No abstract

The effect of calcium carbonate in levels of 1 to 5 phr has been studied. Two types of calcium carbonate with an average particle size of 1 and 3 microns have been tested and for each formulation a graph has been drawn with drop impact strength as a function of mechanical processing at constant melt temperature. The maximum impact strength has been read from the graph. The results show that the content of calcium carbonate has an obvious effect on impact strength and that the effect of the fine‐grained filler is clearly positive and that the effect of the coarse‐grained filler is slightly negative. Resistance to internal pressure has been studied only at a filler level of 3 phr. Here the fine‐grained calcium carbonate gives a better result than the coarse‐grained one at a moderate level of mechanical processing, while the two filler‐types are equivalent at high levels of mechanical processing.

The shear level was increased during twin screw extrusion of PVC at different melt temperatures by inserting a hole plate in front of the screw tips. The variation of shear level did not significantly affect the capillary pressure in capillary viscometry at 135°C. However, the falling weight impact strength was markedly influenced. In internal water pressure tests at 60°C premature failure was obtained for pipes extruded at 198°C at the highest shear level.

It is shown that the new, skinless suspension PVC type is superior to standard suspension PVC in the following respects: a more narrow particle size distribution, shorter time to gelation which allows for a higher output rate, and a higher optimal impact strength.