Lightweight and Tough Polypropylene/Silica Nanoparticle Composite Foam Nucleated from Nanoparticles with Intrinsic Cavities for Plastic Structural Components

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 SiO2 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 × 107 cells/cm3 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 × 107 cells/cm3, 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.