Visualization of gelation inhomogeneity of PVC

The variation of the PVC gelation level in extruded products, usually related to the instability of the extrusion process, leads to inhomogeneity of the local end-use properties. The main task of our research was to develop a simple visualization method, based on swelling and solution effects, allowing determination of the gelation homogeneity in extruded PVC-U products. It was found that the applied visualization technique allowed identification of the regions with a different resistance to attack of a mixture of methylene chloride with cyclohexanone, and thus with various degree of gelation. The DSC and rheological investigations confirmed the results of the visualization measurements. Consequently, it was ascertained that an etching procedure may be used in parallel and/or instead of rheological or DSC measurements for the determination of the homogeneity of the PVC gelation in extruded products.