Co-pyrolysis of biomass and polyethylene: Mechanistic insights into functional group transformations on solid matrix

An in-depth understanding of the co-pyrolysis mechanism of corn straw (CS) and low-density polyethylene (LDPE) is important for improving the combined treatment of straw and mulch film in covered areas. This study investigated the volatile product composition during pyrolysis/co-pyrolysis through thermogravimetric-infrared-mass spectrometry (TG-FTIR-MS). In-situ FTIR spectroscopy was also applied to track variations in five common functional groups (OH, C-O, C = O, C = C, and C-H) on solid matrix. The thermogravimetry results indicated that molten LDPE inhibited CS pyrolysis during low-temperature co-pyrolysis. The TG-FTIR-MS results demonstrated that radicals formed during LDPE pyrolysis reacted with intermediates produced during CS pyrolysis, which promoted the removal of oxygenated functional groups and the generation of aromatic products in gaseous products. The in-situ FTIR spectra implied that the reactivity of the functional groups on solid matrix was OH > C-O > C-H > C = O > C = C. Most importantly, the co-pyrolysis process was divided into an inhibition stage (<300 °C) and a promotion stage (>300 °C). Three pathways for promoting the pyrolysis reaction and two possible pathways for the formation of biochar were also proposed, providing an insightful understanding of the co-pyrolysis mechanism of biomass and plastics.