Fundamental Theme 1 - Composition and structure of bio-assemblies

Theme leader: John R. Mitchell (University of Nottingham, United Kingdom)

Abstract:

For the first eighteen months the research will focus on comparing the amorphous and crystalline phases in starch and cellulose particularly with respect to interactions with (i) water (ii) a hydrogen bond breaking solvent. Model starch and cellulose systems will be selected. The understanding developed will underpin technologically important processes such as dissolution/fibre spinning and chemical modification.
Techniques to be employed will include nmr using 13C enriched bacterial cellulose, calorimetry, thermal mechanical analysis, dynamic vapour sorption and x-ray diffraction.

Objectives:

It was decided to focus on the structure of the amorphous phase in starch and cellulose. The reasons for this were the following:
a) This provided an opportunity to integrate the starch and cellulose communities in EPNOE.

b) Approaches used to study synthetic polymers can be applied to polysaccharides. This will allow polysaccharides to be positioned more precisely within the polymer world in terms of amorphous phase mobility. This is important fundamental information which will assist in the long term replacement of synthetic polymers by polysaccharides.

c) The EPNOE brainstorming sessions revealed that, in cellulose in particular, the amorphous phase was poorly understood but of great importance in terms of solubility and chemical modification

State of the art:

Starch and cellulose are semi-crystalline polymer systems with both crystalline and amorphous phases. The application of approaches developed for synthetic polymers has been successfully applied to understanding aspects of amorphous phase behaviour in starch. Somewhat less is known about the cellulose amorphous phase though recent molecular modelling (Chen et al, 2004) has extended the knowledge gained from earlier studies including those carried by partner 4 (Paakkaria et al, 1989). Studies on the water content dependence of the glass transition temperature of cellulose have been limited e.g. Picker and Hoag (2002) whereas this parameter has underpinned investigations on the properties of starch at low water contents e.g. (Farhat et al, 2002). Of particular interest is whether it will be possible to deconvolute the amorphous phase into a mobile and rigid component. This has been achieved successfully with synthetic polymers using calorimetry (Xu and Cebe, 2005) and solid state nmr (Montes de Oca et al, 2004). It has been shown for biopolymers that information both on the distribution and mobility of the amorphous phase can be related to mechanical properties (Ganster et al 1994, Yakimets et al, 2005).

References:

1) Chen W., Lickfield G.C., Yang C.Q. Molecular modeling of cellulose in amorphous state part II: effects of rigid and flexible crosslinks on cellulose. Polymer (2004); 45(21):7357-7365.
2) Farhat I.A., Blanshard J.M.V. and Mitchell J.R. The retrogradation of waxy maize starch extrudates: Effects of storage temperature and water content. Biopolymers (2000) 53 (5) 411-422.
3) Ganster J., Fink H.P., Fraatz J., Nywlt M. Relation between structure and elastic-constants of man-made cellulosic fibers .1. A 2-phase anisotropic model with contiguity parameter, Acta Polymerica (1994) 45 (4): 312-318.
4) Montes de Oca H., Ward I.M., Klein P.G., Ries M.E., Rose J. and Farrar D. Solid state nuclear magnetic resonance study of highly oriented poly(glycolic acid). Polymer (2004); 45(21):7261-7272.
5) Paakkari T., Serimaa R. and Fink H.P. Structure of amorphous cellulose. Acta Polymerica (1989); 40(12):731-4.
6) Picker K.M. and Hoag S.W. Characterization of the thermal properties of microcrystalline cellulose by modulated temperature differential scanning calorimetry. Journal of Pharmaceutical Sciences (2002) 91 (2): 342-349.
7) Xu H. and Cebe P. Transitions from solid to liquid in isotactic polystyrene studied by thermal analysis and X-ray scattering. Polymer (2005); 46(20):8734-8744.
8) Yakimets I., Wellner N., Smith A.C., Wilson R.H., Farhat I. and Mitchell J. Mechanical properties with respect to water content of gelatin films in glassy state Polymer (2005) 46 (26): 12577-12585.

Programme of the work :

This will be an eighteen month project in the first instance. The programme can be split into three closely related aspects.
a) Structure and mobility of amorphous phase using X-ray diffraction and solid state nmr, calorimetry, sorption isotherm measurement and phase transition analysis in pure amorphous systems

b) Crystallinity and amorphous phase structure and mobility in semicrystalline/semiordered systems. The sample set will be extended to include fibres and films from starch and cellulose and also xanthan gum. The production of fibres and films will allow distribution of structural elements crystals, rigid and mobile amorphous regions to be probed by atomic force and mechanical properties including glass transitions to be followed using dynamic mechanical thermal analysis. The addition of one other plasticizer/solvent as well as water will be studied for starch and cellulose.

c) Technologically relevant properties
Mechanical properties of films and fibres and sorption behaviour will be related to the amorphous phase structure and mobility. Thus the fundamental understanding developed will be applied to industrially important properties.