Xylan sulphate films

Xylan sulphate derivatives with degree of substitution (DS) up to 1.40 at 90% yield for film applications were prepared. The structure and substitution were confirmed by 2D NMR spectroscopy and elemental analysis. The highest DS was obtained by sulphation with sulphur trioxide pyridine complex in N,N-dimethylformamide (DMF) when the least degradative conditions were used. The samples at high DS did not form a compact film. The best mechanical properties of xylan sulphate film were achieved on the partially water soluble derivate with DS 0.07 when sulphated in dimethylsulfoxide (DMSO). It was observed that partially soluble films with low DS and high molar mass of soluble component exhibited better mechanical properties than films with higher DS and low molar mass. This could be explained by adhesion of insoluble components with solubilized xylan sulphate. This was supported also by the shapes of images of samples observed by scanning electron microscopy (SEM). The thermal and thermo-oxidative properties of xylan sulphate were not as good as for films from unmodified xylan, hydroxypropylsulfonated (HPSX) or hydroxypropyltrimethylammonium (HPAX) xylan studied previously. The best mechanical properties obtained on xylan sulphate were superior in comparison to those of HPSX or HPAX.