Crystalline morphology of isotactic polypropylene (iPP) in injection molded poly(ethylene terephthalate) (PET)/iPP microfibrillar blends
Crystalline morphology of isotactic polypropylene (iPP) in injection molded poly(ethylene terephthalate) (PET)/iPP microfibrillar blends
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注塑聚对苯二甲酸乙二醇酯 (PET)/iPP 微纤丝共混物中等规聚丙烯 (iPP) 的晶体形态
DOI：
10.1016/j.polymer.2007.01.056
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发表时间：
2007-03
期刊：
影响因子：
4.6
通讯作者：
中科院分区：
文献类型：
--
作者：
通过“狭缝模挤压-热拉伸-淬火”工艺制备了聚对苯二甲酸乙二醇酯(PET)/等规聚丙烯（iPP）原位微纤维共混物，其中PET根据热拉伸比（HSR，模具横截面面积与挤出物横截面面积）获得直径为0.5-15μm的微纤维。采用常规注射成型（CIM）和剪切定向注射成型（SCORIM）分别制备了纯iPP和PET/iPP共混物的注射成型试样。采用小角x射线散射（SAXS）和广角x射线散射（WAXS）研究了剪切应力和不同形状的PET相对注射成型微纤维样品上层结构及其分布的影响。在CIM和SCORIM过程中，剪切（或伸长）流动可以诱导定向薄片（即由shish诱导的串）。羊肉串结构不仅出现在CIM样品的表皮和中间层中，而且出现在SCORIM样品的整个区域中。对于整齐的iPP样品，SCORIM方法可以在内部区域（中间层和核心层）获得更“拉伸”的羊肉串结构，取向度更高；此外，SCORIM可以在中间层和核心层中生长β型晶体，而CIM获得的纯iPP样品只在中间层中出现β型晶体。有趣的是，在PET/iPP共混物中，微原纤维的加入及其长径比只会影响中间层串的取向度，而低长径比的微原纤维的加入可以显著提高串沿流动方向的取向度。然而，对于SCORIM来说，微原纤维的加入对羊肉串的取向程度影响不大，而且它往往会阻碍羊肉串结构的形成，并明显抑制β型晶体的生长。此外，实验还表明，在剪切和压力的协同作用下，β晶体的生长必须受到PET分散相和热条件（冷却速率）等因素的抑制，才能在iPP熔体中成功生长。
The poly(ethylene terephthalate) (PET)/isotactic polypropylene (iPP) in situ microfibrillar blends have been prepared through a “slit die extrusion–hot stretch–quenching” process, in which PET assumes microfibrils with 0.5–15μm in diameter depending on the hot stretching ratios (HSR, the area of the transverse section of the die to the area of the transverse section of the extrudate). The injection molded specimens of virgin iPP and the PET/iPP blends were prepared by conventional injection molding (CIM) and by shear controlled orientation injection molding (SCORIM), respectively. The effect of shear stress and PET phase with different shape on superstructures and their distribution of injection molded microfibrillar samples were investigated by means of small angle X-ray scattering (SAXS) and wide angle X-ray scattering (WAXS). The shear (or elongational) flow during CIM and SCORIM can induce oriented lamellae (i.e. kebabs induced by shish). The shish-kebab structure appears not only in the skin and intermediated layers of CIM samples, but also in the whole region of SCORIM samples. For the neat iPP samples, a more “stretched” shish-kebab structure with higher orientation degree can be obtained in the interior region (intermediate and core layers) by the SCORIM method; moreover, the SCORIM can result in the growth of β-form crystal both in intermediate layer and in core layer, which only appears in intermediate layer of the neat iPP samples obtained by CIM. For the PET/iPP blends, interestingly, the addition of microfibrils as well as their aspect ratios can affect the orientation degree of kebabs only in the intermediate layers, and the addition of microfibrils with a low aspect ratio can bring out a considerable increase in the orientation degree of kebabs along the flow direction. However, for the SCORIM, the addition of microfibrils seems to be a minor effect on the orientation degree of kebabs, and it tends to hamper the formation of a more “stretched” shish-kebab structure and suppresses the growth of β-form crystal distinctly. Furthermore, It appears from experiment that γ-form crystals can grow successfully in this oriented iPP melt with the synergistic effect of shear and pressure only when the growth of β crystals can be restrained by some factors, such as the PET dispersed phase and thermal conditions (cooling rate).
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