Influence of the graft-copolymerized hydrophilic lignin content on the structure and mechanical properties of gel-spun poly(vinyl alcohol) composite fibers

Lignin is a cost-effective, biobased filler for the fabrication of high-performance poly(vinyl alcohol) (PVA) composite fibers that increases fiber performance and sustainability. However, amorphous and hydrophobic lignin often have poor compatibility with semi-crystalline and hydrophilic PVA matrixes. Moreover, aggregation of the filler at high content could occur to impede the effectiveness of lignin as a reinforcing filler. To address these issues, modified organosolv lignin (OL24) with hydrophilicity was obtained from the graft copolymerization of organosolv lignin and acrylic acid monomers after 24 h of reaction and later used as a reinforcing filler at different ratios of 0%, 5%, 10%, 20% and 30% in PVA to achieve composite fibers with better compatibility between the filler and matrix, and enhanced sustainability. The influence of the graft-copolymerized hydrophilic lignin content on the structure and mechanical performance of gel-spun PVA composite fibers was fundamentally investigated. The results showed that 10% OL24/PVA fiber had outstanding mechanical properties with an average tenacity of 7.8 cN/dtex (tensile strength of 1.02 GPa), average specific modulus of 143.21 cN/dtex (Young's modulus of 18.62 GPa) and toughness of 20.90 J/g. It was concluded that the higher orientation, larger crystal size and stronger hydrogen bonding in the composite fiber structure contributed to the good fiber mechanical performance. These results offer technical support for the mechanical performance optimization of lignin-reinforced polymeric high-performance fibers.