Spin trapping analysis of the thermal degradation of polypropylene

•ESR spin-trapping method was applied to detect radical intermediates generated during the thermal degradation of PP fabric.•Supercritical carbon dioxide (scCO2) treatment was used to impregnate spin-trapping reagent 2,4,6-tri‑tert-butylnitroso-benzene (TTBNB) into PP polymer matrix.•ESR spectra during stepwise heating from RT to 220 °C showed the signals derived from seven radical intermediates by PP thermal degradation.•The degradation of PP is found to be initiated from the tertiary carbon positions via two pathways: homolysis to generate ·CH3 and –CH2–·CH−CH2– radicals, and hydrogen abstraction to generate −CH2−·C(CH3)−CH2− radicals.