Studies on the cross-linking of poly(vinyl alcohol)

This paper is concerned with the cross-linking of poly(vinyl alcohol) (PVA) using maleic acid as the cross-linker. The curative (maleic acid) dose and the curing temperature and time were varied between 2.5 and 60% (w/w), 120 and 160 degrees C and 30 and 120 min, respectively. From a thorough swelling study in both hot and cold water (percentage swelling, gel content, swelling ratio, etc-) the optimum curative dose and curing conditions have been evaluated. The molecular weight between the cross-links exhibited a sharp fall Lip to a maleic acid dose of 20% (w/w). A comparative evaluation of maleic acid cross-linked and heat-treated PVA films has been done. Better heat stability for maleic acid cross-linked PVA was observed from thermogravimetric analysis. A shift in glass transition temperature was observed for both heat-treated and maleic acid treated PVA compared with the virgin one. IR spectroscopic study indicated the presence of an ester linkage and an olefinic double bond in maleic acid treated and heat-treated PVA films, respectively. Maleic acid crosslinked PVA is quite stable in different polar and nonpolar solvents. A definite structural pattern has been observed in maleic acid cross-linked PVA films through scanning electron microscopy.