Thermal behavior, synergistic effect and thermodynamic parameter evaluations of biomass/plastics co–pyrolysis in a concentrating photothermal TGA

The heating rate would significantly impact the pyrolysis process, especially for the reactions containing synergistic effects between two different feedstocks. Co-pyrolysis of two widely available biomass (CC–corncob and PS–peanut shell) with plastic (PET–polyethylene terephthalate and PVC–polyvinyl chloride) was studied in a concentrating photothermal thermogravimetric analysis (CP-TGA) system at three heating rates (100, 500, 1000℃/min). The TG and DTG curves of CC and PS differ due to their polymeric components (holocellulose and lignin); two pronounced levels at 100 and 500 ℃/min heating rates were present in PVC. With increasing heating rate, the lateral shift towards higher temperature regions in the TG and DTG curves exceeded 100 °C. The synergistic effects on the blend samples were concentrated in the main decomposition region (250–580℃) due to rapid volatiles release, and the discrepancy values further stabilized at the final decomposition stages. The activation energy (Ea) was assessed using a comparative study of isoconversional methods, namely Kissinger–Akahira–Sunose (KAS), Flynn–Wall–Ozawa (FWO), and Starink. The isoconversional methods demonstrated that the co-pyrolysis process required about 30 % less activation energy than the pyrolysis of plastic (PET/PVC) alone. Coats-Redfern's (CR) model-fitting approach was used to identify the kinetic triplet of the devolatilization stage. The CR models revealed that biomass–PET blends belong to two to four-dimensional diffusion models, whereas biomass–PVC blends are dominated by chemical reactions of 1.5 and 2 orders. The energy barrier between activation energy (Ea) and change in enthalpy (ΔH) for all the blend samples was lower (∼5–6 kJmol−1), which slightly increased at higher heating rate.