In this work, crystallographic texture evolution in 3D printed trimodal polyethylene (PE) blends and high-density PE (HDPE) benchmark material were investigated to quantify the resulting material anisotropy, and the results were compared to materials made from conventional injection molded (IM) samples. Trimodal PE reactor blends consisting of HDPE, ultrahigh molecular weight PE (UHMWPE), and HDPE_wax have been used for 3D printing and injection molding. Changes in the preferred orientation and distribution of crystallites, i.e., texture evolution, were quantified utilizing the wide angle X-ray diffraction through pole figures and orientation distribution functions (ODFs) for 3D printed and IM samples. Since the change in weight-average molecular weight (M_w) of the blend was expected to significantly affect the resulting crystallinity and orientation, the overall M_w of the trimodal PE blend was varied while keeping the UHMWPE component weight fraction to 10% in the blend. The resulting texture was analyzed by varying the overall M_w of the trimodal blend and the process parameters in 3D printing and compared to the texture of conventional IM samples. The printing speed and orientation (defined with respect to the axis along the length of the samples) were used as the variable process parameters for 3D printing. The degree of anisotropy increases with an increase in the nonuniform distribution of intensities in pole figures and ODFs. All the highest intensity major texture components in IM and 3D printed samples (0° printing orientation) of reactor blends are observed to have crystals oriented in [001] or [001̅]. Overall, for the same throughput, 3D printed samples in the 0° orientation showed greater texture evolution and higher anisotropy compared to IM samples. Most notably, an increase in 3D printing speed increased the crystalline distribution closer to the 0° direction, increasing the anisotropy, while deviation from this printing orientation reduced crystalline distribution closer to the 0° direction, thus increasing isotropy. This demonstrates that tailoring material properties in specific directions can be achieved more effectively with 3D printing than with the injection molding process. Change in the overall M_w of the trimodal PE blend changed the preferential orientation distribution of the crystal planes to some degree. However, the degree of anisotropy remained the same in almost all cases, indicating that the effect of molecular weight distribution is not as significant as the printing speed and printing orientation in tailoring the resulting properties. The 3D printing process parameters (speed and orientation) were shown to have more influence on the texture than the material parameters associated with the blend.

中文翻译：

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3D 打印聚乙烯反应器混合物中的晶体结构演变


在这项工作中，研究了 3D 打印三峰聚乙烯 (PE) 共混物和高密度聚乙烯 (HDPE) 基准材料的晶体织构演化，以量化所得材料的各向异性，并将结果与​​传统注塑 (IM) 制成的材料进行比较样品。由 HDPE、超高分子量 PE (UHMWPE) 和 HDPE_wax 组成的三峰 PE 反应器共混物已用于 3D 打印和注塑成型。利用广角 X 射线衍射通过极图和 3D 打印和 IM 样品的取向分布函数 (ODF) 来量化微晶的择优取向和分布的变化，即纹理演变。由于共混物重均分子量 (M _w ) 的变化预计会显着影响所得结晶度和取向，因此三峰 PE 共混物的总体 M _w 发生变化同时将共混物中 UHMWPE 组分的重量分数保持在 10%。通过改变三峰混合的总体 M _w 和 3D 打印中的工艺参数来分析所得纹理，并与传统 IM 样品的纹理进行比较。打印速度和方向（相对于沿样品长度的轴定义）被用作 3D 打印的可变工艺参数。各向异性程度随着极图和 ODF 中强度不均匀分布的增加而增加。观察到反应器共混物的 IM 和 3D 打印样品（0° 打印取向）中所有最高强度的主要纹理成分均具有以 [001] 或 [001̅] 取向的晶体。 总体而言，对于相同的吞吐量，0° 方向的 3D 打印样品与 IM 样品相比表现出更大的纹理演变和更高的各向异性。最值得注意的是，3D打印速度的增加增加了接近0°方向的晶体分布，增加了各向异性，而偏离该打印方向减少了接近0°方向的晶体分布，从而增加了各向同性。这表明，与注塑工艺相比，3D 打印可以更有效地实现特定方向的材料属性定制。三峰PE共混物整体M _w 的变化在一定程度上改变了晶面的择优取向分布。然而，在几乎所有情况下，各向异性程度保持相同，这表明在调整所得性能时，分子量分布的影响不如印刷速度和印刷取向那么显着。研究表明，3D 打印工艺参数（速度和方向）比与混合相关的材料参数对纹理的影响更大。