TG/FTIR study of the thermal pyrolysis of EVA copolymers

摘要

In this work, the evolution of the gas evolved during the thermal pyrolysis of three commercial ethylene-vinyl acetate copolymers (EVA) has been studied. The decomposition of the copolymers has been carried out in a thermobalance connected to a Fourier transform infrared spectrometry (FTIR) spectrometer through a heated line. The experiments have been performed under N_2 atmosphere at several heating rates, and the results obtained showed that, from the quality of the FTIR data obtained, the higher heating rates produced the best results. The evolution of the spectrograms obtained along the pyrolysis process reveals two events of generation of volatile products, related to the stages of EVA decomposition already described in the bibliography. On the other hand, the TG and Gram-Schmidt curves show the existence of two different stages for the second step of the pyrolysis of EVA, which can be associated to the decomposition of the different domains which appear in the polymeric chain after the first decomposition step. The interpretation of the FTIR spectrograms corresponding to the temperatures of maximum decomposition rate for each decomposition step shows the formation of acetic acid, CO and CO_2 in the first decomposition step (elimination of the acetoxi groups), and the formation of a complex hydrocarbon mixture in the second decomposition step (cracking of the polymeric chain) including alkanes, alkenes and mononuclear aromatic compounds. The evolution of the ratio of the absorbance of bands at 3015 cm~(-1) (olefinic C-H stretching) and 2925 cm~(-1) (asymmetric stretching of -CH_2-), representative of the evolution of the ratio 1-alkenes/alkanes, shows a minimum, for the second decomposition step, close to the temperature of maximum decomposition rate, which reflects the differences in the evolution of the alkanes and alkenes in the two stages of the second decomposition step.