Combustion, kinetics and thermodynamic characteristics of rice husks and rice husk-biocomposites using thermogravimetric analysis

Pyrolysis of rice husk (RH), alkali-treated cellulose-rich rice husk (RHC), chemically modified RHC (RHCM) and RH-biocomposites by thermogravimetric analysis was carried out to determine combustion and kinetic parameters at three different heating rates of 20, 40 and 50 degrees C min-1. Combustion performance was analyzed from results of ignition temperature, burnout temperature, combustion rates, flammability index and combustion characteristic index. Increase in heating rate from 20 to 40 and further to 50 degrees C min-1 increased the onset of degradation, burnout and peak temperatures as observed by curve shifts to the right. Maximum combustion rates were around 0.57-0.59% min-1, 1.03% min-1 and 0.63-0.69% min-1 for RH, RHC and RHCM, respectively. For the RH-biocomposites, the maximum combustion rates were in a 0.76-0.97% min-1 range. Their average pre-exponential factors using KAS method were in the 2.24E-03-8.07E-03 range, respectively, while those for OFW method were in the 7.75E + 04-4.55E + 06 range, respectively. Average activation energies of RH-biocomposites were in the 41.0-58.2 kJ mol-1 and 48.3-67.7 kJ mol-1 ranges for KAS and OFW methods, respectively. The data were well fitting with coefficient of determination (R2) values close to 1. Average Delta G value ranges for RH-biocomposites ranged between 148.2 and 161.7 kJ mol-1. The low-energy barrier (<= 5.4 kJ mol-1) between activation energy and enthalpy changes indicated that reaction initiation occurs easily.