INFLUENCE OF POLYMER GRADE AND COMPATIBILIZER CONCENTRATION ON THE INTERFACIAL SHEAR STRENGTH IN SISAL FIBRE POLYPROPYLENE COMPOSITES

In this work we investigated the interfacial shear strength for the system sisal polypropylene, regarding the presence of a compatibilizer (maleic anhydride grafted polypropylene) as well as the grade of polypropylene, namely two homopolymers with different flow behaviour. Composites containing different concentrations of sisal fibre and compatibilizer were produced using a co-rotating twin screw extruder and subsequently injection moulded to retrieve test specimens. These specimens were investigated for tensile and notched impact properties, as well as the final fibre length in the composites was determined. With this data, a simple rule of mixtures model was applied to evaluate the tensile strength and notched impact strength for the interfacial shear strength. Further, single fibre pull out tests have been carried out with sisal fibres from polypropylene. Data for interfacial shear strength, acquired by the single fibre pull out tests fit the data acquired by the evaluation of the mechanical testing very well. Furthermore the presence of a compatibilizer improves the interfacial shear strength, as well as the polypropylene grade shows an influence, which is also found from the single fibre pull out tests. In conclusion this shows good applicability of single fibre pull out tests for estimating composite properties. However, one has to keep in mind several influences, due fibre orientation and processing method, when comparing the results from macromechanical measurements with single fibre pull out tests. 1