)
- Polylactic acid resin (Purac)
- Glycerol 99.5% (GLY), analytical grade (Q-Rec)
- Acetic acid, analytical grade (Lab Scan)
- Dimethyl sulfoxide-d6, 99.5% (Cambridge Isotope Laboratories)
- Chloroform, for HPLC (ACROS Organics™)
- Silica gel, RS-CHROM (Carlo Erba)
- Distilled water
3.2 Equipment and Instrumental
- Microwave synthesis system (Discover series, CEM co.NC, USA), with
microwave irradiation at a frequency of 2.45 GHz.
- 80 mL Pyrex glass tube for microwave synthesis system
- Magnetic stirrer bar for microwave synthesis system
- Pressure monitoring unit for microwave synthesis system
- Fiber optic temperature probe for microwave synthesis system
- Chemistry laboratory glassware
3.3 Analytical instruments
- Proton nuclear magnetic resonance (1H-NMR) spectrometer, AV-500,
Bruker Biospin
- Fourier Transform Infrared (FTIR) Spectrometer, Nicolet 6700
- Gel permeation chromatography (GPC), Waters e2695
- X-ray Powder Diffraction (XRD), JEOL, JDX-3530
- Differential scanning calorimetry (DSC), Mettler Toledo DSC822e
- High performance liquid chromatography (HPLC), WATERS 2690
Separation Module
- Izod impact tester, CEAST® Charpy, model number 6967
Ref. code: 25605822041702BJS
15
- Tensile tester, T-series Materials Testing machine, model H5TK, Tinius
Olsen LTD., UK
- Internal mixer, CHAREON TUT CO.,LTD., MX105-D40L50
- Compression machine, CHAREON TUT CO.,LTD., PR2D – W300L300
- Scanning Electron Microscopy (SEM), JEOL, JSM-7800F
3.4 Experimental
The overall experimental procedure of this work is divided into two parts, as
follows; chemical recycling of PLA (Purac) by alcoholysis reaction and utilizing of
the resulting alcoholysed products as toughening agent for virgin PLA resin (Nature
Work 4043D)
3.4.1 Chemical recycling of PLA by alcoholysis reaction
3.4.1.1 Alcoholysis reaction
(1) Glycerol 99.5% (GLY) and polylactic acid (Purac), at a
percentage weight of 2:1 as, described in table 3.1, was mixed
in a 80 ml vessel for microwave system.
(2) A magnetic stirrer bar was added into the vessel, which was
then and put under in a microwave irradiation at a frequency of
2.45 GHz.
(3) Connect a microwave system with a fiber optic temperature
probe for monitoring of reaction temperature and setting the
reaction conditions.
(4) Each batch of alcoholysis conditions was conducted according
to the reaction conditions, as summarized in table 3.1.
(5) The alcoholysis reaction was conducted using microwave
irradiation as a heat source.
(6) After a completion of the alcoholysis reaction, the alcoholysed
products (AlcPLA) were recovered and its weight was recorded.
Ref. code: 25605822041702BJS
16
Table 3.1 Alcoholysis conditions of PLA (Purac).
The alcoholysis conditions are summarized in Table 3.1. The high reaction
temperature at 240 °C is favor able for melting of PLA, which is suitable for the
alcoholysis reaction. The PLA/GLY feed ratio of 1:2 wt/wt is appropriate for the
alcoholysis reaction of PLA, because the solubility of PLA in glycerol decreased with
the decrease in glycerol dosage and alcoholysis product is excessive glycerol when
increasing glycerol. Effect of reaction times on chemical structures and properties of
the alcoholysis products were investigated.
Sample
No.
Reaction time
(min.)
PLA:GLY
(percent weight )
Temperature (℃)
1 10 1:2 240 2 15
3 30
Figure 3.1 Experimental setup of the alcoholysis reaction
PLA
(PURAC)
Alcoholysed products
Glycerol
80 ml vessel Microwave synthesis
system
Ref. code: 25605822041702BJS
17
3.4.1.2 Removal of glycerol residues
(1) As the alcoholysed product consist of 2 phases. The samples
were separated by filtration.
(2) The vacuum filter system was connected with a pump and then
put the paper filter with the solid part on the filter funnel.
(3) The glycerol residues were removed by washing with DI water
for several times.
(4) The solid part was dried in an oven at 60 °C for 6 hr.
(5) The dried solid simple was grinded into powder form.
(6) The weight of the remaining solid part was recorded and its %
yield of alcoholysis was calculated.
Figure 3.2 Removal of glycerol residual steps
Dried in a vacuum oven at 60 ⁰C for 6 hr.
DI water
Alcoholysed products
Ref. code: 25605822041702BJS
18
Alcoholysis reaction under
microwave irradiation
Precipitation
Separation of solid and
liquid parts
Removal of residual glycerol
Grind the solid part
Dry in an oven at 60 °C for 24
hr
PLLA (PURAC)
Glycerol
After 30 min.
Liquid part
Glycerol residues
Figure 3.3 The overall experimental procedures of the alcoholysis reactions.
Ref. code: 25605822041702BJS
19
3.4.2 Addition of alcoholysed products as additive reagent into PLA resin
The resulting PLLA alcoholysed products obtained 10, 15 and 30 min were
utilized as additive for toughening of PLA resin. To optimize the mixing ratio for
toughening of PLA resin, the product with different structure and mixing ratio
employed as summarized in table 3.2. The mixing process was carried out in an
internal mixture at were used 170 c and 50 rpm until a constant torque was reached
and amount of samples contained 50 g. The resulting polymer blend were compressed
into film and then prepared as specimens for tensile tests. Those specimens (10
pieces) for were used for investigation of the mechanical properties. The specimens
were prepared in rectangular sheet with a 15 mm width and 100 mm of gauge length,
according to the ASTM D882 for tensile test.
Alcoholysed products obtained at 10, 15, and 30 min were labeled as AlcPLAs
10 min, AlcPLAs 15 min and AlcPLAs 30 min. Those were blend with PLLA resin as
the ratio contents 0.2%, 0.5% and 1.0%. The sample’s name is showed in table 3.2.
Table 3.2 Ratio of alcoholysed content induced to the virgin PLA resin.
Samples Code
Alcoholysis condition
times
Alcoholysed product content
(wt%)
AlcPLAs 10 min 0.2%
10 min
0.2
AlcPLAs 10 min 0.5% 0.5
AlcPLAs 10 min 1.0% 1.0
AlcPLAs 15 min 0.2%
15 min
0.2
AlcPLAs 15 min 0.5% 0.5
AlcPLAs 15 min 1.0% 1.0
AlcPLAs 30 min 0.2%
30 min
0.2
AlcPLAs 30 min 0.5% 0.5
AlcPLAs 30 min 1.0% 1.0
Ref. code: 25605822041702BJS
20
3.4.3 Characterization
3.4.3.1 Fourier transform infrared (FTIR) spectroscopy
Chemical structures of the alcoholysed products were evaluated by
the attenuated total reflection mode FTIR (Thermo Scientific, iD5). Each
spectra was scanned from 400-4,000 cm-1, acquired by accumulation of 32
scans with a resolution of 4 cm-1
3.4.3.2 Nuclear Magnetic Resonance (NMR) Spectroscopy
Chemical structures of the alcoholysed products were examined
using an AVENCE 300 MHz 1H-NMR spectrometer. The samples were
dissolved in dimethyl sulfoxide-d6, 99.5% (DMSO).
3.4.3.3 Gel Permeation Chromatography (GPC)
Average molecular weights and molecular weight distributions ( n,
w and PDI) were measured by GPC using a Waters e2695 separations
GPC module, equipped with a refractive index detector (Viscotek) model
3580. Mono-disperse polystyrene standards were employed.
3.4.3.4 X-ray diffraction (XRD) spectroscopy
Crystallinity of the alcoholysed products were investigated by JEOL
JDX-3530 diffractometer, operating with CuK radiation ( Å).
An interlayer spacing was determined according to the Bragg’s law;
sin θ = nλ / 2d Eq. 3.1
Where λ is a wave length of X-ray radiation used in the diffraction
experiments, d is the space between layers, and θ is the measured
diffraction angle.
3.4.3.5 Differential Scanning Calorimetry (DSC)
Thermal properties of the sample of the blends were investigated by
using DSC (822e; Mettler Toledo), in N2 atmosphere at a flow rate of 60
mL/min. The samples were put in an aluminum crucible of about 5 mg, and
Ref. code: 25605822041702BJS
21
heated from -20 ℃ to 200 ℃, at a scanning rate of 20 ℃/min. Two heating
cycles were performed, with a holding time of 5 minutes. Determination of
the degree of crystallization is calculated by the following equation:
Xc = Hm
H0 x 100 E.q. 3.2
Where, Hm is the enthalpy of melting and H0 denotes the
enthalpy of fusion for a fully crystalline PLA (106 J/g)(Rezabeigi, 2014).
3.4.3.6 High-performance liquid chromatography (HPLC)
HPLC was used to verify the chemical compositions of the samples
in the liquid part and the intensity of the lactic acid in the sample. The
sample was streamed in reverse phase column (Prevail Organic Acid, 5µ,
150x4.6 mm.) with mobile phase (25 mM KH2PO4, pH 2.5 with
phosphoric acid), flow rate of 1.0 mL/min, and detected by UV at 210 nm.
3.4.3.7 Universal Testing Machine (UTM)
Tensile behaviors of the blending films were examined on a
Universal Testing Machine (Instron model 55R4502, Instron Crop.,
USA), with a 100 N load cell and a crosshead speed of 50 mm/min. The
film samples were prepared by a hot-press compression molding machine
(Chareon Tut, Thailand) at 170 ˚C for 15 minutes. The specimens were
then prepared in a rectangular sheet form with 15 mm width and 100 mm
gauge length, according to the ASTM D882 procedures. At least five
specimens were examined and averaged for each sample.
3.4.3.8 Impact Test
The impact resistance of the blended sample was examined with an
impact tester (CEAST®, model number 6967) according to the Izod
pendulum impact resistance of plastic (ATSM D256). Five samples
(dimensions 63.5x12.7x3.2, in mm.) with notch were cracked by a 1 J
pendulum with speed 3.46 m/s.
Ref. code: 25605822041702BJS
22
3.4.3.9 Scanning Electron Microscopy (SEM)
The specimen’s surface was coated with gold under the vacuum
evaporator. Then, the fractured surface morphology was observed through
SEM, which was performed using JSM-7800F Schottky Field Emission
Scanning Electron Microscope (JEOL, Japan) equipment operated at 5 kV
and the magnification of image is 500 µm.
Ref. code: 25605822041702BJS
23
Chapter 4
Results and Discussion
4.1 Chemical recycling of PLA by alcoholysis reaction
PLLA resin was alcoholysed by glycerol at a feed ratio of 2:1 (Gly:PLA)
wt./wt. Effect of reaction time on chemical structures and properties of the products is
investigated. Chemical structures of the alcoholysed products (AlcPLA) and the effect
of reaction conditions are discussed below;
4.1.1 Alcoholysis reaction of PLA under the microwave irradiation
PLA is converted into a mixture of precipitate and liquid part cooled down to
whose compositions depend on reaction time. The precipitate forms when the sample
was room temperature. The sample was separated to examine the weight of each
alcoholysed fractions. Therefore, the alcoholysed products (AlcPLA) consists of two
form, i.e. precipitate or solid part (AlcPLAs) and liquid part (AlcPLAl). The
conversion (%) of PLA under the microwave irradiation is calculated by equation 4.1.
PLA conversion = W1 - W2
W1 x 100% Eq.4.1
Where; W1 is the initial weight of PLA.
W2 is the remaining weight of solid PLA after alcoholysis reactions.
The yield of the solid and liquid parts is calculated form equation 4.2;
Yield of product (%) = Weight of product form
The weight of AlcPLA x 100 Eq. 4.2
4.1.1.1 Effect of alcoholysis conditions.
The alcoholysed products are obtained from different reaction times; 10, 15,
and 30 min. The molecular weight of the original raw material (PLLA L100 IXS) is
155,000 g/mol (R. Ahmed, 2011). GPC curves of alcoholysed products show similar
pattern, and indicate a single peak distribution of mass. The molecular weight of
alcoholysed products were investigated by GPC. The results are summarized in table
4.1.
Ref. code: 25605822041702BJS
24
Table 4.1 Effect of alcoholysis conditions on molecular weight of alcoholysed
products in solid part.
The results show that reaction times impose strong effect on molecular weight
of the alcoholysed products. When the reaction time increased the average molecular
weight of the alcoholysed products decreased. In addition, the glass transition
temperature (Tg) of alcoholysed products from DSC results indicated that the
alcoholysed products obtained at 15 min reaction time have a lowest Tg, due to
changes in their chain mobility when compared with those samples, as show in Figure
4.1.
Figure 4.1 DSC thermograms of alcoholysed products (AlcPLAs).
Gly:PLA
(wt/wt)
Temperature
(C°)
Reaction time
(min.)
Mn
(g/mol)
Mw
(g/mol)
PDI
2:1
240°
10 2,283 3,506 1.53
15 2,587 2,019 1.31
30 2,304 1,843 1.23
Time (minutes)
0.00
0.10
0.20
0.30
0.40
0.50
0.60
0.70
0.80
Abs
orba
nce
0 50 100 150
Wavenumbers (cm-1)
AlcPLAs 30 min
AlcPLAs 15 min
AlcPLAs 10 min
Tg = 26.44 ℃
Tg = 21.48 ℃
Tg = 30.37 ℃
Ref. code: 25605822041702BJS
25
Moreover, the alcoholysis reaction conditions also effect the yield of the solid
and liquid parts. Table 4.2 summarizes effects of the reaction time on the PLA
conversion and yield of alcoholysed products.
Table 4.2 Effect of alcoholysis conditions on PLA conversion and product yield
distribution.
Samples
Temp.
(C°)
Reaction
time
(min)
PLA
conversion
(%)
Yield (%)
Solid part Liquid part
AlcPLAs 10 min
240
10 100 50.6 49.4
AlcPLAs 15 min 15 100 48.1 51.9
AlcPLAs 30 min 30 100 32.4 67.6
The results show that reaction times have strong effect on the % yield of solid
part. When the reaction time increase, higher degradation rate is obtained, leading to
higher contents of liquid part which has lower molecule weights.
4.1.2 Characterization the solid part (AlcPLAs)
4.1.2.1 Chemical stucture
Chemical structures of the alcoholysed products in solid part (AlcPLAs)
were investigated by FTIR spectroscopy, as illustrated in Figure 4.2. The spectra
show characteristic bands at 3360 cm-1
(-OH stretching), 1750 cm-1
(C=O stretching of
esters), 2996 cm-1
and 2945 cm-1
(-CH3 asymmetric and symmetric stretching), and
1456 cm-1
(-CH3 asymmetrical deformation)(Krikorian & Pochan, 2005). The spectra
are normalized to the 1456 cm-1
band for comparison across samples. The normalized
intensities of the 3360 cm-1
band indicate relative contents of –OH end groups of the
products, originated from the end-capping of glycerol units on lactate oligomer
sequences. This, in turn, reflects relative sizes of the alcoholysed products, and hence,
the reaction efficiency. The results show that the products obtained at 30 min reaction
time have higher band intensity, reflecting smaller size products and higher
alcoholysis efficiency, compared to those from the reaction at 10 and 15 min.
Ref. code: 25605822041702BJS
26
Figure 4.2 FTIR spectra of alcoholysed products in the solid part (AlcPLAs), as a
function of reaction times; (a) 30 min, (b) 15 min, and (c) 10 min.
1H-NMR spectroscopy is employed to verify molecular structures of the
alcoholysed products, as shown in Figure 4.3. The resonance of in chain’s methine
proton (-O=C-CH-(CH3)-O) is located at 5.1-5.2 ppm, whereas that of end group (-
O=C-CH-(CH3)-OH) is at 4.3 ppm (d) (Rashkov, Manolova, Li, Espartero, & Vert,
1996). The signal at 4.1 ppm (b) is assigned to methine proton of glyceryl unit (-CH-
O-C=(O)-R) and the signals of methyl of glyceryl unit (-CH2-O-C=(O)-R) is located
at 4.1-4.2 ppm (c). The signals of methine lactate protons of in-chain and terminal
units are at 5.1-5.2 and 4.3 ppm, respectively. The integral ratio of these 2 signals
represents average size of the alcoholysed products, as summarized in Table 4.2. The
results indicate that the lactate oligomers products possess 3-branched structures with
average length of 11 repeat units. It is noted that the appearance of signals at 1.2-1.8
and 3.4-3.9 ppm indicates a presence of unreacted glycerol residues or products which
undergo partially transesterification.
Ref. code: 25605822041702BJS
27
Figure 4.3 1H-NMR spectrum and signal assignments of the alcoholyzed products
obtained at 30 min.
Interestingly, the results indicate that the products obtained at 15 and 30 min
reaction times have similar average arm length. The difference in properties of the
products may likely due to the number of branches per molecule, but not the size of
the lactate sequences. The length of lactate repeat units can be calculated by equation
4.3:
Length of lactate repeat units = Integra of signal at 5.1-5.2 ppm
Integra of signal at 4.3 ppm Eq. 4.3
Table 4.3 Results on average arm length of the resulting AlcPLAs products from 1H-
NMR spectra.
Samples
Integral of
signals at 5.1-
5.2 ppm
Integral of
signal at 4.3
ppm
Length of lactate
repeat units
AlcPLAs 10 min. 1 0.07 13
AlcPLAs 15 min. 1 0.09 11
AlcPLAs 30 min. 1 0.09 11
10 8
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6
1.8A
bs
orb
an
ce
1 2 3 4 5
Wavenumbers (cm-1)ppm
c b
a d
Ref. code: 25605822041702BJS
28
4.1.2.2 Crytalinity of alcoholysis products
XRD analysis results of alcoholysed products (AlcPLAs) are shown in Figure
4.4. The semi-crystalline polylactic acid or PLA shows characteristic sharp peaks at
16.7°, 14.7°, 19.0°, and 22.3° which are the major peak of PLA (Tábi, Sajó, Szabó,
Luyt, & Kovács, 2010). These samples exhibited a broad halo peak at 14.7°, 19.0°,
and 22.3°, whereas a shaper peak local at 16.7° is associated with crystalline of the
alcoholysed products. The relative intensities of these bands vary with the alcoholysis
time, indicating effect of depolymerization on crystallization of PLLA.
Figure 4.4 XRD results of alcoholysed products (AlcPLAs) obtained at different
alcoholysis times.
Ref. code: 25605822041702BJS
29
4.1.3 Characterization of alcoholysed products in the liquid part (AlcPLAl)
4.1.3.1 Chemical stuctures
FTIR spectra of the alcoholyzed products in the liquid part (AlcPLAl) show an
intense band at 3360 cm-1
, due to –OH stretching made of unreacted residual glycerol
and partially-reacted diglycerol or triglycerol which are byproducts of the alcoholysis
reaction in the liquid part, and a C=O stretching band at 1750 cm-1
. These bands can
be used to follow the degree of degradation of PLA. The products with reaction time
of 30 min shows lower intensity of 3360 cm-1
band and higher intensity of 1750 cm-1
band. This results show that the products obtained at 30 min reaction has higher
degree of degradation rate which agree with FTIR spectra of the corresponding
alcoholysed products in solid part. The spectra of alcoholysed products in the liquid
part are shown in figure 4.5.
Figure 4.5 FTIR spectra of alcoholysed products in the liquid part (AlcPLAl), as a
function of reaction time; (a) 10 min, (b) 15 min, and (c) 30 min.
Chemical structures of the products are also observed by spectroscopy. The
signal at 4.5 ppm (Hb) is the resonance of methine proton at the end group (-O=C-
CH-(CH3)-OH) (Espartero, Rashkov, Li, Manolova, & Vert, 1996), whereas the
signal located at 4.4 ppm (Ha) is due to methyl glyceryl (-CH2-O-C=(O)-R). The
integral intensities of methine proton at the end group (-O=C-CH-(CH3)-OH) and
methyl glyceryl (-CH2-O-C=(O)-R) confirm the 3-branch structure of glyceride with
sequences lactic acid units. This observation indicates that the samples have 3-branch
Ref. code: 25605822041702BJS
30
oligomer and terminal oligomer with end-capped lactic acid. 1H-NMR spectra of
AlcPLAl obtained at 10 min reaction time is shown in Figure 4.6 This represents
chemical structures of the alcoholysed product in the liquid part. The results also
show signals of unreacted glycerol residues and partially-reacted by-products of
alcoholysis reaction, which are located at 3.2-3.6 ppm (Kaur, Prakash, & Ali, 2018).
Figure 4.6 1H-NMR spectrum of the alcoholysed product obtained at a 10 min
reaction time.
4.1.3.2 Chemical composit of alcoholysed product separated by HPLC
Chemical compositions of the resulting products were examined by high-
performance liquid chromatography (HPLC). The species with longer repeating units
or more hydrophobic components are eluted at higher retention times, in reversed
phase columns. In contrast, species with shorter repeating units or more hydrophilic
are eluted at the first stage of retention time. The samples were detected by a UV
detector at 210 nm for lactic acid. Chromatograms of the AlcPLAl obtained at
different conditions are shown in Figure 4.7, in which peaks in a range of retention
times from 2 to 18 min are shown. Chemical structures of the alcoholyed products are
examined based on the chromatograms of lactic acid (LA), in which 5 significant
peaks corresponding to proposed number of repeating units of lactate with and
10 7 0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6
1.8
2.0
2.2
2.4
2.6
Abs
orb
an
ce
2 3 4 5
Wavenumbers (cm-1)
b a
ppm
Ref. code: 25605822041702BJS
31
without glycerol are observed. The 5 peaks are due to oligomers containing 1, 2-3, 3-
4, 4-5, and >5 units, respectively. AlcPLAl obtained at 15 and 30 min show peak with
high intensity of the lactic acid with and without glycerol components, which agrees
with the 1H NMR results. The composition of alcoholysed products are summarized
in table 4.3.
Table 4.4 Chemical components of alcoholysed products obtained at different
alcoholysis conditions.
Figure 4.7 Compositions of AlcPLAl products obtained at reaction times of 10, 15,
and 30 min.
0.00
10.00
20.00
30.00
40.00
50.00
60.00
70.00
80.00
90.00
100.00
AlcPLAl 10 min. AlcPLAl 15 min. AlcPLAl 30 min.
Peak area percentage
5.55 8.71 9.99 10.33 11.43 12.64 14.20 18.89
Samples
% Peak area
5.5 min 8.7 min 9.9 min 10.3 min > 10.3 min
AlcPLAl 10 min. 2.03 0.54 1.56 1.52 94.35
AlcPLAl 15 min. 41.09 6.76 18.53 17.20 16.42
AlcPLAl 30 min. 42.90 7.28 17.35 18.19 14.28
Ref. code: 25605822041702BJS
32
Figure 4.8 HPLC chromatograms of alcoholysed products (AlcPLAl) obtained at
different alcoholysis condition times: 10, 15, and 30 min.
4.2 Enhancement of toughness of PLA rasin by using alcoholysed product
The alcoholysed products were added into PLA resin (NatureWork, 4043D)
for toughening of the resin. The properties of the resulting blended films were
investigated and discussed below;
4.2.1 Characterization of film blended with alcoholysis products
Effect of the blend ratios on properties of the resulting blends are examined.
The blend compositions were varied and thermal and mechanical properties of the
resulting blends were investigated.
4.2.1.1 Thermal properties of film blended
DSC analysis was employed to examine thermal property of the alcoholysed
products and the blended films. The results indicates that the alcoholysed product
obtained at 15 min have higher chain mobility, compared to other products. These are
illustrated in Figure 4.9. The crystallinity (Xc) are calculated from the ratio of the
enthalpy of fusion ( Hm)/the enthalpy of fusion of fully crystalline PLA ( H0 = 106
J/g), according to Equation 3.2. The results show that all blended samples have a
single Tg, which varies with the blends contents (Figure 4.9). This indicates a
complete miscible system for all compositions, as the alcoholysed products also
contain similar sequences of lactate units (Supthanyakul et al., 2016). Results on Tg
values and Xc, as a function of the blend compositions, are summarized in Figure 4.9.
Ref. code: 25605822041702BJS
33
Figure 4.9 Tg and Xc of blended samples, as a function of AlcPLAS contents.
When the alcoholysed products are introduced to PLA, its glass transition
temperature (Tg) and crystallinity increases with the blend composition up to 0.5%.
However, when the content reaches 1.0%, a decreasing trend is observed. This is
likely because the -OH terminals of AlcPLA can induce crystallization of PLA,
leading to higher crystalline contents and hence higher Tg. When AlcPLA is further
added, however, the branched structure introduces more free volume to the system,
leading to lower Tg. Interestingly, both blend systems derived from either AlcPLA15
or AlcPLA30 show similar behavior. Nonetheless, the results indicate that an AlcPLA
content of 0.5% is the optimal ratio for strengthening the film’s properties, which also
agrees with mechanical properties results.
57
58
59
60
61
62
63
64
0
5
10
15
20
25
30
35
0.2 0.5 1.0 0.2 0.5 1.0 0.2 0.5 1.0
Neat
PLLA
AlcPLAS 10 min AlcPLAS 15 min AlcPLAS 30 min
Xc (%)
Tg (⁰C)
Tg (C°) Xc (%)
Ref. code: 25605822041702BJS
34
Figure 4.10 DSC thermograms (second heat scans) of blends consisting of different
AlcPLAs obtained at different alcoholysis times, as a function of the blend contents.
Ref. code: 25605822041702BJS
35
4.2.2.2 Mechanical properties of PLA composits
Mechanical properties, in terms of Modulus, tensile strength, and elongation
of the blended films containing various AlcPLA contents are investigated. The results
are shown in Figures 4.11, reflecting improvements in these properties, especially at
an AlcPLA content of 0.5%. The modulus increases from 2427 to 2538 MPa, in
which the tensile strength also increases from 54.5 to 61.7 MPa. The elongation
improves from 2.92 to 3.29%, compared to neat PLA. This is likely due to a
formation of strong hydrogen bonding between AlcPLA additive and the PLA matrix,
and an enhancement in crystalline formation of PLA as a result from induction effect
from AlcPLA’s ends groups.
30.0
35.0
40.0
45.0
50.0
55.0
60.0
65.0
70.0
0 0.2% 0.5% 1.0%
(a) Strength (MPa)
AlcPLAs 10 min AlcPLAs 15 min AlcPLAs 30 min
Ref. code: 25605822041702BJS
36
Figure 4.11 (a) Tensile strength (MPa), (b) Elongation (%), and (c) Modulus (MPa)
of blended samples, as a function of the AlcPLA structures and contents
1.5
2.0
2.5
3.0
3.5
4.0
0 0.2% 0.5% 1.0%
(b) Elongation (%)
AlcPLAs 10 min AlcPLAs 15 min AlcPLAs 30 min
1500.0
1700.0
1900.0
2100.0
2300.0
2500.0
2700.0
2900.0
0 0.2% 0.5% 1.0%
(c) Modulus(MPa)
AlcPLAs 10 min AlcPLAs 15 min AlcPLAs 30 min
Ref. code: 25605822041702BJS
37
Results on impact strength of AlcPLAS/PLA blends and neat PLA are shown
in Figure 4.12. Toughness of the blended samples were investigated by Izod impact
test, using a pendulum of 1 J. The result shows that blends consisting of AlcPLAS 15
min 0.2% have the lowest impact resistance, while that containing AlcPLAS 10 min
0.5% shows the highest resistance, when compared with all blended samples. The
results indicates that an optimum content of alcoholysed products for blending with
PLA resin is 0.5%. This strongly agrees with the tensile results.
The blend samples containing 0.5% AlcPLAs contents which exhibit an
optimum impact resistance were chosen to examine their surface morphology by
SEM, as shown in Figure 4.13. The figure of neat PLA shows smooth, laminated
surfaces, reflecting brittle characteristic, while rough surface indicates higher impact
resistance. The impact fractured surface of neat PLA/alcoholysed blend products
show rough surface, which is different from that of neat PLA, especially that
consisting of AlcPLAs 15 min. This result confirms the high impact resistance and is
in good agreement with the impact resistance results.
2.00
2.05
2.10
2.15
2.20
2.25
2.30
2.35
0.2 0.5 1.0 0.2 0.5 1.0 0.2 0.5 1.0
Neat AlcPLAs 10min AlcPLAs 15min AlcPLAs 30min
Impact reistance (kJ/m2)
Figure 4.12 Results on impact strength of PLA/alcoholysed products blends, using
different AlcPLAs, as a function of the blend compositions.
Ref. code: 25605822041702BJS
38
Figure 4.13 SEM images of impact fractured surfaces of PLA/alcoholysed blends.
Those samples are an optimum ratio contents 0.5%.
SEM images, as shown in Figure 4.13, reflect that phase separation occurs in
the PLA/AlcPLA 10 min blend, in which traditional morphology of immiscible blend
system is observed. The phase separation of these AlcPLA 10 min alcoholysed
products as dispersed domains is likely because of chain entanglements as a result
from their relatively high molecular weight and longer 3-branch lactate oligomer
sequences. This phase separation, in turn, leads to lower impact resistance (Grijpma,
Penning, & Pennings, 1994).
Neat PLA
AlcPLAs 15 min. AlcPLAs 30 min.
AlcPLAs 10 min.
Ref. code: 25605822041702BJS
39
Chapter 5
Conclusions and Future work
5.1 Conclusions
PLA has been used in consumer good and packaging applications instead of
conventional plastics. The consumption rate of this polymer is rapidly increasing due
to environmental and global warming concerns, which is driven by environmental
awareness of general public. This, in turn, inversely leads to a rapid increase in the
postconsumer PLA waste. Chemical recycling is one of effective processes to convert
PLA wastes to other valuable starting materials. In this work, PLA is converted by
using alcoholysis reaction of glycerol under a microwave irradiation. The reaction
conditions were varied to examine optimum production conditions. The resulting
products were used as an additive for toughening of PLA resin. The results indicated
that microwave irradiation is an efficient heating source for alcoholysis reactions.
Reaction conditions impose strong effect on average molecular weight and length of
lactate oligomer sequences of the resulting products. Chemical structures of AlcPLAs
and AlcPLAl were investigated by 1H NMR and FTIR spectroscopy. The results
indicated that lactate oligomers with an average length of 11 (AlcPLAs 15 min and 30
min) and 13 (AlcPLA 10 min) repeat units were produced. The results suggest that the
structure of AlcPLAl products is 3-branched oligomers with end-capped lactic acid
terminals. The resulting products were then blended with PLA resin. Properties of the
resulting blend film samples were examined, in terms of thermal and mechanical
properties and fractured morphology. DSC results revealed that the degree of
crystallization and the amount of overall crystallinity were higher than neat PLA, lead
to better mechanical properties. It is noted that byproducts from partial
transesterification, such as di-glycerides or unreacted glycerol may present in the
system, as can be seen from 1H MNR results.
Ref. code: 25605822041702BJS
40
5.2 Futer work
To obtain insights into mechanisms of the reactions and applications of the
resulting products in property enhancement of PLA, further work is recommended, as
follows. The alcoholysed products in the liquid portion which contain unreacted
glycerol residues should be further examined. Their chemical composition should be
verified by LCMS. Effective purification process of this product should be
developed.
Although this study focuses on application of the solid part as toughness
enhancing agent for PLA resin, potential use of the alcoholysed product in the liquid
part should be investigated. Given that glycerol is a good plasticizer for use in
polymer blend systems, due to its –OH terminal which is able to annex the binary
polymer, the alcoholysed product in the liquid part is show similar –OH terminals in
the structure. In order to improve the toughness of PLA resin, the molecular weight
and length of lactate oligomer should be considered. However, inducing the –OH
terminals to the system may lead to increase in hydrophilicity of the samples. This
may be suitable for use in specific applications, such as active packaging.
Ref. code: 25605822041702BJS
41
References
A., A. K., K., K., & K., P. A. (2011). Biodegradable Polymers and Its Applications.
International Journal ofBioscience, Biochemistry and Bioinformatics, 1.
Bakibaev, A. A., Gazaliev, A. M., Kabieva, S. K., Fedorchenko, V. I., Guba, G. Y.,
Smetanina, E. I., . . . Gulyaev, R. O. (2015). Polymerization of Lactic Acid
Using Microwave and Conventional Heating. Procedia Chemistry, 15, 97-102.
doi: http://dx.doi.org/10.1016/j.proche.2015.10.015
Bouapao, L., Tsuji, H., Tashiro, K., Zhang, J., & Hanesaka, M. (2009).
Crystallization, spherulite growth, and structure of blends of crystalline and
amorphous poly(lactide)s. Polymer, 50(16), 4007-4017. doi:
http://dx.doi.org/10.1016/j.polymer.2009.06.040
Briassoulis, D., Hiskakis, M., & Babou, E. (2013). Technical specifications for
mechanical recycling of agricultural plastic waste. Waste Management, 33(6),
1516-1530. doi: http://dx.doi.org/10.1016/j.wasman.2013.03.004
Buggy, M. (2006). Natural fibers, biopolymers, and biocomposites. Edited by Amar K
Mohanty, Manjusri Misra and Lawrence T Drzal. Polymer International,
55(12), 1462-1462. doi: 10.1002/pi.2084
Chavhan, A. (2016). Recent Developments on biodegradable polymers and their
future trends. Int. Res. J. of Science & Engineering, Vol. 4 (1), 17-26.
Chen, J., Lv, J., Ji, Y., Ding, J., Yang, X., Zou, M., & Xing, L. (2014). Alcoholysis of
PET to produce dioctyl terephthalate by isooctyl alcohol with ionic liquid as
cosolvent. Polymer Degradation and Stability, 107, 178-183. doi:
http://dx.doi.org/10.1016/j.polymdegradstab.2014.05.013
Erwin, T. H. V., Karl, R. R. b., David, A. G., & Patrick, R. G. (2003). Applications of
life cycle assessment to NatureWorksTM polylactide (PLA) production.
Polymer Degradation and Stability, 80, 403–419
doi: doi:10.1016/S0141-3910(02)00372-5
Espartero, J. L., Rashkov, I., Li, S. M., Manolova, N., & Vert, M. (1996).
Macromolecules, 29, 57.
Grijpma, D. W., Penning, J. P., & Pennings, A. J. (1994). Chain entanglement,
mechanical properties and drawability of poly(lactide). Colloid and Polymer
Science, 272(9), 1068-1081. doi: 10.1007/BF00652375
Hamad, K., Kaseem, M., Deri, F., & Ko, Young G. (2016). Mechanical properties and
compatibility of polylactic acid/polystyrene polymer blend. Materials Letters,
164, 409-412. doi: http://dx.doi.org/10.1016/j.matlet.2015.11.029
Hirao, H., Nakatsuchi, Y., & Ohara, H. (2010). Alcoholysis of poly(L-lactic acid)
under microwave irradiation. Polymer Degradation and Stability, 95, 925-928.
doi: 10.1016/j.polymdegradstab.2010.03.027
Hirao, K., & Ohara, H. (2011). Synthesis and Recycle of Poly(L-lactic acid) using
Microwave Irradiation. Polymer Reviews, 51(1), 1-22. doi:
10.1080/15583724.2010.537799
Hopewell, J., Dvorak, R., & Kosior, E. (2009). Plastics recycling challenges and
opportunities. Phil. Trans. R. Soc. B, 364, 2115-2126.
Jamshidian, M., Tehrany, E. A., Imran, M., Jacquot, M., & Desobry, S. (2010). Poly‐
Lactic Acid: Production, Applications, Nanocomposites, and Release Studies.
Comprehensive Reviews in Food Science and Food Safety, 9(5), 552-571. doi:
10.1111/j.1541-4337.2010.00126.x
Ref. code: 25605822041702BJS
42
Kaur, A., Prakash, R., & Ali, A. (2018). 1H NMR assisted quantification of glycerol
carbonate in the mixture of glycerol and glycerol carbonate. Talanta,
178(Supplement C), 1001-1005. doi:
https://doi.org/10.1016/j.talanta.2017.08.103
Krikorian, V., & Pochan, D. J. (2005). Crystallization Behavior of Poly(l-lactic acid)
Nanocomposites: Nucleation and Growth Probed by Infrared Spectroscopy.
Macromolecules, 38(15), 6520-6527. doi: 10.1021/ma050739z
Lasprilla, A. J. R., Martinez, G. A. R., Lunelli, B. H., Jardini, A. L., & Filho, R. M.
(2012). Poly-lactic acid synthesis for application in biomedical devices — A
review. Biotechnology Advances, 30(1), 321-328. doi:
http://dx.doi.org/10.1016/j.biotechadv.2011.06.019
Lidstrom, P., Tierney, J., Wathey, B., & Westman, J. (2001). Microwave assited
organic systhesis Review. Trtrahedron, 57, 9225-9283.
Liu, S., Wang, Z., Li, L., Yu, S., Xie, C., & Liu, F. (2013). Butanol alcoholysis
reaction of polyethylene terephthalate using acidic ionic liquid as catalyst.
Journal of Applied Polymer Science, 130(3), 1840-1844. doi:
10.1002/app.39246
Liu, S., Wang, Z., Li, L., Yu, S., Xie, C., & Liu, F. (2013). Butanol alcoholysis
reaction of polyethylene terephthalate using acidic ionic liquid as catalyst. J.
APPL. POLYM. SCI., 130, 1840–1844. doi: 10.1002/APP.39246
Madival, S., & al., e. (2009). Assessment of the environmental profile of PLA, PET
and PS clamshell. Journal of Cleaner Production, 1183–1194.
Matta, A. K., Rao, R. U., Suman, K. N. S., & Rambabu, V. (2014). Preparation and
Characterization of Biodegradable PLA/PCL Polymeric Blends. Procedia
Materials Science, 6, 1266-1270. doi:
http://dx.doi.org/10.1016/j.mspro.2014.07.201
Nikje, M. M. A., & Nazari, F. (2006). Microwave-assisted depolymerization of
poly(ethylene terephthalate) [PET] at atmospheric pressure. Advances in
Polymer Technology, 25(4), 242-246. doi: 10.1002/adv.20080
Parameswaranpillai, J., Thomas, S., & Grohens, Y. (2014). Polymer Blends: State of
the Art, New Challenges, and Opportunities Characterization of Polymer
Blends (pp. 1-6): Wiley-VCH Verlag GmbH & Co. KGaA.
PlasticEurope. (2016). The total plastic demand in Europe for the year 2014.
http://www.plasticseurope.org/documents/document/20161014113313-
plastics_the_facts_2016_final_version.pdf
R. Ahmed. (2011). Poly(lactic acid) stereocomplex formation in the melt : limitations
and prospectives In D. d.-.-D. o. C. E. a. C. S. P. J. L. c.-s. D. G. Hristova-
Bogaerds (Ed.), (pp. XIV, 114 p.).
Rashkov, I., Manolova, N., Li, S. M., Espartero, J. L., & Vert, M. (1996). Synthesis,
Characterization, and Hydrolytic Degradation of PLA/PEO/PLA Triblock
Copolymers with Short Poly(l-lactic acid) Chains. Macromolecules, 29(1), 50-
56. doi: 10.1021/ma950530t
Rezabeigi, E., Wood-Adams, P. M., Drew, R. A. L. (2014). Production of porous
polylactic acid monoliths via nonsolvent induced phase separation. Polymer,
55,6743-6753.
Ref. code: 25605822041702BJS
43
Sarasua, J.-R., Prud'homme, R. E., Wisniewski, M., Le Borgne, A., & Spassky, N.
(1998). Crystallization and Melting Behavior of Polylactides.
Macromolecules, 31(12), 3895-3905. doi: 10.1021/ma971545p
Siddiqui, M. N., Redhwi, H. H., & Achilias, D. S. (2012). Recycling of poly(ethylene
terephthalate) waste through methanolic pyrolysis in a microwave reactor.
Journal of Analytical and Applied Pyrolysis, 98, 214-220. doi:
http://dx.doi.org/10.1016/j.jaap.2012.09.007
Sin, L. T., Rahmat, A. R., & Rahman, W. A. W. A. (2013). 2 - Synthesis and
Production of Poly(lactic Acid) Polylactic Acid (pp. 71-107). Oxford: William
Andrew Publishing.
Song, J. H., Murphy, R. J., Narayan, R., & Davies, G. B. H. (2009). Biodegradable
and compostable alternatives to conventional plastics. Phil. Trans. R. Soc.
B(360), 2127–2139. doi: 10.1098/rstb.2008.0289
Špitalský, Z., Lacík, I., Lathová, E., Janigová, I., & Chodák, I. (2006). Controlled
degradation of polyhydroxybutyrate via alcoholysis with ethylene glycol or
glycerol. Polymer Degradation and Stability, 91(4), 856-861. doi:
http://dx.doi.org/10.1016/j.polymdegradstab.2005.06.019
Supthanyakul, R., Kaabbuathong, N., & Chirachanchai, S. (2016). Random
poly(butylene succinate-co-lactic acid) as a multi-functional additive for
miscibility, toughness, and clarity of PLA/PBS blends. Polymer, 105, 1-9.
Tábi, T., Sajó, I. E., Szabó, F., Luyt, A. S., & Kovács, J. G. (2010). Crystalline
structure of annealed polylactic acid and its relation to processing. eXPRESS
Polymer Letters, 4(10), 659-668. doi: 10.3144/expresspolymlett.2010.80
Wolf, O. (2005). Techno-economic feasibility of large-scale production of bio-based
polymers in Europe. Paper presented at the Spain: European Communities,
Institute for Prospective Technological Studies, Spain.
Xiaohu F. et al., R. B., Yongchang Z. (2010). Glycerol (Byproduct of Biodiesel
Production) as a Source for Fuels andChemicals – Mini Review. The Open
Fuels & Energy Science Journal, vol.3, pp.17-22.
Yokohara, T., & Yamaguchi, M. (2008). Structure and properties for biomass-based
polyester blends of PLA and PBS. European Polymer Journal, 44(3), 677-
685. doi: http://dx.doi.org/10.1016/j.eurpolymj.2008.01.008
