Crystallization and shear modulus of a forming biopolymer film determined by in situ x-ray diffraction and ultrasound reflection methods

The structure and the rigidity of a forming biopolymer film were determined using concurrent x-ray diffraction and ultrasonic reflection measurements. Film formation of a xylan solution (de-ionized water, 10 g ∕ l xylan, 4 g ∕ l glycerol) was studied during water evaporation at 24 ( ± 2 ) ° C , 37 ( ± 5 ) % RH . X-ray diffraction (XRD) data showed the crystallization and ultrasonic data the increase of the shear modulus ( G ) during water evaporation. Xylan crystallized into small xylan dihydrate crystallites, the number of which increased as water evaporated. Crystallization began earlier than the increase in G during film formation. The increase in G also continued after the crystallites were fully formed, indicating still ongoing structural changes in the amorphous parts. The maximum value of G was 0.1 - 0.5 GPa . XRD measurements performed ex situ showed a crystallinity of 16%-19% ( ± 5 % ) and a fairly isotropic crystallite orientation in the surface plane of the films.