Shear-induced change of phase morphology and tensile property in injection-molded bars of high-density polyethylene/polyoxymethylene blends

Zhang

et al. 2013

Polymer International

The effect of annealing on the microstructural evolution and mechanical properties of high-density polyethylene parts molded via gas-assisted injection molding was investigated using scanning electron microscopy, differential scanning calorimetry, two-dimensional wide-angle X-ray diffraction and tensile testing. The results indicated that a variety of annealing temperatures could induce considerable variations in the hierarchical structures, crystallinity, lamellar thickness and yield stress of the molded bars. According to these results, the annealing temperatures could be divided into three regions. In the low-temperature region of annealing at 80• C, the spatial variation of the superstructure developed along the thickness direction and mechanical properties of the annealed sample were mainly unchanged and similar to those of the original specimen. At 100 and 120• C, the intermediate temperature region of annealing, the thickness of the crystals, degree of orientation and yield stress of annealed samples were greatly improved. Finally, at 127• C, the degree of orientation decreased and yield stress slightly improved, an indication of the high-temperature annealing region being characterized by increasing melting/recrystallization and causing relaxation of oriented molecular chains. A model is proposed to interpret the mechanism of the annealing treatment of the samples at various temperatures.

Section: Resultssupporting

confidence: 52%

Effects of annealing on the hierarchical crystalline structures and mechanical properties of injection‐molded bars of high‐density polyethylene

Zhang

et al. 2013

Polymer International

“…Consequently, with prolonged gas delay time, the yield stress ascended, indicating a better strength for the longer gas delay time sample. The difference of the values of yield stress were mainly caused by the microstructure and hierarchy structures among the HDPE articles and the yield stress was directly proportional to the area of the oriented zone [38,39]. As discussed from the above SEM results, the area of the sub-skin zone of D3 was the largest and the smallest for D1, which was consistent with the yield stress results.…”

Section: Mechanical Propertiessupporting

confidence: 90%

Role of gas delay time on the hierarchical crystalline structure and mechanical property of HDPE molded by gas-assisted injection molding

et al. 2012

The relationship among the processing parameters, crystalline morphology, and macroscopic properties in injected molded bar becomes very complicated due to existence of temperature gradient and shear gradient along the sample thickness. To enhance the shear strength, gasassisted injection molding (GAIM) was utilized in producing the molded bars. The aim of our research was to explore the relationship between processing conditions and the spatial variation of the hierarchy structure as well as the mechanical properties of high-density polyethylene (HDPE) obtained via GAIM. In our previous work [Wang L, Yang B, Yang W et al (2011) Colloid Polym Sci 289:1661-1671], we found that the enhancement of the gas pressure can remarkably increase the degree of molecular orientation in the HDPE samples, which turns out to improve the mechanical performances of GAIM parts. In this work, the hierarchy structure, orientation behavior, and mechanical properties of molder bars under different gas delay time were investigated using a variety of characterization techniques including rheological experiments, scanning electron microscope, tensile testing, differential scanning calorimetry, and two-dimensional wide-angle X-ray scattering. Moreover, the temperature field during the short shot stage of GAIM process was simulated using an enthalpy transformation approach. Our results indicate that these properties were intimately related to each other, and with prolonged gas delay time, GAIM samples with higher degree of orientation and improved mechanical properties were obtained.

“…However, an interesting phenomenon is observed in the co-continuous structure previously mentioned: there are still LDPE domains in the continuous phase of PLA and vice versa, namely sub-inclusions inside every continuous phase or phase-in-phase structure. The formation of sub-inclusions morphology can be explained by the fact that at phase inversion, a small amount of each phase is enclosed by the newly grown continuous phase [41].…”

Section: Morphologymentioning

confidence: 99%

Structural, morphological and mechanical characteristics of polyethylene, poly(lactic acid) and poly(ethylene-co-glycidyl methacrylate) blends

Djellali¹,

Haddaoui²,

Sadoun

et al. 2013

Iran Polym J

In this work, uncompatibilized and compatibilized blends of low density polyethylene (LDPE) and poly(lactic acid) (PLA) were subjected to several investigations: Fourier transform infrared (FTIR) spectroscopy, morphological analysis and mechanical testing (tensile, impact, microhardness). The copolymer (ethylene-coglycidyl methacrylate) (EGMA) was used as compatibilizer. The percentages of PLA in LDPE/PLA samples ranged from 0 to 100 wt% while the EGMA was added to the blend 60/40 (LDPE/PLA) at concentrations of 2, 5, 7, 10, 15 and 20 parts per hundred (phr). FTIR analysis showed the absence of any interaction between LDPE and PLA, but after addition of compatibilizer, reactions between epoxy groups of EGMA and carboxylic or hydroxyl groups of PLA were confirmed. Tensile and impact tests revealed a loss of ductility of LDPE with the incorporation of PLA, except for the composition 80/20 (LDPE/PLA). However, the addition of 15 phr of EGMA led to the maximum increase in the elongation-at-break (about three times the value of uncompatibilized blend) and in the impact strength, but a marginal improvement was observed for tensile strength. SEM micrographs confirmed that the enhancement of mechanical properties is due to the improvement of the interfacial adhesion between different phases owing to the presence of EGMA. The microhardness values of the different blends (uncompatibilized or compatibilized) were in good agreement with the macroscopic mechanical properties (tensile and impact strengths).