Polysaccharide Interactions with Nanocellulose As a Platform for Biomimetic Modifications
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.
Polysaccharide interactions with nanocellulose as a platform for biomimetic modifications
Presented by: Paula Eronen, Karoliina Junka, Martin Häggblom, Janne Laine and Monika Österberg Department of Forest Products Technology, Aalto University
1 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
2 Objectives
• To verify the most suitable polysaccharides adsorbing on cellulose and compare the adsorption properties
new knowledge of polysaccharide adsorption on nanocellulose
important for further adsorption of modified polysaccharides
3 Background TEM
Plant cell-wall: natural nanocomposite structure
AFM phase
Adapted from Sticklen Nature rev. Genetics 2008, 9, 433 Adapted from Pääkkö et al. Biomacromolecules 2007, 8, 1934
4 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)
5 Experimental
• 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 hardwood nanofibrillar cellulose
6 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 fluid-flow/ (Ahola et al.Biomacromolecules 2008,9,1273) evaporation substrate
e x h ultra- au s centrifugation t
Fibril dispersion ω
7 adapted from E.Kontturi chitosan Polysaccharides cellulose
• 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 Æ Mw applied from Cheng et al. Int J Biol Macromol 2002, 31, 29
8 Quartz Crystal Microbalance with dissipation (QCM-D)
Fibril model film (AFM image, 2x2µm)
Combined mass and viscoelastic properties Picture used with permission from Q-Sense
9 Properties of adsorbed layers on NFC film
9 GG 8 MC LBG 7 pH 4.5, 10 mM - XG 6 XYL
NaAc-HAc-buffer, ) 5 T= 24°C -6 4 +
D(10 3
Δ CHI 2 1 0 Irreversible -1 attachment 0 -10 -20 -30 -40 -50 Δf (Hz) Backbone structure and available surface area affect adsorption
10 Effect of molecular weight (Mw) 7 Mw>500 000 g/mol Mw (g/mol) 6 0
1000 5 10 000 g/mol -6 1,000E5 2,500E5 3 D (10 Mw< 10 000 g/mol 5,000E5 Δ 2 1,375E6 1,650E6 1 1,925E6 2,200E6 0 -5 -10 -15 -20 -25 -30 -35 -40 -45 -50 Δf (Hz) No direct correlation (statistical analysis) In the following polysaccharides with similar Mw were 11 chosen Adsorbed amount as a function of time Effect of backbone structure and charge QCM-D Highest adsorbed 1,8 neutral-XG amount of neutral 1,6 1,4 polysaccharide- ) 1,2 similar backbone as 2 1,0 anionic--CMC cellulose 0,8 m(mg/m 0,6 Δ 0,4 cationic-CHI 0,2 Cationic: thin layer 0,0 -0,2 10 11 12 13 14 15 16 17 18 Time (min) bound water included! 12 Viscoelastic properties of the adsorbed polysaccharide layer Effects: 5 neutral-XG Thick, swollen layer 4 anionic-CMC Attaches despite 3 ) electrostatic repulsion -6 2 cationic-CHI D(10 Thin, rigid layer Δ 1 0 10 11 12 13 14 15 16 17 18 Time 13 Estimated results of adsorbed polysaccharide layer mass 3.5 3 2.5 2 1.5 mg/m2 1 0.5 0 m G m GG B XG Cm xyl chi MC GG L CMC M LBG C Sauerbrey Johannsmann SPR Significant amount of bound water attached with polysaccharides! 14 Comparison of estimated layer properties 35 30 25 20 Hydrodynamic (nm) 15 10 thickness 5 0 t G m l C X GG Xyl a M GG LBG CMC Cs LBGm CM 2 -2 1.5 1 )/Nm -3 Shear 0.5 (10 0 viscosity l t m y C XG GG X M GGm LBG CMC LBG CMCsal 15 Voinova et al. Physica Scripta 1999 59(5): 391 Dried films after polysaccharide adsorption ref cmc chi 15 15 15 10 10 10 5 5 5 0 0 0 -5 -5 -5 -10 -10 -10 -15 -15 -15 012345012345012345 μM μM μM Topography AFM 5x5 µm², z-scale 40 nm Adsorbed polysaccharides 16 not visible! DPFM-Digital pulsed force mode-AFM non-resonant, intermittant contact mode adhesion stiffness Schematic PFM- curve 17 Digital pulsed force mode –comparison of films topography stiffness adhesion ref LBG Difference detected! 18 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 19 Future prospects Modified polysaccharide Polysaccharide Transparent&tough New functionalities while nanocellulose film: retaining excellent strength Young’s modulus 2.290 properties via fibril-fibril Tensile stress 125.1 MPa interactions! 20 Acknowledgements • Funding from Naseva-project in collaboration with Tekes (Finnish funding agency for Technology and Innovation) and industrial partners • M.Sc. Tuija Teerinen (VTT Biotechnology) for performing the SPR-measurements 21 Thank you PRESENTED BY Paula Eronen M.Sc. (Tech) Aalto University Please remember to turn in your evaluation sheet... 22