Non-destructive and in-situ determination of the degree of gelation of pvc pipes

Various non-destructive methods, based on different physical principles, were investigated for their ability to differentiate between uPVC pipes having various levels of gelation. It was found that the micro-hardness method was not able to differentiate between uPVC samples of different levels of gelation. A possible explanation is that the affected volume under the indentation does not reach the centre of the pipe wall where differences in the level of gelation are most pronounced. The laser scattering and laser microscopy methods fail because the surface roughness is not only determined by processing temperature (which is related to the level of gelation), but also by other factors in the production process. The Profile NMR-MOUSE is able to scan through the thickness of the pipe wall. However, the amounts and relaxation rates show no significant differences between uPVC samples of different levels of gelation. The NMR results can be explained from DSC measurements, where no detectable differences in crystallinity have been observed for the different ways of processing.