Polysaccharide interactions with nanocellulose as a platform for biomimetic

modifications Paula Eronen, Karoliina Junka, Martin Häggblom, Janne Laine and Monika Österberg

Aalto University, School of Science and Technology, Faculty of Chemistry and Material Sciences Department of Forest Products Technology, P.O. Box 16300, FI-00076 Aalto Abstract We have studied the interactions of nanofibrillar cellulose with different polysaccharides both in molecular- and macroscopic level in aqueous environment. First, basic properties affecting the interactions with polysaccharides were explored using thin films of NFC and two different high-precision adsorption techniques for ultrathin films of NFC. Furthermore, we extended the study from fundamental to practical scale by preparing films from refined and fluidized nanocellulose gels using a filtration based technique. The effect of selected polysaccharide adsorption on film properties was evaluated. Introduction In order to efficiently utilize nanocellulose as raw material in emerging biobased applications the unique properties of cellulose should be retained. Many approaches to increase the low compatibility of cellulose fibrils with other materials due to their strong intrafibrillar aggregation behaviour have been proposed. The problem with direct chemical modifications to cellulose structures, however, is that it often leads to unwanted changes, especially in cellulose strength properties. One proposed way to overcome harsh chemical treatments is to do the compatibilization biomimetically, coating fibrils with material that has natural affinity to cellulose [1], such as polysaccharides. It is known that similar (1→4)-linked β-D -structured backbones of glucose and mannose present in wood cell walls as versatile compounds known as hemicelluloses are known to naturally adhere on cellulose pulps or microcrystalline cellulose [2-5]. Therefore one purpose of this study was to look closer into the interactions of different polysaccharides with nanofibrillated cellulose, after which the chemical modifications and activations of attached polysaccharides, is easier while retaining the important cellulose features. Materials and Methods The nanofibrillar cellulose was prepared from hardwood kraft pulp by high-pressure multiple fluidized process and obtained from the Finnish Center for Nanocellulosic Technologies. Ultrathin films were prepared on sensors by utilizing the method developed by Ahola et al [6]. All polysaccharides tested were commercially available water-soluble products and a simple and fast hydrolysis was performed to selected samples to study the effect of molecular weight on adsorption phenomena. A statistical analysis was performed to find the most important factors governing the attachment of polysaccharides on nanofibrillar cellulose. Main techniques to characterize the attachment were quartz crystal with microbalance (QCM-D) (Q-Sense E4, Västrä Frölunda, Sweden) and surface plasmon resonance (SPR, Biacore 100, GE Healthcare, Uppsala, Sweden), combined with atomic force microscopy AFM (Multimode 3000, Digital Instruments, Santa Barbara CA, USA) imaging to verify the nanofibrillar structure before and after treatments. Films were prepared by casting or filtration based techniques. Results Selected results are collected in Figure 1. Adsorption on nanocellulose film of polysaccharides having similar molecular weight reveals clearly the major role of polysaccharide backbone structure and charge properties. Neutral polysaccharides adsorbed in greater amount and had the expected dispersing effect on the nanofibril film structure, while especially cationically charged formed a thinner layer with strong initial interaction, illustrated in Figure 1a. These results are discussed in detail and compared to literature values and simulations of polysaccharide structures. Nearly all the tested polysaccharides have strong irreversible attachment towards nanofibrillated cellulose film.

When adsorbed mass results are combined with energy dissipation data acquired simultaneously, viscoelastic properties of adsorbed layers were estimated in relation to adsorbed layer thickness and viscosity. However, due to the high content of coupled water both within cellulose fibril network and the polysaccharide layer complementing techniques are needed. Therefore, Surface Plasmon Resonance (SPR) measurements based on the total internal reflection of light were performed and the attachment of polysaccharides was verified (Figure 1b). By combining results from complementary techniques, the relative amount of bound water per polysaccharide was estimated and utilized when moving from molecular scale studies to macroscale, utilizing the strong innate film forming property observed with nanocellulosic fibrils. Furthermore, the structures of both ultrathin nanofibrillar films and macroscaled structures were studied with various techniques, including AFM imaging (Figure 1c). Finally, films (Figure 1d) were prepared with or without polysaccharide modifications and compared emphasizing the need for further chemical modifications of the polysaccharides.

Figure 1. Selected results combining the adsorption studies of polysaccharides with nanofibrillar cellulose with different techniques together with images of nanofibrillated cellulose as ultathin model film and as macroscopic nanocellulose film.

References cited 1. Teeri, T.T., et al., Biomimetic engineering of cellulose-based materials. Trends in Biotechnology, 2007.

25(7): p. 299. 2. Zhou, Q., et al., Xyloglucan in cellulose modification. Cellulose, 2007. 14(6): p. 625. 3. Mishima, T., et al., Adhesion of beta-glucans to cellulose. Carbohydrate Research, 1998. 308(3-4): p. 389. 4. Ishimaru, Y. and T. Lindström, Adsorption of water-soluble, nonionic polymers onto cellulosic fibers.

Journal of Applied Polymer Science, 1984. 29(5): p. 1675-1691. 5. Hannuksela, T., M. Tenkanen, and B. Holmbom, Sorption of dissolved galactoglucomannans and

galactomannans to bleached kraft pulp. Cellulose, 2002. 9(3): p. 251. 6. Ahola, S., et al., Model Films from Native Cellulose Nanofibrils. Preparation, Swelling, and Surface

Interactions. Biomacromolecules, 2008. 9(4): p. 1273.

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Polysaccharide interactions with nanocelluloseas a platform for biomimetic modifications

Presented by:

Paula Eronen, Karoliina Junka, Martin Häggblom, JanneLaine and Monika ÖsterbergDepartment of Forest Products Technology,Aalto University

2

Content of presentation

• Why polysaccharides adsorb on NFC• Water soluble polysaccharides• Main characterization techniques:

– QCM-D (viscoelastic properties)– AFM (morphology) – AFM combined with DPFM (adhesion and

stiffness properties) • Formation thin polysaccharide layer on

nanosized fibril films

3

• To verify the most suitable polysaccharidesadsorbing on cellulose and compare the adsorption properties

Objectives

new knowledge of polysaccharideadsorption on nanocellulose

important for further adsorption of modified polysaccharides

4

Background

Plant cell-wall: naturalnanocomposite structure

Adapted from SticklenNature rev. Genetics 2008,

9, 433

TEM

AFM phase

Adapted from Pääkkö et al. Biomacromolecules 2007, 8, 1934

5

Motivation

• Nanocellulose surface modification via polysaccharide adsorption

• Why polysaccharides?– Biodegradable– Natural ability to adsorb on cellulose– Modifications possible– Have been shown to increase properties such as

tensile strenght of paper (e.g. Petri Myllytie, PhD-thesis, Dep. Forest Products Technology, TKK 2009)

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• Most of preliminary work focused on molecular interactions– literature review of previous studies with pulps

most promising ones chosen

– high precision techniques (QCM-D, AFM, SPR, DPF)

– ultrathin films prepared from hardwoodnanofibrillar cellulose

Experimental

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Model films from cellulose nanofibrils• Necessary for fundamental studies on

molecular level– chemistry and morphology– More information: Kontturi, Tammelin, Österberg, Chem. Soc. Rev.

2006,35,1287

• Preparation: spin-coating of NFC(Ahola et al.Biomacromolecules 2008,9,1273)

ω

exhaust

fluid-flow/evaporation substrate

ultra-centrifugation

Fibril dispersionadapted from E.Kontturi

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• Water-soluble, readily available• Different backbone structure:

– Mannans: • guar (GG) and locust bean gum (LBG)

– Cellulose derivatives:• methyl cellulose (MC) and carboxymethyl cellulose (CMC)

– Xylan from birch (XYL)

– Chitosan (CHI)

• Acid hydrolysis of mannans Mw

Polysaccharides

applied from Cheng et al. Int J Biol Macromol 2002, 31, 29

cellulose

chitosan

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Quartz Crystal Microbalancewith dissipation (QCM-D)

Picture used with permission from Q-Sense

Fibril model film

(AFM image, 2x2µm)

Combined massand viscoelastic

properties

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Properties of adsorbed layers on NFC film

pH 4.5, 10 mMNaAc-HAc-buffer,

T= 24°C

Irreversibleattachment

Backbone structure and available surface area affect adsorption

0 -10 -20 -30 -40 -50-10123456789

LBG

ΔD(1

0-6)

Δf (Hz)

CHI

XYL

MCGG

XG

+

-

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Effect of molecular weight (Mw)

No direct correlation (statistical analysis)In the following polysaccharides with similar Mw werechosen

-5 -10 -15 -20 -25 -30 -35 -40 -45 -500

1

2

3

4

5

6

7Δ

D (1

0-6)

Δf (Hz)

0

1000

10000

2,000E4

1,000E5

2,500E5

5,000E5

1,375E6

1,650E6

1,925E6

2,200E6

Mw (g/mol)

Mw< 10 000 g/mol

10 000 g/mol<Mw<370 000 g/mol

Mw>500 000 g/mol

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Adsorbed amount as a function of timeEffect of backbone structure and charge

QCM-D

bound water included!

Highest adsorbedamount of neutralpolysaccharide-

similar backbone as cellulose

Cationic: thin layer

10 11 12 13 14 15 16 17 18-0,20,00,20,40,60,81,01,21,41,61,8

Δm(m

g/m2 )

Time (min)

neutral-XG

anionic--CMC

cationic-CHI

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Viscoelastic properties of the adsorbedpolysaccharide layer

Thick, swollen layer

Attaches despiteelectrostatic repulsion

Thin, rigid layer

Effects:

10 11 12 13 14 15 16 17 18

0

1

2

3

4

5

cationic-CHI

anionic-CMC

neutral-XG

ΔD

(10-6

)

Time

14

0

0.5

1

1.5

2

2.5

3

3.5

GGGGm

LBGLBGm XG

CMCCMCm xy

l

chi

MC

mg/

m2

Sauerbrey Johannsmann SPR

Estimated results of adsorbedpolysaccharide layer mass

Significant amount of bound water attached with polysaccharides!

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Comparison of estimated layer properties

0

0.5

1

1.5

2

XG GGGGm

LBGLBGm Xyl

CMCCMCsa

lt MC

05

101520253035

XG GGGGm

LBGLBGm Xyl

CMCCMCsa

lt MC

(10-

3 )/N

m-2

(nm

) Hydrodynamicthickness

Shearviscosity

Voinova et al. Physica Scripta 1999 59(5): 391

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0 1 2 3 4 5-15

-10

-5

0

5

10

15

μM

Dried films after polysaccharide adsorption

0 1 2 3 4 5-15

-10

-5

0

5

10

15

μM

0 1 2 3 4 5-15

-10

-5

0

5

10

15

μM

ref cmc chi

Adsorbed polysaccharidesnot visible!

Topography AFM 5x5 µm², z-scale 40 nm

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DPFM-Digital pulsed force mode-AFM

Schematic PFM-curve

non-resonant, intermittant contact

modeadhesion

stiffness

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Digital pulsed force mode –comparison of films

ref

LBG

topography adhesionstiffness

Difference detected!

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Conclusions

• Attachment of polysaccharides verified also for nanoscale films– layer on top of ultrathin fibril film– backbone structure influences most– heterogeneous

• Molecular scale:– no changes in topography– differences in adhesion

• Modifications possible after bi-layer attachment

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Future prospects

Transparent&toughnanocellulose film:

Young’s modulus 2.290 Tensile stress 125.1 MPa

Modifiedpolysaccharide

New functionalities whileretaining excellent strengthproperties via fibril-fibrilinteractions!

Polysaccharide

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• Funding from Naseva-project in collaboration with Tekes (Finnish fundingagency for Technology and Innovation) and industrial partners

• M.Sc. Tuija Teerinen (VTT Biotechnology) for performing the SPR-measurements

Acknowledgements

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Thank youPRESENTED BY

Paula EronenM.Sc. (Tech)Aalto University