Toughened polypropylene with balanced rigidity. III. Compositions and mechanical properties

Toughened polypropylene with balanced rigidity (TRPP) was prepared by therm al mechanical blending of PP resin with a toughening master batch (TMB) in a twin screw extruder. The dependence of the mechanical properties of TRPPs on the ratio of ethylene-propylene to styrene-butadiene elastomers, the to tal elastomer content in the TRPP, and the amount of elastomers in the TMB were investigated. The TRPP with a total elastomer content of 14 wt %, whic h was made from a TMB with 32 wt % elastomer and a 80/20 (w/w) ratio of eth ylene-propylene to styrene-butadiene elastomers, was found to have excellen t balanced mechanical properties. The notched Izod impact strength at 23 de greesC was 762 J/m (23 times that of PP), the flexural modulus was 1078 MPa (92% of that of PP), and the tensile strength at yield was 34.8 MPa (88% o f that of PP). Moreover, its mechanical properties were much better than th e simply blended sample with the same composition, demonstrating that dynam ic vulcanization and polymer-bridge conjunction are excellent techniques to produce a high-impact, high-modulus PP. A sharp brittle-ductile transition was found at 14 wt % total elastomer content, which was assumed to be a pe rcolation phenomenon. (C) 2000 John Wiley & Sons, Inc.