Behavior Of Foams Research Articles

Flame-retardant polymethacrylimide foams modified by grafting with amino-terminated phosphorous polyborosiloxane

To improve the flame retardancy of Polymethacrylimide (PMI) foam, in this study, a series of flame-retardant PMI foams were prepared by grafting with flame retardant amino-terminated phosphorous polyborosiloxane (N-PBSi), using tert-butanol (TBA) as the foaming agent. The structure, mechanical properties, thermal behavior, and flame retardancy of the resultant PMI foams were characterized. These as-prepared foams tended to be more compact in structure as N-PBSi content increased. The tensile, compressive, and bending strength of these PMI foams therefore was greatly enhanced, which were about 2 times, 9 times, and 3 times that of pure PMI foam, respectively. Besides, the introduction of N-PBSi also attributed to PMI foams better performance in char forming, especially in the air, which is beneficial for obtaining better retardancy against flame. Their advantages in flame retardancy and smoke inhabitation were confirmed by limiting oxygen index (LOI) and cone calorimeter tests (CCT). The total heat release (THR) and the peak of smoke generation rate (pSPR) of PMI/N-PBSi-20 were reduced by 23.1% and 69.9%, respectively. The N-PBSi incorporated were thought to not only generate phosphorus-containing fragments to capture free radicals in gas phase, but also rearrange in the solid phase to form a denser carbon layer to provide a better barrier between external heat and internal flammable pyrolysis gases. Given these, it can be envisaged that the flame-retardant PMI foams modified by N-PBSi may be more attractive in a wider range of applications.

Quantitative Analysis of Mechanical Strength of Three-Phase Rigid Polyurethane Foam Composites Immersed with Water

The mechanical properties of rigid polyurethane foam (PUF) will be significantly affected because of the existence of water when applied in dam repair and road maintenance. The related studies generally consider the effects of water and matrix on the mechanical properties of rigid PUF. However, PUF is a three-phase composite consisting of water, air, and matrix in practical engineering. Its mechanical properties are subject to the combined effects of these three composites at the same time. In this case, an improved three-phase viscoelastic model was proposed to quantify the effects of water, air, and matrix on the compressive mechanical behavior of rigid polyurethane foam immersed in water (WRPF). Based on the improved viscoelastic model and piecewise method, a compressive strength prediction model of WRPF was developed to describe the change of WRPF’s compressive strength during the full-service life. Then uniaxial compression tests and electron microscope tests were conducted to verify the rationality of the model. Results show that water and air have reinforcing effects on the compressive property of WRPF in the short-term, unsaturated absorption stage. In contrast, water has weakening effects on its compressive property in the long-term, saturated stage. Finally, at different stages of water absorption, a semitheoretical and empirical formula was developed from the prediction model and the experimental data from compressive tests.

Dynamic interfacial properties and foam behavior of licorice root extract solutions

Licorice (Glycyrrhiza glabra) is a useful plant of the family Fabaceae, with sweet-tasting roots. The root extract of this plant is rich in saponins, so it can be considered a source of natural surfactants. This research provides some applicable information about the dynamic surface tension and foam behavior of aqueous solutions of licorice root extract (LRE). The pendant drop shape analysis was utilized to study the surface tension and dilational surface rheology of LRE at the water/air interface. The Bikerman type experiment was used to measure foamability and foam stability of aqueous LRE solutions. The equilibrium surface tensions reveal that the LRE contains surface-active components and is capable of reducing the surface tension by 25 mN/m at the critical aggregation concentration (CAC). The surface dilational visco-elasticity measurements proved that the adsorption layers are predominantly of elastic nature. Also the foamability and foam stability show a meaningful correlation with the dynamic surface properties. This study aims to contribute to the development of appropriate utilization of the benefits provided by a biosurfactant source in foam-related commercial applications.

Effect of zinc addition on the tribological behavior of aluminum-based close cell metal foams

Effect of zinc addition on the tribological behavior of aluminum-based close cell metal foams

Holistic structural analysis of polymeric foam systems

In the construction industry, materials with density advantages are becoming increasingly prevalent due to the trend toward lightweight construction. These include, above all, synthetic foams based on polyurethane and polypropylene. While they are mainly used for thermal insulation during thermal refurbishment, they are also increasingly being used for structural tasks. On the part of manufacturers, these are still dominated by standardized mechanical test methods such as compression or flexure tests. However, the major drawback of these strength tests is the need for more information about the structural failure behavior of polymer foams in the fracture zone itself, the interface. Since fracture analytical approaches provide only limited vital figures, this work presents a holistic approach that encompasses all areas of evaluation. This influences sample size, orientation (isotropy), fracture zone effects (failure patterns), and structural safety. Common synthetic polymer foam systems (open-cell and closed-cell) are used to represent the broadest possible range of evaluation. The results show that it is not the materials with the highest tensile strength that are most convincing, but those with the most extraordinary fracture energy and damage tolerance. The practical information greatly expands the selection options for decision-makers since technical data sheets from manufacturers can only be used to a limited extent.

Foam and Antifoam Behavior of PDMS in MDEA-PZ Solution in the Presence of Different Degradation Products for CO2 Absorption Process

Absorption is one of the most established techniques to capture CO2 from natural gas and post-combustion processes. Nevertheless, the absorption process frequently suffers from various operational issues, including foaming. The main objective of the current work is to elucidate the effect of degradation product on the foaming behavior in methyldiethanolamine (MDEA) and piperazine (PZ) solution and evaluate the antifoaming performance of polydimethylsiloxane (PDMS) antifoam. The foaming behavior was investigated based on types of degradation product, temperature, and gas flow rate. The presence of glycine, heptanoic acid, hexadecane, and bicine in MDEA-PZ solution cause significant foaming. The presence of hexadecane produced the highest amount of foam, followed by heptanoic acid, glycine and lastly bicine. It was found that increasing the gas flow rate increases foaming tendency and foam stability. Furthermore, increasing temperature increases foaming tendency, but reduces foam stability. Moreover, PDMS antifoam was able to reduce foam formation in the presence of different degradation products and at various temperatures and gas flow rates. It was found that PDMS antifoam works best in the presence of hexadecane with the highest average foam height reduction of 19%. Hence, this work will demonstrate the cause of foaming and the importance of antifoam in reducing its effect.

Keys to improve the efficiency of nanoparticle‐stabilized foam injection based on influential mechanisms

AbstractThe effect of the existence of nanoparticles on foam stability, foamability, and the oil recovery factor (RF) has been studied experimentally, and influential phenomena and mechanisms have been examined. A sequence of experiments, including, ‘foam bulk‐static experiments’, ‘surface tension (ST) measurements,’ and ‘micromodel foam flood,’ were designed and then implemented to study the foam behaviour in two foam systems: (1) anionic‐nanoparticles + cationic‐surfactant and (2) anionic‐nanoparticles + anionic‐surfactant. This study provides a comprehensive insight into the mechanisms affecting the stability of nanoparticle‐stabilized foam. Also, despite previous studies, the effect of Marangoni flow on nanoparticle‐stabilized foam has been discussed briefly. Results show that the interactions of effective mechanisms work differently in the two series. In the like‐charge system, surfactant molecules accumulate in the interface of lamellas due to repulsive forces; therefore, stability and foamability improve as surface tension and molecular diffusion reduce. Additionally, Marangoni flow restitutes the negative impact of gravity drainage. In the unlike‐charge system, observations illustrate that nanoparticles reach the interface. The presence of nanoparticles at the interface increases detachment energy significantly, and as a result, the stability is boosted. The accumulation of nanoparticles in the interface changes it to a solid‐like surface with limited diffusibility and viscosity. Although Marangoni flow is lost, reducing molecular diffusion improves foam stability. Flooding tests show that foam stability increment improves sweep efficiency at near‐wellbore areas even when foamability is weak. Finally, it can be claimed that in the unlike‐charge system, the sweep efficiency and foam stability increase to a greater extent.

The effects of oil contamination on the stability and flow behavior of drilling foams under high-pressure conditions

Foams used in drilling can be contaminated by formation influx containing oil. The stability and flow behavior of foam are affected when it comes into contact with oil. The objective of this study is to investigate the impact of oil on foam drainage and rheology under high-pressure conditions.Drainage and rheology experiments were performed introducing different types of oils (mineral oil, light crude oil, and heavy crude oil) into the surfactant solution at varying concentrations. The tests were performed at three different foam qualities (40%, 50% & 60%). To determine the drainage, the foam was first generated in a flow loop and its rheology was measured. Subsequently, its drainage was evaluated by trapping it in a vertical test section (stability cell) and measuring the pressure profile of the foam column trapped in the cell using ten pressure sensors. The foam drainage was determined as a function of time by analyzing the pressure profile data. Tests were conducted under ambient temperature (25 ± 3 °C).The results show how the foam drainage and rheology were affected by oil type and concentration. Low-quality foam (40%) showed a slight stabilizing effect with increasing mineral oil concentration. However, high-quality foams (50% and 60%) destabilized with increasing the concentration of the mineral oil. Crude oil type was found to affect the stability of the foams. Light crude oil had a more destabilizing effect as compared to heavy crude oil.

Corrosion inhibitor and chelating agent impact on foam stability for formation stimulation applications

Injection of foam into petroleum reservoirs has attracted special interest in the last years. Utilizing foam in well stimulation is promising as it consumes less water than water-based fracturing fluids. Nevertheless, the success of foam application mainly depends on its stability. Thus, it is essential to understand the role of gas type, water chemistry, and other additives such as acids (e.g., chelating agent) and corrosion inhibitors on the generation and stabilization of foam. Hence, a dynamic foam analyzer (DFA) and optical interfacial tensiometer were used to study foam stability under different conditions. Surfactant screening showed that Duomeen TTM and Armovis are superior foamers at low pH (3.5), and therefore were used in this study. The liquid phase typically contained high salinity water, 15 %wt. Chelating agent, L-glutamic acid-N, N-diacetic acid (GLDA), and 1 %wt. surfactant with and without a corrosion inhibitor (CI). First, we investigated the effect of gas types on the stability of the foam. The results revealed that N2-foam is more stable compared to CO2-foam. Also, the results showed that the corrosion inhibitor reduced the foam stability for both N2-foam and CO2-foam. Three types of water were examined; distilled water (DI), produced water (PW), and seawater (SW) for foam stabilization. The water chemistry had little effect on the stability of TTM compared to its impact on Armovis. Finally, we found that GLDA addition to Armovis increased the stability of foam by four times compared to no GLDA addition. Moreover, the stability GLDA/Armovis system was six times higher with CO2 and more than 20 times higher with N2 as compared to TTM stability. The foamability, foam volume, bubble count, and foam structure were studied to determine the foam behavior at given conditions. This study provides a broad understanding of additives’ impact on stimulating foam stability.

Effect of PGMA-saponite brushes on the rheology, crystallization and supercritical CO2 foaming behavior of poly(lactic acid)

In this work, poly(glycidyl methacrylate) (PGMA) were grafted onto the surface of saponite to form polymer brushes (m@g-Sap) via surface-initiated atom transfer radical polymerization (SI-ATRP). Moreover, PLA/m@g-Sap nanocomposites foams were prepared by supercritical carbon dioxide foaming with m@g-Sap as fillers. And its comprehensive performance, structure-properties relationship were investigated. It was shown that m@g-Sap as an efficient nucleating agent enhanced the rheological properties, crystallization behavior and foamability of PLA. The pore density of PLA4 (PLA/m@g-Sap (0.7 wt%) nanocomposites foams) is increased by 3 orders of magnitude and its average pore size is reduced by 84.94%. Furthermore, the unique intercalation structure and branched interpenetration network structure of m@g-Sap effectively improved the compression resistance of PLA based nanocomposites foams. Compared with pure PLA foam, the compressive strength of PLA4 platform region increased by 282%. Finally, what's more, the results of simultaneous rheological and in situ IR, molecular dynamics simulations indicate that there was a significant interaction between m@g-Sap and PLA and CO2, which in turn enhanced the melt strength of PLA based nanocomposites and induced the rapid crystallization of PLA. The above results demonstrated that m@g-Sap had great potential to improve the foaming behavior of PLA.

Mixed-modes (I/III) fracture of aluminum foam based on micromechanics of damage

Nowadays, foam structures have several applications in industries. Basically, discontinuities such as pores cause complications in evaluating the mechanical and fracture behavior. In other words, understanding the multi scale of porous cells in cracked foams can play a significant role in fracture prediction. The present research proposes an analytical approach based on the experimental concept of damage in which the behavior of cracked metal foam was investigated under mixed-mode I/III (tensile and out-of-plane) fracture. In this method, pores in foam are modeled as circular and elliptical defects. In this context, mechanical properties and crack inclination angle are obtained based on loading and configuration of pores. Dispersion of circular and elliptical discontinuities determines the overall modulus and crack inclination angle trajectory based on the experimental results, pure mode I SIF were occurred on (0°) and pure mode III were obtained at (62°) loading angle. The aluminum foams were produced and prepared according to the edge notch disc bend (ENDB) test method to obtain the onset of fracture initiation ( KIc and KIIIc) and trajectory of cracked foam body. The results demonstrated that analytical approach, based on circular pore distribution, had a good agreement with experimental results. Moreover, the results indicated that SIF in mode I and mode III had the most agreement with the experimental results at angles of 0° and 62°, respectively.

Effect of nano‐sized zinc citrate on the supercritical carbon dioxide‐assisted extrusion foaming behavior of poly(lactic acid)

AbstractPoly(lactic acid) (PLA) foams containing various amounts of an epoxy as a chain extender (CE) and nano‐sized zinc citrate as a nucleating agent are prepared by continuous extrusion using supercritical CO2 (sc‐CO2) as a physical foaming agent. Processing parameters such as the CE content, sc‐CO2 flow rate, and foaming temperature are optimized with regard to the apparent density and expansion ratio of the PLA foams. The nano‐sized zinc citrate exhibits a high nucleation activity for the crystallization of the PLA. The addition of 0.5 wt% nano‐sized zinc citrate significantly increases the compressive strength and modulus of the PLA foams from 0.124 MPa and 3.1 MPa to 0.35 MPa and 19 MPa, respectively. The PLA/0.5 wt% nano‐sized zinc citrate foam shows a microcellular structure with an average cell diameter of 17.1 μm.

Sonication of egg and its effect on foaming behavior

Effect of sonication on egg foaming.

Novel Method for the Characterization of the Electrical Conductivity and Eddy Current Damping of Aluminum Foams

In this paper, we present a novel method for indirect characterization of eddy currents damping and loss coefficients, as well as the equivalent electrical conductivity of metal foams. The proposed method is based in the measurement of the braking torque when the metal foams are exposed to an alternating magnetic field generated by a set of rotating permanent magnets. Measurements are carried out in a low-frequency range (< 50 Hz) and for high amplitude magnetic fields (up to 0.4 T), both typical values observed in electromechanical devices. This method was used for accurate characterization of a set of open-cell aluminum foams with different compositions and porosities. Experimental results, in good agreement with the theoretical models, confirm the viscous damping behavior of aluminum foams in the tested frequency range. The quadratic dependency of the damping coefficient on the magnetic flux density is also confirmed in the measurement range.

EFFECT OF MICRO-BALLOON VOLUME FRACTION ON THE TENSILE BEHAVIOR OF EPOXY SYNTACTIC FOAMS REINFORCED WITH GLASS MICRO-BALLOONS

In this study, the effects of volume fraction on the tensile behavior of epoxy syntactic foam reinforced with glass micro-balloons are investigated. Nine different samples with various volume fractions of glass micro-balloons (0&amp;#37;-68&amp;#37;) were prepared. Elastic modulus, maximum tensile stress, and strain at failure of epoxy syntactic foams reinforced with glass micro-balloons are investigated. Scanning electron microscope (SEM) images are taken from the broken samples' surfaces and used to discuss the results. Results show that the specific elastic modulus and specific maximum tensile stress (MTS) of epoxy syntactic foams increased by about 108&amp;#37; and 28&amp;#37; by increasing the micro-balloon volume fraction from 0&amp;#37; to 68&amp;#37;. However, the samples' modulus and strength are respectively decreased by about 5&amp;#37; and 39&amp;#37; with increasing the volume fraction of the glass micro-balloons from 0&amp;#37; to 34&amp;#37;. The main growth of specific strength and elastic modulus was for samples with more than 34&amp;#37; micro-balloon volume fraction. Moreover, the elastic modulus increased by about 11&amp;#37;, and the samples' maximum tensile stress (MTS) decreased by about 32&amp;#37;, increasing the micro-balloon volume fraction from 0&amp;#37; to 68&amp;#37;. With increasing the micro-balloon volume fraction from 0&amp;#37; to 68&amp;#37;, the strain at failure of epoxy syntactic foams is decreased by about 41&amp;#37;.

Time-dependent rheological behavior of pineapple pulp foam and its relationship with foaming properties and quality attributes of dried powder

The time-dependent rheological characteristics of pineapple pulp foam (PPF), prepared by whipping the pulp with varying concentrations (2–6%) of skim milk powder (SMP), were investigated at different shear rates (1, 10, and 50 s−1). The PPF showed time-dependent shear-thinning behavior that could be explained by the Hahn and Figoni-Shoemaker models (|r|≤0.997). The time and shear-rate-dependent structural breakdown coefficients (B- and M-values) varied due to foam properties (stability, expansion, and drainage volume) and SMP concentration. These coefficients could be suitable indices to judge the stability of the foam. The effective moisture diffusivity during foam drying increased significantly with SMP (p ≤ 0.05); the physical properties of powder were also influenced. A strong correlation existed between SMP, foaming, and rheological properties. The principal component analysis (PCA) indicated a good interrelation among rheological properties, foam, and powder characteristics.

Three-dimensional liquid foam flow through a hopper resolved by fast X-ray microtomography.

We probe the complex rheological behaviour of liquid foams flowing through a conical constriction. With fast X-ray tomographic microscopy we measure in situ the displacement and deformation of up to fifty thousand bubbles at any single time instance while varying systematically the foam liquid fraction, the bubble size and the flow direction - convergent vs. divergent. The large statistics and high spatio-temporal resolution allows to observe and quantify the deviations from a purely viscous flow. We indeed reveal an asymmetry between the convergent and divergent flows associated to the emergence of elastic stresses in the latter case, and enhanced as the liquid fraction is reduced. Such effect is related to the reorientation of the deformed bubbles flowing out of the constriction, from a prolate to an oblate shape in average, while they pass through the hopper waist.

Mapping 3D grain and precipitate structure during in situ mechanical testing of open-cell metal foam using micro-computed tomography and high-energy X-ray diffraction microscopy

• 3D grain structure is mapped and tracked during loading of open-cell metal foam. • Challenges included sample size relative to beam size and large ligament motions. • X-ray CT and far-field HEDM measurements collected at incremental displacements. • New scanning and stitching methodology established for far-field HEDM measurements. • Ligament-tracking code used to express crystal orientation in local reference frame. Open-cell metal foams are ultra-low-density cellular metals with complex hierarchical structures that span bulk, cell, ligament, and sub-ligament scales and give rise to desirable properties such as high strength-to-weight ratio and excellent energy absorption. Although literature suggests that intrinsic material structures at sub-ligament length scales (e.g., grains and precipitates) play an important role in mechanical behavior of open-cell metal foams, there are very few experimental measurements of such structures in three dimensions and for meaningful volumes of foam. This study seeks to map and track the three-dimensional (3D) grain and precipitate structures of an intact volume of open-cell aluminum foam by advancing microstructural characterization techniques that leverage X-ray micro-computed tomography ( μ CT ) and far-field high-energy X-ray diffraction microscopy (FF-HEDM). A 6%-relative-density aluminum foam sample was mechanically tested in compression while μ CT and FF-HEDM measurements were collected at interrupted loading states at beamline 1-ID of the Advanced Photon Source. A new scanning strategy and reconstruction algorithm were established to enable characterization of a foam volume with diameter approximately four times wider than the nominal width of the X-ray beam. The result is a set of maps that detail both the 3D grain and precipitate structures throughout the foam volume at successive strain steps. A novel grain tracking procedure was developed to track individual grains within the foam volume by accounting for the large rigid-body motions that individual ligaments can undergo during mechanical loading. The ability to track grains and precipitate structures in three dimensions throughout large bulk deformation of ultra-low-density polycrystalline materials enables new possibilities for validating numerical models and investigating local failure mechanisms. Furthermore, the methods and procedures developed in this study could be applied to other ultra-low-density structures, such as additively manufactured lattices.

Autoclave foaming and steam-chest molding of polypropylene/polybutene-1 blend bead foams and their crystallization and mechanical properties

Expanded polypropylene (EPP) foams have showed wide applications in our daily life, such as automotive and packaging. Usually, autoclave foaming combined with steam-chest molding is the main artwork to prepare the high-precision EPP foam products. However, the foaming behavior of EPP and the excessive pressure required for molding still need to be further improved, which is great significance for energy saving and cost saving, etc. Herein, this study finds that adding a certain amount of polybutene-1 (PB-1) into the PP can help to reduce the temperature and pressure required for foaming/molding, and to broaden the foaming temperature. For example, in order to make the foam beads bonding well and with the expansion ratio of 20, the molding pressure should be higher than 2.7 bar for Neat PP foams, but just 1.5 bar for PP/PB-1 mixtures. Moreover, the effects of PB-1 content on the crystallization properties and foaming/molding behaviors of the PP/PB-1 bead foams are illustrated, and then the mechanical properties are also studied. Furthermore, the low-pressure foaming strategy presented here is beneficial for reducing the barriers of energy consumption and promoting the development of new bead foam materials.

On the physicochemical properties and foaming characteristics of proteins in cement environment

This paper investigates the physicochemical properties of proteins and their foaming characteristics in a synthetic pore solution (SPS) of cementitious materials to aid in understanding their air-entraining performance. A total of 13 proteins with different molecular structures and physicochemical properties were studied. Hydrodynamic size, charge, viscosity, surface tension, and foam capacity and stability of the proteins at different concentrations were characterized. Optical microscopy was employed to study the foam bubble size and structure. It was shown that proteins gained an increased negative charge and their hydrodynamic size generally decreased at high pH relevant to cementitious materials. The effect of SPS on surface tension of the proteins did not show a specific trend. The proteins demonstrated improved foaming in SPS compared to in deionized water (DI) due to the change in their physicochemical properties. The bubble size distributions of the foams were analyzed. Optical microscopy showed increased roughness and thickness of the bubble film in the foam in SPS, indicating enhanced stability compared to the foam in DI. The effect of surface tension of the proteins on their foaming behavior was shown to be less in SPS than in DI.