Pyrolysis behavior of polypropylene and PVC medical waste: multi-scale analysis via TGA, FTIR, GC–MS and kinetic modeling

This study investigates the pyrolysis behavior of two common medical waste polymers—polypropylene (PP) and polyvinyl chloride (PVC)—through an integrated approach that combines thermogravimetric analysis (TGA) with in-situ Fourier transform infrared spectroscopy (FTIR), gas chromatography–mass spectrometry (GC–MS), and model-free kinetic analysis. The TGA/DTG results indicate that PP-based waste (e.g., surgical gown material) undergoes a single-step degradation at approximately 450 °C, producing negligible residual char. In contrast, PVC-based waste (e.g., gloves and tubing) demonstrates a two-stage mass loss: initial devolatilization occurring between 250 °C and 350 °C due to dehydrochlorination and plasticizer loss, followed by char breakdown at temperatures up to 600 °C. FTIR gas analysis reveals that the volatiles generated from PP pyrolysis are predominantly aliphatic hydrocarbons, characterized by strong C–H bands, while the pyrolysis of PVC releases significant amounts of HCl during the first stage and aromatic compounds in the second stage. Correspondingly, GC–MS analysis confirms that PP primarily yields hydrocarbons within the C₅–C₂₀ range, whereas PVC generates a variety of chlorinated and aromatic byproducts. The iso-conversional kinetic analysis indicates a relatively constant activation energy of approximately 200 kJ/mol for PP decomposition, contrasting with a two-phase profile for PVC, which exhibits lower apparent activation energies (ranging from 100 to 180 kJ/mol) during the initial HCl evolution and much higher values (exceeding 400 kJ/mol) during char decomposition. These findings offering valuable insights for optimizing reactor design and emission control strategies in the pyrolysis of medical waste.