In situ assessment of lignin pyrolysis reactions and their interactions with polysaccharides in Japanese cedar wood cell walls by TG-MS and Py-GC/MS

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Abstract

Understanding the thermal degradation of lignin and polysaccharides in wood cell walls is essential for optimizing biomass pyrolysis. In this study, Japanese cedar ( Cryptomeria japonica ) was analyzed using thermogravimetric-mass spectrometry (TG-MS). Coupled with pyrolysis-gas chromatography-mass spectrometry (Py-GC/MS), TG-MS enabled semi-quantitative analysis of key volatile products evolved during thermal degradation, each corresponding to distinct m/z values. Comparison between intact wood and isolated milled wood lignin (MWL) revealed the influence of cell wall supramolecular structures on lignin pyrolysis. The water ( m/z 18) evolution profiles from both materials exhibited six distinct peaks, indicating stepwise lignin decomposition across six temperature ranges up to 1000 °C. β-Ether cleavage predominantly yielded coniferyl aldehyde rather than coniferyl alcohol at early stages, suggesting a polymer effect that promotes in situ C γ oxidation—an observation rarely observed in model compound studies. The formation temperatures of pyrolysis products followed the order: β-ether bond cleavage < side-chain saturation < methoxy group demethylation. In intact wood, secondary reactions such as side-chain saturation and demethylation occurred at significantly lower temperatures than in MWL. Since the pyrolysis product profiles of MWL remained largely unaffected by the addition of sugars, the enhanced reactivity in wood is attributed to the influence of the cell wall ultrastructure. This study is the first to provide detailed in situ insights into the thermal degradation behavior of lignin and polysaccharides within wood cell walls, offering valuable contributions to the field of wood pyrolysis.

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