Hydrogels derived from lignocellulosic compounds: Evaluation of the compositional, structural, mechanical and antimicrobial properties

Hydrogels derived from lignocellulosic biomass and its constituent components have attracted growing interests due to the applications in agriculture, material, environment and biomedical fields. Some ionic liquids (i.e. 1-n-butyl-3-methylimidazolium chloride ([C₄C₁im][Cl] and 1-ethyl-3-methylimidazolium acetate ([C₂C₁im][OAc]) can solubilize all factions of lignocellulosic biomass, while generating hydrogel materials without additional chemical crosslinkers such as epichlorohydrin. The present study explored the use of ionic liquids as solvents for creating physically crosslinked hydrogels from mixtures of cellulose, xylan and lignin to examine how each component affects hydrogel formation. The chemical, physical and mechanical properties of generated hydrogels were characterized using FT-IR, SEM, XRD, compositional analysis, swelling kinetics, and stress-strain analysis then compared against a chemically crosslinked cellulose hydrogel. We further tested hydrogels formed directly from poplar wood and biomass sorghum and examined the antimicrobial resistance of the lignin containing hydrogels. The hydrogels with xylan had significantly higher elastic moduli at 0.1 MPa compared to other hydrogels, while poplar-based hydrogel had the highest strain of 65.3% and a stress of 0.12 MPa prior to rupture. The biomass-based hydrogels exhibited swelling ratio comparable to the chemically crosslinked cellulose hydrogel. All lignin containing hydrogels, besides the sorghum hydrogel, resulted in an 80% reduction in E. coli colony growth, indicating retained antimicrobial activities. This study provides insights into using lignocellulosic biomass for hydrogel production and how these novel hydrogels have tunable mechanical and antimicrobial properties as compared to chemically crosslinked cellulose hydrogels.