Yielding and impact behaviour of pp/sgf/epr ternary composites with controlled morphology

Dependencies of the yield strength (sigma(yc)), yield strain (epsilon(yc)) and Charpy notched impact strength (CNIS) of polypropylene IPP) reinforced with 30 wt% short glass fibres (SGF) and ethylene-propylene random copolymer (EPR) inclusions on EPR volume fraction (v(e)) were investigated within the interval of v(e) varying from 0-0.2. Only one limiting phase morphology has been attained reproducibly using a procedure based on chemical modification of PP. Adhesion enhancement between SGF and PP and complete separation between SGF and EPR was achieved by grafting PP with 2 wt% maleic anhydride (MAH). Two regions existed on sigma(yc) versus v(e) curves in the case of complete separation of the reinforcement and elastomer. The observed increase of sigma(yc) with increasing v(e) within the interval 0 < v(e) < 0.05 was attributed to the change in the mode of fracture from brittle to quasi-ductile. Such an explanation has been supported by a several fold increase in epsilon(yc). Above v(e) = 0.05, a monotonic decrease of sigma(yc) with increasing v,was observed corresponding well with an explanation based on a reduction of matrix effective cross-section. In this interval of v(e) the concentration dependence of sigma(yc) was described quantitatively using existing composite models and satisfactory agreement between predictions and experimental data was obtained. The CNIS increased monotonically up to v(e) = 0.1 for both homo- and copolymer based composites. Above v(e) = 0.1, CNIS, measured at -20 degrees C using 6 x 4 x 50 mm bars, notched accordingly ASTM D256 standard, increased for copolymer based composites while it remained constant for homopolymer based materials. Physical meaning of these data is, however, obscured by the inability to separate effects of v(e) from those of specimen geometry using only a single standard impact strength data.