High Water Resistance Polyvinyl Alcohol Hydrogel Film Prepared by Melting Process Combining with Citric Acid Cross-Linking

The reversibility of physical cross-linking is detrimental to the service life (mainly water resistance) of polyvinyl alcohol hydrogels, so it is necessary to prepare polyvinyl alcohol hydrogel films by irreversible chemical cross-linking. In this paper, the chemically cross-linked polyvinyl alcohol hydrogel films were prepared using citric acid as the cross-linking agent. Polyvinyl alcohol was plasticized by water, starch, and polytetrahydrofuran dibenzoate (PTMGDB) through melt processing firstly. The mesh size decreased when 5 wt % citric acid was incorporated into the hydrogel film, but the crosslink density increased significantly. The increase in the chemical cross-linking point restricts the movement of polyvinyl alcohol molecular chains. It makes the cross-linked structure more stable, so the water-resistance of hydrogel film is significantly improved. Meanwhile, the dense crosslinking network also makes the chemically crosslinked hydrogel film to enhance mechanical properties and to lower swelling ratio. Therefore, hydrogel films prepared by chemical cross-linking with citric acid have a better potential for industrial applications than physically cross-linked polyvinyl alcohol hydrogel films.