Double Yielding in Injection‐Molded Polycarbonate/Polyethylene Blends: Composition Dependence

Abstract

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.imageRepresentative stress‐strain curves for PE10, PE15, PE17.5, and PE20.

Mechanical Characterisation of a New Biodegradable Film

“…It is expected that the difference in mechanical behaviour between the new biodegradable material and the traditional LDPE films become more and more significant as the volume fraction of biodegradable component increases. Such a behaviour is consistent with other studies reported in literature [23].…”

“…For each quantity, the table shows the values averaged over the different experimental tests and the corresponding standard deviations. The data listed in the table are consistent with values indicated in literature for polyethylene blends [20, 23, 29, 30] although those reference values are highly dispersed because of the wide variety of combinations between material compositions and testing conditions analyzed in literature.…”

“…The extensometer field of view is 500 mm, hence large enough to monitor the amount of elongation at break expected for the tested specimens. Data on low density and high density polyethylene blends reported in literature indicate that the elongation at break, at room temperature, ranges between 150 and 800% based on the blend composition [20, 23, 29, 30]. This means that the expected maximum distance between the target points sketched in Figure 6 is 450 mm, which is well inside the measure range of the extensometer used in this research.…”

Flexural Creep Behavior of Unidirectional and Cross‐Ply All‐Poly(propylene) (PURE®) Composites

“…Double yielding behavior has been widely recognized for semicrystalline polymers like PE and its blends. The mechanism of double yielding is related to the microstructure of the polymer and there exist three plausible mechanisms to explain this behavior 39. Li et al detected a double yielding behavior in structurally different injection molded polycarbonate/high‐density polyethylene blends based on their morphology, where the first yield point was due to the high‐density polyethylene and the second yield point was attributed to the injection molded polycarbonate fibers 40–42.…”

Crystallinity variations in the double yield region of polyethylene

“…Double yielding has also been reported for other semicrystalline polymeric systems such as poly(tetramethylene terephthalate) and its copolymers, 17 polyamide 6 and glass bead filled polyamide 6 composites, 18,19 polybutylene terephthalate, 20 polypropylene, 11 polycarbonate/polyethylene blends. 21 It has been thought for a long time that the double yield phenomenon is a characteristic of semicrystalline polymers. However, the existence of double yielding in nanostructured amorphous polymer was reported recently.…”