Thermal and Mechanical Properties of Lignin Derivative–Sulfur Composites

ABSTRACT Lignin, comprising 20%–35% of lignocellulosic biomass, is the second most abundant biopolymer after cellulose. As the bioethanol industry expands, the accumulation of lignin by‐products necessitates innovative valorization strategies. This study explores the synthesis and characterization of lignin‐derived composites. Specifically, the reaction of 20 wt. % lignin‐derived guaiacol or syringol with 80 wt. % elemental sulfur gives composites GS 80 and SS 80 , respectively. The chemical structures of composites were elucidated using GC–MS, 1 H NMR, and UV–Vis spectroscopy, revealing the formation of both SC aryl and SC alkyl bonds. Thermal and morphological analysis (via TGA, DSC, PXRD, and SEM‐EDS) indicated SS 80 has higher crystallinity and thermal stability than GS 80 , attributed to a higher degree of crosslinking and a greater content of dark sulfur. Mechanical testing showed SS 80 exhibits superior compressional and flexural strengths, and enhanced Young's modulus and Shore hardness, compared to GS 80 . Notably, the mechanical strength parameters for SS 80 are comparable to those of C62 class bricks used in construction applications. These findings suggest that lignin‐derived composites, particularly those incorporating syringol, can provide viable alternatives to traditional materials in various applications, contributing to both waste valorization and sustainable materials science.