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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.

Although the influence of hard segment content on the foaming behavior of thermoplastic polyurethane (TPU) has been reported in the literature, most of the studies have been limited to batch foaming, and the relationship between hardness on the foaming quality and the surface quality of TPU is still unclear in injection molding foaming. In this study, three hardnesses of TPU foams were prepared by core‐back injection foaming technique to investigate the relationship between hardness and TPU foaming behavior. Firstly, the relationship between hardness and viscosity of TPU was investigated using rotational rheometer. The results showed that the complex viscosity increased with the increase of hardness, especially the viscosity of high hardness TPU responded more significantly at low frequencies. In addition, a scanning electron microscope was used to analyze the cell morphology of TPU foams with different hardness. It was revealed that the cell morphology of 1098A foam with low hardness was deteriorated and deformed severely, with a cell size and cell density of 172.02 μm and 0.59 × 105 cells/cm3, respectively. With the increase of hardness, the cell morphology of high hardness 1071D foam was regular and rounded, its cell size decreased to 95.98 μm and cell density increased 4.43 × 105 cells/cm3. Surface roughness and mechanical experiments showed that the medium hardness 1065D foam had better surface quality and tensile toughness. The elongation at break of the TPU foams decreased with increasing hardness, while the high hardness 1071D foam had better tensile and flexural strength. This study provides understanding for the selection of a suitable hardness to prepare TPU foams with favorable foaming quality and corresponding mechanical properties. Highlights: TPU foams of different hardness were prepared using core‐back chemical foaming injection molding technology.High hardness TPU foam had excellent tensile strength and flexural strength. [ABSTRACT FROM AUTHOR]

In previous studies, the effect of cell structures of polypropylene (PP) foam materials on flammability behavior had been largely overlooked. In this work, ammonium polyphosphate and pentaerythritol were used as intumescent flame retardants (IFR) for PP, and then the PP‐IFR flame retardant foams were prepared by using injection foaming technology with two different weight reduction methods (same mold volume before foaming and after foaming). The results showed that the average cell size of all the PP‐IFR flame retardant foams in the 10% to 30% weight reduction was less than 100 μm. The PP‐IFR flame retardant foams with an average cell diameter of 26.22 μm and cell density of 7.88 × 106 cells/cm3 had the best limiting oxygen index (LOI) of 27.9%. In addition, the PP‐IFR flame retardant foams with better foaming quality had a higher LOI and a denser foam carbon layer whatever the weight reduction methods, resulting in better flame retardant properties. The escape of gases from the foamed and un‐foamed areas not only reduced the concentration of flammable gases but also led to the collapse and rupture of the foam carbon layer during the combustion process. Hence, it provides guidance for preparing PP foam materials with excellent flame retardancy. [ABSTRACT FROM AUTHOR]

Although a large body of literature has reported that PA6 modification enhances melt strength and improves foam quality, the relationship between melt viscosity and foaming quality remains ambiguous. This paper aims to select four PA6 with different viscosities to explore the effect of the viscosity of the material on foaming quality. First, the foamed materials of four PA6 were prepared by core‐back injection foaming technology. In addition, the crystallization properties and rheological behavior of four PA6 were systematically studied by rotational rheometer and differential scanning calorimetry. The morphologies of composite foams with different viscosities were analyzed using scanning electron microscopy. It was found that the cell size and cell density of M2400 with low viscosity were 114 μm and 1.87 × 105 cells/cm3, respectively. With the increase of viscosity, the cell size and cell density of M2500I decreased to 98.3 μm and 2.66 × 105 cells/cm3, respectively. However, as the viscosity continues to increase, the cell size increases, and the cell density decreases. The findings indicate that the secret to good foaming is rheological behavior. The lower viscosity is challenging to prevent cell growth and easy to break, while high viscosity causes poor fluidity which deteriorates foaming quality and surface quality. It provides guidance for preparing foaming materials with excellent performance and surface through a modification that enhances melt strength. [ABSTRACT FROM AUTHOR]

The incomplete decomposition of foaming agent and tedious process during the preparation of epoxy resin composite foam (ERCF) will reduce the mechanical properties and lead to more complex production. Therefore, in this study, a new and simple negative pressure foaming method was designed innovatively to prepare ERCF under negative pressure using strong gas adsorption capacity of inorganically modified calcium silicate (MCS) particles as air carriers instead of foaming agent, and the density and expansion ratio of ERCF could be precisely controlled by adjusting the negative pressure value in a vacuum oven. The results showed that the density of ERCF could reach a very low value of 0.056 g/cm3 at 15 wt% MCS content with decreased negative pressure, but the negative pressure decreases would damage the quality of cells. At the same time, it was found that a rapid rise in the viscosity of the epoxy composite material system under negative pressure of −0.080 MPa owing to the increase in MCS content, when the MCS content was higher than 15 wt%, the MCS dispersion was reduced, leading to a decrease in the quality of the cells. In addition, the ERCF products prepared by the negative pressure foaming method in this study could be easily molded and possessed a better compressive strength among epoxy foams of similar density. [ABSTRACT FROM AUTHOR]

The α-olefin–maleic anhydride copolymer DIA as a chain extender was used to modify polyamide 6 (PA6) during melt blending. The ability to modulate this modification for PA6 has been shown to be dependent on the effects of its content on the molecular weight distribution, rheological properties, crystalline properties, mechanical properties, and foaming behavior of foam samples. By increasing the DIA content, the viscoelasticity, water contact angle, and elongation at break improved as a result of a significant decrease in water absorption and melt flow rate. Compared with raw PA6, the modified PA6 presented a relatively wider molecular weight distribution. However, the crystallinity of modified PA6 samples decreased, the double melting peaks became one peak, and the α crystallites at 20.3° gradually disappeared with increasing DIA content. The morphologies of composite foams with different contents were analyzed using scanning electron microscopy. It was found that the cell size of different PA6 samples decreased from 160 μm to 83 μm and the cell density increased from 1.1 × 105 cells/cm3 to 5.9 × 105 cells/cm3 when the content of DIA increased from 0 wt% to 5 wt%. Meanwhile, the cell morphology obviously improved and the cell size distribution became narrow. Thus, a preparation technology based on foaming materials with excellent performance, such as better bubble quality and low water absorption, was developed for further research and application. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]