Foaming Characteristics Research Articles

Continuous phase rheology points to paths forward for improving properties of food foams

As the use of edible foams increasingly extends to householdhold preparations, new techniques studying the role of flow in foam characteristics look to improve stability.

Relating the protein composition and air-water interfacial properties of aqueous flour extracts from wheats grown at different nitrogen fertilization levels

Aqueous phase extractable proteins from wheat can play a functional role in foods requiring interfacial stabilization. We here investigated the (protein) composition of aqueous flour extracts from wheats grown at different nitrogen (N) fertilization levels and studied their air–water interfacial characteristics. An important finding was that α- and γ-gliadins were extracted from wheat flour with water, even to an extent that they in the present work comprised 62–71% of the extract proteins. Application of N fertilization during wheat cultivation led to flour extracts with higher foam stabilities and air–water interface dilatational moduli. In all cases, proteins were found to most likely be the dominant constituent at the air–water interface. Analysis of foam protein compositions revealed an enrichment of proteins with molecular weights matching those of α- and γ-gliadins. It thus seems that gliadins can to a large extent determine the foaming characteristics of aqueous wheat flour extracts.

Influence of drying techniques on sensory profile and chlorogenic acid content of instant coffee powders

To ascertain the best technique for retention of sensory properties and chlorogenic acid (CGA) in instant coffee, the present study involved several drying techniques such as spray drying, freeze drying, spray freeze drying (SFD), conductive hydro drying, and compared the effect with a commercial sample. From the analysis of all coffee samples, both by sensory analysis (based on fuzzy logic) and by descriptive analysis (for foaming characteristics), SFD coffee was preferred. This fact was further corroborated by electronic nose-based aroma analysis of coffee. Chromatographic analysis (HPLC) revealed maximum (85%) retention of CGA in SFD (52.35±0.61 mg CGA/g of coffee powder). Overall, SFD emerged as the most preferred technique for the preparation of instant coffee.

Synthesis of Rigid Polyurethane Foams Incorporating Polyols from Chemical Recycling of Post-Industrial Waste Polyurethane Foams.

The preparation and characteristics of rigid polyurethane foams (RPUFs) synthesized from polyols obtained by glycolysis of post-industrial waste RPUFs have been studied. More precisely, waste rigid foams that have been chemically recycled by glycolysis in this work are industrially produced pieces for housing and bracket applications. The glycolysis products have been purified by vacuum distillation. The physicochemical properties of the polyols, such as hydroxyl value, acid value, average molecular weight (Mn) and viscosity have been analyzed. The chemical structure and thermal stability of the polyols have been studied by means of FTIR and TGA, respectively. Partial substitution of the commercial polyol (up to 15 wt.%) by the recycled polyols increases the reactivity of the RPUFs synthesis, according to short characteristic times during the foaming process along with more exothermic temperature profiles. Foams formulated with recycled polyols have a lower bulk density (88.3–96.9 kg m−3) and smaller cell sizes compared to a conventional reference RPUF. The addition of recycled polyols (up to 10 wt.%) into the formulation causes a slight decrease in compressive properties, whereas tensile strength and modulus values increase remarkably.

Influence of admixtures on the characteristics of aqueous foam produced using a synthetic surfactant

Foam characteristics, including density, stability, and texture, influence the properties of end products like foamed concrete. The present work investigates the individual and combined influence of xanthan gum and low-cost sodium-based admixtures (NaOH, NaCl, and Na2CO3) on the viscosity of sodium lauryl sulfate (SLS) foaming solution and the foam characteristics. Where xanthan gum induced its characteristic pseudo-plastic behavior to the foaming solution, the addition of sodium-based admixtures did not affect the Newtonian behavior of the SLS solution. The addition of sodium-based admixtures elevated the critical turbidity and Krafft temperature of the surfactant solution. Xanthan gum substantially reduced the liquid drainage and improved stability to a great extent. However, the increment in foam density was more gradual with increasing xanthan gum dosage, following an increase in lamella thickness. Sodium-based admixtures significantly increased the density of foam while reducing the bubble sizes. Further, the SLS solution admixed with xanthan gum and sodium-based admixture resulted in foam with properties intermediate to the foams stabilized with individual admixtures. The resulting foam had a higher density and a smaller mean bubble size than unstabilized or xanthan gum stabilized foam. In contrast, the stability was more increased compared to unstabilized or sodium-based admixture stabilized foam.

Development of carrot top powders using foam mat drying

Carrot tops are under-exploited greens despite having high nutritional value. The effect of ovalbumin and Emustab® concentration and whipping time on foam characteristics was evaluated, and 10% (w/w) of Emustab® and 10 min of whipping was selected for use. Foam mat drying was performed at 50–70°C, and effects of temperature on physicochemical properties, morphology, and centesimal composition of the powders were investigated. Midilli and Kucuk’s model best represented the drying kinetics (R2 = 0.994). Increasing temperature reduced drying time by more than three-fold and significantly (p < .05) affected the moisture content (6.15–11.82% d.b.), hygroscopicity (1.27–2.57%), rehydration ratio (3.30–3.77), and total color difference (14.07 < ΔE < 16.77) of the carrot tops’ powders. Powder at 50°C showed higher moisture content, lower hygroscopicity, and better rehydration rate. Drying at 70°C produced powders with lower ΔE and higher protein content. For all drying conditions, however, fresh carrot tops yielded stable and porous powders, promising for use in ready-to-cook foods. Practical applications Carrot tops are one of the most underutilized greens of appreciable nutritive value. The foam mat drying proved to be promising for the dehydration of these materials, being the carrot top powders extensively characterized to know its properties and variations caused by drying. The results obtained will benefit both researchers and industry professionals to design better drying processes and innovative products based on carrot tops.

Mechanical performance and cushioning energy absorption characteristics of rigid polyurethane foam at low and high strain rates

This study elucidates the mechanical response of rigid polyurethane foam (RPUF) at different strain rates and densities. A series of quasi-static and dynamic loading tests on the RPUFs were performed to determine the deformation modes, stress-strain curves, and effects on density, strain rate, and energy absorbing performances. Consequently, the static compressive behavior of RPUF significantly depends on density and strain rate, while the dynamic compressive behavior of RPUF significantly depends on density. However, the effect of strain rate is not evident at high strain rates (500 s−1–2500 s−1). The elastic modulus, compressive strength, and yield stress of RPUF increase with a rise in density. The experimental results show that the compressive strength is enhanced at a high strain rate loading when compared with that at quasi-static loading. Based on the measured stress-strain curves, the variation in energy absorption and efficiency with respect to RPUF density was studied. The typical damage mechanism of RPUF with different densities was investigated via scanning electron microscopy. Cell wall buckling is the prominent failure mode in the high-density RPUF; however, the main failure modes of low-density RPUF are wrinkling and stretching of cell faces.

A novel approach for preparing glass ceramic foams from MSWI fly ash: foaming characteristics and hierarchical pore formation mechanism

Powder sintering and in–situ foaming are the primary treatments for the preparation of glass ceramic foams from solid wastes. However, variables such as crystallization and viscosity, which are difficult to regulate at high temperatures. Herein, a novel technology based on alkali activation–crystallization strengthening was developed for the fabrication of glass ceramic foams with hierarchical pores. Vitrified municipal solid waste incineration (MSWI) ashes as the main calcium and aluminum source and secondary aluminum ash (SAA) as a foaming agent were foamed in NaOH solution at room temperature. The effects of solid–liquid ratio and NaOH concentration on the pore structure, individual foam force, phase evolution and physical properties were investigated, including crystallization kinetics and hierarchical pore formation mechanism. The results indicated that the solid–liquid ratio decreased from 60:40 to 40:60, making the pore wall thin and eventually disappear. The pore size in the range of 0–1 mm reaches 99.5% in 3 mol/L NaOH sample, with the lowest mean size of 0.34 mm. The crystallization kinetics parameters of the basic glass at 5–20 K/min showed that grains were primarily precipitated as three–dimensional at 5 K/min, resulting in micropores. The prepared samples exhibit high porosity (79.23–88.35%), adequate compressive strength (0.36–5.55 MPa) and a bulk density of 0.68–0.76 g/cm3. This work develops the function of SAA as a foaming agent at room temperature, as well as a new idea for the preparation of glass ceramic foams from solid waste containing glass phase or needing vitrification.

Investigation of the effect of polymers on dermal foam properties using the QbD approach

Dermal foams are promising drug delivery systems due to their many advantages and ease of application. Foams are also considered a novelty in the field of dermatology. In particular, they are beneficial for the treatment of skin conditions where patients have highly inflamed, swollen, infected and sensitive skin, as the application of the foam to the skin surface to be treated minimizes the need for skin contact. In order to formulate foams, it is necessary to know which material and process parameters influence the quality characteristics of foams and which methods can be used to study foams; this part of the research is assisted by the QbD approach. By using the QbD concept, it contributed during the development process to ensure quality-based development. With initial risk assessment, the critical material attributes (CMAs) and the critical process parameters (CPPs) were identified to ensure the required critical quality attributes (CQAs). During the initial risk assessment, five high-risk CQAs, namely foam volume stability, foam expansion, cross point, the initial values of the number and size of bubbles, and three medium-risk CQAs, namely spreadability, relative foam density and viscosity of the liquid system were identified and investigated. In this research, different types of polymers (xanthan gum, hydroxyethylcellulose, different types of hyaluronic acids) were used to improve the properties of foam formulations. The formulations containing xanthan gum and high molecular weight hyaluronic acid had good foam properties and will be appropriate delivery systems for an active pharmaceutical ingredient. Overall, the polymer content had a great effect on the properties of the foams. Different polymers affect the properties of foams in different ways. When used in combination, the methods reinforce each other and help to select a formula for dermal application.

Effects of ultrasound-assisted glycosylation on the interface and foaming characteristics of ovotransferrin

Ovotransferrin (OVT) is one of the major functional proteins in egg white protein. Most of the industry only paid attention the biological activity of OVT in iron supplement, antibacterial and other aspects, few reports were carried out on its processing characteristics such as foaming, interfacial behavior such as emulsification and foaming, which was an important processing functional attribute affecting its application scenario. In this study, the effects of ultrasound-assisted glycosylation on the interface and foaming characteristics of OVT were investigated. The results showed that proper ultrasonic treatment had a significant effect on the structure and physicochemical properties of OVT glycosylation products. When ultrasonic treatment lasted for 20 min, the grafting degree of OVT was 20.98%, the particle size decreased and the absolute value of potential increased. The foaming ability of OVT increased first and then decreased after ultrasonic-assisted glycosylation treatment. The foaming ability of OVT increased from 43.54% to 96.73% and the foaming stability increased from 68.92% to 89.19% after ultrasonic-assisted glycosylation treatment for 20 min. The experimental study effectively discovered the effect of ultrasound-assisted glycosylation on the foaming property of OVT, and would provide important technical references for expanding its application in food, biology, medicine and other fields.

PH-Dependent Binding Behavior of the α-Lactalbumin/Glycyrrhizic Acid Complex in Relation to Their Foaming Characteristics in Bulk.

This work aimed to understand the relationships of the interaction mechanism and foaming characteristics of α-lactalbumin (α-La) and glycyrrhizic acid (GA) after acidic (pH 2.5) and neutral (pH 7.0) treatment. The critical aggregation concentration (CAC) of GA in the presence of α-La was 0.6 mM at pH 7.0, while it was 1.0 mM at pH 2.5. Also, in the presence of a GA concentration of 0-15.00 mM, more GA molecules combined onto the α-La surface at pH 2.5 than at pH 7.0, as evident from the binding isotherms. The turbidity and particle size of α-La/GA were greater in acidic solution than those under neutral conditions. This result could be interpreted by the formation of aggregates under higher GA concentration at pH 2.5. Meanwhile, the viscosity of the complex was higher at pH 2.5 than at pH 7.0 in the presence of 3.00-15.00 mM GA, as analyzed from the rheological properties. The foaming ability (FA) of α-La was significantly enhanced in the presence of 10.00 mM GA. Simultaneously, acidic solution could generate a more stable foaming system with a thicker film layer stabilized by the complex compared with neutral solution. These findings could be beneficial for developing a kind of acidic food-grade foaming agent.

Characteristics and main factors of foam flow in broken rock mass in coal mine goaf.

To protect the environment and reduce the occurrence of coal mine fire, foam injection in goafs is an effective measure for preventing and extinguishing mine fires. The flow characteristics of foams injected into goafs have a significant impact on the prevention and extinguishment of such fires. To study the flow characteristics of foam injected into a goaf, we first independently constructed a set of experimental platforms for the visualization of goafs. Next, we performed physical experiments on foam injection using similarity theory. Flow characteristics were simulated under different foam concentrations, flow rates, and goaf porosities. The exponential function was found to provide a good fit to the trajectory of the foam's stacking edge in the goaf. According to the foam injection volume, the trend of the fitting equation parameter a could be divided into two stages. The first stage was the rapidly decreasing stage, and the second stage was the stable stage. It was inferred that the stacking height and diffusion radius of the foam under different conditions were related to the speed of liquid film drainage. The results of this study can provide a valuable reference for the use of fire prevention and extinguishment technology in the goaf.

Experimental investigation of the flow and extinguishment characteristics of gel-stabilized foam used to control coal fire

For understanding the extinguishing effectiveness of gel-stabilized foam fluids, the rheological law, flow characteristics, and extinguishment process were analyzed systematically in this study. The results revealed that gel-stabilized foam was non-Newton fluids, and the foam demonstrated shear-thinning behavior due to the orientation changes in molecular chains and structure destruction of three-dimensional gel at high shear rate. By fitting shear rate-shear stress curves, it was found that power-law equation of pseudoplastic fluid could descript the rheological behavior of foam well, and coefficients of determination for fitting results in all expansion ratios were lager than 0.9950. In addition, a simplified experiment platform of the goaf filled with coals was employed to investigate the flow characteristics of the foam fluids to extinguish coal fire. Analysis showed that gel-stabilized foam presented the hemispherical diffusion shape in porous media, and foam fluids would quickly cover to extinguish the open coal fire with excellent thermal stability. Moreover, the foam fluids also captured the hidden fire source efficiently in porous media by the quick seepage, finally cooling the high-temperature coal fire from 760 °C to 30 °C after injecting foam. The research would provide theoretical guidance for extinguishing coal fire using gel-stabilized foam.

Preparation, properties of foamed basic magnesium sulfate cements and their foaming mechanisms with different activators

Balancing mechanical and thermal properties of inorganic foamed composites has been a practical and technical challenge for decades. In this paper, we present a systematical investigation about the effects of different activators on the foamability and foaming mechanisms, pore characteristics and performance of foamed basic magnesium sulfate cement (FBMSC) by using hydrogen peroxide as foaming agent. The results reveal that the activators at a small amount have no tangible impact on the crystal growth of 5 Mg(OH)2·MgSO4·7H2O (5·1·7 phase) in FBMSC. Besides crystalline 5·1·7 phase that is responsible for high mechanical strength, the pore characteristics and thermal insulation of FBMSC are dependent on the foamability. Compared with KMnO4 and MnO2, FBMSC with the presence of KI exhibits a more gentle foaming process and a better pore structure. Thus the mechanical strength and thermal resistance of KI-FBMSC with lower densities can meet the criteria of Autoclaved Aerated Concrete (AAC, GB 11968-2006 of China Standard) and Foamed Concrete (FC, Chinese Building Materials Industrial Standard JG/T 266–2011) with higher densities. The excellent performance and environmental friendliness, simple synthesis procedure with energy saving of FBMSC make it appealing to prefabrication insulation panel industry.

Fabrication of a Ceramic Foam Catalyst Using Polymer Foam Scrap via the Replica Technique for Dry Reforming.

Megapores with spherical-like cells connected through windows and high porosities make up catalyst supports in the form of ceramic foams. These characteristics provide significant benefits for catalytic processes that are limited by mass or heat transport. This study focuses on the manufacture of ceramic foam using a polymeric sponge replica process and polymer foams as a template for catalyst supports, which are industrial waste from the packaging sector. To make ceramic foam catalysts, they were dipped in a catalyst solution, followed by a breakdown stage and a sintering process. Experiments focused on determinants that affect the desired characteristics of ceramic foams, such as the types of polymer foams that affect foam morphology, the rheology of catalyst solution that affects catalyst dispersion, and the polymer decomposition rate that affects catalytic performance during dry reforming of the methane process. The cell architectures of polyurethane and polyvinyl alcohol foams are attractive for catalyst support preparation because they have 98–99% porosity and typical cell sizes of 200 and 50 μm, respectively. The polyurethane performance was superior to the performance of polyvinyl alcohol in terms of higher porosity and better catalytic-solution absorption offering high catalyst active areas. The catalyst prepared from concentrated 10 wt % Ni/Al2O3–MgO (10NAM) slurry had the highest surface area (59.18 m2/g) and the highest metal oxide dispersion (5.65%). These results are relevant to the flow behavior of catalyst slurry which plays a key role in coating the catalyst gel on the polymer template. The thermal decomposition rate used to remove the polymer template from the catalyst structure is proportional to the ceramic foam structure (catalyst support structure). The slow decomposition rate bent and fractured foam-cell struts more than the faster rate. On the other hand, achieving good catalyst dispersion on catalyst supports necessitated a high sintering rate. When sintering was adjusted at a high sintering rate, the metal–particle dispersion was relatively high, around 7.44%, and the surface area of ceramic foam catalysts was 64.61 m2/g. Finally, the catalytic behavior toward hydrogen production through the dry reforming of methane using a fixed-bed reactor was evaluated under certain operating conditions.

On hygrothermal wave dispersion characteristics of embedded graphene foam

This investigation discusses wave propagation characteristics of porous graphene foam (PGF) beam resting on an elastic medium within the framework of the refined higher-order beam theory for the first time. The beam is considered to be in the hygrothermal environment. Additionally, the pores are distributed through the thickness direction uniformly and symmetrically. The motion equations of the PGF beam are derived via the Hamiltonian approach incorporated with the kinetic relation of refined higher-order shear deformation beam theory. Next, an analytical method is implemented in order to solve the governing equations of the PGF beam. The various parameters’ effect, including wave number, porosity coefficient, various types of porosity distribution, Winkler–Pasternak coefficients, hygrothermal environment, and slenderness ratio on the variation of wave frequency and phase velocity of PGF beam are investigated.

Experimental study on the dynamic properties of rigid polyurethane foam in stress-controlled cyclic uniaxial tests

Frequent major earthquakes in Japan necessitate earthquake-resistant infrastructure. The dynamic deformation characteristics of rigid polyurethane foam, used as a lightweight embankment material, is examined in this study. The effect of the initial static stress on the shear modulus of single-layer samples was small, while the shear modulus of two-layer samples increased with increasing initial static stress. The damping ratio of single-layer samples converged to 4–5%, but decreased with increasing initial static stress up to 30 kPa in two-layer samples before increasing above 40 kPa. Results from cyclic uniaxial and triaxial tests were compared. The dynamic properties depended on restriction conditions and the deformation direction.

Rheological and morphological characteristics of foam fluid using hydroxypropyl guar and surfactant

In order to systematically study the rheological and morphological characteristics of foam fracturing fluid, hydroxylpropyl guar (HPG) was selected as the foam stabilizer, sodium dodecyl sulfate (SDS) and cetyl trimethyl ammonium bromide (CTAB) were selected as the foaming agents, and foam fracturing fluid used for coalbed methane (CBM) stimulation was prepared. The viscosity, quality and half-life of foam fracturing fluid under different additive concentration levels were tested, and the bubble morphology and its relationship with half-life were observed and quantitatively analyzed with microscopy. In addition, the influence of pulverized coal on foam stability was also studied. The results show that the influence of pulverized coal on the basic parameters of the foam fracturing fluid correlated with the particle size and concentration of the pulverized coal. The small particle size of pulverized coal increased the liquid phase viscosity and half-life of the foam, but reduced the foam quality. With increasing pulverized coal concentration, the effects were enhanced. The average bubble diameter decreased with increasing HPG concentration, and the changing trend of the bubble diameter conformed to the gamma distribution. The foam half-life had a positive and negative correlation with the bubble morphology parameters α and β, respectively. The results can deepen the understanding of the influence of foaming agents, foam stabilizers, and coal particles on the properties of foam fracturing fluids, and provide a reference for the optimization of foam fracturing fluid formulations.

Direct Pore-Scale Simulations of Fully Periodic Unit Cells of Different Regular Lattices

Abstract Open-cell metal foams are known for their superior heat dissipation capabilities. The morphological, pressure drop, and heat transfer characteristics of stochastic metal foams manufactured through traditional “foaming” processes are well established in the literature. However, employment of stochastic metal foams in next-generation heat exchangers is challenged by the irregularity in the pore- and fiber-geometries, limited control on the pore-volume, and an inherent necessity of a bonding agent between foam and the heat source. On the other hand, additive manufacturing (AM) is capable of printing complex user-defined unit cell topologies with customized fiber shapes directly on the substrates subjected to heat load. Moreover, the user-defined regular lattices are capable of exhibiting better thermal and mechanical properties than stochastic metal foams. In this paper, we present a numerical investigation on fully periodic unit-cells of three different topologies, that is, tetrakaidecahedron (TKD), rhombic-dodecahedron (DDC), and Octet with air as the working fluid. Pressure gradient, interfacial heat transfer coefficient, friction factor, and Nusselt number are reported for each topology. Rhombic-dodecahedron yielded the highest averaged interfacial heat transfer coefficient whereas Octet incurred the highest flow losses. Pore diameter, defined as the maximum diameter of a sphere passing through the polygonal openings of the structures, when used as the characteristic length scale for the presentation of Nusselt number and Reynolds number, resulted in a single trendline for all the three topologies.

EFFECT OF ULTRASOUND ON REAGENT COMPOSITIONS FOAMING PROPERTIES USEDIN MINERAL FLOTATION

The article considers the effect of foam-forming compositions of flotation reagents (hydro-chloric amine solution, hydrochloric amine solution with addition of polyethylene glycol 200M and hydrochloric amine solution with addition of triethylene glycol) ultrasonic treatment on the prop-erties of two-phase foams. It was determined that ultrasonic activation of reagent compositions increases a foam specific volume and foam capacity by10.3 and 12.1%, respectively, while the foams become drier by15.2% (in the case of the hydrochloric amine solution), 15.6% (in the case of the hydrochloric amine solution with addition of polyethylene glycol 200M) and 13.3% (in the case of the hydrochloric amine solution with addition of triethylene glycol). In addition, there is an increase in the foam layer stability with an increase in the ultrasonic treatment power by63.1% (in the case of the hydrochloric amine solution), which indicates the ability to control the stability and other characteristics of the foamusing the acoustic method. Due to ultrasonic dispersion, amine floccules are more efficiently distributed over the entire volume of the emulsion, includingthe sur-face of the liquid. It was found that ultrasound changes the above foam characteristics by reducing the surface tension of foam-forming compositions and decreasing collector micelles.