Su Run, Wang Ke, Zhang Qin, Chen Feng, Fu Qiang, Xu Wenfei, Na Bing
Department of Polymer Science & Materials, Sichuan University, State Key Laboratory of Polymer Materials Engineering, Chengdu, 610065, PR China.
J Phys Chem B. 2009 May 28;113(21):7423-9. doi: 10.1021/jp900625b.
In this article, molecular orientation of crystalline and amorphous phases of both linear low-density polyethylene (LLDPE) and isotactic polypropylene (iPP) and epitaxy in the LLDPE/iPP blends prepared via dynamic packing injection molding have been investigated with the aid of polarized Fourier transform infrared (FTIR) spectroscopy and two-dimensional X-ray scattering (2D-WAXS). In LLDPE-rich blends, LLDPE was oriented along the shear flow direction, and iPP kept very low orientation. No epitaxial growth between LLDPE and iPP was observed. However, for the blends with LLDPE content less than 50 wt %, where iPP was the matrix and LLDPE formed the droplets, iPP was highly oriented along shear flow direction and LLDPE epitaxially grew onto iPP. The contact planes were (100)LLDPE and (010)iPP, and LLDPE molecules were about 50 degrees apart from the shear direction. The epitaxy fraction in LLDPE/iPP blends could be tentatively calculated from the values of orientation function of the LLDPE crystalline a-axis (fa) and that of crystalline b-axis (fb). Both tensile strength and tensile modulus decreased with the increase of LLDPE composition, indicating they were composition dependent, though shear-induced orientation and epitaxial crystallization might play some role. The impact strength of the blend samples reached a plateau in the LLDPE composition range of 20-50%, due to the contribution of orientation and epitaxy.
在本文中，借助偏振傅里叶变换红外光谱（FTIR）和二维X射线散射（2D-WAXS），研究了通过动态保压注塑制备的线性低密度聚乙烯（LLDPE）和等规聚丙烯（iPP）的结晶相和非晶相的分子取向以及LLDPE/iPP共混物中的外延生长。在富含LLDPE的共混物中，LLDPE沿剪切流动方向取向，而iPP的取向程度很低。未观察到LLDPE和iPP之间的外延生长。然而，对于LLDPE含量小于50 wt%的共混物，其中iPP为基体，LLDPE形成液滴，iPP沿剪切流动方向高度取向，LLDPE外延生长在iPP上。接触面为（100）LLDPE和（010）iPP，LLDPE分子与剪切方向成约50度角。LLDPE/iPP共混物中的外延分数可以根据LLDPE结晶a轴（fa）和结晶b轴（fb）的取向函数值初步计算。拉伸强度和拉伸模量均随LLDPE组成的增加而降低，表明它们与组成有关，尽管剪切诱导取向和外延结晶可能起了一定作用。由于取向和外延的作用，共混物样品的冲击强度在LLDPE组成范围为20-50%时达到平稳。
