Effects of crosslinking agent ratio and gelation temperature on the performance of microcrystalline cellulose hydrogels

Hydrogel is a network polymer with low crosslinking density that has the ability to swell and retain large amounts of water. Nowadays, hydrogels are widely used in various fields, such as drug delivery, hygiene products, agricultural water retention materials, cell culture, and biomaterials. Cellulose is the most abundant renewable resource on earth and has attracted much attention in hydrogel production due to its high hydrophilicity, good biocompatibility and biodegradability. In this study, microcrystalline cellulose was added to a mixture of urea/NaOH/H 2 O to form a cellulose solution by stirring and repeated freezing and thawing. Then, the cellulose solution was reacted with epichlorohydrin at different epichlorohydrin/cellulose (E/C) ratios and different temperatures to prepare cellulose hydrogels. The results show that the repeated freezing-thawing process is an effective method for increasing the solubility of cellulose. After dissolution and drying, the crystal structure of cellulose changes from cellulose-I to cellulose-II. The cellulose solution can be reacted with epichlorohydrin. The larger the E/C ratio, the easier the reaction and the greater the mechanical strength of the cellulose hydrogel, but the lower the water absorption of the dried hydrogel. Heating can promote the reaction, but reduce the structural uniformity and mechanical strength of the hydrogel.