X‐ray investigation of the crystallization behaviour of swollen polyvinyl alcohol

Abstract

AbstractX‐ray measurements as function of temperature were made from pure polyvinyl alcohol (PVA) and concentrated PVA‐solutions in water, glycerine, and glycol. The solutions form gels at adequate low temperatures. As the formation of a chemically bound network can be excluded gel formation must be related to physical crosslinking. From the results of wide angle X‐ray measurements it is concluded that the gels are partially crystalline systems. In this case the polymer network is a physical one, consisting of crystalline regions connected by macromolecules in the amorphous state. At room temperature the used PVA is about 20% crystalline. By quenching from temperatures above the melting point down to temperatures far below the glass temperature we succeeded in producing approximately amorphous PVA.Water is the best and glycol is the poorest of the agents used for solving PVA. Crystallization and gel formation following from it take place at the lower temperatures the better the solvent is. The differences in the degree of crystallinity of PVA in these solvents is not caused, however, by the solvent itself but mainly by the different gel formation temperatures. Crystallisation and gel formation in bad solvents occur at higher temperatures than in good solvents. The degree of crystallinity of the gels is the same as that of pure PVA samples crystallized at the same temperatures. In the case of glycol the highest degree of crystallinity was found similar to the case of pure PVA, of about 42%.In the wide angle X‐ray diagrams of the gels investigated the positions of the crystal interferences are unchanged. Therefore it can be concluded that the solvents do not enter into crystals to an appreciable amount. The continuous scattering curves of the amorphous part, however, are changed during gel formation. In comparison with the pure polymer the medium distance of the amorphous part of the sample is enlarged and the distance distribution around the medium distance is broadened.