Morphology Dependent Double Yielding in Injection Molded Polycarbonate/Polyethylene Blend

Abstract

Summary: Polycarbonate (PC)/polyethylene (PE) blend was injection molded at different molding temperatures. The morphological observation by scanning electronic microscope (SEM) indicated that the sample molded at 190 °C contained only uniformly dispersed spherical PC particles. The samples molded at 230 and 275 °C had a typical skin‐core structure, and there were many injection‐induced PC fibers in the subskin. While the sample molded at 190 °C had the usual stress‐strain behavior, the samples obtained at 230 and 275 °C showed apparently double yielding behavior. It was suggested that the double yielding points were morphology‐dependent. The first one was the result of the yielding of PE at low strain, and the second one was caused by the yielding of the PC fibers. Moreover, it is the frictional force in the interfaces between PC and PE that transferred the stress to the PC fibers, hence giving rise to the reinforcement of PE by PC.Stress‐strain curves of PC/PE blends injection molded at various temperatures showing first (I) and second (II) yielding points.magnified imageStress‐strain curves of PC/PE blends injection molded at various temperatures showing first (I) and second (II) yielding points.

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

“…The neat PE and PE5 are very ductile and the ultimate ruptures have not been achieved due to the limit of the distance between two crossheads. They shows similar stress‐strain behaviors except a slight higher yield stress for PE5, indicating some reinforcement of PC on PE 30. In addition, PE5 displays a typical single yield behavior as neat PE does.…”

“…Typical anisotropic skin‐core structures were observed for all the blends as in many other injection‐molded blends,33–42 in which the dispersed PC particles exhibit different shapes and sizes in the core, sub‐skin, and intermediate layers. Although the phase viscosity ratio (ratio of viscosity of the dispersed phase to that of the matrix) is more than one,43 amorphous PC particles can deform under strong shear and elongational fields 30. In the core layer, most PC particles remained spherical in shape except a few slightly deformed ones, as shown in Figure 2.…”

“…The resins used are HDPE and PC. Their properties and characteristics have been summarized elsewhere 30. In this study, The PC/HDPE blends with PC contents ranging from 0 to 45 wt.‐% were prepared and injection molded into samples for morphological observation and tensile testing.…”

“…In our previous investigation,30–32 the double yielding phenomenon was detected in an injection‐molded polycarbonate (PC)/high‐density polyethylene (HDPE) blend with 15 wt.‐% PC. Obviously, the mechanisms mentioned above cannot be applied to interpret the double yielding in the immiscible PC/HDPE blends because of the great morphology difference in the two systems.…”

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

“…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. It is suggested that a similar reason may be proposed for the all‐PP composites, where the copolymer matrix may be responsible for the first yielding and the reinforcing PP homopolymer responsible for the second yield point.…”