Dynamic mechanical and impact properties of PP/SEBS blend

Abstract

AbstractStudies on impact behaviour of the blend of isotactic polypropylene (PP) with styrene‐b‐ethylene‐co‐butylene–b‐styrene triblock copolymer (SEBS) in the composition range 0–25 wt % SEBS at three temperatures, viz., ambient, −30°C, and −190°C, are presented. Dynamic mechanical properties on a torsion pendulum in the temperature range −100−100°C are also studied for this blend at various compositions. Scanning electron microscopic studies of the impact‐fractured surfaces are presented to illustrate the differences in the mode of fracture at the three temperatures of impact tests. Choice of the three temperatures for impact tests was such that the effect of shear yielding mechanism of toughening of PP at ambient temperature remains suppressed at −30°C, whereas at the lowest temperature (i.e., −190°C) the elastomeric role of the inclusion SEBS is suppressed. The observed considerably large difference in impact toughening at ambient temperature and at −;30°C seems not entirely accountable by the prevalence of shear yielding or crazing mechanisms in the respective temperature regions. A third mechanism, viz., viscoelastic energy dissipation, is invoked to account for the observed large difference of impact toughening at these two upper temperatures. Correlation of peak area of dynamic mechanical loss peaks occurring below the impact test temperature with the impact strength is also shown. This suggests greater significance of viscoelastic energy dissipation mechanism in the toughening of this blend at ambient temperature than at −30°C.