Phase morphology of injection‐molded blends of nylon‐6 and polyethylene and comparison with compression molding

An experimental study is presented of the development of phase morphology in injection and compression molding of 80/20 and 60/40 nylon-6/polyethylene blends and its evolution during annealing. The phase morphology of the compression-molded part is isotropic, while that of both screw and ram injection-molded parts is both heterogeneous and anisotropic through the cross section. In the injection-molded parts, the morphology exhibits its greatest level of isotropy in the core and becomes increasingly anisotropic approaching the mold wall (through the thinnest cross section); i.e., the 2 direction. There is an intermediate position of maximum anisotropy. Sections made in various directions indicate that the dispersed phase forms platelets oriented in the plane of the machine and width directions. The position of maximum anisotropy seems to represent a frozen layer thickness that increases with decreasing mold temperature and with decreasing injection rate into the mold. Annealing studies show coalescence in both compression- and injection-molded bars. The greatest coalescence occurs in the injection-molded parts near the positions of greatest anisotropy of morphology. This suggests that coalescence is associated with collisions between dispersed phase globules as their sphericity increases.