In the rubber, plastic, and elastomer manufacturing sectors, foaming agents serve as the unsung heroes that impart core properties such as lightweight, thermal insulation, and cushioning to materials. Among these, OBSH stands out as the preferred foaming agent for high-end products like automotive seals (e.g., EPDM rubber gaskets), electronic packaging foam, and athletic shoe midsoles, owing to its low toxicity, excellent foam uniformity, and superior compatibility with substrates. As global environmental regulations tighten, traditional highly toxic foaming agents are gradually being replaced, with OBSH's market demand maintaining an annual growth rate of 8%-10%.
OBSH, chemically known as 4,4'-oxydiphenylsulfonylhydrazine, with the molecular formula C₁₂H₁₄N₄O₅S₂. It appears as a white powder and decomposes stably within the temperature range of 150-180°C, releasing nitrogen gas (approximately 95%) and a small amount of water vapor. It does not produce harmful gases such as carbon monoxide or formaldehyde, a characteristic that significantly surpasses the environmental performance of traditional AC blowing agents (azodicarbonamide).
In terms of performance advantages, OBSH's core value manifests in three aspects: First, foam uniformity—the bubbles produced during decomposition have a diameter concentrated between 50-100μm, enabling precise density control of rubber or plastic foam within 0.3-0.8g/cm³, preventing defects like large bubbles or bubble collapse. Second, substrate compatibility: It exhibits excellent compatibility with mainstream materials like EPDM, nitrile rubber, PVC, and PP, without causing substrate yellowing or degradation of mechanical properties. Third, processing stability: Its decomposition rate can be adjusted by adding co-blowing agents (such as zinc oxide), adapting to different molding processes (extrusion, compression molding, injection molding).
In practical applications, OBSH is widely used across multiple high-demand sectors: - Automotive industry: Manufactures lightweight rubber seals, reducing weight per meter of seal by 30% while enhancing sound insulation. - Electronics industry: Used in PC/ABS alloy foams to provide cushioning protection for chips and sensors. - Footwear industry: OBSH foaming increases rebound performance of athletic shoe midsoles by 20%, balancing comfort and durability.
Core Raw Materials for OBSH Production
OBSH production relies on four key raw materials. The purity and impurity content of each directly impact final product performance. Raw material costs account for 60%-70% of OBSH's total expenses, making raw material selection the critical first step in production.
4,4'-Dihydroxydiphenyl ether
As the primary precursor for OBSH, bisphenol O must achieve a purity exceeding 99% with moisture content ≤0.5%. Insufficient purity (e.g., phenolic impurities) leads to incomplete sulfonation reactions, resulting in yellowing of the final OBSH product and expanded decomposition temperature fluctuations (±5℃ or more), compromising foam molding stability. Currently, industrial-grade bisphenol O is predominantly produced via phenol-formaldehyde condensation. Procurement must prioritize hydroxyl value testing (≥980 mg KOH/g) to ensure reactivity.
Sulfuric Acid and Thionyl Chloride
Sulfuric acid (H₂SO₄), serving as the sulfonation reaction catalyst, requires 98% industrial-grade concentrated sulfuric acid with impurity content (e.g., iron, heavy metals) ≤0.001%. Otherwise, side reactions may occur in the reaction system, forming black carbides. Thionyl chloride (SOCl₂) is used to convert the hydroxyl group of bisphenol O into a sulfonyl chloride group. Its purity must be ≥99.5%, with free chlorine content ≤0.1%. Excess free chlorine reacts with subsequently added hydrazine to form toxic hydrazine chloride, increasing environmental risks.
Hydrazine Hydrate
Hydrazine hydrate serves as the core raw material in the hydrazination reaction, playing a crucial role in converting sulfonyl chloride to sulfonylhydrazine. Industrially, 80% concentration hydrazine hydrate is commonly selected, with free ammonia content ≤0.5%. Excessive free ammonia reacts with sulfonyl chloride to form aminosulfonyl compounds, reducing OBSH purity and enlarging foam pore size. Additionally, hydrazine hydrate exhibits strong reducing properties; procurement requires strict adherence to storage conditions (sealed, cool, dark) to prevent oxidation-induced degradation.
Solvents and Auxiliary Reagents
Toluene is commonly used as the reaction solvent in production and must meet industrial-grade standards (purity ≥99.8%, moisture ≤0.1%). Toluene not only dissolves bisphenol O and sulfonyl chloride but also helps maintain uniform reaction temperature. Deionized water (conductivity ≤10μS/cm) must be used during washing to prevent calcium and magnesium ions in water from reacting with residual acids to form salt impurities. When necessary, a small amount of sodium hydroxide (NaOH) may be added to adjust pH. Analytical grade NaOH (purity ≥96%) must be selected to ensure pH control precision.
OBSH Production: Five Critical Steps from Reaction to Finished Product
The OBSH production process comprises five core steps: sulfonation, hydrazination, filtration/washing, drying/grinding, and quality inspection/packaging. Each step requires strict control of parameters such as temperature, time, and material ratios. Deviations at any stage may result in product scrap.
Step 1: Sulfonation Reaction—Formation of 4,4'-Oxydiphenyl Sulfonyl Chloride
The sulfonation reaction forms the foundation of OBSH production, converting the hydroxyl group of bisphenol A into a sulfonyl chloride group. The specific procedure is as follows:
Feedstock Loading and Heating: In a reactor equipped with stirring, temperature monitoring, and tail gas absorption, add bisphenol O and 98% sulfuric acid at a 1:3 mass ratio. Initiate stirring (300 rpm) while gradually heating to 80–90°C. Maintain this temperature for 30 minutes to ensure complete dissolution of bisphenol O, forming a transparent solution.
Addition of Thiosulfochloride: Slowly add thiosulfochloride to the reactor at a molar ratio of 1:2.2 relative to bisphenol O (addition rate: 50 mL/h). Maintain the temperature between 85-90°C during addition to prevent localized overheating and carbonization of the raw materials. After completion of the addition, continue the reaction under constant temperature for 3-4 hours until no HCl gas is released (no bubbles appear in the tail gas absorption tower). At this point, the solution appears pale yellow and transparent, indicating the formation of 4,4'-oxydiphenylsulfonyl chloride solution.
Critical Control: Temperature must be maintained within ±2°C. If below 80°C, sulfonation is incomplete, leaving unreacted bisphenol O. Above 95°C causes thiosulfochloride decomposition, generating SO₂ and Cl₂ that contaminate the product. Simultaneously, HCl in the tail gas must be absorbed using 20% NaOH solution. The resulting NaCl solution can be recovered as a byproduct, meeting environmental requirements.
Step 2: Hydrazination Reaction—Core OBSH Synthesis Step
The hydrazone reaction is critical for converting sulfonyl chloride into sulfonylhydrazine, directly determining OBSH purity and yield. Key operational points are as follows:
Solvent Transfer and Cooling: Transfer the post-sulfonation 4,4'-oxydiphenylsulfonyl chloride solution to another reactor. Dilute with toluene (1:1 volume ratio with sulfonyl chloride solution) and activate the cooling system to reduce temperature to 50-60°C.
Hydrazine Hydrate Addition and pH Adjustment: Slowly add 80% hydrazine hydrate to the reactor at a molar ratio of 1:2.1 (sulfonyl chloride:hydrazine hydrate), maintaining a drop rate of 30 mL/h. Simultaneously control the reaction pH between 7-8 by titrating with 10% NaOH solution (monitored in real-time with an online pH meter). After completion of the addition, raise the temperature to 65-70°C and maintain stirring for 2-3 hours. A white flocculent precipitate will gradually form in the solution, representing the crude OBSH product.
Critical Control: pH is the core parameter for the hydrazone decomposition reaction. If pH < 6.5, hydrazine hydrochloride exists in protonated form and cannot react with sulfonyl chloride. If pH > 8.5, sulfonyl chloride undergoes hydrolysis, generating sulfonic acid impurities and reducing OBSH yield. Additionally, the hydrazine hydrate addition rate must not be too rapid, as this may cause localized excess hydrazine formation. This excess reacts with sulfonyl chloride to form polyhydrazine compounds, adversely affecting product performance.
Step 3: Filtration and Washing — Impurity Removal and Purity Enhancement
Crude OBSH contains unreacted raw materials and salt impurities (e.g., NaCl), requiring purification through filtration and washing:
Filtration Separation: After hydrazine decomposition completes, transfer the reaction mixture to a plate-and-frame filter. Filter under 0.3 MPa pressure to collect a white filter cake (crude OBSH). Distill the filtrate (toluene and unreacted hydrazine hydrate) to recover toluene, reducing costs.
Water Washing for Salt Removal: Transfer the filter cake to a washing tank. Add deionized water (solid-liquid ratio 1:5), stir for 30 minutes, then filter. Repeat water washing 3-5 times until the wash water pH reaches 6.5-7.5 (tested with pH paper) and conductivity ≤50 μS/cm (indicating no salt residue).
Ethanol dehydration: To shorten subsequent drying time, soak the washed filter cake in 95% ethanol (solid-liquid ratio 1:3) for 20 minutes. Filter to obtain wet product OBSH; ethanol is recoverable for recycling.
Step 4: Drying and Grinding—Controlling Moisture and Particle Size
Drying and grinding directly impact OBSH's storage stability and application dispersibility. Procedures are as follows:
Vacuum Drying: Place wet OBSH in a vacuum drying oven. Dry at 80-90°C under -0.09 MPa vacuum for 4-5 hours. Sample and test moisture content hourly until ≤0.3% (using Karl Fischer moisture analyzer). Drying temperature must not exceed 100°C, as higher temperatures cause premature decomposition and reduced product activity.
Air-jet Milling: Place the dried OBSH into an air-jet mill. Adjust the milling pressure (0.8 MPa) and classifier wheel speed (3000 rpm) to achieve a particle size of 10-50 μm (measured using a laser particle size analyzer), ensuring uniform particle size distribution. If particle size is too large (>50 μm), OBSH disperses unevenly in the substrate, potentially causing localized insufficient foaming. If particle size is too small (<10μm), it readily absorbs moisture and caking occurs, affecting usability.
Step 5: Quality Inspection and Packaging—Ensuring Product Compliance
OBSH finished products undergo rigorous testing and must meet industrial standards (e.g., HG/T 4805-2015) before packaging and shipment:
Core testing parameters: Purity (≥98% via HPLC), decomposition temperature (150-180°C via DSC), heavy metal content (Pb ≤10ppm, Cd ≤5ppm via AAS), foaming performance (simulated rubber foaming with cell uniformity assessment).
Packaging and Storage: Moisture-proof bags (25kg/bag) with inner PE film and outer kraft paper layers, sealed tightly to prevent moisture absorption. Store in cool, dry conditions (temperature ≤30°C, relative humidity ≤60%). Shelf life: 24 months.
OBSH Production Quality Control: Avoiding Common Defects
Quality control spans the entire OBSH production process. The following three critical control points require special attention to prevent product defects:
1. Incoming Raw Material Inspection
All raw materials must undergo batch-specific testing: - Bisphenol O: Purity and hydroxyl value - Sulfuric acid: Concentration and heavy metal content - Hydrazine hydrate: Free ammonia content - Toluene: Moisture content and purity If raw materials fail inspection (e.g., bisphenol O purity below 97%), even with precise subsequent process control, OBSH purity may fall below 95%, resulting in inconsistent bubble sizes during foaming.
2. Real-time Monitoring During Reaction Processes
The sulfonation reaction requires real-time temperature monitoring via thermocouples, with readings recorded every 30 minutes. The hydrazone decomposition reaction necessitates continuous pH monitoring using an online pH meter; adjust the NaOH addition rate promptly if deviations exceed ±0.2. During filtration and washing, monitor the pH and conductivity of the wash water to ensure no impurities remain. For example, a factory once failed to adjust the pH promptly when it dropped to 6.0 during the hydrazination reaction, resulting in a 10% decrease in OBSH yield and a decomposition temperature reduction to 145°C, which failed to meet customer requirements.
3. Finished Product Sampling Inspection
Each batch must yield three samples for testing purity, moisture content, particle size, and other indicators. If any single sample fails, double the sampling size for retesting. Should any sample still fail, the entire batch must be reprocessed.
As a leading eco-friendly foaming agent, OBSH's competitiveness hinges directly on the precision of its production process. From raw material screening to final packaging, every step requires strict control to produce high-purity, stable-performance OBSH that meets the demands of high-end sectors like automotive, electronics, and footwear materials. For manufacturers, mastering core OBSH production technologies not only reduces costs and enhances product quality but also secures market share amid growing environmental trends.
If you encounter process optimization or quality challenges in OBSH production, or require high-purity OBSH raw materials, contact
SHUNTAITECH. We provide customized production consulting services and industrial-grade OBSH products to ensure your operations are efficient and compliant.
Frequently Asked Questions
1. What is the typical production cycle for OBSH? A single batch cycle takes approximately 8-10 hours (including raw material preparation, reaction, drying, and quality inspection). Large-scale production using continuous reactors can achieve daily output of up to 1000kg.
2. How does OBSH production differ from AC blowing agent production? OBSH is produced from bisphenol O via sulfonation and hydrazinolysis, yielding no harmful byproducts. AC blowing agent uses urea and hydrazine hydrate in a condensation reaction, potentially releasing CO during decomposition, making it less environmentally friendly than OBSH.
3. What are the storage conditions for OBSH? Store in a cool, dry place (temperature ≤30°C, relative humidity ≤60%). Keep packaging sealed and avoid contact with acids or alkalis. Shelf life is 24 months.
