Temperature dependence of lamellae orientation of a branched low molecular weight polyethylene/ultrahigh molecular weight polyethylene blend film under a controlled temperature gradient

Temperature dependence of lamellae orientation of a branched low molecular weight polyethylene (B-LMWPE)/ultra-high molecular weight polyethylene (UHMWPE) blend film has been studied by using transmission electron microscopy (TEM), two-dimensional wide angle X-ray diffraction (2D-WAXD) and two-dimensional small angle X-ray scattering (2D-SAXS). The film was prepared by solution casting under a controlled temperature gradient (T-gradient). TEM and X-ray scattering observations demonstrate that no clear lamellar crystal exists in B-LMWPE-rich phase while a large amount of lamellae are found in UHMWPE-rich phase. And these lamellae show a significant temperature dependence of preferred orientation. Results of 2D-WAXD and 2D-SAXS indicate that the lamellae stack regularly and preferentially parallel to the film surface at lower temperatures. At the temperatures near to the transition region, namely near to the gelation temperature, a part of the lamellae become to orient in an irregular way. At higher temperatures, almost all of the lamellae preferentially orient along the normal to the film surface and they randomly distribute around that direction. Itʹs worth noting that the preferred orientation of the lamellae may influence the drawability of B-LMWPE/UHMWPE blend films.