Effects of an acidic catalyst on the barrier and water resistance properties of crosslinked poly (vinyl alcohol) and boric acid films

Abstract

Although the high oxygen-barrier property of poly (vinyl alcohol) (PVA) makes it attractive for packaging applications, its complete valorization is hindered owing to its low water resistance and poor thermal properties. To overcome these drawbacks, boric acid (BA)-crosslinked PVA (BCPVA) films were prepared using the solution casting method in the presence of different amounts of HCl as the acidic crosslinking catalyst. The properties of the pure PVA film showed a strong dependence on the HCl content. The enhancement of the crosslinking density in the pure PVA film imparted hydrophobicity to the film; as a result, the water sorption was remarkably reduced and the water resistance was enhanced. The existence of numerous crosslinking units in the matrix of the BCPVA film led to a reduction in crystallinity, while improving the barrier properties owing to the formation of extensive diffusion pathways within the matrix. The pure PVA film showed an OTR of 5.51 cc/m2·day, which significantly decreased for the BCPVA films from 1.33 to 0.79 cc/m2·day. Higher concentrations of HCl lead to a reduction in transparency and the formation of crystalline-like residues. Overall, this study demonstrated that adding HCl remarkably increased the crosslinking reaction between PVA and BA in the films, which in turn improved their oxygen barrier and water resistance. Therefore, the as-prepared PVA films crosslinked with BA and HCl can be used as barrier materials for various packaging applications.