Comparative study of polysaccharide crystallinity by X-ray diffraction and solid state NMR

Team Leader: Johannes Ganster (Fraunhofer Institute for Applied Polymer Research, Germany)

Abstract:
Cellulose and starch are the most abundant naturally occurring polysaccharides. Both are partially crystalline in nature, i.e. they consist of crystalline regions and a less ordered, so called amorphous phase. In particular for cellulose, due to the tight hydrogen bond systems within the crystallites, only the amorphous phase is accessible for solvents, dyes and reactants and thus plays an important role for conversion processes and end uses. Therefore, the determination of the amount of amorphous phase present in a sample or, as it is more common, the degree of crystallinity is the first parameter to be assessed in the phase structure analysis. The two most important methods for determining crystallinity in polysaccharides, i.e. wide angle X-ray scattering (WAXS) und solid state NMR are performed within EPNOE at several institutions, thus the project aims at comparing both the two methods and the values determined by the various institutions for setting up a common EPNOE standard. Due to the limited number of possible participants and the intricacy and variability of the methods, a round robin test in the true sense including statistical evaluation of the results (Z-Scores etc.) is not feasible. However, an EPNOE standard is to be established as a conversion matrix, allowing to calculate crystallinity values as obtained by one method/lab from the values of another method/lab and thus setting up a common language between EPNOE partners.

Objectives:
Contribution of the project: Bio assemblies Knowledge of natural polysaccharide supermolecular assemblies. Cellulose and starch are the most abundant naturally occurring polysaccharides. Both are partially crystalline in nature, i.e. they consist of crystalline regions and a less ordered, so called amorphous phase. While the crystallites have a well defined three dimensional crystallographic symmetry (mostly triclinic, monoclinic and hexagonal crystal classes) and are well described by X-ray, electron and neutron scattering crystal structure analysis, the structure of the amorphous regions is much less understood. This understanding is intended to advance in the Fundamental Theme 1 research project. Complementary to that, the present project aims at establishing a well defined crystallinity parameter.

Importance for EPNOE community and industrial partners:
The two most important methods for determining crystallinity in polysaccharides, i.e. wide angle X-ray scattering (WAXS) und solid state NMR are performed within EPNOE at several institutions, thus the project aims at comparing both, the two methods and the values determined by the various institutions for setting up a common EPNOE standard. Due to the limited number of possible participants and the intricacy and variability of the methods, a round robin test in the true sense including statistical evaluation of the results (Z-Scores etc.) is not feasible. However, an EPNOE standard is to be established as a conversion matrix, allowing calculating crystallinity values as obtained by one method/lab from the values of another method/lab and thus setting up a common language between EPNOE partners.

Since each EPNOE participating partner will have access to this information it will be used to equalize the results, define a common standard and supply scientific and industrial partners with additional substantiated information.

Industrial partners can profit from this common language within EPNOE by the definition of a well defined crystallinity parameter which can be related to chemical and physical processes (derivatisation, solubility, dyeability, sorption) in their respective production processes.

Importance for the characterisation of the polysaccharide raw materials:
The following important raw materials will be characterised: bacterial cellulose, cotton, birch craft pulp bleeched 35% crystallinity and spruce dissolving pulp. Moreover, to have a cellulose II crystal allomorph in the series, modal fibres will be included.

Importance for the characterisation of polysaccharides processability:
As a basic structural parameter on the supermolecular level, crystallinity is important for chemical and physical processes and properties like heterogeneous derivatisation, solubility, dyeability, and sorption. The higher reactivity of the amorphous phase plays a key role in the majority of industrially used heterogeneous derivatisation reactions. Cellulose derivatisation opens up the vast application fields of cellulose ethers and esters, such as pastes (wallpaper), thickeners (drilling fluids), tablet additives, printable films, tool handles and many more.

Many other value adding finishing processes following in the production chain as well as the processes to be developed for future high tech applications of cellulose materials take place at the solid-liquid interface (polar liquids) and in the amorphous, less organized region between the crystallites. The description of the interface region, the amorphous regions structure an the correlation with the accessibility for interaction processes (electrostatic and non electrostatic interaction - hydrophobic interaction) in polar liquids is important in order to improve the understanding of these technological extremely important processes taking place at interfaces.

Applicability to the different kind of polysaccharides:
At present, only cellulose will be considered in the project. This material was chosen to start with, since in the starch case complications arise due to the biphasic structure of starch (amylose/amylopectin) and the sensitivity of crystallinity to moisture. Considering these points carefully and using the experience gained in the present project, a second round robin test can be anticipated for selected starch samples. Other partially crystalline polysaccharides of interest can be studied as well.

Potentiality to transform them into marketable products:
The product to be offered concerned with these kinds of measurements is a crystallinity parameter and the necessary reference material.
The group intends to market the product in four ways:
1. Publish the common effort journal has to be selected
2. Offer the results to standardization organisation
3. Provide pre-treated reference samples to scientific and industrial clients
4. Offer determination of cristallinity as a service