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.

Deformation, yield and fracture of elastomer‐modified polypropylene

“…Moreover, a larger elastic shear modulus of the rubber, by means of a slight crosslink, due to either physical or chemical constraints, enhances the shear properties of the rubber and therefore is also important in band stabilization. 1 This prediction is confirmed by the experimental findings of Adriaensens and coworkers 25 in rubber modified nylon. They found that the blend in which the rubbery phase had superior elastic properties, due to physical and topological constraints, also showed enhanced toughness and a more extended plastic zone ahead of the crack tip.…”

“…1 Recent experimental papers support this theoretical prediction. 25,26 In particular, a NMR imaging study of stress-induced material response carried out by Adriaensens and coworkers 25 on rubber modified nylon has shown that the toughness of the material is strongly related to the load bearing capacity of the cavitated rubber particles in dilatational bands. In fact, after cavitation, the biaxial stretching of the rubbery layer attached to the cavity walls 26 can stabilize the growing dilatational band by absorbing elastic energy, delaying strain localization and premature failure.…”

Influence of epoxy resin on the properties of maleic anhydride functionalized acrylonitrile–butadiene–styrene copolymer toughened polyamide 6 blends

“…It exhibits a high resistance to crack initiation, which imparts a high unnotched impact toughness. However, its low resistance to crack propagation leads to embrittlement in the presence of a notch 2, 3. Core–shell polymers, such as acrylonitrile–butadiene–styrene copolymer (ABS), methyl methacrylate–butadiene–styrene copolymer, and acrylic impact modifiers, are one kind of important impact modifier for PA6 4–6.…”

Influence of the phase morphology on the molecular orientation at the crack tips in rubber‐modified nylon 6: A micro Fourier transform infrared study

“…Despite some controversies in the aforementioned toughening mechanisms, extensive plastic deformation in the matrix without the initiation of any premature fracture processes is crucial for achieving superior toughness in rubber‐modified semicrystalline polymers. The role of the dispersed rubber phase is expected to induce an overall plastic deformation in the entire matrix rather than a localized one 13, 14. To date, evidence of plastic deformation at the crack tips has been indirectly deduced from the undulate fracture surface or from the elongated rubber particles embedded in the matrix, mostly by electron microscopy techniques 9, 15, 16.…”

“…The main problem for the in situ detection of plastic deformation events at the crack tips arises from the extreme deformation gradient close to the crack tips, which can only be resolved by some specific experimental methods with high spatial resolution. In fact, position‐resolved X‐ray experiments and NMR imaging have been developed to study the structural evolution in the bulk ahead and near the crack tips in poly(vinylidene fluoride),17 poly(styrene‐ co ‐acrylonitrile‐ co ‐butadiene),18 and rubber‐modified nylon 6 14. In our previous study,19 alternatively, we demonstrated that spatially resolved micro Fourier transform infrared (micro‐FTIR) is powerful for probing the molecular orientation, especially in the amorphous phase at crack tips, which is advantageous over other techniques, such as X‐ray scattering measurements.…”