Synergistic pyrolysis mechanism of polypropylene and common plastics with biomass investigated by TG-MS and in-situ FTIR

The aim of this study is to investigate the role of different carbon-based structures on the pyrolysis pathway and gas product distribution of polypropylene (PP). Using in situ DRIFTS coupled with thermogravimetric mass spectrometry, this study investigated the synergistic mechanisms between polypropylene (PP) and common plastics and biomass at the molecular level. The following mechanisms were revealed: 1) Polyethylene erephthalate (PET) induces demethylation of PP through oxygenated fragments, which weakens the stability of its main chain and synergistically reduces the pyrolysis temperature. The high-temperature polyene structure of polyvinyl chloride (PVC) promotes further breakage of the PP main chain, synergistically driving the directional conversion of gas products to unsaturated hydrocarbons and chlorine-containing compounds. The phenyl groups in polystyrene (PS) trigger PP activation at low temperatures, improving the yield of toluene gas. 2) PP inhibits the decomposition of blended components through physical entanglement at low temperatures. At high temperatures, polyenes, phenyl groups and other cleavage products reorganize with PP hydroxyl fragments, promoting the enrichment of olefins, aromatics and chlorinated compounds. 3) In PP-biomass systems, it is hypothesized that the PP pyrolysis pathway is altered, enhancing the selectivity for short-chain hydrocarbons and monocyclic aromatics. This effect is likely mediated through ash-catalyzed reactions and induction by oxygen-containing fragments. This study employs in situ Fourier-transform infrared (FTIR) spectroscopy to monitor in real time the molecular-level evolution of PP-based mixed waste plastics and biomass pyrolysis, revealing fundamental carbon-chain structure-property relationships. These findings establish a mechanistic framework for the rational design of high-efficiency pyrolysis systems with precisely controlled product distributions through synergistic interactions.