Correlating structure of (arabino)xylans and their derivatives to dispersibility and film properties

Licentiate thesis, 2023

Wood glucuronoxylans and wheat bran arabinoxylan represent significant sources of underutilized natural polymers. In this work, I aim to address a key challenge to their effective valorization, which is their complex chemical-structure-property relationship. I investigated how the composition of hardwood xylans affects their dispersibility in two common solvents: water and DMSO, and how this relates to the nanoscale conformations of individual xylan chains using small-angle neutron scattering. We also investigated whether introducing flexible hinges to the stiff polysaccharide chains through periodate oxidation and borohydride reduction would alter their dispersibility and conformations in these solvents. The results showed that the dispersibility of the xylans is linked to their solvent interactions, and consequently, their conformation in water or DMSO. The oxidation and reduction modification did indeed change the solvent interactions of the xylans but only led to slight improvements in dispersibility in water and, in some cases, worsened dispersibility in DMSO.

For arabinoxylan (AX), we showed that the chemical composition of AX is a large factor in controlling the mechanical properties of modified thermoplastic films. We obtained compression moldable films from AX with low and high branching ratios. The low-branched modified AX films showed more brittle and stiff behavior, whereas the higher-branched modified AX films were softer, and could be stretched up to 140 % strain. We linked the properties to their relaxation mechanisms in dynamic mechanical testing (DMA) and the nano-structures observed via X-ray scattering. The observed nano-structures involved phase separation into nano-domains, we further showed that the sizes and mobility of nano-domains were dependent on the AX structure and composition. Therefore, by selecting specific chemical compositions of AX, materials with tuneable stiffness and ductility can be designed.