The effects of the cell size and distribution on the mechanical properties of polypropylene foam were simulated and analyzed by finite element modeling with ANSYS and supporting experiments. The results show that the reduced cell size and narrow size distribution have beneficial influences on both the tensile and impact strengths. Decreasing the cell size or narrowing the cell size distribution was more effective for increasing the impact strength than the tensile strength in the same case. The relationship between the mechanical properties and cell structure parameters has a good correlation with the theoretical model.

Microcellular foamed polymers have been widely used in the traffic field. However, it is difficult to successfully manufacture microcellular foamed products that simultaneously possess good cell morphology, small size, high cell density, and great surface quality. In this paper, polyamide 6 (PA6) injection microcellular foams were manufactured via short-shot and core-back foaming process to investigate the effect of the foaming process on cell quality and surface quality. Results showed that the core-back injection PA6 foams possessed a smaller cell size, higher cell density, lower cell deformation, and greater surface glossiness than short-shot foams. The cell density of core-back PA6 microcellular foams reached to 12.5 × 10⁵ cell/cm³, which is almost 3.5 times greater than that of the short-shot foams when the weight reduction was 10%. The PA6 microcellular foams manufactured via the core-back foaming process had higher surface glossiness with different weight reduction, whereas the surface glossiness of short-shot microcellular foams dramatically declined with an increase in weight reduction. Hence, the core-back foaming process can be used to fabricate microcellular foamed polymers with good cell morphology, small size, high cell density, and fine surface quality under high weight reduction; this was beneficial for producing products that have good surface quality and high weight reduction and are used in automobiles, high-speed trains, and airplanes to reduce energy consumption.

Foaming EVA was prepared with molding method in this paper, the effect of the cell size, cell wall thickness and filling gas type on thermal insulation performance of foaming EVA were analysed by the mechanism of insulation. The results show that the cell size, cell wall thickness and filling gas type have a significant influences on the insulation performance. When the cell size is 71.3 μm, the thermal conductivity is the smallest at low frequency 1000 Hz, which is 0.042 W/ (m.k). When the cell wall thickness is 8.2 μm, thermal conductivity of foaming EVA is minimal, which is 0.045 W / (m.K), the insulation effect is ideal. When the filling gas is hydrogen, the thermal insulation performance of foaming EVA is poor, but when the filling gas is nitrogen, the result is opposite.

Thermal expansion microcapsules were prepared by using acrylonitrile and methyl methacrylate as polymerization monomer and isooctane as the blowing agent. The structure, composition, appearance, and thermal expansion properties of microcapsules were analyzed by SEM, FTIR, TG, DSC, and TEM. The cell structure and surface quality of PP foaming composites were characterized by SEM, optical microscopy, and gloss meter. Results show that sodium chloride in the aqueous solution can significantly improve the appearance of microcapsules. At 15.1 and 19.1 wt.% sodium chloride, the appearance of microcapsules was regular. At 19.1 wt.% sodium chloride, the thermal expansion microcapsules were coated with 25.0 wt.% of the blowing agent. The microcapsules exhibit an expansion temperature of 201 °C and can remain stable after expansion. Moreover, the microcapsule shell of the data (thickest part − thinnest part)/(core diameter) decreased to approximately 0.05. The glossiness of PP/(T-5) increased to 65.6. The surface of PP/microcapsule foaming composite is smoother than that of the PP/AC foaming composites, and the pores of thermal expansion microcapsules are difficult to deform during processing.

Ethylene-Vinyl Acetate (EVA) polymer foam was prepared using a mold for this investigation. The effect of the cell structure parameters and pore filling gas type on the sound absorption performance of the EVA foam materials were analyzed in terms of their sound absorption capability. The results show that the cell size, cell wall thickness and pore filling gas type have significant influence on the sound absorption performance. When the cell size is 71.3 μm, at low frequency (1000 Hz) the absorption coefficient was the largest at 0.487 and the absorption effect was good. With the increase of the cell wall thickness, the peak value of the sound absorption coefficient first increased and then decreased, and gradually transferred to the low frequency area. When the cell wall thicknesses were 14.3 μm, the foam material had optimal sound absorption properties. The cell filling gas was hydrogen, the EVA foam material had optimal sound absorption effect, and the sound absorption peak value was 0.553 at 800 Hz in the low frequency range (Ⅰ), the sound absorption performance of the foamed materials was ideal.