Increasing mold temperature is effective to improve the surface quality of injection molding foamed products, but high mold temperature often leads to deteriorative cellular quality. Based on this, the polypropylene/high melt strength polypropylene (PP/HMSPP) composites with temperature insensitivity were prepared by a simple melt blending method, the rheological behavior and crystallization behavior of PP/HMSPP composites were studied by rotational rheometer and DSC at different cooling rates, respectively. In addition, foamed PP/HMSPP composites were prepared by chemical foaming injection molding, and their cellular quality, surface quality, and mechanical properties were analyzed. The results showed that when the content of HMSPP came to 50 wt%, the effect of the cooling rate on the rheological behavior of PP/HMSPP composites could be ignored. Furthermore, when the mold temperature increased from 60 to 120°C, the surface quality increased significantly, with the average cell diameter only increasing from 15.92 μm to 19.03 μm, and the cell density decreasing from 2.3 × 107 cells/cm3 to 1.9 × 107 cells/cm3. The tensile strength, bending strength, and impact strength were maintained at 24.15 MPa, 38.11 MPa, and 3.24 kJ/m2, respectively. This temperature‐insensitive PP/HMSPP composite foaming material can be used as guidance for the industrial stable production of PP injection molding chemical foaming. And this work suggested new thinking for future research on the modification of other polymer foam products at a high mold temperature.

Lightweight plastic foam materials can save resources and energy and reduce environmental pollution. However, these plastic components with large cell sizes present unsatisfactory mechanical properties. Here, we describe a successful strategy to fabricate lightweight and tough polypropylene/nucleating agent (PP/NA) composite foams with high cell density and small cell size by combining designed nanoparticles with intrinsic cavities as nucleating agents and chemical foam injection molding technologies. The influences of nucleating agents with different contents, morphologies, and process parameters on the cell morphology of pure PP and PP/NA foam samples were studied systematically. Owning to the effective increase of the number of nucleation sites by introducing SiO 2 nanoparticles with pits on the surface (NAC), the lightweight and tough PP/NAC composite foam that the addition amount of NAC of 1 wt % (PPC1) was prepared with a high cell density of 1.22 × 10 7 cells/cm 3 and a small cell size of 27.99 μm, which enhanced the tensile strength from 21.47 to 24.31 MPa and caused a 356.06% increase in tensile toughness. Furthermore, the effects of packing time on the foaming behavior of PPC1 were studied. When packing time is 5 s, the average cell size is 17.01 μm and the cell density reaches 3.01 × 10 7 cells/cm 3 , enhancing the tensile strength to 25.36 MPa and causing a 557.52% increase in the tensile toughness. Therefore, this work provided insights into fabrication of lightweight and tough PP/NA composite foams, which have great promise as structure materials for future use in many applications, such as automotive.

The process of nucleation and growth of secondary bubbles was observed by using visualizations of the mold-opening foam injection molding (MOFIM).