Formation of an amorphous single phase of poly(vinyl alcohol) subjected to mechanical milling

Abstract

The mechanical milling of poly(vinyl alcohol) (PVA) under an Ar atmosphere was carried out at room temperature. So far, no single phase of amorphous PVA has been reported to be synthesized by any other method. Bragg peaks of the crystal phase in the PVA, however, became broader with increasing milling time. After 200 hours of millings a halo pattern dominated. The density of the PVA gradually decreased with increasing milling time and became constant after 80 hours of milling. The amorphization of the PVA was also confirmed through the observation of low energy excitation by inelastic neutron scattering. These results, therefore, led us to conclude that the amorphous phase of the PVA was formed by the mechanical destruction of the crystal structure. No drastic change of the short-range atomic distribution in the radial distribution function RDF(r) was observed. On the contrary, the correlation distance of the atomic distribution became shorter with increasing milling time. The results suggest that the milling transforms straight long chain molecules into tangled ones in PVA through the kneading process.