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Foaming agent

A foaming agent is a substance, such as a surfactant or blowing agent, that facilitates the formation, expansion, and stabilization of foam by reducing the surface tension of liquids or generating and trapping gas bubbles within a matrix, enabling applications in diverse fields including materials science, personal care, food processing, and fire suppression.^[1]^[2] Foaming agents are broadly categorized into three main types based on their mechanism and composition. Surfactants, which are amphiphilic molecules with hydrophilic and hydrophobic components, lower surface tension to create and stabilize air-liquid interfaces, forming micelles that trap gas bubbles; common subtypes include anionic (e.g., sodium lauryl sulfate), amphoteric (e.g., cocamidopropyl betaine), cationic, natural (e.g., derived from plant proteins or lipids like lecithin), and synthetic varieties.^[3]^[4] Chemical foaming agents, often solids or liquids, decompose under heat or pressure to release gases such as nitrogen, carbon dioxide, or ammonia, with examples including azodicarbonamide and sodium bicarbonate used in thermoplastics like polyethylene and PVC.^[1]^[5] Physical foaming agents, in contrast, involve the direct introduction of inert gases like nitrogen or carbon dioxide through mechanical processes such as injection or pressure release, often combined with nucleating agents to control bubble size and distribution.^[1]^[5] These agents play critical roles in industrial applications by enhancing product properties such as lightness, texture, insulation, and efficacy. In plastics manufacturing, they reduce density by creating cellular structures, leading to weight savings of up to 20-30%, improved thermal insulation, and shorter production cycles while minimizing material use and environmental impact.^[5]^[6] In the food industry, they aerate products like baked goods, whipped creams, and beverages—using proteins (e.g., egg albumin), polysaccharides (e.g., guar gum), or emulsifiers (e.g., polysorbates)—to improve volume, stability, and mouthfeel via mechanisms like the Gibbs-Marangoni effect that prevents bubble coalescence.^[4]^[7] Personal care products rely on them for lathering in shampoos and soaps, where factors like pH, concentration, and water hardness influence foam durability and sensory appeal, though milder non-ionic types are preferred to reduce irritation.^[3] In firefighting, surfactant-based foaming agents in concentrates generate expandable blankets that smother flammable liquid fires by excluding oxygen and cooling surfaces, with formulations evolving from per- and polyfluoroalkyl substances (PFAS) to fluorine-free alternatives for environmental safety; this shift is accelerated by regulations such as the European Union's restriction on PFAS in firefighting foams adopted in October 2025.^[8]^[9]^[10]

Overview

Definition and Basic Properties

A foaming agent is a substance, such as a surfactant or a blowing agent, that promotes foam creation by reducing surface tension in liquids or generating gas bubbles in solids or liquids, leading to a dispersion of gas within a liquid or solid matrix.^[11]^[12] These agents are essential in processes requiring cellular structures, where they enable the incorporation of gas phases into continuous matrices to achieve lightweight, porous materials.^[11] Key properties of foaming agents include their capacity to lower surface tension, typically reducing it from 72 mN/m in pure water to 25-40 mN/m, which facilitates bubble formation and stabilization.^[13] Surfactant-based foaming agents exhibit amphiphilic characteristics, with hydrophilic and hydrophobic moieties that adsorb at air-liquid interfaces to stabilize foam bubbles; a representative example is sodium lauryl sulfate (SLS), an anionic surfactant that achieves surface tensions around 40 mN/m at and above its critical micelle concentration (CMC).^[14] In contrast, blowing agents demonstrate gas-generating capacity through thermal or chemical decomposition; for instance, azodicarbonamide (ADC), a common chemical blowing agent, decomposes above 200°C to release nitrogen gas and other byproducts, expanding the matrix without altering its chemical composition significantly.^[11]^[12] Foaming agents differ fundamentally from anti-foaming agents, as the former stabilize bubbles to maintain foam structure, while the latter destabilize or prevent bubble formation by promoting coalescence and rupture.^[15] Broadly, foaming agents are classified into surfactant-based types, which primarily generate and stabilize aqueous foams through interfacial tension reduction, and blowing agents, which produce gas for expanding polymer foams.^[11]

Historical Development

The development of foaming agents traces back to the early 20th century, when they were first employed in the rubber industry to create cellular structures. In the early 1900s, gas-generating chemicals such as sodium and ammonium carbonates were added to natural rubber latex to produce sponge rubber, marking the initial industrial application of basic foaming agents.^[16] Concurrently, the concept of metallic foams gained traction, with the first patent for closed-cell metal foams issued in 1926 to M.A. de Meller, who described foaming light metals via inert gas injection or blowing agents to achieve lightweight structures.^[17] Advancements accelerated in the mid-20th century, particularly with the commercialization of chemical blowing agents in the 1950s for plastics foaming. During this period, compounds like azodicarbonamide (ADC) and toluene sulfonyl hydrazide (TSH) were developed and introduced, enabling controlled gas release for expanded polymer products such as shoe soles and insulation materials.^[18] The 1960s further expanded options with the adoption of chlorofluorocarbons (CFCs), notably CFC-11, as blowing agents in polyurethane foams, valued for their low thermal conductivity and stability in rigid insulation applications.^[19] Environmental imperatives reshaped the field in the late 20th century, culminating in the phase-out of CFCs during the 1980s and 1990s due to their role in ozone depletion. The Montreal Protocol, signed in 1987, mandated the global elimination of ozone-depleting substances like CFCs, with production in developed countries ceasing by 1996 for foam applications.^[20] This prompted a transition to alternatives including hydrofluorocarbons (HFCs) such as HFC-245fa and hydrocarbons like cyclopentane, which provided comparable foaming efficiency without ozone harm.^[21] The 21st century has emphasized sustainability, with natural surfactants emerging as eco-friendly foaming agents since the 2000s, offering biodegradability and lower toxicity for applications in personal care and industrial processes.^[22] Recent developments as of 2025 include the widespread adoption of hydrofluoroolefins (HFOs) as low global warming potential (GWP) physical blowing agents and bio-based chemical foaming agents derived from renewable sources, driven by regulations like the EU's REACH updates and US EPA PFAS restrictions to minimize environmental impact. Over the past century, extensive evaluation of hundreds of materials has driven innovation, alongside refinements in the 1950s that standardized techniques for consistent foam production, facilitating scalable industrial use.^[23]^[17]

Types

Surfactant-Based Foaming Agents

Surfactant-based foaming agents are amphiphilic compounds that reduce the surface tension of aqueous solutions, enabling the entrapment of air to form stable bubbles and foams.^[24] These agents adsorb at the air-liquid interface, stabilizing the thin films surrounding gas bubbles and promoting foam generation through mechanical agitation or gas incorporation.^[25] By lowering interfacial tension, they facilitate the dispersion of gas into the liquid, resulting in expanded volumes of foam suitable for applications in liquid media.^[26] Surfactants used as foaming agents are classified into four main subtypes based on their ionic nature in solution. Anionic surfactants, such as sodium lauryl sulfate (SLS) and sodium laureth sulfate, carry a negative charge and are known for producing high volumes of dense foam due to their strong surface activity.^[27] Nonionic surfactants, including alkyl polyglucosides derived from natural sugars and fatty alcohols, lack charge and offer milder foaming properties with good stability in hard water, often preferred for their biocompatibility.^[28] Cationic surfactants, like quaternary ammonium compounds (e.g., cetyltrimethylammonium bromide), possess a positive charge and provide antimicrobial benefits alongside moderate foaming, though they may interact unfavorably with anionic species.^[29] Amphoteric surfactants, such as betaines (e.g., cocamidopropyl betaine), exhibit both positive and negative charges depending on pH, enabling pH-balanced foaming that is gentle and compatible with other surfactant types.^[30] Co-surfactants, particularly short-chain alcohols like ethanol or fatty alcohols (e.g., lauryl alcohol), enhance foam quality by altering micelle structures, promoting the formation of elongated worm-like micelles that increase viscosity and bubble stability.^[31] At the molecular level, surfactants consist of a hydrophilic (polar) head group and a hydrophobic (nonpolar) tail, typically a hydrocarbon chain, which drives their self-assembly at interfaces.^[32] The critical micelle concentration (CMC) represents the threshold surfactant concentration above which micelles form in bulk solution, marking a sharp drop in surface tension and optimal onset of foaming efficiency.^[33] This efficiency is quantified through the relationship derived from the Gibbs adsorption isotherm, where surface tension \gamma decreases as:

\gamma = \gamma_0 - RT \Gamma \ln(C)

Here, \gamma_0 is the surface tension of pure solvent, R is the gas constant, T is temperature, \Gamma is the surface excess concentration, and C is the surfactant concentration; foaming is most effective near the CMC, as lower values indicate higher interfacial activity with minimal surfactant use.^[34] Natural surfactant-based foaming agents, such as saponins extracted from plants like Quillaja saponaria or soybeans, offer biodegradable alternatives to synthetic ones, providing rich, creamy foams with superior long-term stability due to their glycoprotein structure.^[35] These natural agents excel in environmental compatibility and lower toxicity, enhancing solubility of hydrophobic compounds without bioaccumulation risks.^[36] In contrast, synthetic surfactants, often petroleum-derived like linear alkylbenzene sulfonates, generate higher initial foam volumes and are cost-effective for large-scale production, but they may pose greater ecological persistence and irritation potential.^[37] While natural options like saponins yield more uniform bubbles and better resistance to drainage, synthetic variants provide tunable performance at the expense of sustainability.^[38]

Blowing Agents

Blowing agents are compounds capable of releasing inert gases to expand polymeric materials, such as plastics and rubbers, into low-density cellular foams that enhance insulation, lightness, and structural properties.^[39] These agents create voids or cells within the material matrix during processing, typically through thermal or pressure-induced mechanisms, without altering the base polymer's chemical composition beyond expansion.^[40] Blowing agents are categorized into chemical and physical subtypes. Chemical blowing agents decompose thermally or via reaction to generate gases directly within the polymer melt, enabling uniform foam formation without specialized equipment. A prominent example is azodicarbonamide (ADC), which decomposes between 190–210°C to yield nitrogen, carbon monoxide, ammonia, and carbon dioxide gases, producing approximately 220 mL/g of gas.^[39] In contrast, physical blowing agents, such as carbon dioxide or nitrogen, are introduced as gases or liquids under pressure and expand upon release, undergoing no chemical change and allowing for reversible processes in some applications.^[41] Within chemical blowing agents, reactions are further distinguished as endothermic or exothermic. Endothermic agents, like sodium bicarbonate, absorb heat during decomposition (typically at 145–150°C), which promotes controlled gas release and finer, more uniform cell structures in the foam.^[39] Exothermic agents, such as ADC, release heat alongside gases, accelerating expansion but potentially requiring activators to adjust decomposition temperatures for precise control.^[40] Processing with blowing agents demands careful alignment of decomposition temperatures and gas yields with the polymer's melt viscosity and thermal stability, ensuring effective nucleation and expansion. For instance, ADC offers gas yields of 120–220 mL/g and is compatible with polymers like polyvinyl chloride (PVC) and polystyrene, where it is often incorporated as a masterbatch to prevent premature reaction.^[39] Physical agents like CO₂ require pressure vessels for injection, suiting extrusion processes in polyolefins.^[42] In response to environmental concerns, modern blowing agents increasingly favor hydrocarbons, such as n-pentane or isopentane, over hydrofluorocarbons (HFCs) due to the latter's high global warming potential (GWP > 1000). These hydrocarbon alternatives maintain effective expansion while achieving near-zero ozone depletion potential and lower GWP values, aligning with regulatory shifts in foam production.^[42]

Mechanisms

Foam Formation

Foam formation begins with the nucleation stage, where gas pockets form within a liquid or solid matrix to initiate bubble creation. This process typically occurs at interfaces, such as solid surfaces or impurities, through heterogeneous nucleation, which is more common due to lower energy barriers compared to homogeneous nucleation in the bulk phase.^[43] Heterogeneous nucleation predominates in practical systems like aqueous solutions or polymer melts, as it allows gas pockets to form on pre-existing sites, facilitating easier bubble initiation.^[44] During bubble growth, the initial gas pockets expand via gas diffusion from the surrounding medium and pressure-driven expansion, leading to the development of foam structure. Surfactants play a crucial role by reducing surface tension (σ), which lowers the energy required for nucleation and promotes easier bubble formation.^[45] The Marangoni effect further aids growth, as surfactants migrate to the expanding bubble interfaces, creating surface tension gradients that stabilize the interface and prevent premature rupture during expansion.^[45] In systems using blowing agents, these compounds provide the necessary pressure difference (ΔP) through gas release, often via thermal decomposition or phase change, driving bubble expansion in materials like polymers.^[46] Several factors influence the extent of foam formation, including agitation, which introduces mechanical energy to entrain gas and promote nucleation sites, such as through stirring or ultrasonic methods.^[44] Temperature affects gas solubility and release rates from blowing agents, generally increasing foam volume by enhancing diffusion and expansion kinetics.^[46] Similarly, the concentration of foaming agents modulates foam volume; higher surfactant levels reduce surface tension more effectively, leading to greater bubble numbers and overall foam expansion, though optimal levels avoid excessive drainage.^[45] For instance, anionic surfactants can promote high-volume nucleation in certain systems due to their strong surface activity.^[45]

Foam Stability and Collapse

Foam stability refers to the capacity of a foam structure to resist destabilization processes that lead to its eventual dissipation. The primary factors influencing stability include drainage, coalescence, and Ostwald ripening. Drainage involves the gravity-induced flow of liquid from the foam's Plateau borders and nodes, governed by Poiseuille-like flow with a characteristic velocity v = \frac{\rho g r^2}{3\eta}, where \rho is the liquid density, g is gravitational acceleration, r is the radius of curvature of the border, and \eta is the liquid viscosity.^[47] This process thickens the films between bubbles but depletes the overall liquid content, accelerating other instabilities if unchecked. Coalescence occurs through the rupture of thin liquid films separating adjacent bubbles, often initiated by van der Waals attractions when film thickness reaches nanometers, leading to bubble merging and larger voids. Ostwald ripening, meanwhile, drives gas diffusion from smaller to larger bubbles due to Laplace pressure differences, resulting in progressive bubble size polydispersity and foam coarsening.^[48] Foaming agents play a crucial role in enhancing stability by mitigating these factors. Surfactant-based agents adsorb at air-liquid interfaces to form viscoelastic films with high surface elasticity and viscosity, which resist deformation and slow drainage by creating rigid barriers that dampen liquid flow in Plateau borders.^[49] For instance, surfactants like dipalmitoylphosphatidylcholine generate immobile interfaces at elevated surface pressures, reducing drainage rates by orders of magnitude compared to mobile interfaces. Blowing agents, used in solid foam production such as polyurethanes, promote closed-cell architectures where gas is trapped within impermeable polymer walls, conferring permanent structural stability against drainage and gas diffusion even after liquid evaporation.^[11] Foam collapse is precipitated by mechanisms that overcome these stabilizing features, including antifoam interactions and environmental influences. Oil-based antifoams destabilize foams via bridging, where hydrophobic droplets enter the aqueous films, spread across the interfaces, and stretch to form pseudo-emulsions that rupture the lamellae under capillary forces.^[50] Environmental factors, such as elevated temperature, exacerbate collapse by increasing gas diffusivity and reducing solution viscosity, thereby accelerating Ostwald ripening and coarsening rates—often following an Arrhenius-like dependence on temperature through enhanced molecular diffusion coefficients.^[48] Foam stability and collapse are quantified through techniques that track structural evolution over time. A common metric is the foam half-life, defined as the duration for foam height to decay to half its initial value under gravity, providing a simple indicator of overall longevity influenced by all destabilization processes.^[51] For microscopic insight, optical microscopy measures lamella thickness and film drainage dynamics, revealing rupture thresholds at thicknesses below 50 nm and linking local instabilities to macroscopic collapse.^[52]

Applications

Industrial and Manufacturing Uses

Foaming agents play a pivotal role in the production of polymer foams through extrusion and injection molding processes, enabling the creation of lightweight materials with enhanced properties for industrial applications. In foam extrusion molding, physical blowing agents such as supercritical carbon dioxide (CO₂) or nitrogen (N₂) are introduced into the polymer melt using a co-rotating twin-screw extruder, where the gas reduces melt viscosity and promotes cell nucleation upon pressure drop at the die.^[46] This technique is commonly applied to polystyrene for expanded polystyrene (EPS) insulation, where pentane serves as the expansion agent in a two-step bead foaming process involving steam pre-expansion followed by molding, achieving densities as low as 0.010–0.035 g/cm³ compared to the solid polymer's density of approximately 1.05 g/cm³.^[53] Similarly, polyurethane foams for cushions and insulation utilize chemical blowing agents like isocyanates that release CO₂ during reaction, or physical agents like supercritical CO₂ in injection molding, where the polymer-gas solution is injected into a mold to form uniform cells with densities reduced to around 0.03 g/cm³ or lower.^[46] These processes yield materials with superior thermal insulation, as seen in EPS panels for building walls and polyurethane rigid foams for refrigerators, where thermal conductivity ranges from 0.030–0.040 W/m·K.^[53] In the construction industry, surfactants function as foaming agents to produce lightweight foamed concrete blocks by generating stable aqueous foams that are incorporated into cement-sand slurries. Protein-based or anionic surfactants, mixed at 2.5 wt% with water and compressed air, create foams with densities below 40 kg/m³ and bubble sizes under 2 mm through emulsification, which are then blended with cement (300 kg/m³), sand (150–240 kg/m³), and water (w/c ratio 0.53) before molding and 28-day curing.^[54] The resulting foamed concrete exhibits densities of 600–700 kg/m³ and porosity of 29–37 vol%, providing compressive strengths above 2 MPa suitable for non-structural lightweight blocks with thermal conductivity below 0.2 W/m·K for insulation purposes.^[54] Additionally, aqueous film-forming foams (AFFF) employ fluorosurfactants at 0.6–1.5 wt% to suppress Class B fires involving flammable liquids like fuels in industrial settings, as these surfactants lower surface tension to form a thin aqueous film that spreads rapidly over hydrocarbons, preventing vapor release and reignition by acting as a thermal barrier—extinguishing oil fires 70–88% faster than fluorine-free alternatives.^[55] For rubber and composite materials, chemical blowing agents are integral to manufacturing ethylene-vinyl acetate (EVA) foams used in footwear midsoles, where agents like azodicarbonamide (AC) at 1.35 phr decompose at 170–190°C to release nitrogen gas, creating closed-cell structures with densities of 0.15–0.25 g/cm³.^[56] This foaming, often combined with peroxide crosslinking, enhances shock absorption through the foam's elastic modulus and loss tangent, while also providing thermal insulation via low thermal conductivity and resilience for energy dissipation during impact.^[56] Such properties make EVA foams ideal for industrial production of durable, lightweight composites in footwear and protective gear. Processing techniques for industrial foaming vary between batch and continuous methods, each influencing nucleation site control and cell uniformity. Batch foaming, typically conducted in an autoclave, involves saturating the polymer with gas under pressure followed by rapid depressurization, where nucleation occurs simultaneously with growth and is governed by pressure release rate—faster rates increase nucleation density for more uniform cells, though limited to smaller specimen sizes.^[57] In contrast, continuous foaming via extrusion processes induces nucleation through flow-induced shear stress and cavitation at die wall roughness, enabling high-volume production but requiring precise control of processing parameters like temperature and gas content to achieve uniform cell sizes of 50–400 μm and avoid irregularities.^[57] Nucleation site control in both methods often incorporates additives like nanoparticles to promote homogeneous bubble formation, ensuring consistent foam morphology for applications demanding structural integrity.^[57]

Consumer and Specialized Uses

In personal care products, foaming agents such as surfactants play a key role in shampoos and soaps, where they generate lather that enhances the sensory experience and aids in even distribution during cleansing. Sodium lauryl sulfate (SLS), a common anionic surfactant, is typically incorporated at concentrations of 10-25% in shampoos to produce rich foam, which consumers associate with effective cleaning despite the foam itself not directly contributing to surfactant-based dirt removal.^[58] In soaps, similar surfactants like SLS facilitate foam formation that spreads the product over the skin, improving perceived efficacy through a luxurious lathering sensation.^[59]^[60] In food and beverages, natural foaming agents like proteins and polysaccharides contribute to texture and aeration in products such as whipped cream and beer. Egg white proteins, primarily albumins, stabilize air bubbles when whipped into whipped cream, creating a light, voluminous structure through protein denaturation and network formation around gas pockets.^[61] In beer, the head is supported by proteins such as lipid transfer proteins alongside polysaccharides like arabinoxylans, which increase liquid viscosity to enhance foam stability and prevent rapid collapse.^[62] These agents aerate the product, improving mouthfeel and visual appeal without synthetic additives. Firefighting applications utilize protein-based and synthetic foaming agents specifically for Class B fires involving flammable liquids like hydrocarbons, where the foam forms a vapor-suppressing blanket to isolate the fuel from oxygen. Protein foams, derived from natural hydrolysates, produce stable blankets with expansion ratios typically ranging from 4:1 to 20:1 for low-expansion types, though high-expansion variants can reach up to 1000:1 to cover large spill areas effectively.^[63]^[64] Synthetic foams, often hydrocarbon-surfactant based, offer similar blanketing on hydrocarbons while providing faster knockdown due to improved flow characteristics.^[9] Specialized uses extend to medical and agricultural fields, where foaming agents enable targeted delivery and coverage. In medical wound dressings, hydrophilic polyurethane foams absorb exudate while maintaining a moist environment, with the foam structure—composed of polymer matrices with dispersed air voids—facilitating autolytic debridement and protection against mechanical stress.^[65] In agriculture, foaming agents are added to pesticide sprays to create foam that improves canopy penetration and adhesion, reducing drift and ensuring uniform coverage on crops compared to liquid applications.^[66]

Safety and Environmental Aspects

Health and Safety Considerations

Foaming agents, particularly anionic surfactants such as sodium lauryl sulfate (SLS), can cause skin and eye irritation upon direct contact. SLS at concentrations greater than 2% is considered irritating in human patch tests, potentially leading to reversible inflammation, dryness, and dermatitis, with risks increasing with exposure duration.^[67] High concentrations of SLS, such as 20% in rinse-off products, may induce eye irritation after repeated exposure, though proper formulation in consumer products typically mitigates these effects.^[67] Blowing agents like azodicarbonamide (ADC) pose inhalation risks due to thermal decomposition products, including ammonia gas, which can irritate the respiratory tract and contribute to symptoms such as coughing and shortness of breath.^[68] In occupational settings, powder forms of foaming agents present dust explosion hazards if airborne concentrations reach flammable levels during handling or processing. Adequate ventilation is essential in manufacturing environments to control exposure; OSHA has no specific permissible exposure limit (PEL) for azodicarbonamide, with exposures evaluated under general particulates not otherwise regulated (PNOR) standards of 5 mg/m³ for respirable dust over an 8-hour time-weighted average (TWA), though some health evaluations suggest these limits may not fully account for its toxicity.^[69] Repeated inhalation of azodicarbonamide dust may sensitize workers, leading to asthma-like respiratory symptoms including wheezing and chest tightness.^[68] For consumer applications, certain foaming agents in cosmetics exhibit allergenicity, though coconut-derived alternatives like cocamidopropyl betaine are generally milder but can still trigger contact dermatitis in sensitive individuals, particularly with prolonged hand exposure.^[70] In food products, select foaming or defoaming agents are deemed generally recognized as safe (GRAS) by the FDA when used within specified limits, such as those outlined in 21 CFR 173.340 for processing aids that inhibit or promote foam as needed.^[71] Emergency measures for exposure to foaming agents emphasize immediate decontamination. For skin or eye contact with surfactants like SLS, flush the affected area with copious amounts of water for at least 15 minutes to alleviate irritation.^[72] In cases of inhalation, move the individual to fresh air and seek medical attention if respiratory distress persists; for ingestion, rinse the mouth with water but do not induce vomiting without professional guidance.^[72]

Environmental Impact and Regulations

Foaming agents, particularly fluorosurfactants such as per- and polyfluoroalkyl substances (PFAS), pose significant environmental concerns due to their persistence and bioaccumulative properties in aquatic ecosystems. PFAS break down very slowly, leading to accumulation in water bodies, sediments, and biota, which can result in long-term contamination and trophic magnification through food chains.^[73]^[74] Physical blowing agents like hydrofluorocarbons (HFCs) contribute to climate change through their high global warming potential (GWP); for instance, HFC-134a has a 100-year GWP of 1,110 (IPCC AR6, 2021), compared to hydrocarbons such as pentane with a GWP of about 5.^[75]^[76] Pollution from foaming agents occurs primarily through releases during manufacturing, application, and disposal, resulting in pathways that contaminate surface waters and generate persistent aquatic foam sheens visible on rivers and lakes. Surfactants in these agents can form stable foams that disrupt oxygen exchange and harm aquatic life. Early chlorofluorocarbons (CFCs) used as blowing agents depleted stratospheric ozone by releasing chlorine atoms upon atmospheric breakdown, exacerbating ultraviolet radiation exposure to ecosystems.^[77]^[78] International and national regulations have addressed these impacts through phased restrictions. The Montreal Protocol, adopted in 1987, mandated the global phase-out of ozone-depleting CFCs, including those in foam blowing, leading to near-total elimination by the early 2000s in developed nations. In the European Union, the REACH regulation imposes restrictions on certain PFAS-containing surfactants due to their environmental persistence, with 2025 updates under Commission Regulation (EU) 2025/1988 specifically targeting PFAS in firefighting foams—effective October 23, 2025, with labeling requirements from October 23, 2026, and full prohibition for concentrations ≥1 mg/L from October 23, 2030—to curb releases.^[20]^[79]^[80] In the US, the Environmental Protection Agency (EPA) has enforced guidelines since the 1990s requiring zero-ozone-depleting potential (ODP) blowing agents under the Significant New Alternatives Policy (SNAP), promoting transitions to HFCs and later low-GWP options; additionally, as of 2025, several states including California and New York have implemented bans on PFAS-containing firefighting foams, with phase-outs beginning January 1, 2025.^[81] Sustainable alternatives, such as biodegradable natural foaming agents derived from amino and α-hydroxy acids, mitigate these effects by enhancing degradability and reducing aquatic toxicity. For example, certain bioderived surfactants exhibit up to 80% lower toxicity to zebrafish larvae compared to synthetic sodium dodecyl sulfate (SDS), based on median toxic concentration tests, while maintaining effective foaming properties.^[82]

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Consequently, saponins can enhance the solubility of other substances. Compared to synthetic surfactants, saponins are more effective in enhancing polycyclic ...Missing: cons | Show results with:cons
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Ecofriendly Natural Surfactants in the Oil and Gas Industry - NIH
Although natural surfactants are less toxic than synthetic surfactants, they can still rupture erythrocytes, and their use must be carefully controlled. Large- ...
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Preparation and Application of Foaming Agent Based on the ... - NIH
Oct 21, 2022 · This study provides a new idea for the design of an advanced foaming agent with soybean residue protein (SRP) as a potential protein source.Missing: definition blowing
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(PDF) State-of-the-Art Review on the Characteristics of Surfactants ...
The focus of this work is to provide a review on characteristics of surfactant (foaming agent) and foam for use in foam concrete production. ... Read more ...
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[PDF] PHYSICS OF FOAM FORMATION ON A SOLID SURFACE IN ...
In literature two mechanisms of bubble formation are mentioned: homogeneous and heterogeneous nucleation. Homogeneous nucleation is thede novoformation of a ...
[41]
[PDF] The science of foaming
Apr 18, 2015 · Examples of foam generation via bubble nucleation and growth. (a) Continuous bubble generation and rise at nucleation sites at the wall of a ...
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Formulation of Foams - Wiley Online Library
The Gibbs–Marangoni effect explains the maximum foaming behaviour at inter- mediate surfactant concentration [6]. This is shown schematically in Figure 16.2.
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Recent Trends of Foaming in Polymer Processing: A Review - PMC
Chemical blowing agents are classified into two categories, i.e., inorganic and organic foaming agents. The blowing agents can also be separated into two types, ...Missing: definition | Show results with:definition
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A Screening Scenario to Assess the Effects of Salinity and pH on ...
Apr 19, 2022 · The stability of the foam is therefore estimated by calculating the foam's half-life; the time is taken for the foam height to become half of ...
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Polystyrene Foam - an overview | ScienceDirect Topics
Expanded polystyrene (EPS) is defined as a lightweight foam material made from polystyrene, characterized by a density as low as 10 kg m−3 and composed of ...
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Preparation and characterization of foamed concrete using a ...
Foamed concrete was made with cement, sand, and a foaming agent. The process involves mixing cement and sand with water, then adding foam. The resulting ...
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(PDF) Fluorosurfactants in Firefighting Foams - ResearchGate
Hence, AFFF is preferred for extinguishing high-hazard Class B res. In use ... Fluorosurfactants also provide oil repellency to re ghting foams,.
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Comparative Study of the Foaming Behavior of Ethylene–Vinyl ... - NIH
Jul 27, 2024 · Chemical blowing agents such as azodicarbonamide (AC) and 4,4′-oxybis(benzenesulfonyl hydrazide) are widely utilized in the preparation of EVA ...Missing: shock | Show results with:shock
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Visual Observations of Batch and Continuous Foaming Processes ...
It was found that the nucleation mechanism in the continuous foaming, i.e., extrusion foaming, was different from that of batch foaming. In the continuous ...
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A Review on the Incorporation of Sodium Lauryl Sulfate into ...
Mar 3, 2025 · The SLS concentration of SLS for shampoos are around 10-25%, and the incorporation of ACV can bring the pH closer to the scalp and hair ...
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A review of shampoo surfactant technology: consumer benefits, raw ...
Nov 2, 2017 · This review has covered all of the key uses of surfactants in shampoos, cleaning, foaming, rheology control, mildness and polymer deposition.
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Essentials of Hair Care often Neglected: Hair Cleansing - PMC - NIH
Most shampoos contain foaming agents to introduce gas bubbles into the water. The foam, also known as lather, is important, as it functions to spread the ...
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Comparative Study on Foaming Properties of Egg White with Yolk ...
Sep 21, 2021 · The aim of this study was to simulate the industrial EWP (egg white protein with 0.5% w/w of egg yolk) and characterize their foaming and structural properties
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Foam - Brewing Forward
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[PDF] Fire Extinguishers & Foam Agents - SDFD Training Division
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[PDF] Equipment Compatibility and Logistics Assessment for Containment ...
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Mechanical and contact characteristics of foam materials within ...
Foams in wound dressings are composed of a solid polymer phase and a dispersed air phase. In addition to offering storage space for excess exudate in the voids ...
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[PDF] AERIAL SPRAY ADJUVANTS Drift Control - USDA Forest Service
Foaming agents may be used with water soluble herbicides, with oil-in- water emulsions, and with wettable pow- ders. They act only upon the water phase of the ...Missing: foamed | Show results with:foamed<|control11|><|separator|>
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Azodicarbonamide (CICADS) - INCHEM
The most frequently reported effects of repeated exposure to azodicarbonamide are respiratory symptoms as well as, to a lesser extent, skin sensitization ...
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[PDF] Health Hazard Evaluation Report 83-451-1547 - CDC
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Coconut diethanolamide allergy - DermNet
Coconut diethanolamide can rarely cause allergic contact dermatitis, particularly on the hands. Leave-on products (hand-protection foams) cause sensitisation ...
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21 CFR 173.340 -- Defoaming agents. - eCFR
Defoaming agents can be used in food processing if they are safe, and added in amounts not exceeding what is needed to inhibit foaming.
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[PDF] Surfactant
May 5, 2016 · If eye irritation persists: Get medical advice/attention. First-aid measures after ingestion. : Rinse mouth with water. Do NOT induce vomiting.
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Our Current Understanding of the Human Health and Environmental ...
One common characteristic of concern of PFAS is that many break down very slowly and can build up in people, animals, and the environment over time. PFAS Can Be ...What Epa Is Doing · Pfas Can Be Found In Many... · Exposure To Pfas May Be...
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Environmental impacts, exposure pathways, and health effects of ...
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[PDF] Transitioning to Low-GWP Alternatives in Building/Construction Foams
The European Union phased out HCFCs in 2003 and much of the building/construction sector transitioned directly to HCs, having used these blowing agents since.
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Comparing the Environmental Impacts of Foam Panel Insulation
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Surfactant pollution, an emerging threat to ecosystem: Approaches ...
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CFCs and their substitutes in stratospheric ozone depletion.
CFCs can destroy stratospheric ozone. Whereas CFCs are safe to use in most applications and are inert in the lower atmosphere, they decompose in the upper ...Missing: pathways sheens
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Per- and polyfluoroalkyl substances (PFAS) - ECHA - European Union
European Commission restricts the use of PFAS in firefighting foams, 3 October 2025 · EU Member States vote in favour of restricting PFAS in fire-fighting foams, ...
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Phaseout of Class II Ozone-Depleting Substances | US EPA
Aug 7, 2025 · HFCs have zero ODP because they do not contain chlorine. A table of ... CFCs are commonly used as refrigerants, solvents, and foam blowing agents.
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Synthesis, physicochemical characterization and aquatic toxicity ...
Sep 13, 2023 · We investigated the synthesis, foaming properties, critical micelle concentration and potential aquatic toxicity of surfactants derived from natural products.