Qualitative study of the evolution of the composition of the gas evolved in the thermal and HY-catalytic oxidative degradation of EVA copolymers

In this work, a study of the evolution with the temperature of the qualitative composition of the gas evolved in the degradation of ethylene-vinyl acetate (EVA) copolymers under air atmosphere has been carried out using on-line analysis by thermogravimetry (TGA) combined with FTIR spectrometry (TGA/FTIR). Three commercial EVA copolymers were selected, and the results obtained in the experiments performed in the presence and in the absence of HY zeolite are compared. The air atmosphere causes significant differences among the thermal and catalytic pyrolysis. The oxidative pyrolysis involves four main decomposition steps, and each of them also involves different types of reactions. In the first stage, the loss of acetoxi groups of the VA units occurs, with formation of acetic acid, but also CO, CO2 and carbonylic compounds are produced, increasing the formation of these compounds as the VA content of the copolymer decreases. The second and third decomposition steps, which are better distinguished as the VA content of the copolymer increases, correspond to the degradation of the polymeric chain which results from the previous step, and involves cracking reactions, without O2 consumption, as well as oxidation reactions. Finally, the fourth reaction step corresponds to the slower oxidation of the carbonous residues formed in the previous stages. The presence of the HY zeolite contributes to a decrease of the CO and CO2 formation, or in other words, to an increase of the reactions without oxygen consumption.