Compounding of glass-fiber-filled polymers using a quad screw extruder

Degradation of glass fibers during compounding with twin screw extruders reduces the mechanical properties of the resultant parts. To reduce fiber degradation, this work investigated compounding of glass fiber-reinforced polypropylene using quad screw extruders which have greater free volume than twin screw extruders. The influence of glass fiber content, screw speed, and screw configuration was evaluated for fiber dispersion and fiber length in the compounded materials and mechanical properties of injection molded parts. Results showed that screw configuration had a much greater effect on fiber degradation than fiber content and screw speed. Elimination of kneading blocks during mixing reduced the fiber degradation, but still provided excellent dispersion of the glass fibers in the polymer matrix. In addition, comparisons of fiber degradation and mechanical properties were made for glass fiber-reinforced polypropylene compounded using a twin-screw extruder with a similar diameter and length.