Insight into the structure and mechanical performance of high content lignin reinforced poly (vinyl alcohol) gel-spun fibers via the regulation of esterified hydrophilic lignin composition for better sustainability

Lignin is an effective low-cost renewable reinforcement material for composite fibers at low concentration. In general, reinforcing synthetic polymeric fibers with high content lignin are preferred due to the fibers' enhanced sustainability. However, aggregation and disruption of fiber crystallinity often occurred at high lignin content, which often deteriorated fiber performance. Esterified hydrophilic lignin (modified lignin, ML) obtained from the esterification of organosolv lignin (OL) and D-gluconic acid has good interaction with poly (vinyl alcohol) (PVA) matrix in gel-spun fibers at low content. To investigate the effect of this ML on the structure and performance of high content lignin/PVA composite fibers at 30%, gel-spun PVA fibers were prepared with different ratios of OL/ML (1/0, 2/1, 1/1, 1/2 and 0/1) in this work. The optimal mechanical performance was observed in 30% lignin mixture (OL/ML = 1/1) reinforced PVA fiber with a tensile strength of 1.1 GPa, modulus of 28 GPa, and toughness of 22 J g(-1), which were 50%, 60%, and 28% higher than that of 30% OL/PVA (OL/ML = 1/0) fiber, respectively. The excellent mechanical properties are mainly attributed to increased fiber crystallinity, molecular anisotropy, and interfacial bonding of the composite fibers.