High-Strength and Tough Cellulose Hydrogels Chemically Dual Cross-Linked by Using Low- and High-Molecular-Weight Cross-Linkers

Hydrogels are the focus of extensive research interests due to their potential application in the fields of biomedical materials, biosensors, agriculture, and cosmetics. Natural polysaccharide is one of the good candidates of these hydrogels. However, weak mechanical properties of cellulose hydrogels greatly limit their practical application. Here, chemically dual-cross-linked cellulose hydrogels (DCHs) were constructed by sequential reaction of cellulose with low- and high-molecular-weight cross-linkers to obtain relatively short chains and long chains cross-linked networks. Both the distribution and density of the cross-linking domains in the hydrogel networks were monitored by three-dimensional Raman microscopic imaging technique. Interestingly, the ruptured stress of DCHs in tensile and compressive tests were 1.7 and 9.4 MPa, which were 26.3- and 83.9-fold larger than those of chemically single-cross-linked cellulose hydrogel. The reinforcement mechanism of DCH was proposed, as the breaking of the short-chain cross-linking in the networks effectively dissipated mechanical energy, and the extensibility of the relatively long-chain cross-linking maintained the elasticity of DCH. Therefore, both the strength and toughness of DCH was enhanced, and the dual networks consisting of short-chain and long-chain cross-linking played an important role in the improvement of the mechanical properties of the cellulose hydrogels. The application prospect of the robust cellulose hydrogels with bimodal network structure would be greatly broadened in the sustainable biopolymer fields.