Kinetic and thermodynamic insights into the thermal degradation of PE plastic waste from active landfill sites

Abstract

Plastic waste, especially polyethylene (PE), represents a major challenge in municipal solid waste (MSW) management, particularly in rapidly urbanizing regions. While the thermal degradation of virgin PE has been widely studied, there is limited understanding of the kinetic and thermodynamic behavior of PE plastics that have undergone long-term exposure in operational landfills—where material properties can be significantly altered by environmental and aging effects. This study presents, for the first time, comprehensive kinetic and thermodynamic analyses of PE plastic waste recovered from an active landfill site in Hat Yai, Southern Thailand. Multiple model-free (Friedman, Kissinger–Akahira–Sunose, Ozawa–Flynn–Wall) and model-fitting (Criado) methods were employed to determine the activation energy, pre-exponential factors, and reaction mechanisms governing the pyrolysis of landfill-aged PE. The results revealed that PE decomposition follows a contracting cylinder (R3) mechanism, a model validated by the Friedman (FR) method. The activation energy and the pre-exponential factor (A) were determined to be 281 kJ/mol and 5.016–5.353 × 10⁹ min⁻¹, respectively. Additionally, the enthalpy, Gibbs free energy, and entropy values were found to be in the ranges of 287.54–287.73 kJ/mol, 198.85–200.11 kJ/mol, and 0.12 J/mol K, respectively. These insights are essential for the design and optimization of scalable pyrolysis-based waste-to-energy technologies, particularly in the context of municipal landfill mining and sustainable resource recovery in Asia. This work not only bridges a critical knowledge gap regarding landfilled PE waste but also provides a scientific baseline for future policy development and industrial implementation of advanced MSW management strategies.