Study on the pyrolysis mechanism of polyethylene, polystyrene, and polyvinyl chloride by TGA-FTIR

The pyrolysis behaviors of three kinds of typical plastics like polyethylene (PE), polystyrene (PS) and polyvinyl chloride (PVC) were investigated through thermal gravimetric analysis (TGA) and Fourier transform infrared spectroscopy (FTIR). The results showed that the thermal stability of these plastics increases following the sequence of PVC < PS < PE. PE pyrolysis is a typical one-stage reaction and involves irregular chain scission; the products of PE pyrolysis are complicated and changed gradually during the pyrolysis process: alkanes are the main products in the preliminary stage, while alkenes with trace amount of alkynes are the main products in the rest of pyrolysis process. PS pyrolysis is also a typical one-stage reaction with styrene as the main product, which suggests that the main reaction is depolymerization of PS to styrene monomer. PVC pyrolysis includes two events, i.e. dechloridation of PVC and rearrangement of conjugated polyene, in which aromatic compounds were found in the pyrolysis products; the dechloridation of PVC and the rearrangement and cyclization of conjugated polyene may take place simultaneously, which creates the potential for producing dioxin during PVC pyrolysis.