Yao Xuerong, Shi Ying, Tang Yujing, Luo Chunxia, Hou Liping, Ren Minqiao, Zheng Cui, Liu Li-Zhi
SINOPEC (Beijing) Research Institute of Chemical Industry Co., Ltd., Beijing 100013, China.
Advanced Manufacturing Institute of Polymer Industry, Shenyang University of Chemical Technology, Shenyang 110142, China.
Polymers (Basel). 2023 Apr 19;15(8):1940. doi: 10.3390/polym15081940.
The crystallization of polyethylene (PE) blends is a highly complex process, owing to the significant differences in crystallizability of the various PE components and the varying PE sequence distributions resulting from short- or long-chain branching. In this study, we examined both the resins and their blends through crystallization analysis fractionation (CRYSTAF) to understand the PE sequence distribution and differential scanning calorimetry (DSC) to investigate the non-isothermal crystallization behavior of the bulk materials. Small-angle X-ray scattering (SAXS) was utilized to study the crystal packing structure. The results showed that the PE molecules in the blends crystallize at different rates during cooling, resulting in a complicated crystallization behavior characterized by nucleation, co-crystallization, and fractionation. We compared these behaviors to those of reference immiscible blends and found that the extent of the differences is related to the disparity in crystallizability between components. Furthermore, the lamellar packing of the blends is closely associated with their crystallization behaviors, and the crystalline structure varies significantly depending on the components' compositions. Specifically, the lamellar packing of the HDPE/LLDPE and HDPE/LDPE blends is similar to that of the HDPE component owing to its strong crystallizability, while the lamellar packing of the LLDPE/LDPE blend is approximately an average of the two neat components.
由于各种聚乙烯（PE）组分的结晶能力存在显著差异，以及短链或长链支化导致的PE序列分布各异，聚乙烯共混物的结晶是一个高度复杂的过程。在本研究中，我们通过结晶分析分级法（CRYSTAF）研究了树脂及其共混物，以了解PE序列分布，并通过差示扫描量热法（DSC）研究了块状材料的非等温结晶行为。利用小角X射线散射（SAXS）研究了晶体堆积结构。结果表明，共混物中的PE分子在冷却过程中以不同速率结晶，导致了以成核、共结晶和分级为特征的复杂结晶行为。我们将这些行为与参考不相容共混物的行为进行了比较，发现差异程度与组分间结晶能力的差异有关。此外，共混物的片晶堆积与其结晶行为密切相关，并且晶体结构会因组分组成的不同而有显著变化。具体而言，由于HDPE的结晶能力强，HDPE/LLDPE和HDPE/LDPE共混物的片晶堆积与HDPE组分相似，而LLDPE/LDPE共混物的片晶堆积大约是两种纯组分的平均值。
