Wet stable and mechanically robust cellulose nanofibrils (CNF) based hydrogel

Freeze dried, highly porous materials made from cellulose nanofibrils (CNF) hydrogels are capable of absorbing and storing a significant quantity of liquid inside their 3D structure, with total absorption capacity increasing linearly with porosity. One of the challenges of freeze dried high porosity CNF gels is their propensity to break down rapidly in aqueous environments. Here we explore a method to overcome this deficiency by incorporating methacrylate functionalized carboxymethyl cellulose (MetCMC) into the CNF system followed by UV irradiation leading to crosslinking of the methacrylate groups of MetCMC. The resultant polymer composite matrix successfully maintains a robust 3D structure, without collapsing, even when rewetted and stored in water. When freeze dried, the CNF-MetCMC composite maintains its size and shape whereas air drying induces significant shrinkage. In contrast, air dried CNF-MetCMC hydrogels swell when rewetted. Swelling and shrinkage of CNF-MetCMC hydrogels were tuned by controlling the ratio between CNF and MetCMC in the composite. The crosslinking between the methacrylate groups of MetCMC also enhances the dry and wet modulus of CNF-MetCMC gels significantly. We invoke a simple model involving a balance between hydrogen bonding and crosslinking to explain these data. (C) 2018 Elsevier Ltd. All rights reserved.