Double yielding in injection-molded polycarbonate/polyethylene blends: Composition dependence

A fiber-dependent double yielding phenomenon was recently observed in a structurally different blend, PC/HDPE, in which the first yield point is yielding of HDPE, and the second is caused by the yielding of injection-induced PC fibers. The present study described the composition dependence of the double yielding in PC/HDPE blends with PC contents ranging from 0 to 45 wt.-%. Morphology observation indicated that the injection-molded PC/HDPE blends displayed a typical skin-core structure with more or less injection-induced elongated PC particles in the sub-skin layers, and spherical PC particles in the core layers. Stress-strain curves indicated that the blends with PC contents from 10 to 20 wt.-% exhibit double yielding behavior and the cold drawing zone after the second yield point shortens with increasing PC content. The blends with too low- or too high-PC contents exhibited only one yield point. Scanning electronic microscope micrographs of the blend with 15 wt.% PC showed that when the strain was beyond the first yield point the PC fibers notably yielded and even were broken, which served as an evidence that the yielding of PC phase was responsible for the second yielding. The origin of the composition dependence of the double yielding was discussed in detail through the interfacial stress transfer.