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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]

The type and structure of nucleating agents have an important influence on the properties of the final foam as well as on the nucleation of the bubbles during injection foaming. In this study, a simple melt blending method was used to prepare polypropylene/nucleating agents (PP/NAs) composites containing nucleating agents with different structures, and the rheological behavior of the PP/NAs composites was studied using a rotational rheometer. According to the rheological data, the structure of the nucleating agent was not the primary reason for influencing polymer viscosity. Additionally, PP/NAs composite foams were prepared by chemical foaming injection molding process and the bubble dynamics, cell quality and tensile properties were investigated. The results exhibited that polymers with β-cyclodextrin (β-CD), which had a self-contained cavity-circular table structure, as the nucleating agent have better bubble nucleation dynamics. The tensile toughness of PP/β-CD foam was increased from 8.21 MJ/cm3 to 20.54 MJ/cm3, an improvement of 150.34% by comparison with pure PP foam, which was attributed to having an average cell diameter of 23.98 μm and a cell density of 2.36 × 107 cells/cm3. Therefore, this study provides a reference for the design of efficient nucleating agents for the preparation of structural foam materials with lightweight and tough properties. [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 quality of foam in polypropylene/basalt fiber (PP/BF) composite materials is currently unsatisfactory, which restricts their use in industrial applications. To address this limitation, the objective of this study is to improve the foaming properties of PP/BF composite foam by modifying their rheological and crystallization behavior using polyethylene–octene (POE) blending modification. The results demonstrate that the inclusion of POE has a beneficial impact on the rheological and crystallization characteristics of PP/BF composites. Consequently, this creates favorable conditions for the foaming process of PP/BF composite foam. It is conducive to obtaining high foaming quality PP/BF composite foam. The results demonstrate that a 5 wt% POE content yields the best foaming performance for the PP/BF composite foam, with the most uniform cell distribution, a cell size of 54 μm and a cell density is measured at 3.43 × 107 cells/cm3. The optimal temperature range for foaming is between 180 and 200°C. The introduction of POE in PP/BF composite foam may lead to a decrease in its tensile and flexural strength. However, this drawback is offset by a significant improvement in the notch impact strength of the foam. This study's findings will enhance our understanding of the production and application of PP/BF composite foam, making it a valuable material for applications that require exceptional toughness. Highlights: Improved the crystallization and rheological properties of PP/BF composites.Significantly improve the foaming quality of PP/BF composites.Make PP/BF composite foam has excellent impact toughness. [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]

In this study, high strength and light weight polyamide 6/carbon fiber (PA6/CF) composite foams were prepared by chemical injection foaming method. The foaming performance, electromagnetic interference (EMI) shielding efficiency total(SET), and mechanical properties of PA6/CF composite foams with different CF contents were investigated. The results show that the shear viscosity and strain hardening behavior obvious increased with the augment of CF content, which helped to PA6/CF composite foams to take the cell structure with smaller size, greater density, and more regular morphology. PA6/CF composite foam with cell size of 56.8 μm, and cell density of 1.81 × 106 cells/cm3 was achieved at 22 wt% CF. Meanwhile, PA6/CF composite foam had good EMI SET, at 22 wt% CF addition. The specific EMI SET of PA6/CF composite foam is 36.6 dB, 27.6% higher than that of solid 26.5 dB, the excellent cell structure helps to improve the EMI SET. In addition, PA6/CF composite foams also had excellent mechanical properties. Therefore, PA6/CF composite foams had broad application prospect in EMI shielding materials field, combining the advantages of simple preparation process, light weight and EMI shielding. [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]

Foamed Polymer is an important polymer material, which is one of the most widely used polymer materials and plays a very important role in the polymer industry. In this work, foamed polypropylene (PP) composites are prepared by injection molding, and the cell deformation process within them is studied by combining visualization technology and COMSOL software simulation. The results shows that the deformation of isolated cells depends in temperature, and there is no macroscopic deformation. There was no significant difference between the stress around adjacent cells at different temperatures, but the stress at different positions around the adjacent cells has obvious changes, and the maximum stress at the center of the adjacent cells was 224.18 N·m−2, which was easy to cause a lateral deformation of the cells. With the increase in temperature, the displacement around the adjacent cell gradually increased, the maximum displacement of the upper and lower symmetrical points of the cell was 14.62 μm, which is most likely to cause longitudinal deformation of the cell; the deviation of the cell deformation parameter gradually increased, which led to deformation during the growth of the cell easily. The simulation results were consistent with the visualized cell deformation behaviors of the foamed PP composites. [ABSTRACT FROM AUTHOR]

In this paper, polypropylene (PP) and chemical foaming agent (AC) were taken as the research objects, and the influence of different injection molding foaming environment on the bubble formation process was studied by using the visualization device. And the mathematical model formula was used to fit the curve of bubble number (N) with time (t) in the foaming process. Among them, the change of injection temperature and foaming agent content only changed the bubble formation rate and the final bubble number. With the increase of injection temperature, the foaming agent decomposed in advance in the barrel. The change of injection pressure had the most obvious effect on the nucleation process. Through the nonlinear fitting of N-t curves under different foaming environments, the correlation coefficient R2 was always greater than 0.98, indicating that the process of foaming nucleation could be described intuitively through the mathematical model. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

This paper investigates the bubble nucleation of polymer (LDPE) foams using nucleation theory and establishes a mathematical model based on in-situ observations and measurements. The effects of different foaming agent contents and shot sizes on bubble nucleation were studied in an injection foaming experiment and a new mathematical model describing the bubble nucleation kinetics was obtained based on classical nucleation theory. The model fittings were obtained for different experimental conditions. The process of foaming nucleation could be characterized intuitively through this model and can be used as a general form for other nucleation processes. [Display omitted] • A new model for the nucleation density versus the time in microcellular foams is developed. • The model is verified by changing the foaming agent content and shot size. • The nucleation kinetics is discussed. [ABSTRACT FROM AUTHOR]

Microcellular epoxy/multi-walled carbon nanotube (EP/MWCNT) composite foams loaded with 2 wt% (mass fraction) of MWCNT were prepared through the free-foaming process (Fre-foam) and limited-foaming process (Lim-foam) using chemical foaming agent (CFA), respectively. The morphologies of EP/MWCNT composite foams with different densities were analyzed by scanning electron microscopy (SEM). It was found that the cell size of both Fre-foam and Lim-foam decreased with increasing the density, while Lim-foam exhibited a smaller cell size and a higher cell density in contrast to those of Fre-foam at similar density. In addition, the dynamic mechanical properties, thermal stability, and electrically and thermal conductive properties of the EP/MWCNT foams in the density range of 0.278 g/cm3–1.108 g/cm3 were investigated and the difference in performances between Fre-foam and Lim-foam was analyzed. Lim-foam had an obviously lower crosslink density than that of Fre-foam due to the effect of compressed gas, which was clearly reflected in the results of gel fraction, glass transition temperature (T g), molecular weight between crosslinks (M c), and initial thermal decomposition temperature. Compared with Fre-foam, Lim-foam had superior thermal conductive property and exhibited weak electrically conductive property, indicating the conductive pathway was affected by the foaming process. [ABSTRACT FROM AUTHOR]