Comparative catalyst screening of polyethylene, polypropylene, and polystyrene degradation over Cu-SSZ-13 using thermogravimetric analysis

Plastics produce enormous amounts of waste, causing environmental pollution. It is essential to understand their thermal degradation behaviour for effective recycling. In this paper, the catalytic degradation of polyethylene (PE), polypropylene (PP), and polystyrene (PS) was investigated using non-isothermal thermogravimetric analysis over Cu-SSZ-13 zeolite (0–20 wt%). The Cu-SSZ-13 catalyst was synthesised via a hydrothermal route and characterised using XRD, SEM-EDS, FTIR, BET, and NH₃-TPD, revealing a high surface area (490 m2 g−1), bimodal porosity, and accessible Brønsted and Lewis acid sites. The Šesták-Berggren model-fitting kinetics was employed to rank polymer-catalyst interactions under identical conditions (10 °C min−1). A clear hierarchy of catalytic responsiveness was established: PP > PE > PS. For PP, apparent activation energy decreased from 143.3 to 73.4 kJ mol−1 with increasing catalyst loading (minimum at 15 wt%, 70.6 kJ mol−1), accompanied by a 24 °C reduction in peak degradation temperature. PE exhibited non-monotonic behaviour, with the apparent activation energy increasing from 164.3 to 233.1 kJ mol−1 at 10 wt% loading, then decreasing to 190.1 kJ mol−1 at 20 wt%, suggesting competing diffusion and surface catalysis effects. PS showed minimal catalytic sensitivity (Apparent activation energy = 90.0–93.5 kJ mol−1), consistent with radical-dominated depolymerisation. Strong kinetic compensation effects were observed for PP (R2 = 0.997) and PE (R2 = 0.991), while PS showed none. The Šesták-Berggren exponents (m, n, p) provided mechanistic discrimination beyond apparent activation energy alone. These results demonstrate that single-rate TGA screening with model-fitting kinetics effectively ranks polymer-catalyst interactions for plastic waste valorisation.