Interactions between biomass-derived components and polypropylene during wood-plastic composite pyrolysis

Wood-plastic composite (WPC) is a commonly used material in decking applications with good mechanical and physical properties. Due to their non-biodegradable property, WPC wastes can be converted by pyrolysis. In this study, the interactions of poplar wood components (cellulose, hemicellulose, and lignin) and polypropylene (PP) during WPC pyrolysis (with or without HZSM-5 catalyst) were investigated using thermogravimetric (TGA) and Py-GC/MS analyses. TGA results showed that the decompositions of cellulose and hemicellulose were inhibited while lignin decomposition was slightly improved by PP. PP decomposition peak shifted to higher temperatures due to the thermal stabilization of biomass-derived char. The formation of carbonyl compounds and furans were inhibited, whereas the formation of anhydrosugars, cyclopentenones, and phenols were promoted in the presence of PP, indicating that PP changed the pyrolysis pathways of cellulose, hemicellulose, and lignin through H-transfer reactions. Biomass-derived components promoted the beta-scission of PP chain and facilitated the formation of light hydrocarbons with carbon number of 3n. An increase in hydrocarbons (aromatics + olefins) demonstrated the existence of strong catalytic interactions between biomass-derived components and PP in the presence of HZSM-5 zeolite. Graphical abstract Novelty: This work studied the interactions between biomass components and PP with or without HZSM-5, which is beneficial to the conversion of WPC wastes into fuels.