In sectors such as plastic packaging, rubber products, and building insulation materials, chemical blowing agents serve as core additives for achieving “lightweighting, cost reduction, and performance enhancement.” However, the market offers a complex array of options—including AC blowing agents, OBSH blowing agents, and sodium bicarbonate composite blowing agents—where improper selection can result in uneven foaming and substandard strength at best, and at worst, trigger production halts and environmental compliance risks.
Define Application Scenarios
Plastic processing (PVC, PE, PP substrates) is the primary application for chemical blowing agents. Selection hinges on “temperature compatibility” and “bubble control”:
Temperature compatibility is fundamental: - PVC soft goods (e.g., foam slippers, IV tubing) typically process at 160-180°C. Prioritize standard AC blowing agents (azobisisobutyronitrile) with decomposition temperatures of 160-175°C to prevent premature decomposition and bubble escape.PP products (e.g., automotive bumper foam layers) require processing temperatures as high as 180-220°C. Modified AC blowing agents or H blowing agents (N,N'-dinitro-pentamethylenetetramine) must be used to prevent agent failure at elevated temperatures.
Foam uniformity depends on product thickness: Thin-walled plastic parts (e.g., packaging liners, toy shells) require slow-decomposing blowing agents combined with accelerators like zinc oxide to prevent “large bubble voids.” Thick-walled sheets (e.g., PP hollow panels) necessitate controlled decomposition cycles to ensure gradual internal bubble formation and minimize fusion rupture. Medium-speed blowing agents with a 10-15 minute decomposition duration are recommended.
Rubber products (tires, seals, sponge) undergo a dual process of “vulcanization shaping + foaming.” Foaming agents must synchronize with the vulcanization process:
Decomposition cycle must match vulcanization time: Rubber vulcanization typically occurs at 140-180°C over 10-30 minutes. Using agents with excessively fast decomposition (e.g., standard sodium bicarbonate) causes bubbles to rupture before vulcanization completes.Recommended alternatives include rubber-specific AC foaming agents or OBSH foaming agents (4,4'-oxydibenzosulfonylhydrazine), which decompose over 15-20 minutes for seamless vulcanization synchronization.
Environmental compliance is critical: Food-contact-grade rubber (e.g., silicone seals, baby pacifiers) strictly prohibits DPP foaming agents(potassium diphenyl sulfonate) — its decomposition produces harmful phenolic compounds. Switch to OBSH blowing agent and provide FDA 21CFR 177.2600 or GB 4806 certification reports to ensure no toxic substance migration.
Foam concrete, insulation boards, and other building materials must withstand “long-term load-bearing” and “outdoor environmental” challenges. Foaming agents must balance “high expansion ratio” with “high stability”:
Foaming expansion ratio + compressive strength dual compliance: Foam concrete requires a foaming expansion ratio of 20-30 times (i.e., 1kg of foaming agent generates 20-30L of gas), while the product's compressive strength must be ≥0.5MPa.Recommended: Aluminum powder-based chemical foaming agents — react with cement alkalinity to generate hydrogen gas. Paired with sodium dodecylbenzenesulfonate (SDBS) foam stabilizer, they form fine, stable bubble structures.
Weather Resistance for Outdoor Applications: Exterior wall insulation boards and roof insulation layers must withstand temperatures ranging from -20°C to 60°C while resisting UV aging. Inorganic foaming agents (such as sodium bicarbonate composite foaming agents) offer greater stability than organic alternatives, minimizing bubble rupture due to temperature fluctuations and preventing the leaching of harmful substances.
Evaluate 4 Core Performance Metrics
After defining the application scenario, focus on the core parameters of
chemical blowing agents—these serve as the “quantitative basis” for selection. All 4 metrics must be verified individually, with none omitted.
Foaming Rate:
Foaming rate refers to the gas volume (mL/g) produced per unit mass of blowing agent, serving as a key indicator of foaming efficiency. However, blindly pursuing high foaming rates can lead to pitfalls:
High Foaming Rate Applications: Lightweight products (e.g., foam plastics, hollow building materials) may opt for high-foaming agents like AC foaming agents (250-300 mL/g), which significantly reduce product density. However, a robust foam stabilization system (e.g., calcium stearate + glycerol) is essential; otherwise, excessive gas may cause bubble rupture, lowering product yield.
Low Foaming Rate Applications: High-density products (e.g., rubber seals, load-bearing building materials) require controlled foaming rates. Sodium bicarbonate foaming agents (70-100mL/g) prevent excessive bubbles that compromise strength. For instance, automotive rubber shock absorbers with excessively high foaming rates may see compressive strength drop by over 30%, failing to meet performance requirements.
Note: When purchasing, request an “actual foaming rate report” rather than theoretical values. Some low-quality foaming agents contain 20%-30% impurities, resulting in actual foaming rates 20%-30% lower than labeled values. This directly increases production material costs.
Decomposition Temperature:
Decomposition temperature (the temperature at which the foaming agent begins to generate gas) is the “critical threshold” for chemical foaming agents. Mismatch here can paralyze the entire production process:
Risks of Low Decomposition Temperature: If the foaming agent decomposes below the processing temperature, it breaks down prematurely before the substrate melts. After gas escape, the product exhibits minimal foaming effect. For example, using a foaming agent with a decomposition temperature of 140°C in PVC processing at a melting temperature of 160°C causes complete bubble loss, resulting in a final product density identical to unfilled material.
Risk of excessively high decomposition temperature: If the decomposition temperature exceeds the processing temperature, the blowing agent begins decomposing only after the substrate has cooled and set. This generates “internal stress” within the product, leading to cracking and deformation. For example, using a blowing agent with a decomposition temperature of 230°C in PP processing at 220°C causes the agent to decompose after cooling, directly resulting in surface cracking of the sheet.
Recommendation: For production processes with significant temperature fluctuations (±5°C), prioritize foaming agents with a “wide decomposition temperature range,” such as modified AC foaming agents (decomposition range 150-190°C). These offer higher tolerance to minor temperature variations, reducing defective products caused by slight temperature shifts.
Gas Purity
The purity of gases produced during chemical foaming agent decomposition directly impacts product safety and environmental compliance. Key impurities to investigate include:
Common harmful byproducts: DPP foaming agents decompose into phenol (carcinogenic), while certain azo-based foaming agents decompose into nitrosamines (strong carcinogens). These products are prohibited under EU REACH regulations and China's GB/T 27630 standard. Exporters must strictly avoid them.
High-purity gas standards: Environmentally friendly foaming agents should decompose into harmless substances like water and carbon dioxide. For example, OBSH foaming agents decompose only into H₂O and CO₂, while sodium bicarbonate composite foaming agents produce CO₂ and Na₂CO₃ (with no volatile impurities).When purchasing, request suppliers to provide a “Gas Composition Test Report” to confirm the absence of heavy metal (lead, cadmium, mercury) and volatile organic compound (VOC) residues.
Decomposition Rate
The decomposition rate (time for the foaming agent to complete gas release) must match the product thickness and cooling speed; otherwise, uneven foaming may occur:
Rapid Decomposition (1-3 minutes): Suitable for thin-walled products (e.g., plastic packaging films, thin rubber gaskets). Completes foaming before rapid substrate cooling, preventing bubble collapse due to excessive cooling speed. For example, PE films for food packaging: if decomposition is too slow, only the surface foams after cooling, leaving no internal bubbles and failing to achieve insulation.
Slow decomposition (5-10 minutes): Suitable for thick-walled products (e.g., foam concrete blocks, large rubber sponges). This ensures uniform internal bubble formation and prevents bubble coalescence due to slow internal heat dissipation. For instance, in a 50mm-thick rubber sponge, excessively fast decomposition creates “large voids” inside, reducing compressive strength by over 50%.
Four Common Misconceptions in Foaming Agent Selection:
Misconception 1: Blindly Pursuing High Foaming Rates
Many believe higher foaming rates are more cost-effective, but this is not necessarily true.
Correct Approach: Calculate the required foaming rate based on the product density requirement. For example, if the target product density is 0.5 g/cm³, use the formula: Foaming Rate = (Base Material Density - Product Density) / Product Density × 1000. Then select the appropriate model.
Misconception 2: Ignoring Decomposition Byproducts
Focusing solely on foaming performance without checking decomposition products can lead to product compliance failures.
Misconception 3: Ignoring batch consistency
Significant performance variations between batches of the same model can destabilize production processes. Correct approach: After receiving each batch, conduct small-scale tests (using 50g samples to measure foaming rate and decomposition temperature). Only proceed with bulk use after confirming consistency with previous batches. If variations exceed 5%, contact the supplier for adjustments or returns.
Misconception 4: Failing to Test Compatibility with Additives
Directly combining new foaming agents with existing additives risks incompatibility conflicts. For example, a rubber plant replacing AC foaming agent with OBSH without testing compatibility with peroxide vulcanizing agents resulted in vulcanization time doubling from 15 to 30 minutes, halving production efficiency.
Correct Practice: Before switching foaming agents, conduct a “small-scale additive compatibility test.” Mix the foaming agent with stabilizers, vulcanizing agents, etc., at production ratios to evaluate foaming performance and vulcanization speed. Only proceed to mass production after confirming no conflicts.
