Comprehensive analysis of the molecular structure of lignin from microwave-assisted fractionation

Lignin is a complex aromatic biopolymer derived from biomass, holds significant potential for addressing energy crises and environmental challenges through its valorization, thereby advancing the development and application of biomass derived materials. This study systematically investigated the effects of reaction conditions and woody materials on microwave dissociation of lignin. The results demonstrated that acid concentration and reaction temperature critically influenced lignin properties, including color, yield, molecular weight, chemical bonds, and thermal stability. Among them, the condition of 150°C and 0.75 % acid concentration is optimal. Variations in color, yield, molecular weight, chemical bonds, thermal stability, pyrolysis behavior, and structural unit ratios were observed among lignin from different woody materials. Notably, Taiwania(TS, Taiwan fir genus in the cypress family) exhibited the highest yield (18.3 %), molecular weight (9642 g/mol), and maximum degradation temperature (400°C). Distinct guaiacyl (G), Ssyringayl (S), and p-hydroxyphenyl (H) unit distributions were characterized across woody materials. TS was G dominant with minimal S unit content (<1.5 %), while herbaceous and hardwood lignin displayed unique S/G/H ratios. These findings provide foundational insights into the structure-property relationships of lignin and establish a reference framework for its targeted valorization, supporting the development of high value applications in sustainable biorefinery systems. • Acid concentration and temperature critically influenced lignin properties. • Differences in GHS unit were observed among biomass species. • Taiwania was G dominant with minimal S unit content. • Herbaceous and hardwood lignin displayed unique S/G/H ratios.