Thermal degradation kinetics and reaction mechanisms of HDPE and PS plastic wastes using a micro combustion calorimeter

The kinetics of the pyrolysis process is a key parameter for the design, optimization, and operation of industrial applications of polymer pyrolysis systems. Determining the kinetic triplet of activation energy, kinetic reaction mechanism, and pre-exponential (frequency) factor is the key of understanding of pyrolysis process. The objective of this study is to determine the kinetic triplet and the heat release rate of polystyrene (PS), high-density polyethylene (HDPE), and their blend using a micro combustion calorimeter (MCC). Estimation of the activation energy for each polymer was investigated using four iso-conversional methods: the Friedman, Kissinger–Akahira–Sunose, and Flynn–Wall–Ozawa methods and an advanced iso-conversional method. Comparative and detailed analyses of the reliability of these methods were conducted at heating rates from 0.25 to 1.5 K/s. The reaction mechanism f(α) was determined using a master plot and compared with commonly used reaction functions. The heat release rate increased with increasing heating rate for the pure polymers and their blend. The peak heat release rates of HDPE, PS, and the blend at a heating rate of 1.5 K/s were 1880, 466, and 860 W/g, respectively. The activation energies of HDPE, PS, and the blend were 225.4, 186.86, and 249.93 kJ/mol, respectively. The obtained results provide essential data for calculating the heat release and kinetic triplet and selecting a suitable model for HDPE, PS, and the HDPE/PS blend in potential pyrolysis reactors.