2017 Volume 66 Issue 1 Pages 29-34
Mechanical properties at low temperature (-180℃~RT) of polyethylene (PE) were investigated. Charpy impact strength of Ultra-high molecular weight polyethylene (UHMWPE) was much higher than that of HDPE. From dynamic mechanical analysis result, they had the γ relaxation at around -120 ℃, but the intensity of the peak of UHMWPE was much higher than that of HDPE. Moreover, when taking the result that they had almost the same degree of the crystallinity into consideration, mechanical properties at low temperatures of PE were influenced by not only the molecular weight but also the molecular motion at low temperature regions of PE. When the samples were prepared by stacking inflation-films of UHMWPE, HDPE, and their blends, it was found that Stacking Inflation Blend-film sample (SIB) had the better mechanical properties at low temperatures in comparison with the other blend samples, especially for Direct Molding sample (DM). This result indicated that mechanical properties at low temperatures of PE were influenced by the preparation methods of the samples. Furthermore, the rheological dissipation energy derived from the γ relaxation of the samples showed the good liner correlation with the Charpy Impact strength at -100 ℃, indicating that the molecular motion of PE at low temperature region affected the mechanical properties of PE. Finally, it was found that UHMWPE which had the highest mechanical properties at low temperature region had the smallest anharmonicity of all samples, and HDPE which had the poorest mechanical properties at the same region had the highest anharmonicity, and SIB and DM samples had the intermediate values of them. Therefore, it was deduced that anharmonicity of a polymer could also affect the mechanical properties at low temperatures of the polymers.
