The effect of weld-lines on the morphology and mechanical properties of amorphous polyamide/poly(ethylene- ran-propylene) blend with various amounts of an in situ compatibilizer

Abstract

The effect of weld-lines on the morphology and mechanical properties of 80/20 (wt/wt) amorphous polyamide and poly(ethylene- ran-propylene) (EPR) blend with various amounts of maleic anhydride grafted EPR (EPR-M) as an in situ compatibilizer was investigated. In this blend, the effect of crystallization on weld-line strength was completely excluded; thus mechanical properties depend upon the blend morphology and interfacial adhesion strength. As the amount of EPR-M was increased, the dispersed domain sizes were reduced, whereas the shear modulus and the viscosity of the blend increased. We have shown that the injection-molded blend without weld-lines exhibited traditional skin–core morphology. Namely, the dispersed domains at sub-skin layers are strongly elongated toward the flow direction, while those at core regions are not deformed. The sub-skin layer of specimens without weld-lines was significantly reduced with increasing amount of EPR-M. For specimens with weld-lines, the dispersed domains of the blend without EPR-M at sub-skin layer are elongated perpendicularly to the flow direction. However, with increasing EPR-M content, very fine and isotropic morphology is observed. Both the elongation at the break and Izod impact strength of the weld-specimen increased steadily with increasing amount of EPR-M. But these values are still lower than those of non-weld specimens, even for blends with large amounts of EPR-M. This is because some dispersed domains in weld specimens are elongated perpendicularly to the tensile (or impact) direction. However, the ‘V-notch’ found at the weld-line of specimens does not affect the mechanical properties.