Kinetics study of the thermal decomposition of date seed powder/HDPE plastic blends

Abstract

The extensive examination of the impact of agricultural waste on the thermal stability of polymers has garnered significant attention in petrochemical industries worldwide. This study provides a pioneering analysis of the kinetics and thermodynamics of biodegradable date seed (PD), high-density polyethylene (HDPE), and their composites (PD/HDPE). The composites were fabricated by mechanically blending the two materials in varying ratios. The estimation is based on the thermogram characteristics of these materials, which are obtained at various degradation temperatures (ranging from 25 to 600 °C), heating rates (10, 20, and 40 °C.min⁻¹), and compositions. The Coats-Redfern (CR) model fitting, in conjunction with a first-order solid-state reaction mechanism, as well as the model-free Flynn-Wall-Ozawa (FWO) and Kissinger-Akahira-Sunose (KAS) isoconversional methods, were utilized to investigate the thermal stability of the materials across a conversion range of 0.5 to 60 wt%. This methodological approach facilitated the estimation of the kinetic parameters of the materials, specifically the activation energy ($E_A$) and the pre-exponential factor ($A$). The estimated values for these kinetic parameters, derived from the three methods, were observed to be higher for high-density polyethylene (HDPE) in comparison to PD materials. Furthermore, the continuous incorporation of PD into the blends consistently reduced the thermal stability of HDPE, suggesting a synergistic interaction between the compositions of the plastic and biomass materials. The activation energy estimated using the CR method ranged from 22.903 to 101.51 kJ·mol⁻¹, while the FWO method yielded values between 71.282 and 138.990 kJ·mol⁻¹, and the KAS method produced values between 63.212 and 137.101 kJ·mol⁻¹. The estimated values of these parameters, as provided by established models, may prove valuable for manufacturers seeking to enhance the practical applicability of these composites. This, in turn, could facilitate the widespread utilization of the abundant and discarded date seeds to produce polymer composites, while also contributing to a reduction in energy consumption during the degradation of these materials in the pyrolysis process.