The inherently linear polypropylene suffers unsatisfying foaming behavior due to its low melt strength. To overcome this drawback, polypropylene‐/polypropylene‐grafted glycidyl methacrylate/thermoplastic polyester elastomer (PP/PP‐g‐GMA/TPEE) blending foam is prepared by the chemical foaming method in this study. The foaming mechanism of blending was studied from the aspects of the rheological behavior and the crystallization property. The results show that TPEE disperses in the PP matrix with fine particles and forms ideal interfaces, which provide a large number of nucleation sites for the foaming process of blending, inducing heterogeneous nucleation. Both of the 15 wt% and 20 wt% TPEE‐modified PP composites show higher shear viscosity and obvious strain hardening behavior. It has been proved that the cross‐linking network structure formed by TPEE and PP‐g‐GMA reaction improves the melt strength. The cell size decreases from 37.6 to 24.8 μm, and the cell density increases from 2.9 × 106 cells/cm3 to 2.5 × 107 cells/cm3. Compared with PP composites, the foaming window of the PP/PP‐g‐GMA/TPEE composites was widened.

The branched/micro-crosslinked structure formed by chain extension reaction between EGMA and PLA improved the rheological behavior and crystallization properties of PLA, which ameliorated the foaming performance of various PLA samples.

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Polyamide 6 (PA6) was modified with ethylene maleic anhydride syndiotactic copolymer resin (ZeMac), and triglycidyl isocyanurate (TGIC) as modifiers to prepare a grafting structure and a long-chain branching structure, respectively. The effects of two modifiers on the rheological behavior, crystallization properties, foaming performance, and mechanical properties of PA6 were systematically studied by rotating rheometry, differential scanning calorimetry and scanning electron microscopy. The results showed that there were differences in crystallization properties between the two modification methods, but they significantly improved the rheological, foaming performance, and mechanical properties of PA6. In particular, PA6 with long-chain branching structure through TGIC modification showed better performance in various physicochemical characterizations. The introduction of ZeMac reduced the average diameter of bubbles in pure PA6 from 146.32 to 88.12 µm, and the density of bubbles increased from 1.69 × 105 to 5.35 × 105 cells·cm−3. The introduction of TGIC reduced the average diameter of bubbles in pure PA6 from 146.32 to 64.36 µm, and the density of bubbles increased to 1.31 × 106 cells·cm−3. Moreover, the mechanical properties of both nonfoamed and foamed samples were improved after modification.

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.

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.

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