Oriented crystallization of long chain branched polypropylene induced by step-shear deformation in pre-crystallization regime
Oriented crystallization of long chain branched polypropylene induced by step-shear deformation in pre-crystallization regime
复制标题
DOI：
10.1016/j.polymer.2017.02.005
复制
发表时间：
2017-05
期刊：
影响因子：
4.6
通讯作者：
S. Kitade;Hideo Kurihara;Kazuo Asuka;Katsuno Satoshi;I. Akiba;K. Sakurai
中科院分区：
文献类型：
--
作者：
S. Kitade;Hideo Kurihara;Kazuo Asuka;Katsuno Satoshi;I. Akiba;K. Sakurai
通过同步时间分辨广角和小角x射线散射（WAXS和SAXS）测量，研究了长链超支化聚丙烯（LCB-PP）在预结晶过程中剪切变形诱导的定向结晶过程，并与线性PP （L-PP）进行了比较。在LCB-PP中，在预晶区应用阶梯剪切诱导了高取向结晶；相反，L-PP的晶片有轻微的取向。LCB-PP还形成了a轴沿剪切方向取向的子片层。阶梯剪切作用下LCB-PP的定向结晶与其初级结构的关系如下：由于支链的存在增加了LCB-PP链的弛豫时间，使得LCB-PP链在阶梯剪切变形后保持的时间更长。此外，LCB-PP的分支点有助于点状前体的结晶形成。因此，这些点状前体沿着剪切方向排列并转化为线状前体。这导致了高度定向的羊肉串结构的迅速形成。此外，由于LCB-PP中导致子薄片形成的短链被共价拴住在串部分上，因此子薄片的生长受到空间限制，导致LCB-PP中子薄片的a轴沿剪切方向取向。
The oriented crystallization of long chain hyper-branched polypropylene (LCB-PP) induced by shear deformation in the pre-crystallization regime was investigated through simultaneous time-resolved synchrotron wide-angle and small-angle X-ray scattering (WAXS and SAXS) measurements and compared with that of linear PP (L-PP). Highly oriented crystallization was induced in LCB-PP by the application of a step-shear in the pre-crystalline regime; in contrast, the crystalline lamellae of L-PP were slightly oriented. In addition, LCB-PP formed daughter lamellae whose a-axis was oriented along the shear direction. The oriented crystallization of LCB-PP induced by the step-shear was related to its primary structure in the following manner. Since the existence of branched chains increased the relaxation time of the LCB-PP chains, the elongated LCB-PP chains were remained for longer after the step-shear deformation. In addition, the branching points of LCB-PP aided the formation of point-like precursors for crystallization. Consequently, these point-like precursors were arrayed along the shear direction and transformed into thread-like precursors. This caused the rapid formation of highly oriented shish-kebab structures. Furthermore, since short chains that caused the formation of daughter lamellae were covalently tethered to the kebab parts in LCB-PP, the growth of the daughter lamellae were spatially restricted owing to which the a-axis of the daughter lamellae in LCB-PP was oriented along the shear direction.