Behavior Of Foams Research Articles

Investigations into the foaming behavior of ABS by means of granule extrusion using expandable microspheres

The following investigations address the production of syntactic polymer foams using thermally expanding microspheres (TEM) in the extrusion process. A process model for the foaming behavior of acrylnitrile butadiene styrene (ABS) with thermally expanding microspheres as masterbatch is derived by varying the two basic process parameters extruder rotational speed and extruder temperature in a test matrix with five stages each. The investigations include the production of unfoamed and foamed strands and the measurement of process relevant properties and parameters such as extrusion mass flow, relative density of the structures, die-swelling and the characterization of the generated foam structures. The achievable density reduction is within the order of 50%. The process model resulting from the investigations allows the production of homogeneously foamed strands. These results are intended to serve as the basis for a transfer to the Large Scale Additive Manufacturing (LSAM) process.

Bead‐to‐Bead Analysis: Introducing an Innovative Methodology for Accelerated Quantitative Analysis of the Welding Behavior of Bead Foams

ABSTRACTPerformant lightweight components made of bead foams are essential for a sustainable transformation of industry in multiple areas. An in‐depth understanding of the welding process is key in reaching maximum mechanical properties. This study presents the novel methodology of Bead‐to‐Bead analysis, providing a superior way in directly and quantitatively evaluating the welding behavior of bead foams compared with current approaches. Individual beads of expanded polystyrene (EPS) and expanded thermoplastic polyurethane (ETPU) are welded in a rheometer at defined parameters. A subsequent tensile test in combination with the analysis of the welded surface allows the evaluation of shrinkage/softening of the beads during welding and their tensile strength. For EPS, softening of the amorphous material is observed at the beginning of glass transition (~95°C) in addition to an increased welding quality. Residual stresses in ETPU lead to initial shrinkage followed by softening above 140°C. Welding of ETPU starts at 100°C and reaches a maximum at 140°C. The subsequent thermal analysis of the welded beads show the importance of recrystallization processes during cooling due to the formation of new crystalline domains across the bead interfaces. In the absence of such domains, sufficient bonding between beads is not possible.

Evaluation of critical process parameter on the production of sustainable bead foams based on polylactic acid

A commercial grade of polylactic acid (PLA) was foamed without using modifiers to obtain expanded polylactic acid bead foams (EPLA). Typically, the foaming process is influenced by both melt properties and crystallization behavior. While factors like water temperature, die structure, and die temperature are known to have effects on bead foam processing, these aspects have not been thoroughly explored in the context of PLA bead foam production. To address this gap, a comprehensive investigation was undertaken, varying water temperature, die structure, and die temperature to discern their impact on PLA processing behavior. Results revealed that water temperature significantly influenced foaming behavior, particularly at elevated temperatures near the glass transition of PLA. Additionally, the study demonstrated that die size wielded a notable influence on all foam properties, dictating process limits. With the selection of an appropriate die size, the die temperature could be manipulated within the range of 190°C to 160°C, revealing a substantial impact on the overall process. Remarkably, the lowest densities achieved were 63 kg/m3 with an average cell size of 36 µm and a cell density of 1.1*107 cells per cm3.

Investigation of Tensile Properties and In Situ Analysis of Fracture Behavior in High-Porosity Open-Cell Nickel Foam.

Nickel foam offers excellent conductivity, a high surface area, and lightweight structure, making it ideal for applications, like battery electrodes, catalysts, and filtration systems. Its durability and corrosion resistance further enhance its performance in various industries. However, few studies focus on the tensile anisotropy of nickel foam and its tensile fracture process. In this study, the anisotropic tensile behavior of nickel foam with varying relative densities has been investigated, along with its tensile fracture behavior using in situ techniques. The tensile properties of nickel foams show strong anisotropy due to the flattening process in the production process. The results show that the tensile properties, including the yield strength, tensile strength, and elastic modulus, increase with the increasing relative density, while the elongation percentage has no relationship with the relative density. The experiment data on tensile strength are in agreement with Gibson's formula and Liu's formula. In situ tensile tests are conducted to explore the microscopic fracture mechanism of nickel foam. The results show that the struts of nickel foam are tensile fractures or shear fractures near the joints, and the fracture process of struts is clearly recorded and analyzed. This study is significant as it provides critical insights into the anisotropic tensile behavior of nickel foam and fracture mechanism, enabling the optimization of production processes and broadening its potential applications.

Shape Memory Polymer Foam Based on Nanofibrillar Composites of Polylactide/Polyamide.

This paper presents the novel development of a shape memory polymer foam based on polymer-polymer nanocomposites. Herein, polylactide (PLA)/biosourced polyamide (PA) foams are fabricated by in situ fibrillation of polymer blends and a subsequent supercritical CO2 foaming technique. In this system, PLA serves as a shape memory polymer to endow this foam with a shape memory effect (SME), and in situ generated PA nanofibers are employed to reinforce the PLA cell walls and provide an additional permanent phase. A concentration of PA, 5 wt.%, was chosen to form an entangled nanofibrillar network. Foams of PLA/PA nanoblends with the same content of constituents were fabricated to reveal the effect of minor phase morphology on the cell structure and shape memory behavior of polymer foams. Profiting from the reinforcing effect of PA nanofibers, the PLA/PA nanocomposite foam exhibits smaller foam cells, a narrower cell size distribution and a comparable cell concentration than the PLA/PA nanoblend foam. In addition, PA nanofibers, unlike PA nanodroplets, favor the shape fixation ratio and recovery ratio and shorten the shape recovery time.

Study on foaming behavior of block copolymer/inorganic particles co‐construction of toughened epoxy resin foams

AbstractLow toughness and brittleness limit its application range of thermosetting epoxy resin (EP) based foams. In current research, inorganic particles are commonly utilized as heterogeneous nucleating agents to enhance foaming quality and EP toughness. However, the increasing inorganic particle content usually leads to particle agglomeration, which negatively impacts foaming quality and reduces EP performance. Block copolymers, which appear as liquid to effectively mitigate agglomeration, are employed as toughening materials for EP. In this study, a small number of modified calcium silicate particles (MCS) were used as anchor points to induce the distribution of block copolymers (P‐F68) to improve EP toughness and effectively enhance cell nucleation, thus, EP/MCS/P‐F68 foams performance was improved. The research results showed that EP foams obtained excellent cell structure and very small foam density (0.256 g/cm3) at the P‐F68 content of 10 wt%. The continuous increase of P‐F68 content would lead to the thickening of cell wall and the increase of cell size. Simultaneously, the core‐shell structure formed by P‐F68 in EP effectively enhanced the toughness of EP foams and mitigated its brittleness, offering crucial theoretical guidance for toughening and regulating the cell structure of EP foams.

Methodological approach to characterize the interfacial and foaming properties of carbonated beverages

The adjustment and control of specific product characteristics, e.g., foaming behavior of carbonated beverages, requires an understanding of influencing factors along with reliable analytical methods. However, due to the overlay of different phenomena, i.e., release of CO2 and action of surface-active molecules contained in such beverages, it is difficult to assess their respective contribution to foam appearance and stability. This study aimed at evaluating a new methodological approach to investigate the interfacial and foaming properties of carbonated beverages. Using beer as an example, it was attempted to establish a correlation between interfacial properties and foaming behavior. To ensure a comprehensive dataset, surface tension, interfacial dilatational rheology, and foaming properties including foam structural characteristics of six different German beers of three different types (i.e., Pils, wheat beer and Koelsch), which are known to exhibit distinct foaming behavior, were measured. While foams prepared with CO2 as sparging gas did not show any differences in foam aging, use of air for foaming enabled differentiation based on beer type. Differences observed in foam structural characteristics and stability could not be related to dynamic surface tension but might be linked to interfacial dilatational properties. Overall, the presented multiscale approach can be seen as promising concept for further experimental studies on carbonated beverages.

Understanding the impact of nickel coating on the mechanical and corrosion behaviour of copper foams

ABSTRACT This study used a sponge replication technique to fabricate open-cell copper (Cu) foams with varying pore sizes. Nickel coating was applied via electrolysis to produce nickel-copper (NiCu) foams to enhance the Cu foams' energy absorption efficiency and corrosion resistance. The foams were characterized under static conditions to assess their compressive and corrosion properties. The nickel coating improved compressive strength by increasing foam strut thickness and reducing defects, as observed via scanning electron microscopy (SEM). The 10 Pores per inch (PPI) NiCu foam shows a substantial increase in compressive strength, close to 17.7%, compared to the 10 PPI Cu foam, resulting in a maximum compressive strength of 11.3 MPa. Similarly, 20PPI NiCu foam shows an increase of compressive strength of 20% when compared to 20 PPI Cu foam. NiCu foams significantly reduced corrosion current density compared to uncoated Cu foams, indicating enhanced corrosion protection from the nickel coating.

Highly efficient flame retardancy and fire spread behavior of rigid polyurethane foams with extremely low content of flame retardant

In recent years, flame-retardant rigid polyurethane foam (RPUF) has once again captured the scholars’ attention due to the growing the growing demands in the field of building energy efficiency. However, the inherent flammability of RPUF is high and the complexities of its flame-retardant mechanisms remain inadequately understood. In this study, a modified biomass material, amino starch phosphate ester was successfully synthesized which was then combined with expandable graphite (EG) and incorporated into RPUF. The research delved into the optimal ratio and minimal flame-retardant additive required to achieve the stringent UL-94 V-0 rating, while also thoroughly investigating the flame retardancy and thermal properties of the composite system. The findings revealed that with just 6 wt.% of flame retardants, the RPUF achieved the UL-94 V-0 rating, with a 41.1 % reduction in peak heat release rate (pHRR) and a 23.7 % decrease in total heat release (THR). Additionally, it diminishes the flame's size and width, leading to quicker extinction, while also lowering the internal combustion temperature of the polyurethane, thereby delaying both preheating and combustion times. The synergistic interaction between amino starch phosphate ester and EG during combustion results in the formation of a dense, continuous char layer, effectively inhibiting the pyrolysis and combustion of RPUF. This study provides a theoretical foundation for the development of efficient flame-retardant systems for RPUF.

An Interactive Fluid–Solid Approach for Numerical Modeling of Composite Metal Foam Behavior under Compression

Composite metal foams (CMF) are renowned for their high strength‐to‐density ratio, high stiffness, and energy absorption capabilities. Homogenized finite element models of CMF have been numerically solved to understand the mechanical behavior of the material under a variety of external loading conditions. This work aims to pioneer a comprehensive finite element model for steel–steel composite metal foam by incorporating the interactions between embedded stainless‐steel hollow spheres with entrapped air inside stainless‐steel matrix. The material behavior of hollow spheres, surrounding matrix, and air are modeled using Johnson–Cook (JC) plasticity, Deshpande–Fleck (D–F) foam, and linear polynomial equation of state in LS DYNA. Further, the finite element model utilizes a combination of Lagrangian solid elements and meshfree smooth particles hydrodynamics with appropriate contacts to effectively model the interaction of entrapped air within stainless‐steel hollow spheres with surrounding metallic spheres and matrix. The strain rate and the crosshead velocity of 65 s−1 and 2.4765 m s−1 are used for quasistatic compression analysis. Finally, the results obtained from the computational model are compared and validated using previously reported experimental quasistatic compression data. The numerical model corroborates stress–strain response of CMF with 5.6% error for plateau stresses average within 25% and 30% strain.

Experimental and analytical study on the compressive behavior of PMI foam with different densities and cell sizes under intermediate strain rates

Polymethacrylimide (PMI) foam materials have great potential for applications in the field of protective energy absorption owing to their superior compressive properties. Existing studies on the mechanical behavior of PMI foams are limited, particularly for loading at intermediate strain rates. This paper presents a comprehensive experimental study of PMI foam with four different densities under quasi-static and intermediate strain rate compression (0.001 s−1 to 100 s−1). Each density included three different cell sizes to determine their effects on the compressive performance. Loads parallel and perpendicular to the foam rise direction were considered to investigate the anisotropic behavior. Intermediate strain rate tests were conducted using a high-speed hydraulic servo testing machine, which achieved a stable strain rate while ensuring consistent specimen sizes in both quasi-static and dynamic tests. In all the experiments, the compression process was captured using a high-speed camera and the macroscopic deformation mode and microscopic deformation mechanism were analyzed by combining Digital Image Correlation (DIC) and Scanning Electron Microscopy (SEM). The PMI foam with finer cell sizes exhibited an enhanced compression performance. As the strain rate increased, the strain rate effect became more evident in the high-density specimens and an increase in cell size diminished this effect. A modified analytical model incorporating the cell-size correction term was developed based on Gibson and Ashby's model. The modified model exhibited an average error of 4.9 % in the predicted plateau stress of PMI foam with different cell sizes at the same density.

Compressive behavior of closed-cell metal foams under cryogenic conditions

Abstract Cellular materials in general and foams (polymeric, metallic and ceramic) in particular have seen a major development in recent years. Most of the data are reported at room temperature (RT), while the area of extreme temperatures is little studied. This work presents the quasi-static compression behavior of metallic foams (MFs). The MFs have closed cells and are manufactured from aluminum alloys (AlSi10) through powder metallurgy route. The mechanical tests are performed at cryogenic temperature (CT), and the results are compared with those at RT. It was found that as the temperature drops (CT), the samples become more brittle and withstand higher loads. The collapse mechanisms differ depending on the used test condition. The highest energy absorption performances are highlighted at CT. Also, the characteristic strains associated with the strength properties are influenced by the test temperature.

A statistical approach towards determining the governing parameters in volume expansion behavior of polypropylene foams

This study delves into the complex relationship between molecular structures and properties within polypropylene (PP) foams, with a particular focus on how various material parameters influence foamability. Multiple linear regression was adopted to efficiently assess the impact of eleven material parameters on foam expansion behavior. A primary finding is the significant role of branching index (g'vis) in shaping the expansion profile (i.e., the foaming window, maximum expansion ratio (Φmax), and optimum foaming temperature (Toptimum)). Additionally, Z-average molecular weight (Mz) is identified as crucial factor influencing the foaming window. Furthermore, the Winter-Chambon parameter n, indicator of the relaxation behavior of a resin in the terminal zone, is distinguished as a key parameter in determining Φmax. The crystallization temperature (Tc) also plays a pivotal role, particularly in its relationship with Toptimum. The research further highlights the significance of long-chain branching (LCB) and suggests strategies for cost reduction by minimizing the degree of LCB without compromising foaming performance, achievable through the adjustment of Mz and n. This strategy was exemplified through the comparison of two LCB PP resins, PP-12 and PP-22, demonstrating the feasibility of achieving similar foamability with adjustments in material parameters. The findings offer a detailed assessment of these parameters' influence on foamability, presenting valuable guidelines for optimizing PP foam production and customizing material properties for targeted applications.

Role of pulse globulins and albumins in air-water interface and foam stabilization

Pulse protein isolates are promising substitutes for animal protein in foam preparation, but they typically are complex mixtures of multiple proteins, and the contribution of the individual proteins to the behavior of the mixture in air-water interface stabilization is largely unknown. The major protein fractions in isolates are the globulins and albumins, and this study systematically investigated the molecular properties, and interfacial and foaming properties of these two fractions for three different pulses: lentils, faba beans and chickpeas. The key parameters of these pulse proteins in air-water interface and foam stabilization were investigated by correlation analysis. Based on this, low denaturation enthalpy tends to result in both high foamability and foam stability, most likely due to a greater conformational flexibility that allows for a faster adsorption to the air-water interface, and higher degree of structural rearrangement at the interface, which increases interfacial network stiffness. For globulin-rich pulse protein fractions, vicilins and convicilins tend to introduce high surface hydrophobicity, which increases the affinity of the proteins for the interface, and increases protein-protein in-plane interactions through hydrophobic interactions, resulting in the enhancement of interfacial network connectivity and the level of network branching. These factors increase the interfacial resistance to large deformations and increase foam stability. Vicilins and convicilins also tend to have a high value of the surface charge and further promote foam stability by increasing electrostatic repulsion between air bubbles. Legumins tend to reduce foamability since they adsorb to the air-water interface slowly and tend to disrupt the interfacial network structure. These findings provide deeper insights in the role of pulse globulins and albumins in air-water interface and foam stabilization. The proposed key parameters will benefit the predictability of the interfacial and foaming behavior of pulse proteins.

Preparation, pore structure and properties of uniformly porous glass-ceramics sintered from granite powder using SiC@SiO2 foaming agent

Granite sludge produced during the processing of granite blocks should be efficiently recycled for environmental protection and as a sustainable resource. In this work, porous glass-ceramics were prepared by stepwise sintering of granite powder using core-shell SiC@SiO2 foaming agent. The SiC and SiC@SiO2 foaming agents were compared in terms of the sintering and foaming behaviors of the powder compacts by thermal expansion, thermogravimetry and mass spectroscopy. The foaming agent and foaming temperature were investigated to study their effects on the pore structure and properties of the porous glass-ceramics. The SiO2 shells of the SiC@SiO2 particles inhibited the oxidation of the SiC cores and the release of CO2 at the early stage of the sintering process, thus preventing pore coalescence and increasing the densification and specific strength of the sintered glass-ceramics. As the foaming temperature increased, the porous glass-ceramics exhibited a linear relationship between pore size and foaming temperature, and the specific strength first increased and then decreased due to pore coalescence and reduced crystallinity. Furthermore, the linear relationship between thermal conductivity and porosity indicates a closed pore structure, as demonstrated by computed tomography. At a foaming temperature of 1220 °C, the porous glass-ceramic has a porosity of 50.1 %, a specific strength of 16.6 kN⋅m/kg and a thermal conductivity of 0.747 W/(m⋅K). Numerical simulation confirms that lightweight glazed glass-ceramics have potential applications in energy-efficient building tiles.

Impact of citrus pectin on the foaming behavior, structures, and barrier properties of the starch foam blocks

The starch foam displays weak barrier properties under humid storage, which limits its applications in the food industry. In this study, citrus pectin was loaded to strengthen the starch foam. Results showed that the pectin (4 wt% ∼ 8 wt%) effectively modified the cell structures of the starch foam block. This was attributed to the increased viscosity of the starch melt during foaming and the enhanced cell stability during cooling, which was promoted by the formation of entanglements, hydrogen bonds, and ester bonds between pectin and starch, as confirmed by FTIR and DSC. Moreover, the pectin-starch foam displayed improved mechanical properties under wet storage conditions, mainly due to the limited moisture adsorption and water migration. The foam containing 4 wt% of pectin exhibited the highest compression-recovery ratio (76.7 %) and a reduced adsorbed moisture content (19.22 %) under 95 % RH. Overall, citrus pectin could improve the starch foaming process and the foam blocks barrier properties.

Cellulose nanofibers enabled strong and flexible plant-derived thermoplastic polyester elastomer foams for high-performance thermally insulating applications

Flexible thermal insulation materials have garnered significant attention owing to the proliferation of flexible electronic devices and their diverse application environments. Plant-derived thermoplastic polyester elastomer (TPEE) foams emerge as promising candidates in the field of flexible thermal insulation. However, inevitable shrinkage behavior of TPEE foams would result in reduced porosity and inferior thermal insulation performance. Hence, a pioneering approach is proposed wherein cellulose nanofibers (CNF) are integrated into TPEE matrixes, complemented by microcellular foaming, aimed at mitigating shrinkage process and enhancing thermal insulation properties. In this work, the relaxation behavior of nanocomposite, corresponding to shrinkage process, has been elucidated through dynamic mechanical analysis. It's found that entanglement of CNF could heighten the internal friction with TPEE molecular chains, coupled with establishment of hydrogen bonds, thereby curbing relaxation phenomena and facilitating the attainment of foams with enhanced and stable porosity. The shrinkage ratio of TPEE/CNF composite foam could be reduced by 20 % without compromising the final porosity. The thermal conductivity would decrease to 37.9 mW/m·K for the TPEE/CNF composite foam with the higher porosity of 0.947. Moreover, the utilization of CNF presents a novel avenue for fabricating TPEE/CNF nanocomposite foams endowed with flexibility, lightweightness, increased porosity, and reduced thermal conductivity.

Prediction of Stress Relaxation Behavior of Polymer Foam Using Artificial Neural Network

Prediction of Stress Relaxation Behavior of Polymer Foam Using Artificial Neural Network

Mesostructural Model for the Fatigue Analysis of Open-Cell Metal Foams

Metallic foams exhibit unique properties that make them suitable for diverse engineering applications. Accurate mechanical characterization is essential for assessing their performance under both monotonic and cyclic loading conditions. However, despite the advancements, the understanding of cyclic load responses in metallic foams has been limited. This study aims to propose a mesostructural model to assess the fatigue behavior of open-cell metal foams subjected to cyclic loading conditions. The proposed model considers the previous load history and is based on the analogy of progressive collapse, integrating a finite element model, a fatigue analysis model, an equivalent number of cycles model, and a failure criterion model. Validation against experimental data shows that the proposed model can reliably predict the fatigue life of the metallic foams for specific strain amplitudes.

Evaluation of foaming performance for polymer modified and virgin asphalt binders

The pavement suffers rapid deterioration as a result of the weak bonding strength exhibited by the foamed virgin asphalt in the mixture. Consequently, it is crucial to develop a modified asphalt suitable for foaming. The expansion height and bubble size of foamed asphalt can be continuously and simultaneously monitored by binocular ranging equipment. By analyzing these dynamic responses, the evolution of the spatial domain expansion characteristics and the geometric features of the surface bubbles of foamed thermoplastic resin modified asphalt (TRA) was analyzed. Meanwhile, multi-stress creep recovery (MSCR) and bending beam rheometer (BBR) tests were conducted to analyze its rheological properties. Subsequently, the dispersibility of foamed TRA in the mixture was explored. The results showed that thermoplastic resin significantly improved the physical performance stability of foamed asphalt, as evidenced by an increase in its half-life by 2–3 times compared to the virgin asphalt when the dosage of thermoplastic resin reached 8 %. Foamed modified asphalt has fewer bubbles, but it has larger bubble sizes and more uniform distribution of bubbles. Meanwhile, the TRA exhibited excellent high-temperature deformation resistance and elastic recovery ability. The dispersion uniformity of foamed TRA in the mixture was superior to that of virgin asphalt. This study serves as a valuable reference for the exploration of foaming behavior in modified asphalt and the utilization of foamed modified asphalt in the mixture.