Enzymatic synthesis of highly flexible lignin cross-linked succinyl-chitosan hydrogels reinforced with reed cellulose fibres

This study reports on a novel strategy for laccase mediated synthesis of highly flexible succinyl chitosan (SucCTS) hydrogels cross-linked with lignosulfonates whose mechanical properties were further enhanced by incorporating glycerol as a plasticizer and reed cellulose fibres as reinforcement agent. Laccase enzyme was used to oxidize lignosulfonates resulting in the formation of phenoxyl radicals that reacted with -NH2 groups SucCTS either through radical coupling or Michaels addition. The oxidation of lignosulfonates resulted in 51 decrease in lignosulfonate -OH groups and 74% SucCTS-NH2 groups, and concomitant gradual increase in molecular weight of the copolymer from an average 15 kDa to above 600 kDa. Incorporation of glycerol as plasticizer prevented stiffness, shrinking and random breaking of the hydrogels, as evidenced by the remarkable increase in elongation at break (up to160%) of the hydrogels. The laccase remained active and completely reduced oxygen to water in a closed system, making it suitable for application as oxygen barrier system. This study therefore demonstrate an environmentally friendly process for synthesizing 100% biobased (chitosan based hydrogels) using naturally occurring lignin as cross-linking agent and laccase as biocatalyst.