Filament-based material extrusion additive manufacturing (MEAM) is one of the most commonly used techniques in additive manufacturing (AM). In spite of recent notable development in the MEAM process, there is still a need to develop more materials that can be printed consistently using this technique. Isotactic polypropylene (PP), a popular thermoplastic material, undergoes rapid crystallization and subsequent volume contraction. This can lead to residual stress buildup in PP parts when processed using MEAM, resulting in poor adhesion to the printing platform, poor geometric tolerance, and mechanical performance. In this work, the effects of varying composition of low molecular weight hydrocarbon resins incorporated to PP are investigated. Specifically, the thermal behavior, crystallization, morphology, and printability of the blends are studied. The rapid crystallization of PP has been delayed by the addition of hydrocarbon resins that provided a larger time window for the residual stresses to relax. The addition of the resins to the pure PP matrix lowers the crystallization temperature of PP from 121.8 to 116.0 °C, which further enables additional diffusion during the solidification process. Polarized optical microscopy demonstrates the differences in crystalline morphology, which is expected to impact the structure at the interlayer boundaries between deposited layers. The combination of modifications in crystallization rate, time, and morphology significantly affects the interlayer adhesion and residual stress state, which directly controls the mechanical properties and part warpage of printed parts. Tensile bars of the different blends were printed in two different orientations to analyze the mechanical performance and study part anisotropy. The maximum tensile stress of pure PP (26.8 ± 2.1 MPa) printed at a ±45° raster angle increased with addition of 20 wt % hydrocarbon resin (32.4 ± 3.0 MPa) when printed under the same conditions. The improvement in the tensile strength is due to a combination of changes in crystallinity, morphology, and improved interlayer adhesion during printing. The parts were annealed postprinting to improve polymer chain diffusion across the layers, thereby improving interlayer adhesion and resulting in tensile modulus and strength values in excess of 90% of injection-molded PP parts.

中文翻译：

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基于材料挤压的聚丙烯和烃树脂共混物的增材制造

基于长丝的材料挤压增材制造（MEAM）是增材制造（AM）中最常用的技术之一。尽管最近在MEAM工艺中取得了显着进展，但仍需要开发更多可以使用此技术进行一致印刷的材料。等规聚丙烯（PP）是一种流行的热塑性材料，它会快速结晶并随后发生体积收缩。使用MEAM处理时，这可能导致PP零件中残留应力累积，从而导致与印刷平台的粘合性差，几何公差和机械性能下降。在这项工作中，研究了掺入PP中的低分子量烃类树脂组成变化的影响。具体地，研究了共混物的热行为，结晶，形态和可印刷性。PP的快速结晶因添加烃类树脂而延迟，烃类树脂为残余应力的松弛提供了更大的时间窗口。将树脂添加到纯PP基体中可将PP的结晶温度从121.8降低到116.0°C，从而在固化过程中进一步实现额外的扩散。偏振光学显微镜证明了晶体形态的差异，这有望影响沉积层之间的层间边界处的结构。结晶速率，时间和形态的修改的组合会显着影响层间附着力和残余应力状态，从而直接控制印刷零件的机械性能和零件翘曲。以两种不同的方向印刷不同混合物的拉伸棒，以分析机械性能并研究零件的各向异性。当在相同条件下打印时，在±45°光栅角下打印的纯PP（26.8±2.1 MPa）的最大拉伸应力随添加20 wt％的烃类树脂（32.4±3.0 MPa）而增加。拉伸强度的改善归因于结晶度，形态的变化以及印刷过程中层间附着力的改善的结合。零件在印刷后经过退火处理，以改善聚合物链在整个层中的扩散，从而改善层间粘合力，并导致拉伸模量和强度值超过注塑PP零件的90％。在相同条件下打印时，通过添加20 wt％的烃类树脂（32.4±3.0 MPa），以±45°光栅角打印的图像会增加1 MPa）。拉伸强度的改善归因于结晶度，形态的变化以及印刷过程中层间附着力的改善的结合。零件在印刷后经过退火处理，以改善聚合物链在整个层中的扩散，从而改善层间粘合力，并导致拉伸模量和强度值超过注塑PP零件的90％。在相同条件下打印时，通过添加20 wt％的烃类树脂（32.4±3.0 MPa），以±45°光栅角打印的图像会增加1 MPa）。拉伸强度的改善归因于结晶度，形态的变化以及印刷过程中层间附着力的改善的结合。零件在印刷后经过退火处理，以改善聚合物链在整个层中的扩散，从而改善层间粘合力，并导致拉伸模量和强度值超过注塑PP零件的90％。