Polyamide-rubber blends: microscopic studies of the deformation zone

The morphology of injection moulded samples of polyamide-polybutadiene blends (85.15) with an average particle size of 0.3 pm was studied. The samples were fractured in a notched tensile test at crosshead speeds of 10m4 and 1 rns-’ and the structure of the deformation zone was studied using various techniques: polarized light microscopy, scanning electron microscopy, transmission electron microscopy on stained cut samples and carbon replicas, and selected area electron diffraction transmission electron microscopy. The deformation zone of samples tested at 10d4 m SC’ was found to consist of two layers. Far from the fracture surface a layer was observed with more or less round cavities and with cavities in the rubber particles, while near the fracture surface a layer with strongly deformed cavities (length/diameter ratio of 5-10) could be seen. In the samples tested at 1 m s-’ the deformation zone was found to have three layers. In addition to the two previous layers an extra layer next to the fracture plane was found. This layer was 2-3 pm thick with round rubber particles and no orientation of the matrix material. This indicates that, at the high deformation speed of the test, relaxation in the melt took place, suggesting that the material around the crack tip was molten during fracture.