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- MakaleAçık Erişim2023Scopus SJRQ2Thermal, rheological, and mechanical characterization of compression and injection molded ultra-high molecular weight polyethylene, high density polyethylene, and their blends
Yang, Huaguang; Yilmaz, Galip; Jiang, Jing; Langstraat, Thomas; Chu, Raymond; van Es, Martin; Garg, Priya; Turng, Lih-Sheng
Tensile and impact test samples of ultra-high molecular weight polyethylene (UHMWPE), high-density polyethylene (HDPE), and their blends at various UHMWPE/HDPE weight ratios were prepared via compression molding and injection molding for thermal, rheological, and mechanical characterization. A twin-screw extruder with either a tapered die with air-cooling or a regular die was used to compound and extrude the materials prior to pelletization and molding. To the best of our knowledge, there has been no publication on pelletizing neat UHMWPE using a regular extruder. The differential scanning calorimetry analysis suggested the occurrence of re-crystallization and co-crystallization for all the blends. The rheology test confirmed that all the blends exhibited a solid-like behavior and the degree of compatibility increased with increasing HDPE content in the blends. A strong synergistic effect was observed the blends possessed a higher tensile and impact strength than their neat UHMWPE and HDPE counterparts. The compression molded (95/5) UHMWPE/HDPE samples extruded using the tapered die yielded the highest tensile strength (50.1 MPa), which was about 40% higher than that of the neat UHMWPE samples. The best composition of these blends for compression and injection molded parts is 10% HD and 50% HD, respectively.
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İncele - MakaleAçık Erişim2022Scopus SJRQ1Conventional and Microcellular Injection Molding of a Highly Filled Polycarbonate Composite with Glass Fibers and Carbon Black
Yilmaz, Galip; Devahastin, Apichart; Turng, Lih-Sheng
Conventional solid injection molding (CIM) and microcellular injection molding (MIM) of a highly filled polycarbonate (PC) composite with glass fibers and carbon black were performed for molding ASTM tensile test bars and a box-shape part with variable wall thickness. A scanning electron microscope (SEM) was used to examine the microstructure at the fractured surface of the tensile test bar samples. The fine and uniform cellular structure suggests that the PC composite is a suitable material for foaming applications. Standard tensile tests showed that, while the ultimate strength and elongation at break were lower for the foamed test bars at 4.0–11.4% weight reduction, their specific Young’s modulus was comparable to that of their solid counterparts. A melt flow and transition model was proposed to explain the unique, irregular “tiger-stripes” exhibited on the surface of solid test bars. Increasing the supercritical fluid (SCF) dosage and weight reduction of foamed samples resulted in swirl marks on the part surface, making the tiger-stripes less noticeable. Finally, it was found that an injection pressure reduction of 25.8% could be achieved with MIM for molding a complex box-shaped part in a consistent and reliable fashion.
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İncele - MakaleAçık Erişim2022Scopus SJRQ1Pelletizing ultra-high molecular weight polyethylene (UHMWPE) powders with a novel tapered die and addition of high density polyethylene (HDPE): Processing, morphology, and properties
Yang, Huaguang; Yilmaz, Galip; Jiang, Jing; Xie, Jun; Langstraat, Thomas; Chu, Raymond; van Es, Martin; Garg, Priya; Turng, Lih-Sheng
The extremely high molecular weight and molecular entanglement have rendered ultra-high molecular weight polyethylene (UHMWPE) superior properties. However, poor inter-particle diffusion makes it difficult to pelletize UHMWPE powders for easy processing/handling. A novel tapered die with air cooling was proposed to pelletize UHMWPE and a UHMWPE blend with 5 wt% high-density polyethylene (HDPE) for compression molding and material characterization. The tensile strength of samples prepared with the tapered die outperformed those by the regular die or from virgin powders. The addition of HDPE further improved the tensile strength. Fourier transform infrared spectroscopy (FTIR) revealed little chain scission and the lowest amount of oxidation from the tapered die. Intrinsic viscosity (IV) measurements confirmed the negligible chain scission and showed an increment in IV for the UHMWPE/HDPE blend. Multi-angle light scattering with size-exclusion chromatography (SEC-MALS) indicated no change in the UHMWPE molecular weight distribution, but some crosslinking in the blend. Polarized optical microscopy (POM) showed that the HDPE and extrusion led to a finer UHMWPE domain size and better fusion between UHMWPE and HDPE. The combined effect of enhanced molecular chain diffusion, improved consolidation, and lower oxidation using the tapered die led to 40% improvement of tensile strength for the UHMWPE/HDPE blend.
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