Cross-linked bio-based hydrogels generated from solutions derived from the deconstruction of sisal fibers

Abstract

The lithium chloride/N,N dimethylacetamide (LiCl/DMAc) solvent system, with or without catalytic volumes of trifluoroacetic acid (TFA), was used to deconstruct sisal lignocellulosic fiber to further dissolve its main components (cellulose, hemicelluloses, and lignin) in the solvent medium. LiCl/DMAc was used as the solvent system because of its high efficiency in dissolving cellulosic pulp and its high degree of recovery after use. Unfiltered solutions were used (to benefit from both dissolved and suspended components in the medium) to generate hydrogels. The hydrogels investigated in this study were formed from lignocellulosic fibers as a whole, which eliminated steps regarding the cellulose-based ones reported in the literature, which require prior extraction of lignin and hemicelluloses from the starting fibers.The formed hydrogels were cross-linked using polymeric methylene diphenyl diisocyanate to improve their compressive strength and also to evaluate the impact of cross-linking in other properties. Scanning electron microscopy of the cross-linked hydrogels showed that microspheres (microgels) were formed, which may favor applications involving the release of different additives. The cross-linked hydrogels formed from a higher content of undissolved components (no TFA in the solvent system) exhibited an increase of 629% in the compressive modulus compared to the uncrosslinked hydrogels. This impressive stiffening of the network structure was accompanied by a reduction of 55% in water absorption capacity. However, the amount of water retained was still significant, and cross-linking did not affect the hydrogel biocompatibility parameter (evaluated through cell viability). The results indicate potential application in fields where significant compressive strength is required, for instance, in biomedicine and agriculture, to block water penetration for systems that must remain anhydrous. As far as is known, the present study is unprecedented.