Investigating the interactions between lignocellulosic biomass and synthetic polymers during co-pyrolysis by simultaneous thermal and spectroscopic methods

The aim of this study was to investigate the effects of synthetic polymers during co-pyrolysis. To this end, a non-edible lignocellulosic biomass, walnut shells, and three synthetic polymers that were obtained from a recycling plant (PET, PS and PVC) were co-pyrolyzed in pairs using a thermogravimetric analysis (TGA) device coupled online with a mass spectrometer (MS) and an FT-IR spectrometer. The simultaneous usage of the combined techniques allowed collection of information about the pyrolysis and co-pyrolysis processes, as well as identification of the gases that evolved. During dynamic experiments, different heating rates were used and the characteristic temperatures, kinetic parameters, and evolved gases of co-pyrolysis of each pair of the materials were compared to those obtained from the pyrolysis of the individual materials. In order to calculate the activation energy and elucidate the reaction chemistry, four models which use iso-conversional approaches, namely Friedman, Kissinger–Akahira–Sunose, Starink, and Flynn–Wall–Ozawa, were applied to the TGA data and the same trends of results were observed in all models. The activation energy values of the pyrolysis and co-pyrolysis showed fluctuations related to the conversion points which indicated the complex nature of the samples, or interactions occurred during the process. Moreover, PET, PS, and PVC blending resulted in synergy with the biomass depending on the nature of the polymer, and volatile products including methyl, water, methoxy, carbon dioxide, water, benzene, acetaldehyde, styrene, and hydrochloric acid were monitored to obtain their evolution profiles related to decomposition range.