The strength of heterogeneous fibres such as wood is largely determined by the strength of association between hemicellulose and cellulose. Understanding the association at the molecular level permits a rational evolution of pulping processes, and opens new avenues to the development of designer-made fibres based on agricultural products.
In this multidisciplinary project the association between hemicellulose and cellulose fibres will be studied at several levels of molecular detail, both experimentally and theoretically. Hemicellulose such as glucomannan and xyloglucan bind tightly to cellulose in a very specific patterns. The co-crystallisation reduces the number of accessible conformations, which will lower the conformational entropy. The driving force behind efficient binding are hydrogen bonds. These interactions are highly specific, setting high demands on structural complementary. For flexible polymers such as carbohydrates structural changes upon association of the polymer to the substrate can be expected. For small carbohydrate complexes these structural changes are observed. For these small systems desolvation entropy contributes significantly to the affinity, which is probably even larger for polymeric systems. All these issues (specificity, structural changes, entropic effects, desolvation) will be addressed in varying molecular detail to obtain a comprehensive understanding of hemicellulose-cellulose association.
The methodological approach is based on state-of-the-art physico-chemical methods. Energetic aspects of the association between hemicellulose and cellulose will be studied by binding assays of radioactive labelled oligomers. Isotherms valid for all densities validated by these experiments will be derived from models with molecular detail, which will relate the structural information obtained in X-ray diffraction experiments to the binding experiments. IR spectroscopy of the bound oligomers will reveal functional groups that are mainly responsible for the association, and their dynamics. 13C solid state NMR of the complex will provided structural and dynamical details, such as short-range order, structural effects due to the association, and hindered motions of surface groups. All structural observations from X-ray diffraction, IR spectroscopy and 13C solid state NMR will be used to formulate a single atomistic model of the hemicellulose-cellulose complex with the
aid of theoretical approaches such as Molecular Dynamics and Monte Carlo. The structure of the hemicelluloses in solution, essential to this objective, will be determined by solution state NMR. The atomistic model derived this way can of be related to the binding data in the low density limit, and be used to refine the molecular binding model valid for all densities.
Using this integral approach, significant progress towards a comprehensive understanding of hemicellulose-cellulose association will be made. The results of this explorative research project will then be used in further R&D programmes which aim at optimizing existing procedures, or develop function, carbohydrate-base polymers. To ensure an effective dissemination, a symposium will be organized upon completion of the project. Simultaneously, results will filter through to industries efficiently due to the participation of two industrial research institutes.
Funding SchemeCSC - Cost-sharing contracts
114 86 Stockholm
842 38 Bratislava
3584 CH Utrecht