Xenon lamp weathering induced structural evolution and pyrolysis mechanisms of HDPE-ethanol processing residue composites

This study investigates how accelerated weathering influences the pyrolysis behavior of a bio-based composite prepared from high-density polyethylene (HDPE) and lignocellulosic ethanol-processing residue (EPR). The composites were subjected to xenon-lamp exposure for varying durations and subsequently analyzed using thermogravimetric analysis (TGA), TG-FTIR, Py-GC/MS and kinetic modelling. TGA results showed that weathering enhanced the crystallinity of the HDPE phase and reduced the maximum mass-loss rate, indicating inhibited volatilisation in the HDPE-dominated decomposition region. Iso-conversional kinetics further revealed a conversion-dependent response: the apparent activation energy decreased in the low-to-mid conversion region dominated by the residue fraction, whereas the activation energy associated with the HDPE-dominated region increased, consistent with crystallinity-enhanced resistance to polyethylene chain scission. The increased residual mass after aging is attributed not only to pre-loss/leaching of labile fractions during weathering but also to the formation of more stable residue structures (e.g., photo-induced crosslinking and lignin-derived condensed aromatic clusters) that persist during pyrolysis. TG-FTIR indicated a general decline in the intensity of functional-group absorption peaks, reflecting attenuated volatilization of both polymeric and lignocellulosic structures. Py-GC/MS demonstrated significant changes in product distribution: weathered samples generated higher yields of short-chain hydrocarbons such as propene, 1-pentene, and 1-decene, while oxygen-containing compounds (e.g., alcohols, esters, phenols) were reduced. These results clarify how controlled weathering alters the structural and chemical evolution of HDPE–EPR composites during pyrolysis. The findings provide new insights for optimizing thermochemical recycling and energy-recovery strategies for residue-derived or weathered bio-plastic composites. • Xenon-lamp weathering altered pyrolysis of HDPE–EPR composites. • Weathering increased HDPE crystallinity and reduced mass-loss rates. • Solid residue increased progressively with weathering duration. • Iso-conversional kinetics showed a conversion-dependent E a response after weathering. • Product selectivity shifted to light hydrocarbons/α-olefins with fewer oxygenates (TG-FTIR, Py-GC/MS).