EFFECT OF SCREW DESIGN ON FIBER DAMAGE IN EXTRUSION COMPOUNDING AND COMPOSITE PROPERTIES

The mechanism of fiber length degradation during twin screw extrusion compounding and methods to reduce it through process and machine desig n are extremely important in discontinuous fiber reinforced composites . Fiber damage along the screw and the extruder die are determined for three screw designs with different mixing sections. The pellet qualit y, wet-out, and fiber dispersion in the extruded strands are compared. The fiber orientation distributions In the screw are determined to id entify regions of higher fiber interaction. The fiber damage during su bsequent injection molding has also been determined. The tensile, flex ural, and impact properties of the tensile bars are compared. It is fo und that the residence time, fill-up, and the intensity of mixing duri ng extrusion compounding have a predominant effect on fiber length deg radation. The screw designs were seen to have a greater effect on the fiber damage in the 40 wt% glass-filled polymer than the 30 wt% glass- filled polymer. However, the mechanical properties of the 30 wt% glass -filled polymer showed an increasing trend compared to the 40 wt% glas s filled polymer. A screw design that provides a balance of the fiber length, wet-out, and fiber dispersion was noted to give consistent mec hanical properties.