Impact Properties of the Polymer Blend of Polypropylene and Thermoplastic Elastomer

Improvement of the impact strength with little sacrifice of the modulus for polypropylene (PP) blends was investigated by blending PP with isoprene-styrene block copolymers (ISR-A, B, C, and D) and ethylene-propylene random copolymer as thermoplastic elastomers. Neither of the blends whose flexural modulus ranged from 1530 MPa, that of PP, to 1400 MPa showed a significant improvement of the notched Izod impact strength (< 47 J/m) as compared with that of PP (32 J/m). The blend of PP and the isoprene-styrene diblock copolymer with the weight percent of the feed styrene of 30 wt% (ISR-A) (weight ratio of PP/ISR-A, 80/20 and 70/30) had a very high impact strength (83 and 100 J/m). The flexural moduli of the blends were 1280 and 1070 MPa, respectively. From the SEM micrographs, it appeared that the PP/ISR-A (70/30) blend is a microphase-separated sytem with a good dispersion of the elastomer. In the dynamic viscoelastic curves of PP/ISR (70/30) blends, the height of the tan δ peak at around −50°C related to the glass transition of polyisoprene segment was the highest in the PP/ISR-A blend, in agreement with the high impact strength.