聚丙烯片晶厚度对受限空间内聚丁烯-1三方晶型形成的影响

The Effect of Lamellar Thickness of iPP on the Formation of Trigonal Modification of PB-1 under Confinement Environment

当聚丁烯-1以小液滴的形式分散在另一种树脂基体中时,会表现出不同的成核路径,即发生“分级结晶”现象.前期研究结果表明将聚丁烯-1以≤20%的比例与聚丙烯进行共混,动力学优先的晶型Ⅱ的成核会受到抑制,使得聚丁烯-1小液滴相界面处更容易发生界面诱导成核形成三方的晶型Ⅰ’.本工作采用自成核与调控聚丙烯等温结晶温度的方法,改变了聚丙烯/聚丁烯-1界面处聚丙烯的片晶厚度,发现聚丙烯的片晶越厚,晶型Ⅰ’的结晶速率越慢,进一步证明了三方晶的形成是由界面处聚丙烯诱导得到.原位广角X射线衍射结果显示,聚丁烯-1的晶型Ⅰ’是否发生重结晶取决于体系中是否存在晶型Ⅱ晶核.纯净的晶型Ⅰ’在升温过程中会直接熔融而不会转化为晶型Ⅱ.

Polybutene-1(PB-1) could behave different crystallization paths when it is finely dispersed into large number of small droplets, which is so-called “fractioned crystallization” phenomenon. According to our previous research, the nucleation of the kinetic favored form Ⅱ could be suppressed when it is blended with polypropylene(i PP) with content lower than 20%. In this situation, trigonal form Ⅰ’ could be generated at the interface of the droplets. Self-nucleation and the manipulation of isothermal crystallization temperature methods are involved to modify lamellar thickness of iPP in this work. These results clearly show that crystallization temperature of PB-1 trigonal crystals is controlled by Tstemperatures. According to Gibbs-Thomson equation, it could be concluded that the nucleation of form Ⅰ’ could be hindered by thicker i PP lamellae. In situ wide angle X-ray diffraction(WAXD) experiment is also conducted, which confirms that the melt and re-crystallization of PB-1 is controlled by the existence of form Ⅱ nuclei generated at low temperature. Pure form Ⅰ’ could melt directly without transforming into form Ⅱ crystals during heating process. Our results shed new lights on understanding the effect of interface on fractionated crystallization.