Summary: 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.
Representative stress‐strain curves for PE10, PE15, PE17.5, and PE20. 相似文献
Summary: Polycarbonate (PC)/high density polyethylene (HDPE) in situ microfibrillar blends were fabricated by a slit die extrusion, hot stretching, and quenching process. Despite PC and HDPE having a high viscosity ratio, which is usually disadvantageous to fibrillation, the morphological observation indicated that the blends had well‐defined PC microfibrils. The size and amount of the PC fibrils were nonuniform through the thickness of the extrudate, and were also affected by the PC concentration and hot stretch ratio. There were coarse and dense fibrils in the core zone, while these fibrils became finer and reduced in number toward the surface. The melt flow rate (MFR) of the PC/HDPE microfibrillar blend decreased with the increase of PC concentration, but increased with the larger hot stretching rate (or hot stretching ratio, HSR). Besides, it was found that the fibrillar blend had better flowability than the common blend with spherical particles at the same PC concentration. Temperature was also an important factor influencing the MFR due to the temperature dependence of PC and HDPE viscosity, and the PC phase morphology. The PC microfibrils could not be preserved beyond 230 °C and transformed into spherical particles. The rheological behaviors at various shear rates were studied by capillary rheometer. The orientation of PC fibrils and HDPE molecules with higher shear rate led to a decrease in the viscosity of microfibrillar blend. The data obtained in this study can help construct the technical foundation for recycling and utilization of PC and HDPE waste by manufacture of microfibrillar blends in future work.
SEM micrograph of the PC/HDPE microfibrillar blend. 相似文献
