Influence of fiber geometry and sizing on glass fiber breakage

During the processing of short and long fiber reinforced plastic, fiber breakage occurs due to fiber-fiber and fiber-polymer interaction as well as contact between fibers and the machine surfaces. This degradation in fiber length results in a decreasing reinforcing effect and lower mechanical properties. In the experimental investigations the influence of fiber geometry and sizing on fiber breakage is investigated. Therefore, different chopped glass strands are compounded into polypropylene and polyamide 6 using a twin-screw extruder. The chopped glass strands differ in initial length, sizing chemistry, glass type and cross section geometry. For all material blends the same screw configuration and screw speed is used. To determine the occurring fiber breakage in the different material blends, melt samples are taken at the die plate and an underwater pelletizer is used to produce granule for each blend. For each material the fiber length is measured in the melt sample as well as in the granules. The different material blends are then processed on an injection molding machine and tensile test specimens are produced. The mechanical properties, determined by testing these specimens, are compared with each other to identify to which extent the fiber parameters influence the tensile strength and modulus.