EXTRUSION OF SHORT-FIBER-REINFORCED PP

Data regarding the influence of screw geometry on homogeneity and fibre length reduction during single screw extrusion of short glass fibre reinforced PP are presented. Three screw geometries, two grades of PP with different melt flow indices, and four levels of filling (10 to 40 wt.%) were the main variables studied. The fibre breakage mechanism was evaluated with respect to solid and melt conveying and melting mechanisms in the screw channels. The screw with a long compression zone produced a material of poor homogeneity, a stable melting mechanism and a medium level of fibre length reduction. The very short compression zone screw produced unstable melting which considerably improved the homogenization process of the fibres in the polymer matrix. In this way the extrudates remained smooth up to the 30 wt.% filling level. The homogeneity was comparable to that obtained by a process including two steps of compounding: twin screw and single screw extrusion. However, the fibre degradation in the screw with a very short compression zone was substantially lower than in the process including two compounding steps.