Initial Foam Density Research Articles

Enhancing mass transfer and preserving heat-sensitive quality of mango through foam mat drying

Mango puree was foamed using hydroxypropyl methylcellulose to achieve foam densities ranging from 0.3 to 0.8 g/cm3. Subsequently, these mango foams were dried at temperatures ranging from 60 to 80 °C. The experimental results showed that mango foam drying was in the falling rate period. The effective moisture diffusivity (D eff ) was well described by the Arrhenius equation, with the pre-exponential factor (D 0) and activation energy (Ea ) closely related to the void area fraction in mango foam. This relationship led to higher D eff and shorter drying times at higher void area fractions. The minimum loss of total phenolics content (TPC) was observed in mango foams with an initial foam density of 0.3 g/cm3 dried at 60ºC, with only a 7% loss. Increasing drying temperatures to reduce drying time did not mitigate TPC loss. Similarly, the minimum reductions in antioxidant activities, as measured by both the 2,2-azino-bis-3-ethylbenzothiazoline-6-sulfonic acid and ferric reducing antioxidant power assays, were observed in mango foams with an initial foam density of 0.3 g/cm3 dried at 60 °C, with values of 14% and 18%, respectively. Dried mango foams with lower densities exhibited more pronounced color changes due to the presence of more sponge-like voids. However, the drying temperature did not significantly affect the product color. In addition, dried mango foams with lower initial foam densities displayed a more brittle and spongy texture.

Investigations on the performance of xanthan gum as a foam stabilizer and assessment of economic and environmental impacts of foam concrete production

The properties of foam concrete are greatly influenced by the quality of the foam used. The stability of the foam is a vital property that needs dire attention when selecting surfactant. This paper evaluates the role of Xanthan gum (XG) as an additive in the performance improvement of foam produced with two different surfactants, viz., Hingot (Natural surfactant) and Nonylphenol ethoxylate (NPE) (Synthetic surfactant). Different characteristics of foam and surfactant, such as initial foam density, foam drainage, foam bubble microstructure, surface tension, and viscosity of surfactants, are experimentally evaluated. Addition of XG results in a 10-fold increment in viscosity for both Hingot and NPE surfactant solutions. The above enhancement in viscosity results in a substantial reduction in bubble size and an increment in lamella thickness. Further, the reduced surface tension of Hingot surfactant also contributes to a significant reduction in the rate of bubble coalescence. Having studied the surfactant and foam behaviour, the next phase comprises studies on the influence of XG on consistency, setting behaviour, compressive strength, and thermal conductivity of foam concrete with two different densities, viz., 1000 kg/m3 and 1500 kg/m3. Results show that the addition of XG results in a reduction in consistency and an increase in demoulding time of foam concrete. Besides improvement in foam performance, a substantial increase in compressive strength and reduction in thermal conductivity of FC is also observed due to XG addition, indicating that foam bubble microstructure has a significant impact. The last phase involves the life cycle assessment (LCA) of the FC produced with the aforementioned surfactants, which is the first of its kind study that considers the impact of surfactants across various environmental categories. Results of the LCA analysis show that the total cumulative energy demand of preparation of 1 kg of Hingot solution is less than that of 1 kg of NPE surfactant solution. The environmental impact analysis also favours Hingot as a sustainable and economical alternative to NPE surfactant. Results of LCA analysis of FC indicate that foam concrete with 1000 kg/m3 performs better than AAC block and conventional clay brick. Furthermore, the studies highlighted that there is more scope for improving the performance of LCA of FC through using various mineral admixtures as replacement for cement.

Studies on influence of characteristics of surfactant and foam on foam concrete behaviour

This paper describes an extensive laboratory-based investigation conducted to evaluate the relative performance of foam produced with two different synthetic surfactants namely Sodium lauryl sulphate (SLS) and Nonylphenol ethoxylate (NPE) along with an additive Carboxymethyl cellulose sodium salt (CMC) for use in foam concrete. The different essential characteristics of foam and surfactants such as initial foam density, foam stability, average bubble size and viscosity of surfactant solution are investigated in the present study through systematic experimental design based on response surface methodology. Further, based on studies on microstructure of foam concrete, it is found that selection of surfactant and CMC concentration have significant influence on foam characteristics and hence on the air void size distribution of foam concrete. In addition, the dependence of the compressive strength and water permeation characteristics of foam concrete on the air void size parameters of concrete is also investigated. Experimental outcomes indicate that increase in surfactant concentration from 3% to 6% results in 24%–44% reduction in median air void diameter in concrete which eventually led to 29%–37% enhancement in compressive strength of foam concrete mixes. In the same line, addition of CMC to surfactant solution enhances viscosity of surfactant solution significantly and thereby results in improvement of foam microstructure, concrete air void microstructure and eventually improves compressive strength of foam concrete. Further, improved microstructure with smaller air voids in foam concrete with NPE + CMC results in 10%–25% relatively higher compressive strength than SLS + CMC foam concrete mixes.

Assessment of the potential of a naturally available foaming agent for use in the production of foam concrete

This paper evaluates the performance of naturally available saponin based hingot fruit (Balanites aegyptiaca) as an alternative to synthetic foaming agent for use in foam concrete. Two methods of hingot surfactant preparation viz (i) water soaking for 24 h without heating and (ii) with the heating of hingot pericarp over a range of temperature (i.e., 25–100 °C) are evaluated in this study. Assessment on the essential properties of foam such as initial foam density (IFD), foam stability and bubble microstructure for different parameters viz., hingot concentration, the rotational speed of stirrer, temperature and duration of heating process of surfactant extraction are carried out. Comparative studies on two different methods of hingot extraction indicate that the heating process adopted in hingot surfactant extraction is efficient method as it facilitates maximum extraction of saponin. Hence the resulting foam is of better quality with relatively greater amount of air, lesser drainage and smaller size bubble microstructure when compared to surfactant extracted without heating process. For instance, a maximum reduction of 50% in IFD is achieved when the temperature of heating of hingot surfactant extraction process is increased from 25 °C to 75 °C for duration of 5 h. Based on the studies on influence of surfactant production parameters on foam properties, the optimum surfactant production parameters (5% hingot concentration, 5 h of heating of surfactant preparation solution at 75 °C, stirrer speed of 3600 rpm) are derived. Further, the chosen value of surfactant production parameters is verified to be satisfactory for the production of stable foam concrete mix according to the guidelines of ASTM C796 and ASTM C896.

Evaluation of performance of foam produced with different methodologies for use in foam concrete production

For the production of foam concrete which finds applications in many areas, generally as a function of its relatively lightweight, the use of stable and quality foam is the key requirement. However, the literature available on the influence of characteristics of foaming agent and foam on the properties of foam concrete are rather limited. Hence a more systematic research is needed in this direction. The present work focuses on the relative performance evaluation of foam (initial foam density, foam stability, viscosity of surfactant solution and bubble size) using a typical synthetic surfactant and additive using two different foam production methodologies namely stirrer and foam generator. Comparative studies on foam production methods indicated that foam produced based on compressed air method (foam generator) is of better quality with lesser liquid fraction and drainage compared to that of foam produced with stirrer. Also studies have proved that there is a strong relationship between viscosity of surfactant solution, initial foam density, foam stability and bubble microstructure.

Development of a green foaming agent and its performance evaluation

With a view to replace synthetic foaming agents in the production of foam concrete, renewable and naturally available soapnut (SN) fruit has been studied as a foaming agent. Soapnut foaming solutions are prepared in two ways, viz., water soaking for 24 h without heating and with heating of soapnut pericap over a range of temperature (i.e.70 °C–90 °C). The foam generated from the above foaming solutions are studied for properties such as initial foam density and foam stability. However, the use of this foam from soapnut led to cement setting problem, which is caused by the compounds present in soapnut. The setting problem is resolved by using alum as an accelerator. The addition of alum resulted in the formation of additional ettringite and enabled the concrete to set, which is confirmed through powder XRD. The properties of foam concrete produced with water soaked SN with heating is noted to be marginally better compared to those of concrete prepared by water soaked SN without heating. The pore size and shape are analysed using an image analysis technique, which gives good correlations with density and strength of foam concrete.

Effect of Adsorption Conditions on Effective Diffusivity and Textural Property of Dry Banana Foam Mat

Foamed banana product, a crispy snack, can quickly adsorb the moisture from the moist air, leading to loss of textural property. The main purpose of this research was therefore to study moisture adsorption kinetics of dry banana foam mat and its texture quality change. The adsorption isotherm experiments were carried out with a standard static method using saturated salt solutions over a wide range of relative humidities from 32 to 82% and temperatures of 35, 40, and 45°C. Three dry banana foam densities of 0.21, 0.26, and 0.30 g/cm3 adsorbed water vapor under controlled conditions. Fick's second law coupled with an optimization technique was used to estimate the effective moisture diffusivity at sorption conditions. Empirical equations with two and three constant parameters for describing the dependence of the effective moisture diffusivity on moisture content were tested. The two constant parameters could suitably describe the variation of the effective moisture diffusivity with moisture content. The initial foam density, relative humidity, and temperature significantly affected the effective moisture diffusivity. The banana foam mats for all densities lost their crispy texture at moisture content of 0.078 kg/kg db.

Laser-driven cylindrical compression of targets for fast electron transport study in warm and dense plasmas

Fast ignition requires a precise knowledge of fast electron propagation in a dense hydrogen plasma. In this context, a dedicated HiPER (High Power laser Energy Research) experiment was performed on the VULCAN laser facility where the propagation of relativistic electron beams through cylindrically compressed plastic targets was studied. In this paper, we characterize the plasma parameters such as temperature and density during the compression of cylindrical polyimide shells filled with CH foams at three different initial densities. X-ray and proton radiography were used to measure the cylinder radius at different stages of the compression. By comparing both diagnostics results with 2D hydrodynamic simulations, we could infer densities from 2 to 11 g/cm3 and temperatures from 30 to 120 eV at maximum compression at the center of targets. According to the initial foam density, kinetic, coupled (sometimes degenerated) plasmas were obtained. The temporal and spatial evolution of the resulting areal densities a...

Analysis of the Foam Generated Using Surfactant Sodium Lauryl Sulfate

The performance evaluation of a sodium lauryl sulfate to qualify as a foaming agent is presented in this paper. When new surfactants are used a systematic study of production parameters on the foam characteristics needs to be undertaken unlike proprietary foaming agents and foam generator for which manufacturer has predefined the parameters. The relative influence of the foam parameters and optimization of factors were carried out through a systematic experiment design. The foam production parameters namely foam generation pressure and dilution ratio of foaming agents are observed to have significant effect on all foam characteristics with the exception of foam output rate on which only foam generation pressure has influence. The foam with good initial foam density need not necessarily be stable foam. The optimum levels of foam production parameters are determined for the surfactant Sodium lauryl sulfate which can be used to produce stable foam for foam concrete production.

Relative assessment of density and stability of foam produced with four synthetic surfactants

Selection of the surfactant has an impact on many of the foam properties as it affects the surface tension and gas–liquid interfacial properties. The objective is to produce stable aqueous foam of required density. These two characteristics are influenced by the type of surfactant, its concentration and foam generation pressure. This study compares the density and stability of foam produced using four synthetic surfactants namely sodium lauryl sulfate, sodium lauryl ether sulfate, sulfanol and cocodiethanolamide through a systematic experiment design based on response surface methodology. The relative performance has also been assessed in terms of their suitability for use in foamed concrete production based on ASTM test method. The effect of surfactant concentration has relatively lesser effect on foam density for sodium lauryl sulfate and sulfanol irrespective of foam generation pressure adopted. The drainage is proportional to the initial foam density for all the surfactant concentration for ionic surfactants at different foam generation pressures. For all the four surfactants under the optimum foam generation pressure, a stable foam with drainage less than 12% in 300 s (by considering economy as a factor) is achieved. From the foam stability test based on ASTM C 796-97, it is observed that all the four surfactants are suitable for use in foamed concrete production when optimized foam production parameters are adopted.

Modeling of Diffusion with Shrinkage and Quality Investigation of Banana Foam Mat Drying

A diffusion model including shrinkage has been developed for predicting the change of moisture content in banana foam mats during drying. Two solution methods, moving boundary using variable grid and immobilizing boundary using the Lagrangian referential coordinate, were used in exploring their capabilities to predict the moisture change. Banana foam mats with initial foam densities of 0.3, 0.5, and 0.7 g/cm3 were dried at 60, 70, and 80°C and superficial air velocity of 0.5 m/s. The qualities of the final products in terms of texture and microstructure were determined. The moving boundary method can predict the moisture content more accurately than the immobilizing boundary method especially in the case of low-density foam. The quality determinations showed that the initial foam density strongly affected hardness, crispness, and morphology of dried banana foam mats, whereas the drying temperature had no significant effect on those qualities.

Effect of milk homogenisation and foaming temperature on properties and microstructure of foams from pasteurised whole milk

Differently homogenised and HTST-heated milk (3.5% fat) was foamed at temperatures between 4 and 60 °C. Foaming was achieved by air injection through fritted glass. Initial foam density, drainage and corresponding bubble size were analysed. Transmission electron microscopic (TEM) images completed the study. The studies showed that whole milk was better foamable between 50 and 60 °C than at lower temperatures. This was mainly due to the completely liquid milk fat and the increased protein adsorption at the air–serum interface. The resulting bubbles of these two foams maintained their spherical shape also for 20 min of draining. However, the average bubble diameter and the drainage mass in relation to the initial foam mass increased from about 20 g/100 g after 1 min to about 80 g/100 g after 20 min. It was surprising to learn that milk homogenisation and corresponding fat globule size had only marginal effect on foam formation and stability. TEM images suggested that the air–serum interface consisted mainly of protein monomers and oligomers, while casein micelles were not directly adsorbed. The membrane of the homogenised fat globules was destroyed near the interface and coalesced liquid fat formed a restricted film on the bubble that was obviously of minor importance for the foam properties.

Drying characteristics and quality of banana foam mat

The combination of foaming and drying is an alternative method to produce crisp banana chips. The influences of whipping time and egg albumen concentration on the foam density were studied. The influences of foam density, drying temperature and egg albumen concentration on the drying characteristics and qualities of the final products in terms of shrinkage, texture and microstructure were subsequently evaluated. Banana puree with egg albumen, which was used as the foaming agent, was foamed to the densities of 0.3, 0.5 and 0.7 g/cm 3. Banana foam mats with 5 mm thickness were then dried to the moisture content of 0.03 kg/kg db at 60, 70 and 80 °C and superficial air velocity of 0.5 m/s. The experimental results showed that the extensive porous structure of foams with lower densities resulted in higher drying rates, moisture diffusivities and shrinkage. Dried banana foams with lower foam densities also had lower hardness and crispness values. The drying temperature and the egg albumen concentration did not influence the textural properties of the final products, however. To produce banana chips, the initial foam density of 0.5 g/cm 3 and drying temperature of 80 °C were recommended.

Quasistatic and high strain rate uniaxial compressive response of polymeric structural foams

The behavior of a family of polymeric structural foams with various initial bulk densities (porosity levels) was experimentally investigated under quasistatic and high strain rate loading conditions. The high strain rate loading for the low-density ( < 1 g / cm 3 ) foams was implemented using a polymer split Hopkinson pressure bar (SHPB) and for the high-density ( > 1 g / cm 3 ) foams using a magnesium SHPB. It was found that the Young's modulus, the yield strength, the maximum stress and the strain to failure increased with increasing initial foam density under quasistatic loading. The fracture modes were also found to be considerably different for these foams. The low-density foams fractured in a brittle manner, especially under dynamic loads, where as, the high-density foams exhibited shear-dominated failure at all strain rates. Under dynamic loading, the failure strength increased with strain rate but the strain to failure decreased. Based on the quasistatic and dynamic test results, the strain rate sensitivity of failure strength was determined and it was found that this rate sensitivity parameter increases with increasing foam density.

Effect of polymer foam morphology and density on kinetics of in vitro controlled release of isoniazid from compressed foam matrices.

The purpose of this study was to compare the effect of polymer foam morphology and density prior to compaction on the kinetics of isoniazid (INH) release from the final high-density extruded matrices. The feasibility of preparing low density foams of several biopolymers, including poly(L-lactide) (PLLA), poly(glycolide) (PGA), poly(DL-lactide-co-glycolide) (PLGA), poly(gamma-benzyl-L-glutamate) (PBLG), and poly(propylene fumarate) (PPF), via a lyophilization technique was investigated. Low-density foams of PLGA, PBLG, and a mixture of PLGA and PPF were successfully fabricated by lyophilization of the frozen polymer solutions either in glacial acetic acid or in benzene. The morphology of these foams depends on the polymer as well as the solvent used in the fabrication process. Thus, PLGA produces a capillary structure when lyophilized from benzene solution and a leaflet structure from glacial acetic acid, but PBLG yields a leaflet structure from benzene. Matrices were prepared by impregnating these foams with aqueous solutions of INH, removing the water by a second lyophilization, and then compressing the low-density INH containing foams by compaction and high-pressure extrusion. The resulting nonporous matrices had densities of approximately 1.30 g/cm3. In vitro kinetics were in accord with the Roseman-Higuchi diffusion model and demonstrate that release rates depend on the initial foam density, while foam structure has little influence on the release kinetics.

Mechanism of antifoaming action of simethicone.

The mechanism of the foam-inhibiting action of simethicone, mainly used against flatulence, has been studied. Its effect on foaming systems containing synthetic gastric juice and a surface-active substance (anionic surfactant, cationic surfactant, soap solution) was quantitated by measuring the surface tension, foam stability and initial foam density. The effect of simethicone on each of the examined systems was the result of the combination of two actions: the drainage of liquid from foam films and the rupture of relatively thick liquid films. The mechanism of these actions may be described as the liquid drainage followed by bridging of the liquid film by polydimethylsiloxane droplets, helped by hydrophobic silica particles also present in the antifoaming agent, leading to the rupture of the film surface and air escape.