Pure and Applied Chemistry

Synopsis: We have conducted a detailed investigation of the change in deformational, structural, molecular and rheological characteristics that are attendant on a PVC-p compound experiencing higher processing temperatures. Our study reflects an experience that occurs in the PVC industry and for which a loss of processing performance accompanies the excursions to higher temperatures. It is apparent that as this process continues the material will eventually become unprocessable, unless changes are made.

The change that accompanies the material as it passes from an experience of low processing temperatures to high processing temperatures has been thoroughly mapped. However, it has been difficult to make precise observation of the molecular and structural changes occurring. This has not been without application of a number of likely candidate methodologies, including DSC, TGA, WAXS, GPC and fluorescence spectroscopy. It would seem that some additional crystallization is accompanying the increase in gelation that occurs at higher processing temperatures. At the same time, the observations on the influence of annealing hint that this is not the only consideration and that diffusion of the plasticiser into the PVC particles might also be playing a role or even residual stresses in the materials might be important.

This study has not only been concerned with an in depth materials characterisation; it has also explored ways of alleviating the loss of processability. Two particular lines of study involving pre-shear history and blending with higher plasticised compounds have provided interest albeit inconclusive results. On the other hand, there are strong implications from the DSC study that reversibility of the "process aging" is not likely.

In conclusion, it is interesting to observe that by conducting this study through an IUPAC Working Party it has been helpful to pool the resources and experience of an international community of scientists which has likely given us an opportunity of conducting this study at much lower costs than might have otherwise been the case.