Structure and properties of polyvinyl alcohol/polyurethane blends

Abstract

In order to explore the way for improving the toughness of polyvinyl alcohol (PVA), water-soluble polyurethane (WPU) with high toughness was applied for the first time to be blended with PVA. It was found that the small difference of the solubility parameters of the two polymers, the positive value of β12 from Nielsen formula and the fact that the two Tg of the PVA and WPU-rich phase in blends shifted to the inside of their respective original Tg indicated that the blend system was miscible. The FTIR and Peakfit software analysis showed that with increasing PVA content, large amount of hydroxyl groups were provided to form hydrogen bonding with the carbonyl group of WPU, resulting in the significant increase of total degree of hydrogen bonding. Above 10wt% WPU, the stress–strain curves of the blends exhibited the characteristic of a ductile fracture. With increasing WPU content, the storage modulus of the blends decreased over the whole temperature range of test. Addition of WPU destroyed the regularity of PVA molecular chains and weakened the crystallization ability of PVA. The spherical particles of WPU dispersed homogeneously in PVA matrix and with increasing WPU content, the fractured surface became rough, resulting in the brittle–ductile transition. The tensile fracture surface of the blend was covered with the curled WPU phase, PVA matrix was also torn to continuous tape and the surface exhibited the character of fully regularly distant striations, indicating the severe plastic deformation and the character of tough fracture.