On the analysis of wide-angle X-ray diffraction curves of poly(vinyl chloride) samples

Abstract

The calculation of crystallinity values based on wide-angle X-ray diffraction (WAXD) curves of poly(vinyl chloride) (PVC) is subject to three conditions, which are not always explicitly stated. First, the sample should have no orientation or else an averaging factor must be applied to the intensity data. Secondly, on subtracting the non-crystalline component from the WAXD profile the resulting crystalline curve must conform to some identifiable unit cell. Thirdly, the potential presence of a mesomorphous phase implies that there may be no unique non-crystalline profile applicable to all PVC WAXD curves. This last condition is highlighted through the use of a Fourier-transform filtering function, which can be applied to separate the amorphous contribution from the overall WAXD profile. While this technique has been found to be applicable to a wide variety of semicrystalline polymer WAXD profiles, it consistently fails in the case of commercial PVC WAXD curves. The presence of a variable mesomorphous phase can alter the expected intensity relation between the 200 and 110 reflections, thus interfering in any straightforward crystallinity calculation based on WAXD profiles.