Effects of compounding and extrusion variables on degree of fusion and impact strength of PVC window profile

The effects of temperature in twin screw extrusion of a window profile compound have been studied. Compounds were made with and without an acrylic impact modifier. Fusion levels of the extruded profiles were rated from values of the rubbery plateau modulus at temperatures near 110°C. Impact strength was measured at room temperature using notched tensile specimens at 1 m/s jaw separation rate. The impact strength of these materials does not increase with fusion level once an adequate degree of gelation has been achieved. The impact-modified compound shows a dramatic improvement in impact strength when the melt temperature was increased from 319°F to 343°F. A further increase to 365°F had no effect. The compound without impact modifier exhibited no improvements in impact strength over the whole extrusion temperature range. Conflicting reports in the literature on effects of fusion level on impact strength of PVC articles probably reflect different interactions between extrusion conditions and compound composition.