Study On Formulation And Co-extrusion Technology For PVC Foamed Sheets With Double Layers

Polyvinyl chloride (PVC) foamed sheet with double layers was prepared by means of Co-extrusion technology. The selection of the base resins was discussed in the thesis. Effects of AC blowing agent content, wax lubricant content, processing temperature, back pressure and the release space were also studied in the research.The results showed that the sheet has regular pore structure and good mechanical properties with the PVC 2500 used in the flexible layer while PVC SG-5 in the rigid layer. The density of the flexible layer was decreased gradually and then increased, while the volume expansion rate (VER) had the opposite result with the AC content increased. It was observed that the density of each layer was reduced and then increased with the wax content increased. The processing temperature could affect the volume expansion rate greatly, thus it should be controlled strictly with the metering temperature 180℃and the die lip 155℃.Furthermore, both heat stability property and the rheological property were also studied. The results showed the apparent viscosity of the flexible layer formulation system was not changed greatly according to the shear rates which indicated that it was not sensitive to the temperature changes between 160℃and 180℃. The apparent viscosity of the rigid layer formulation system was increased when the temperature went beyond 180℃because the back pressure was raised by the volume expansion of the melt.Finally, the mechanical properties of the sheet produced under the optimal processing technology and formulation were tested. The results showed that the prepared PVC foamed sheet could meet all property indices.