High-Temperature Viscoelastic Relaxation in All-Cellulose Composites

All-cellulose composites were prepared across a range of different crystallinities in order to examine relationships between phase composition and viscoelastic behaviour in the temperature range of 270 degrees C to 340 degrees C corresponding to the alpha(1) mechanical relaxation. Composite films were prepared by partial dissolution of microcrystalline cellulose in a LiCl/N,N-dimethylacetamide (LiCl/DMAc) solvent system using the film casting technique. Dynamic mechanical analysis showed two contributions to alpha(1) relaxation, with tan delta maxima at 303 +/- 2 degrees C and at approximately 325 degrees C. The height of the maximum or shoulder at 303 +/- 2 degrees C decreased with increasing crystallinity, and was therefore assigned to molecular motion associated with chemical decomposition in non-crystalline domains. The maximum at 325 degrees C was assigned to chemical decomposition in chains associated with the surfaces of crystalline domains. Composites with high crystallinity showed best retention of the dynamic storage modulus when tested at 300 degrees C.