Co-pyrolysis kinetics and thermal behaviour of polyethylene and medium density fiber board mixture using thermogravimetric analysis

Pyrolysis, one of the thermochemical conversion processes, which is among the technologies used to produce energy, is an impressive method in many respects. Copyrolysis, on the other hand, is a pyrolysis process carried out by combining two or more substances. Evaluation of biomass wastes together with plastics that have the potential to harm the environment using this process offers a significant advantage. In this study, high-density polyethylene (HDPE) as plastic and medium-density fiberboard (MDF) as biomass, two important products obtained from industrial processes and containing large amounts of waste, were used. By using these wastes, thermal characterization, synergistic effect and activation energies were investigated by thermogravimetric analysis method. The studies were performed in the presence of nitrogen gas, at three different heating rates (10, 20 and 40 °C/min) and at five different HDPE-MDF mixture ratios (20%-80%; 40%-60%; 50%-50%; 60%-40% and 80%-20%). As a result of thermal characterization, it was determined that the MDF sample decomposed in the temperature range of 235-420 °C, and the HDPE sample decomposed in the temperature range of 453-535 °C. In addition, it was observed that the pyrolysis of the MDF sample consisted of three pyrolysis stages, one of which was active, and the pyrolysis of the HDPE sample consisted of two pyrolysis stages, one of which was active. The copyrolysis of HDPE-MDF mixtures in different ratios consists of four pyrolysis stages, two of which were active. As a result of the copyrolysis of HDPE and MDF samples, the presence of synergistic effect was detected. The highest synergy was determined as 10%, at heating rates of 20 °C/min and 40 °C/min, in the temperature range of 484-502 °C, in 80%HDPE 20%MDF mixture. The amount of mass remaining at the end of the pyrolysis decreased with the increase in the HDPE ratio in the mixtures and showed a 95% decrease at the heating rate of 40 °C/min, at the mixing ratio with the highest synergistic effect. Activation energy values were calculated by using KAS, Starink and FWO methods from model-free integral methods. The average activation energies of the mixtures at different ratios were determined between 133.2-241.2 kJ/mol for the KAS method, 133.5-241.5 kJ/mol for the Starink method, and 136.4- 241.3 kJ/mol for the FWO method. The average activation energy values calculated by KAS, Starink and FWO methods were calculated respectively for MDF and HDPE, 137.3 and 243.9; 137.6 and 244.2; 140.2 and 243.9 kJ/mol. Keywords: Copyrolysis kinetics, Medium density fiberboard, High density polyethylene, Synergistic effect