NMR imaging study of stress-induced material response in rubber modified polyamide 6

Abstract

The fracture behavior of two different types of extruded polyamide 6 (PA6)/maleic anhydride grafted ethylene-propylene (EPM-g-MA) blends is examined by magnetic resonance imaging (MRI). TEM micrographs demonstrate a clear difference in morphology: where one blend type contains pure rubber particles dispersed in the PA6 matrix, the other type contains PA6 occlusions within the rubber particles and is significantly more tough. MRI experiments on notched specimens of both blend types under critical load reveal a gradual increase of rubber cavitation toward the crack tip which can be quantified on the basis of the localized proton spin density. A clear relation is observed between the toughness and the dimensions of the plastic zone: the toughest blend has a significant more extended plastic zone ahead of the crack tip. The enhanced toughness of the blends with occlusions can be attributed to a more pronounced delocalization of energy, which is suggested to result from a different deformation mechanism in which the load bearing capacity of the rubbery chains plays an important role.