Simultaneous strengthening and toughening lignin/cellulose nanofibril composite films: Effects from flexible hydrogen bonds

Abstract

Inspired by the lignin-cellulose network in natural wood, we developed a strategy to produce cellulose nanofibril (CNF) composite films using lignin nanoparticles (LNPs) with varied contents of phenolic hydroxyl (Ph-OH) groups as a reinforcing agent. Regulated LNPs with lower molecular weight, higher Ph-OH content, and uniform morphology were successfully prepared by phenolation and anti-solvent precipitation. CNFs mixed with phenolated LNPs of high Ph-OH content (8.23 mmol/g) exhibited a higher tensile strength (∼190 MPa), increased toughness (∼15 MJ/m3), and enhanced UV-blocking ability (∼99 %) compared to lignin-free CNFs and CNF composites with lower Ph-OH content. Thus, hydrogen bonds between Ph-OH groups on lignin and hydroxyl groups on CNFs are vital for enhancing the mechanical strength of composite films. Similar enhanced mechanical properties were found by adding phenolated LNPs into polyvinyl alcohol as a fortifier. This study provides novel insights into producing lignin-reinforced cellulose composite films with UV shielding, thermal stability, and biodegradability.