Thermal decomposition of cellulose ethers

The thermostability and thermal decomposition kinetics of methyl cellulose (MC), ethyl cellulose (EC), carboxymethyl cellulose (CMC), hydroxyethyl cel lulose (HEC), and hydroxypropyl-methyl cellulose (HPMC) were characterized in nitrogen and air by thermogravimetry (TG). Various methods of kinetic an alysis were compared in case of thermal degradation of the five cellulose e thers. The initial decomposition temperature (T-d), temperature at the maxi mum decomposition rate (T-dm), activation energy (E), decomposition reactio n order (n), and pre-exponential factor (Z) of the five cellulose ethers we re evaluated from common TG curves and high-resolution TG curves obtained e xperimentally. The decomposition reactions in nitrogen were found to be of first order for MC, EC, and HPMC with the average E and In Z values of 135 kJ/mol and 25 min(-1), although there were slight differences depending on the analytical methods used. The thermostability of cellulose ethers in air is substantially lower than in nitrogen, and the decomposition mechanism i s more complex. The respective average E, n, In Z values for HEC in nitroge n/air were found to be 105/50 kJ/mol, 2.7/0.5, and 22/8.3 min(-1), from con stant heating rate TG method. The respective average E, n, and In Z values for three cellulose ethers (EC/MC/HPMC) in air are 123/144/147 kJ/mol, 2.0/ 1.8/2.2, 24/28/28 min(-1) by using high-resolution TG technique. (C) 1999 J ohn Wiley & Sons, Inc.