Effect of atmosphere on the thermal decomposition of chlorinated natural rubber from latex

The kinetics of the thermal decompositions of chlorinated natural rubber (CNR) from latex under both air and nitrogen atmospheres were studied with thermogravimetric analysis (TGA). The thermooxidative decomposition of CNR had two weight-loss step changes in the TGA curves, which occurred at the two distinct temperature ranges of about 160-390 and 390-850 degreesC, respectively. The gaseous products of the first step change were mainly HCl with a little CO2, and the apparent reaction order (n) was 1.1. The reaction activation energy (E) increased linearly with the increment of heating rate (B), and the apparent activation energy (E-0), calculated by extrapolation back to zero B, was 101.7 kJ/mol. Bs ranging from 5 to 30 degreesC/min were used. The initial temperature of weight loss (T-0) was 1.31B + 252 degreesC, where B is in degrees Celsius per minute. The final temperature of weight loss (T-f) was 0.93B + 310 degreesC, and the temperature of maximum weight-loss rate (T-P) was 1.03B + 287 degreesC. The decomposition weight-loss percentage at T-P (C-P) and that at T-f. (C-f) were not affected by B, and the average values were 38 and 60%, respectively. The second weight-loss stop change was an oxidative decomposition of the molecular main chain. The value of n was 1.1. E increased linearly with the increment of B, and E-0 was 125.0 kJ/mol. C-f after the second step approached 100%, which indicated complete decomposition. The thermal decomposition of CNR in a N-2 atmosphere had only one weight-loss step change with an n of 1.1. E increased linearly with the increment of B, and E-0 was 98.6 kJ/mol. T-0 was 1.25B + 251 degreesC, T-f was 0.91B + 315 degreesC, and T-P was 1.09B + 286 degreesC. C-p and C-f were not affected by B, and the average values were 37 and 68%, respectively. The weight percentage of more stable, nonthermal decomposed residue was about 30%. The thermal decompositions of CNR in both atmospheres were similar, mainly by dehydrochlorination, at the low temperature range (160-390 degreesC) but were different at the high temperature range (390 - 850 degreesC). (C) 2001 John Wiley & Sons, Inc.