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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.

The morphology, size and surface roughness of the nucleating agent significantly affect the nucleation effect for foaming in the polymer. In this work, four nucleating agents with different morphologies, namely DE, MS, OMMT and β- CD as heterogeneous nucleation agents were selected for a polypropylene (PP) foaming injection molding process to explore nucleation mechanism. A theoretical assumption (cavity nucleation) in polymer foaming had been put forward about how to enhance the efficiency of bubble nucleation based on classical nucleation theory (CNT). Subsequently, the cavity nucleation was validated by chemical core-back injection foaming molding and in-situ visualization and elaborated by establishing a formula. Finally, designed petals shape particles as nucleating agents to further test this theory. The confirmation of this theory effectively improved the nucleation efficiency and foaming quality, which has important guiding significance to the development of lightweight products.

In this paper, the dynamic foaming process of micro-foaming polypropylene (PP) in different foaming environments in real time was obtained via a visualization device. The relationship curve between cell number (n) and foaming time (t) was plotted, and then the nucleation kinetics of foam cells was analyzed. Results showed that the formation rate of cells changed obviously with the variation of melt temperature and the content of the foaming agent. The n-t curves presented a typical “S” shape, which indicated that the appearance of the cell number increased slowly in the initial foaming period, then increased rapidly in a short time, and finally maintained a certain value. When a certain pressure was applied to the PP melt, the external force had a great influence on the n-t curve. With the increasing external force, the rate of cell formation increased rapidly, and the shape of the n-t curve changed from “S” to “semi-S” without an obvious slow increase. The investigation of the n-t relationship in the PP dynamic foaming process under different foaming environments could provide effective bases for improving the foaming quality of injection molding foaming materials.

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.

Epoxy foams with different densities and microstructures were prepared by changing the process parameters including the foaming temperature, chemical foaming agent (CFA) content and precuring extent. The microstructure of foams reveals a smaller cell size, higher cell density, and more homogeneous distribution of cells at higher precuring extent. However, the cell size and distribution are not affected by the foaming temperature and CFA content without precuring process. In addition, the bubbles migration, which resulted in non-uniform cell density distribution, was promoted by increasing the foaming temperature and depressed by increasing the CFA content and precuring extent. The flexural properties of the non-uniform epoxy foams were also studied. Results showed that the flexural modulus was related to the cell morphology, while the flexural strength was affected by both the cell morphology and the position of the specimens during test. It was also found that the relative flexural modulus and strength exhibited a power-law dependence with respect to the relative density. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 41175.