Thermo-oxidative Degradation of Natural Rubber Coagulated by Microorganisms

The structure of natural rubber coagulated by microorganisms (NR-m) was characterized by Fourier transform infrared spectroscopy (FTIR). Thermogravimetry analysis (TG) and differential thermal analysis (DTA) were utilized to study thermo-oxidative degradation behaviors of NR-m in 30 degrees C similar to 600 degrees C. The effect of microbial-coagulating process on thermo-oxidative stability of NR-m was discussed. The results show that the absorptions of the proteins in NR-m at 1575 cm(-1),compared to natural rubber coagulated by acid (NR-a), become significantly weaker, nearly disappear, which indicates that during the process of microbial coagulation, microorganisms digest most of the proteins by metabolism. Thermo-oxidative degradation of NR-m in air is a two-step reaction which was taken place mainly in the temperature range of 300 degrees C similar to 550 degrees C. Thermo-oxidative degradation of NR-m is exothermic. In the first step reaction, the initial degradation temperature T-o=314.3 degrees C, the temperature at the maximum degradation rate T-p=365.7 degrees C and the final degradation temperature T-f=407.2 degrees C, whereas in the second step reaction, T-o=407.2 degrees C, T-p=507.7 degrees C and T-f=593.2 degrees C. The activation energy (Ea) of thermo-oxidative degradation is calculated and the peak temperatures obtained from DTA curve of NR-m are analyzed.