The injection molding of ultra-high molecular weight polyethylene (UHMWPE) large industrial products has always been a significant challenge. This study demonstrated that the addition of bimodal polyethylene (BPE) can reduce the melt viscosity of UHMWPE, enabling the injection molding of UHMWPE products with high-performance, large size, and complex shapes. Detailed analyses including microbeam wide-angle X-ray diffraction (WAXD)/small-angle X-ray scattering (SAXS), differential scanning calorimeter (DSC), and scanning electron microscope (SEM) were conducted to investigate the crystal structural differences across various regions of UHMWPE products with different BPE contents. This study revealed that those products with low BPE content exhibited larger lamellar crystal sizes and higher tensile strength, albeit with poor microstructure uniformity, resulting in low elongation at break. Conversely, products with high BPE content had more uniform microstructures but low degrees of crystal perfection, significantly improving elongation at break. Impact performance tests revealed that adding BPE did not damage the mechanical properties of UHMWPE, showing an ultra-high impact strength of 500 kJ/m2. Furthermore, this study identified the significant effect of the complex flow field and molecular weight fraction of BPE on the crystal structure of the products. At low BPE concentrations, the low molecular weight portion of BPE predominated in the plasticizing effect during injection mold. Under weak flow conditions, this increased molecular chain relaxation in UHMWPE, making it difficult to maintain the oriented structure. Conversely, strong flow conditions promoted the formation of the oriented structure. However, at high BPE concentrations, the high molecular weight portion of BPE predominantly hindered the movement of UHMWPE, resulting in chain entanglement that does not improve significantly. In this context, the differences in the injection-molded samples under weak and strong flow conditions are minimal.

中文翻译：

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大型工业超高分子量聚乙烯产品的注塑成型：双峰聚乙烯对结构和机械性能影响的微束 WAXD/SAXS 研究


超高分子量聚乙烯 （UHMWPE） 大型工业产品的注塑成型一直是一个重大挑战。这项研究表明，双峰聚乙烯 （BPE） 的添加可以降低 UHMWPE 的熔融粘度，使 UHMWPE 产品具有高性能、大尺寸和复杂形状的注塑成型。通过微束广角 X 射线衍射 （WAXD）/小角 X 射线散射 （SAXS）、差示扫描量热仪 （DSC） 和扫描电子显微镜 （SEM） 等详细分析，研究了不同 BPE 含量的 UHMWPE 产品在不同区域的晶体结构差异。这项研究表明，那些 BPE 含量低的产品表现出更大的层状晶体尺寸和更高的拉伸强度，尽管微观结构均匀性差，导致断裂伸长率低。相反，BPE 含量高的产品具有更均匀的微观结构，但晶体完美度较低，显著提高了断裂伸长率。冲击性能测试表明，添加 BPE 不会损害 UHMWPE 的机械性能，显示出 500 kJ/m2 的超高冲击强度。此外，本研究确定了 BPE 的复杂流场和分子量分数对产物晶体结构的显着影响。在低 BPE 浓度下，BPE 的低分子量部分在注塑成型过程中的塑化效果中占主导地位。在弱流动条件下，这增加了 UHMWPE 中的分子链松弛，使其难以维持定向结构。相反，强流动条件促进了定向结构的形成。 然而，在高 BPE 浓度下，BPE 的高分子量部分主要阻碍了 UHMWPE 的运动，导致链缠结没有显着改善。在这种情况下，在弱流动和强流动条件下，注塑样品的差异很小。