In the field of polymer and composite materials processing, lightweighting and high performance have become core demands for industry advancement, with chemical blowing agents serving as the key additives to fulfill these dual requirements. From everyday foam plastics to lightweight automotive components, from insulation materials in construction to elasticity optimization in rubber products, chemical blowing agents play an irreplaceable role throughout.
Shuntai Chemical Foaming Agents Manufacturing
Chemical foaming agents are a class of substances that, under specific conditions such as heating or pressurization, decompose through their own chemical reactions to produce gases (e.g., carbon dioxide, nitrogen, ammonia) and form uniform bubble structures within polymeric materials. Their core function is to reduce material density, enhance thermal insulation, shock absorption, or elasticity without compromising the substrate's properties, ultimately achieving dual objectives of product lightweighting and functionalization. From a chemical perspective, the reaction process of chemical foaming agents must satisfy two key requirements: controllability and compatibility. This means ensuring the gas release rate aligns with the material processing rhythm while preventing reaction byproducts from adversely affecting the substrate's properties.
Chemical Blowing Agents vs. Physical Blowing Agents
In industrial applications, foaming agents are primarily categorized into chemical and physical blowing agents, with fundamentally distinct mechanisms of action:
Physical Blowing Agents generate gas through physical state changes (e.g., liquid vaporization, solid sublimation). Common types include hydrocarbons (e.g., pentane), fluorocarbon compounds (e.g., HFCs), and compressed gases The advantage of these agents is the absence of chemical reaction residues. However, they demand extremely precise control over processing temperature and pressure, and gas solubility is easily affected by the substrate, making it difficult to form a uniform, fine-cell structure.
Chemical Blowing Agents generate gas through chemical bond breaking, offering a more stable reaction process. Gas release volume and rate can be precisely controlled by adjusting formulations (e.g., adding catalysts or stabilizers), making them particularly suitable for complex-shaped products or high-temperature processing scenarios (e.g., plastic injection molding, rubber vulcanization). Additionally, chemical blowing agents do not require high-pressure equipment, providing greater production flexibility and cost advantages in small-to-medium batch customized manufacturing.
Why Chemical Blowing Agents Are Indispensable in Modern Polymer & Composite Manufacturing?
As downstream industries demand increasingly advanced material properties, the irreplaceable role of chemical blowing agents has become increasingly evident:
First, amid the automotive lightweighting trend, foam plastic components using chemical blowing agents can reduce vehicle body weight by 10%-20% while enhancing sound insulation and vibration damping, directly helping automakers achieve energy conservation and emission reduction goals. Second, in building insulation, foam concrete and insulation boards produced with chemical blowing agents achieve thermal conductivity as low as 0.03 W/(m·K), delivering far superior insulation compared to traditional materials. Finally, in rubber processing, chemical blowing agents create closed-cell structures within rubber, preserving elasticity while reducing product density. This makes items like shoe soles and seals lighter and more durable. It can be said that chemical blowing agents have become the critical link connecting fundamental research in polymer materials with industrial applications.
Classification of Chemical Blowing Agents: Organic vs. Inorganic Types
Organic Chemical Blowing Agents
Organic chemical blowing agents primarily consist of elements such as carbon, hydrogen, and nitrogen. They feature low decomposition temperatures (typically 100-250°C) and high gas yield, making them suitable for medium-to-low temperature processing applications in plastics and rubber. Currently the most widely used type in industrial applications, they mainly include the following:
AC Foaming Agents: As the most widely used organic blowing agent, ADC is extensively applied in PVC, PE, PP, and rubber products. With a decomposition temperature of 190-220°C, it produces 200-250mL of gas per gram (primarily nitrogen and carbon dioxide). Its high gas yield and uniform cell structure make it suitable for general-purpose foam products (e.g., foam slippers, PVC foam boards). Additionally, ADC is cost-effective and stable in storage, making it the preferred foaming agent for small and medium-sized enterprises.
TSH Foaming Agents: Decomposition temperature ranges from 110-130°C, positioned between BSH and ADC. Gas yield is approximately 140mL/g, forming fine-cell structures with diameters of 10-50μm. Suitable for foam products requiring high surface finish (e.g., ABS foam plastic parts, precision rubber seals).
OBSH Foaming Agents: Decomposition temperature ranges from 150-170°C, offering excellent thermal stability. The decomposition process produces no harmful gases like formaldehyde or ammonia, meeting food contact material standards. Consequently, OBSH is commonly used in applications demanding high safety, such as foam plastics for food packaging and rubber components in baby products.
DNPT Foaming Agents: Decomposition temperature ranges from 130-160°C. Primarily releases nitrogen gas with high purity and can proceed synchronously with rubber vulcanization. Commonly used for rubber vulcanization foaming (e.g., tire cushion layers, rubber hoses). Note: DNPT must be stored away from acidic substances to prevent premature decomposition.
Inorganic Chemical Blowing Agents
Inorganic Chemical Blowing Agents primarily consist of inorganic compounds such as carbonates and bicarbonates. They feature high decomposition temperatures (typically above 200°C) and strong chemical stability, making them suitable for high-temperature processing in composite materials or construction materials. The main types include:
Sodium Bicarbonate (Baking Soda): The most common inorganic blowing agent, decomposing at 270-300°C and releasing approximately 120mL of carbon dioxide per gram. Its advantages include extremely low cost, non-toxicity, and the ability of its decomposition product (sodium carbonate) to react with acidic substances in the substrate, enhancing material corrosion resistance. It is suitable for producing lightweight concrete and high-temperature-resistant plastic foam products.
Ammonium Carbonate and Ammonium Bicarbonate: These have lower decomposition temperatures (60-100°C), releasing ammonia gas and carbon dioxide. However, their gas yield is low (approximately 70-90mL/g), and the ammonia gas has a pungent odor. They are only suitable for low-value-added, non-enclosed applications (e.g., foaming paper adhesives, low-end coatings).
Calcium Carbonate: Unlike other inorganic blowing agents, calcium carbonate requires acidic catalysts (e.g., citric acid, stearic acid) to release carbon dioxide. Its decomposition temperature can be adjusted (150-250°C) based on catalyst dosage. Its advantages include excellent compatibility with polymeric materials, serving dual functions as both a filler and foaming agent. It is well-suited for high-filler-content polymer composites (e.g., glass fiber-reinforced PP, construction plastic formwork).
Hybrid Chemical Blowing Agents
Single-type chemical blowing agents often have limitations (such as poor high-temperature resistance in organic blowing agents and low gas yield in inorganic blowing agents), making composite chemical blowing agents the direction of industry development. These agents achieve performance optimization through the blending of organic and inorganic components. Common types include:
Sodium Bicarbonate + Citric Acid System: Citric acid acts as an acidic catalyst, lowering sodium bicarbonate's decomposition temperature from 270°C to 150-180°C while increasing gas yield (up to 150mL/g). This system is suitable for medium-temperature foaming of general-purpose plastics like PE and PP.
ADC + Inorganic Stabilizer System: Adding inorganic stabilizers like zinc oxide or magnesium oxide to ADC raises its decomposition temperature to 230-250°C while reducing harmful gases (e.g., carbon monoxide) in decomposition products. This suits high-temperature processing of engineering plastics (e.g., PC, PBT).
The core advantage of composite blowing agents lies in their adjustability—by modifying the ratio of organic to inorganic components, they can precisely match the processing temperature and cell density requirements of different substrates. They are now widely used in automotive plastic components, high-end building insulation materials, and other fields.
How Do Chemical Blowing Agents Work?
The core function of chemical foaming agents is controlled gas generation + uniform foam formation. Their action process involves four stages: thermal decomposition gas generation → bubble formation → bubble stabilization → foam curing. The precision of control at each stage directly impacts the final product quality.
Thermal Decomposition
Thermal decomposition is the first and most critical step for chemical foaming agents—only at specific temperatures do the chemical bonds within the foaming agent molecules break, releasing gas. Different types of foaming agents exhibit varying thermal decomposition mechanisms:
Organic foaming agents (e.g., AC): Gas is produced through the cleavage of azo bonds (-N=N-). For instance, at temperatures above 190°C, ADC undergoes azo bond cleavage to generate nitrogen gas, accompanied by carbon-nitrogen bond cleavage that produces byproducts such as carbon dioxide and carbon monoxide.
Inorganic blowing agents (e.g., sodium bicarbonate): Gas is produced through the thermal decomposition of carbonates, specifically 2NaHCO₃ → Na₂CO₃ + CO₂↑ + H₂O↑. This reaction involves no chemical bond breaking, only a change in material state.
The core factor influencing thermal decomposition is temperature. Insufficient temperature leads to incomplete decomposition of the foaming agent and inadequate gas yield. Excessive temperature accelerates decomposition too rapidly, causing bubbles to rupture before stabilizing. Therefore, industrial production requires temperature control equipment (such as the heating section of injection molding machines or the temperature control systems of rubber vulcanizers) to maintain processing temperatures within the decomposition range of the foaming agent (typically fluctuating no more than ±5°C).
Key Reactions
The type of gas produced by chemical blowing agents directly impacts foam properties (such as water resistance and corrosion resistance). Common gases and their characteristics are as follows:
Nitrogen (N₂): Primarily generated by organic blowing agents (e.g., ADC, OBSH, DNPT). Exhibits strong chemical stability, does not react with polymeric materials, and has low solubility in plastics and rubber. Forms closed-cell structures, enhancing foam water resistance and thermal insulation properties. Considered the most ideal foaming gas.
Carbon Dioxide (CO₂): Primarily generated by inorganic blowing agents (e.g., sodium bicarbonate, calcium carbonate). It is low-cost and non-toxic. However, it exhibits high solubility in polar polymeric materials (e.g., PVC, PA), easily causing bubble coalescence and enlarged cells. Suitable for applications with low cell density requirements (e.g., lightweight concrete, low-end foam plastics).
Ammonia (NH₃): Primarily generated by ammonium carbonate and amino-based organic blowing agents. It has a pungent odor and readily reacts with acidic substances to form salts, potentially causing foam yellowing and performance degradation. Currently used only in non-food-contact, non-sealed low-end products.
In industrial production, nitrogen-producing blowing agents (e.g., AC, OBSH) are prioritized to ensure foam stability and durability. Carbon dioxide or ammonia-producing foaming agents are used only in cost-sensitive applications with low performance requirements.
Factors Influencing Chemical Foaming Agents Decomposition
In addition to temperature, processing time, additive types, and substrate properties also influence the decomposition process of chemical blowing agents:
Processing time: The decomposition reaction requires a certain duration. If processing time is too short (e.g., excessive injection speed), the blowing agent may solidify with the substrate before complete decomposition, resulting in uneven foam density. Conversely, excessive processing time may cause excess gas to escape from the substrate surface, leading to missing bubbles.
Additives: Catalysts can lower the decomposition temperature of foaming agents (e.g., citric acid reduces the decomposition temperature of sodium bicarbonate), while stabilizers can slow the decomposition rate (e.g., zinc oxide stabilizes the decomposition process of ADC). Other additives such as flame retardants and plasticizers may react with the foaming agent, affecting gas production efficiency (e.g., certain phosphorus-based flame retardants inhibit the decomposition of ADC).
Base Material Properties: Higher melt viscosity of the base material promotes bubble stability (e.g., PVC's melt viscosity exceeds PE's, making it more suitable for fine-cell foaming). Conversely, excessively low melt viscosity (e.g., PP) requires viscosity-enhancing agents to prevent bubble rupture.
From Gas Bubbles to Uniform Foam
The gas generated by chemical blowing agents must form uniform, stable cells within the substrate. This process requires careful control of the following stages:
Bubble Formation Stage: Gas forms bubble nuclei within the molten substrate. Nucleation density depends on the dispersion of the blowing agent—finer particles (typically 5-20μm) and more uniform dispersion yield more nuclei, resulting in finer cells.
Bubble Growth Stage: Bubble nuclei gradually expand under pressure differentials. Here, controlling the melt viscosity of the substrate is crucial — excessively high viscosity inhibits bubble growth, resulting in overly dense foam; conversely, excessively low viscosity causes bubbles to grow too rapidly, merge, and form large bubbles or rupture.
Foam Curing Stage: The substrate solidifies through cooling, vulcanization, or similar processes, trapping bubbles within the material. For instance, plastic foaming solidifies via cooling in injection molding machines, while rubber foaming undergoes cross-linking and curing in the holding section of vulcanizers. Sudden temperature changes must be avoided during this stage to prevent foam shrinkage or deformation.
Industrial quality assessment typically evaluates foam density (number of cells per unit volume) and cell uniformity (cell diameter deviation rate). Premium foam generally achieves a density of 10⁵–10⁶ cells/cm³ with a cell diameter deviation rate not exceeding 20%.
Major Applications of Chemical Blowing Agents Across Industries
Polymer Plastics Industry
Plastics represent the primary application area for chemical blowing agents, accounting for over 60% of global blowing agent consumption. They are mainly used to produce the following foam plastics:
PVC Foam: Utilizing AC or OBSH as blowing agents to produce soft PVC foam (e.g., sofa cushions, toys) and rigid PVC foam (e.g., advertising boards, construction formwork).
PE/PP Foam: PE foam commonly employs a composite blowing agent of sodium bicarbonate + citric acid to produce food packaging cushioning materials and water floats; PP foam requires OBSH or composite blowing agents to address PP's low melt viscosity and bubble fragility, primarily used in automotive door panels and trunk liners.
EPS: While EPS traditionally employs physical blowing agents (e.g., pentane), recent years have seen the adoption of blended systems combining AC and physical blowing agents to meet environmental requirements. This reduces volatile organic compound emissions while enhancing foam compressive strength.
Rubber Manufacturing
Adding chemical blowing agents to rubber products reduces density while preserving elasticity. Key applications include:
Tire Industry: DNPT blowing agents are used in tire cushion layers and airtight layers to form closed-cell structures. This enhances shock absorption and airtightness while reducing tire weight (achieving a 1-2kg weight reduction per vehicle tire).
Sealing Industry: OBSH or TSH-based rubber seals (e.g., door/window gaskets, automotive seals) exhibit foam structures that boost compression recovery rates (from 50% in standard rubber to over 70%), extending service life;
Daily-use rubber products: Foam soles using AC foaming agents create porous structures that are lightweight (30% weight reduction), slip-resistant, and breathable. Medical rubber gloves using BSH foaming agents reduce rubber hardness, improving wearing comfort.
Building Materials Sector
The construction industry's demand for chemical blowing agents centers on two primary applications: “thermal insulation” and “lightweighting.” Key uses include:
Insulation Panels: XPS (extruded polystyrene) insulation boards utilize ADC foaming agents to create closed-cell structures exceeding 90% closed-cell content, achieving thermal conductivities as low as 0.028 W/(m·K). These panels are suitable for exterior wall and roof insulation.
Lightweight Concrete: Sodium bicarbonate or calcium carbonate foaming agents are used to produce lightweight concrete with densities ranging from 500 to 1000 kg/m³. Compared to standard concrete (density 2400 kg/m³), this reduces weight by over 60% while maintaining sufficient compressive strength (≥3 MPa), making it suitable for partition walls and floor slabs in high-rise buildings.
Waterproof coatings: Adding composite foaming agents to asphalt waterproof coatings creates a foamed coating layer. This enhances the coating's ductility (increasing elongation at break from 300% to 500%) while improving waterproofing performance. Suitable for roof and basement waterproofing projects.
Automotive Industry
The automotive sector represents the fastest-growing application area for chemical blowing agents, primarily utilized in the following scenarios:
Lightweighting of plastic components: For instance, PP+OBSH foaming systems applied to automotive dashboards and center consoles reduce component weight by 15-20% while enhancing sound insulation (noise reduction of 5-10dB).
Acoustic damping materials: Foam rubber (using DNPT as the blowing agent) in automotive floor panels and door interiors creates a porous structure that absorbs vibration noise during driving, enhancing ride comfort;
Structural Component Reinforcement: Utilizing PC/ABS + composite foaming agents in structural components like bumpers and pillars. Through “foam reinforcement” technology, this approach reduces weight while increasing impact strength (over 20% improvement), meeting automotive safety standards.
Textile and Adhesive Industries
Beyond the aforementioned mainstream applications, chemical blowing agents also serve specialized purposes in the textile and adhesive sectors:
Textile Industry: Adding trace amounts of AC blowing agent during the spinning process of synthetic fibers (such as polyester and nylon) creates microscopic air pockets within the fibers. This enhances thermal insulation and breathability, making it ideal for high-end down jackets and thermal underwear.
Adhesives Industry: Incorporating ammonium bicarbonate foaming agents into hot-melt and water-based adhesives produces foam adhesives. This allows adhesive layer thickness to increase from 0.1mm (standard) to 0.5mm while maintaining bonding strength, making it suitable for wood joinery and paper lamination.
Key Performance Metrics to Evaluate Chemical Blowing Agents
Gas Yield (Volume per Gram)
Gas yield refers to the volume of gas produced per gram of foaming agent after complete decomposition (unit: mL/g). It is a key indicator determining foam density—higher gas yield means more foam can be produced from the same weight of foaming agent, resulting in lower material density.
Gas yield ranges for different foaming agents
AC (200-250 mL/g) > OBSH (120-150 mL/g) > Sodium Bicarbonate (100-120 mL/g) > BSH (90-110 mL/g).
Selection Recommendations: For low-density foams (e.g., foam plastics, lightweight concrete), prioritize high-gas-yielding agents (e.g., AC). For high-density, high-strength foams (e.g., automotive structural components), select low-gas-yielding agents (e.g., OBSH).
Decomposition Temperature Range
The decomposition temperature range refers to the temperature interval from the onset to complete decomposition of the blowing agent. It must precisely match the processing temperature of the substrate material. For example: PVC processing temperatures range from 160-200°C, making ADC (190-220°C decomposition) suitable; PE processing temperatures range from 180-220°C, allowing selection of ADC or OBSH (150-170°C decomposition, requiring stabilizers to elevate decomposition temperature).
Note that while the decomposition temperature of some blowing agents can be adjusted via additives (e.g., catalysts to lower temperature, stabilizers to raise temperature), the adjustment range typically does not exceed ±30°C. Therefore, the substrate processing temperature remains the primary consideration for selection.
Particle Size & Dispersion
The smaller the particle size of the foaming agent and the better its dispersibility, the greater the number of bubble nuclei formed in the substrate, resulting in finer and more uniform pores. Industrial requirements for foaming agent particle size:
Plastic Foaming: Particle size 5-20μm, ensuring uniform dispersion in molten plastic;
Rubber Foaming: Particle size 10-30μm, matching rubber particles (typically 50-100μm) to prevent agglomeration;
Building materials: Particle size 50-100μm, where fine-cell structure is unnecessary to reduce production costs.
If foaming agents disperse unevenly, it can cause localized bubbles to be excessive (resulting in low density) or insufficient (resulting in high density), affecting product appearance and performance. Therefore, dispersion must be enhanced using equipment such as high-speed mixers and dispersants, along with additives.
Thermal Stability
Thermal stability refers to the foam agent's stability during storage and pre-processing (before reaching decomposition temperature), typically measured by half-life (the time required for 50% decomposition at a specific temperature).
Requirements for high-quality foam agents:
At storage temperatures (typically 25-35°C), half-life must exceed 1 year. During the preheating stage before substrate processing (e.g., plastic drying temperature 60-80°C), the half-life must exceed 10 hours to prevent premature decomposition.
For example, ADC exhibits excellent thermal stability with a half-life exceeding 2 years at 25°C; conversely, DNPT has poor thermal stability and requires storage in a cool, dry place with a maximum shelf life of 6 months to prevent decomposition and loss of efficacy.
Compatibility with Polymers & Additives
Compatibility refers to the ability of a blowing agent to disperse uniformly without adverse reactions with the substrate or other additives (such as plasticizers, stabilizers, or flame retardants). Poor compatibility can lead to the following issues:
Incompatibility with substrate: Foaming agent agglomerates, forming large bubbles or causing bubble collapse;
Incompatibility with additives: Reacts with flame retardants, reducing flame retardancy; reacts with plasticizers, causing substrate softening.
Selection Recommendations:
- For polar substrates like PVC and rubber, prioritize polar foaming agents (e.g., ADC, BSH); For non-polar substrates like PE and PP, prioritize non-polar blowing agents (e.g., OBSH); If the formulation contains flame retardants, select blowing agents compatible with them (e.g., AC is compatible with brominated flame retardants, OBSH with phosphorus-based flame retardants).
Chemical Foaming Agents Solutions-ShuntaiTech
As a leading domestic provider of chemical additive solutions, we have dedicated 17 years to the field of chemical blowing agents. Centering on “technological innovation and consistent quality,” we deliver customized blowing agent products and technical services to global clients.
Our comprehensive chemical blowing agent portfolio encompasses the full range of products including AC, NC, OBSH, DNPT, and more. To date, our client base spans multiple industries such as plastics, rubber, automotive, and construction, with products exported to over 30 countries and regions.
Should you require assistance in selecting chemical blowing agents, please feel free to contact us at any time. Based on your specific requirements (such as substrate type, processing techniques, and product performance specifications), we will provide complimentary samples and technical solutions to jointly achieve our collaborative goals of cost reduction, efficiency enhancement, and sustainable development.
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