Impact of fiber length and fiber content on the mechanical properties and electrical conductivity of short carbon fiber reinforced polypropylene composites

This paper evaluates the influence of fiber length and fiber content on the mechanical and electrical properties of injection molded short carbon fiber (CF) reinforced polypropylene (PP) composites. At first, four injection molded PP/CF composites containing 10 vol.% CF were produced using varying compounding parameters in order to achieve different fiber length distributions. Subsequently, the processing conditions giving the longest fibers in the final composites were used for the production of PP/CF test specimens containing varying amounts of CF (5, 10 and 15 vol.%). Identical processing parameters were used for the varying fiber contents. The fiber length distributions of all composites were determined. Furthermore, the tensile and impact properties were tested as well as heat deflection temperature and electrical conductivity. Within the investigated range, composite properties were dependent on fiber length and fiber content. Tensile strength, tensile modulus, notched impact strength and electrical conductivity showed highly accurate linear correlation with the weight average fiber length. Tensile strength and modulus even showed a very well fitting linear correlation with the fiber volume content. The best results were achieved for a composite containing 15 vol.% CF, with 98 MPa tensile strength, 14.4 GPa tensile modulus and an electrical conductivity of 10 2 S/cm.