Poor surface appearance and decreased mechanical performance are critical factors limiting the broad application of Microcellular injection molding (MIM) in foamed polymer products. Herein, in-situ polytetrafluoroethylene (PTFE) nanofibrils reinforced polypropylene (PP) foams with high strength, impact resistance, and enhanced surface quality were prepared by mold opening microcellular injection molding (MOMIM). PTFE nanofibers with different diameters were introduced into the PP matrix via twin screw extrusion and significantly enhanced the crystallinity and viscoelasticity of the PP matrix with the enhancement being more pronounced for the finer PTFE fibers. High-density oriented cellular structures were formed in the MOMIM PP/PTFE foams owing to the heterogeneous nucleation of PTFE and the stretching effect of the mold opening process. The optimum MOMIM PP/PTFE foam fabricated possesses a high cell orientation angle close to 90° and a large cell aspect ratio of 5.3, which reached a 34.37 % increase in tensile strength and a 73.08 % increase in impact strength owing to the synergetic effects of the PTFE network and the highly oriented fine cell structure, which effectively dissipated the tensile stress and impact stress by cell wall twisting and folding deformation. Furthermore, the MOMIM PP/PTFE foam showed a significantly enhanced surface quality compared to the MIM foam due to the reduced dragging flow in MOMIM, which greatly hindered cell rupture on the foam surface. Therefore, this work provides insights into the MOMIM of polymer composites containing fibrous fillers and the enhancement of tensile properties, impact resistance, and surface quality of foam products.

中文翻译：

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通过开模微孔注射成型实现高强度、抗冲击的 PP/PTFE 复合泡沫，具有增强的表面外观


表面外观差和机械性能下降是限制微孔注射成型（MIM）在泡沫聚合物产品中广泛应用的关键因素。在此，通过开模微孔注射成型（MOMIM）制备了具有高强度、抗冲击性和增强表面质量的原位聚四氟乙烯（PTFE）纳米原纤增强聚丙烯（PP）泡沫。通过双螺杆挤出将不同直径的PTFE纳米纤维引入PP基体中，显着增强了PP基体的结晶度和粘弹性，其中对于更细的PTFE纤维，增强更明显。由于PTFE的异质成核和开模过程的拉伸作用，MOMIM PP/PTFE泡沫中形成了高密度定向多孔结构。最佳的 MOMIM PP/PTFE 泡沫具有接近 90° 的高泡孔取向角和 5.3 的大泡孔长径比，由于两者的协同作用，拉伸强度提高了 34.37%，冲击强度提高了 73.08%。 PTFE网络和高度定向的细小泡孔结构，通过泡孔壁扭曲和折叠变形有效地消散拉应力和冲击应力。此外，与 MIM 泡沫相比，MOMIM PP/PTFE 泡沫的表面质量显着提高，因为 MOMIM 中的拖曳流减少，这极大地阻碍了泡沫表面的泡孔破裂。因此，这项工作为含有纤维填料的聚合物复合材料的 MOMIM 以及泡沫产品拉伸性能、抗冲击性和表面质量的增强提供了见解。