The water resistance of polyvinyl alcohol was improved by cross-linking with maleic acid (commonly known as maleic acid, MA). The esterification crosslinking of PVA membrane is achieved through the esterification reaction between PVA molecule and MA at high temperature. The esterification crosslinking reaction actually introduces carbonyl group into the polymer chain of PVA, forming a new polymer, but the main chain of the whole PVA polymer remains unchanged.
The PVA after esterification with MA only has chemical crosslinking, and does not produce a stable crystal structure, so the PVA film is easy to be swollen by water and destroy the structure of the film. Therefore, the PVA film should be heat treated. Since the esterification reaction in the liquid phase is characterized by reversibility, the crosslinking of polymers in the PVA film during the heating process makes the esterification reaction irreversible due to the partial water that has not been removed in the casting liquid and the complete volatilization of the water generated by the esterification reaction of PVA and MA, and the cross-linked PVA film is stable.
PVA can improve the water resistance and poor mechanical properties of PVA by chemical crosslinking with MA. Proper concentration of crosslinker and heat treatment conditions can make PVA obtain better water resistance.
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