Behaviour of Poly (vinyl alcohol) at High Temperatures

I. On the Wide Angle Diffraction of X-Ray

Abstract

A X-Ray diffraction apparatus was constructed, in which polymer specimen could be kept at any temperature between room temperature and 400°C, and the diffraction intensity could be measured by using a X-ray counter. Poly (vinyl alcohol), (PVA), as a typical crystalline polymer, was chosen for the present study and the behaviour in the wide angle diffraction at high temperatures was investigated. The crystal lattice of PVA-fibres which have been heat-treated is expanded on heating from room temperature to 210°C. For example the spacing of (100) increases from 7.80 to 8.04A on heating. The crystalline diffraction intensity remains constant between room temperature and 180°C and is somewhat decreased at 210°C. For the samples which have not been heat-treated, the effect of the heat-treatment i.e. the contraction of the lattice is supperposed upon that of the thermal expansion. The crystalline diffraction intensity increases on heating from temperature to 200°C. PVA on heating upto 230°C gives a liquid diagram. Although samples, which have been heated up to 270°C, gives the typical crystalline X-ray diagram of PVA on cooling down to room temperature, samples heated above 290°C gives only an amorphous diagram when cooled to room temperature. However in the latter, appreciable chemical changes such as oxydation and thermal decomposition might have taken place on heating process.