Novel flexible, strong, thermal-stable, and high-barrier switchgrass-based lignin-containing cellulose nanofibrils/chitosan biocomposites for food packaging

Chitosan/lignin-containing cellulose nanofibrils (CS/LCNF) biocomposites were prepared by a facile and green method that combined hydrothermal pretreatment, mechanical fibrillation, and dry casting. LCNFs were isolated from switchgrass with various lignin contents, and their effects on the transparency, micromorphology, mechanical properties, interfacial compatibility, thermal stability, surface wettability, and barrier properties of the CS/LCNF biocomposites were comprehensively investigated. Their transparency was affected by changing the lignin and cellulose contents, as well as the order degree of cellulose. The hydrophobic micro/nano- lignin particles with the optimum contents (33.8%) coated on CNFs or embedded their networks prompt the dispersion of LCNF in CS matrices and enhance interfacial interaction of CS and LCNF. This synergistically improved the mechanical properties and thermal stability of CS/LCNF biocomposites. CS/LCNF8 maintained a ductility of 503% and showed a tensile strength that was 46.7% higher than that of CS/CNF, as well as a Tmax and WCA that were 2.6 °C and 11.06° higher, respectively. Furthermore, CS/LCNF8 displayed a more competitive OTR (0.20 cc/(m2 day)) than those of pure chitosan, mechanically-fibrillated CNFs, carboxymethylated CNFs, and TEMPO-oxidized CNF/CS films at the same ratio. This study provides promising environmentally-friendly biocomposite films with outstanding comprehensive performance for green food packaging.