Abstract
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.
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