The Influence of Short Chain Branch on Formation of Shear Induced Crystals in Bimodal Polyethylene at High Shear Temperatures

Libin Jiang, Minfang An, Feng Wu, Weijun Miao, Zongbao Wang, Yaopeng Zhang, Benjamin S. Hsiao

Index: 10.1016/j.eurpolymj.2018.03.036

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Abstract

The shear-induced crystallization of bimodal polyethylene with high molecular weight fraction having different content of short chain branch at low shear rate and high temperatures was investigated by in-situ small-angle X-ray scattering (SAXS) and wide-angle X-ray diffraction (WAXD) techniques. SAXS and WAXD results indicate that shish crystals form at different shear temperatures of 139 and 136 °C, subsequently kebab crystals and oriented lamellae form at the isothermal crystallization temperature of 121 °C. The presence of short chain branch significantly promotes the formation of shish-kebab crystals owing to the increase of the relaxation time, but overmuch short chain branch impedes the formation of shish-kebab crystals and form more oriented lamellae. These evidences clearly indicate that even though the existence of short chain branch impedes the crystallizability, it can still effectively promote the formation of shish-kebab crystals at high shear temperatures.