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Keywords: polypropylene ; toughening ; beta phase Reference LTC-ARTICLE-2002-005doi:10.1016/S0032-3861(02)00135-0View record in Web of Science URL: http://www.sciencedirect.com/science/journal/00323861 Record created on 2006-06-26, modified on 2016-08-08

The influence of cure temperature, composition and chemical structure on the morphology resulting from chemically induced phase separation has been investigated for different epoxy functionalized dendritic hyperbranched polymers blended with diglycydil bisphenol A and an aliphatic diamine. The cure temperature window chosen highlighted the influence of both the kinetics of phase separation and the thermodynamics of mixing on the final morphology. In relatively immiscible blends and at low cure temperatures, phase separation occurred immediately after mixing. However, increasing the miscibility by raising the temperature or modifying the chemistry of the dendritic hyperbranched polymers resulted in a homogeneous mixture prior to cure, and at low modifier contents, cure induced phase separation was thought to be associated with homogeneous nucleation of modifier rich spherical domains. Complete suppression of the phase separation could be achieved combining the effects of modifier solubility and reaction kinetics, by increasing the catalyst content in the most compatible blends.

The fracture behaviour of an isotactic polypropylene and an impact modified isotactic polypropylene containing 15 wt% of ethylene–propylene rubber has been investigated at test speeds of between 0.1 mm/s and 14 m/s, using compact-tension specimens. The homopolymer displayed a ductile–brittle transition as the test speed was increased, which was associated with a transition from shear deformation to crazing. Deformation of the modified polypropylene was characterized by stable crack propagation over the whole range of test speeds, stress-whitening at the crack tip and, at lower speeds, by the formation of extensive shear lips on the fracture surfaces. An observed increase in the size of the crack tip damage zone with test speed suggested a transition from plane stress to plane strain conditions. This is discussed in terms of a simple model, which takes into account the variation of the sample stress state as the test speed increases.