DTA STUDY OF THERMAL-DEGRADATION OF BAGASSE AND RICE STRAW HEMICELLULOSES

DTA curves of the title substances were recorded up to 773 K, in static air. Bagasse hemicellulose (B) exhibited three overlapping exothermic effects, at 545, 618 and 700 K, while rice straw hemicellulose (R) displayed two exothermic effects, at 548 and 635 K. The absence of the third effect for R is ascribed to the catalytic effect of silica ash in promoting volatilization of the degradation products without allowing a "char residue" intermediate. The activation energy associated with each stage was derived by applying the Borchardt-Daniels general method, the Prout-Tompkins law, and integrated peak areas plotted as log g(a) vs. 1/T. A second-order linearization of the data proved best, with apparent activation energies of 143, 249 and 289 kJ mol-1 for B, and 131 and 189 kJ mol-1 for R. The total peak areas for R, when normalized to ash-free mass, were equal to those evaluated for B, indicating that approximately identical energies are evolved in the temperature range studied.