Combination of acid treatment and dual network fabrication to stretchable cellulose based hydrogels with tunable properties.

Cellulose based hydrogels with a relatively high stretchability were fabricated in the NaOH/urea system via sequential chemical crosslinking and dual network fabrication. The first step involved crosslinking of cellulose using epichlorohydrin as a crosslinker. Cryo-electron microscopy analysis revealed the utilization of diluted acid to treat hydrogels significantly affected the morphology of the first network and improved the mechanical properties. After diffusion of precursors into the first network, the dual network hydrogels were generated after the UV light-initiated polymerization. Raman spectroscopy demonstrated a spatial distribution of second networks within the first network. The compression strength of hydrogels synthesized under the optimized conditions was effectively enhanced from 0.04 MPa to 10.9 MPa. In addition, the tensile properties of hydrogels were easily adjusted via copolymerization of acrylic acid with acrylamide. The highest strain could reach 219.5% with a tensile strength of 1.4 MPa. This work provides a promising and simple strategy to develop a cellulose based hydrogel with enhanced and tunable mechanical properties for wide applications.