The morphology and microstructure as well as their forming mechanism of the parts in microinjection molding process are critical. In this work, the coupling effect of scale factor and injection speed on the morphology of the microparts was systematically investigated. Neat isotactic polypropylene parts with thicknesses of 1 mm, 200 μm, and 100 μm were molded at different injection speeds. Polarized light microscope and wide‐angle X‐ray diffraction were used to inspect the microstructures along the sample thickness. In this way, three kinds of typical morphology were observed in the parts, including typical skin‐core structure for the parts with the thickness of 1 mm, noncore shear layer structure for the parts with the thickness of 200 μm, and special skin‐core structure with large fraction of columnar crystal for the parts with the thickness of 100 μm. Most interestingly, it was intuitively and straightforward found that the wall slip occurs when the injection speed exceeds a certain value. Specifically, opposite morphological change trend can be obtained when the parts were molded at different levels of injection speeds. Based on these experimental observations, the formation mechanism was proposed to interpret the morphological evolution. Our work provides a new insight for better understanding the morphology evolution mechanism for microinjection molding parts.

中文翻译：

---

尺度效应和注射速度对微注射成型等规聚丙烯零件形态和结构的影响

显微注射成型过程中零件的形态，微观结构及其形成机理至关重要。在这项工作中，系统地研究了比例因子和注射速度对微零件形态的耦合作用。以不同的注射速度模制厚度为1 mm，200μm和100μm的整齐的等规聚丙烯零件。偏光显微镜和广角X射线衍射用于检查沿样品厚度的显微结构。这样，在零件中观察到了三种典型的形态，包括厚度为1 mm的零件的典型皮芯结构，厚度为200μm的零件的无芯剪切层结构，对于厚度为100μm的零件，采用特殊的皮芯结构，其中含有大量的柱状晶体。最有趣的是，直观直观地发现，当注射速度超过一定值时，就会发生壁滑。具体而言，当零件以不同的注射速度水平成型时，可以获得相反的形态变化趋势。基于这些实验观察，提出了形成机理来解释形态演化。我们的工作为更好地了解显微注射成型零件的形态演变机理提供了新的见识。当零件以不同的注射速度成型时，可获得相反的形态变化趋势。基于这些实验观察，提出了形成机理来解释形态演化。我们的工作为更好地了解显微注射成型零件的形态演变机理提供了新的见识。当零件以不同的注射速度成型时，可获得相反的形态变化趋势。基于这些实验观察，提出了形成机理来解释形态演化。我们的工作为更好地了解显微注射成型零件的形态演变机理提供了新的见识。