Effect of Atmosphoere on the Thermal Decomposition of Chlorinated Natural Rubber from Latex

摘要

The kinetics of the thermal decompositions of chlorinated natural rubber (CNR) from latex under both air and nitrogen atmospheres 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 deg C, respectively. The gaseous products of the first sstep change were mainly HCl with a little CO_2, 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_O), calculated by extrapolation back to zero B, was 101.7 kJ/mol. Bs ranging from 5 to 30 deg C/min were used. The initial temperature of weight loss (T_O) was 1.31B + 252 deg C, where B is in degrees Celsius per minute. The final temperature of weight loss (T_f) was 0.93B + 310 deg C, and the temperature of maximum weight-loss rate (T_p) was 1.03B + 287 deg C. 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 step 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_O 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_O was 98.6 kJ/mol. T_O was 1.25B + 251 deg C, T_f was 0.91B + 315 deg C, and T_p was 1.09B + 286 deg C. 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 inboth atmospheres were similar, mainly by dehydrochlorination, at the low temperature range (160-390 deg C) but were different at the high temperature range (390-850 deg C).