Shear-Induced Precursor Relaxation-Dependent Growth Dynamics and Lamellar Orientation of β-Crystals in β-Nucleated Isotactic Polypropylene
Shear-Induced Precursor Relaxation-Dependent Growth Dynamics and Lamellar Orientation of β-Crystals in β-Nucleated Isotactic Polypropylene
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DOI：
10.1021/acs.jpcb.5b01480
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发表时间：
2015-04-30
影响因子：
3.3
通讯作者：
Li, Zhong-Ming
中科院分区：
文献类型：
--
作者：
Chen, Yan-Hui;Fang, Du-Fei;Li, Zhong-Ming
虽然剪切流场和β-成核剂（β-NAs）可以以有效的方式分别诱导等规聚丙烯（iPP）中β-晶体的形成，但我们以前遇到过困难，当应用这两个因素时，由于α-和β-晶体的竞争性生长，难以获得丰富的β-晶体。在当前的研究中，为了诱导形成高牵引力的β-晶体，提出了在施加剪切流场之后但在冷却以使β-成核的iPP结晶之前引入松弛过程的策略。取决于剪切诱导取向前体的弛豫状态，确实形成了具有精细取向形态的丰富的β-晶体。生产这些晶体的关键在于部分溶解的剪切，诱导取向的前体，作为松弛过程的能力，通过诱导形成针状β-NAs产生β-晶体的结果。因此，β-晶体的含量随着弛豫时间逐渐增加，而整体结晶动力学逐渐降低。此外，需要更多的时间的β-相的含量增加到（最大）值观察到在静态结晶比流动结晶动力学的影响被完全消除。观察到定向β-纤维的c轴垂直于而不是平行于针状β-NA的纤维轴，这首先由获得的独特的小角X射线散射图案证明。松弛过程的重要性表现在调节剪切、β成核iPP中取向β晶体的含量和形态，从而控制iPP的结构和性能。
Although a shear flow field and beta-nucleating agents (beta-NAs) can separately induce the formation of beta-crystals in isotactic polypropylene (iPP) in an efficient manner, we previously encountered difficulty in obtaining abundant beta-crystals When these two factors, were applied:due to the competitive growth of alpha- and beta-crystals. In the current study, to induce the formation of a high traction of beta-crystals, a strategy that introduces a relaxation process after applying a Shear flow field but before cooling to crystallize beta-nucleated iPP was proposed. Depending on the relaxation state of the shear-induced oriented precursors, abundant beta-crystals with a refined orientation morphology were indeed formed. The key to producing these crystals lay in the partially dissolved shear, induced oriented precursors as a result of the relaxation process's ability to generate beta-crystals by inducing the formation of needlelike beta-NAs. Therefore, the content of beta-crystals gradually increased with relaxation time, whereas the overall crystallization, kinetics progressively decreased. Moreover, more time was required for the content of the beta-phase to increase to the (maximum) value observed in quiescent crystallization than for the effect of flow on crystallization kinetics to be completely eliminated. The c-axis of the oriented beta-lamellae was observed to be perpendicular, rather than parallel, to the fiber axis of the needlelike beta-NAs, as first evidenced by the unique small-angle X-ray scattering patterns,obtained., The significance of the relaxation process was manifested in regulating the content and morphology of oriented beta-crystals in sheared, beta-nucleated iPP and thus in the structure and property manipulation of iPP.