Dimethylpolysiloxane Silicone Defoamer(CAS#63148-53-8)–Multipurpose Antifoam Agent

1. Properties:

• Appearance and Physical Form: Dimethylpolysiloxane (CAS#63148-53-8) silicone defoamer is supplied as a white, milky liquid emulsion (water‑base) for water‑based industrial systems, or as a colourless to light yellow transparent viscous liquid when delivered as the 100% active silicone oil neat product for oil‑based and non‑aqueous formulations.
• Solubility and Miscibility: The emulsion grades form a good dispersion with complete water miscibility, making them exceptionally easy to incorporate into water‑based industrial processes such as textile finishing baths, paper machine white water loops, and wastewater treatment systems. The neat oil is immiscible with water but fully soluble in most organic solvents, hydrocarbon systems, and oils for non‑aqueous defoaming applications.
• Chemical Properties: Dimethylpolysiloxane is a high‑molecular‑weight linear silicone polymer consisting of repeating [Si(CH₃)₂O] units (PDMS). The unique alternating silicon‑oxygen backbone imparts exceptionally low surface tension (~20 mN/m, significantly lower than water at ~72 mN/m) and outstanding spreading characteristics. This enables the defoamer to rapidly spread across foam lamellae, reduce the surface tension of the liquid film, and cause immediate foam bubble collapse. The product exhibits excellent chemical stability over a wide pH and temperature range and is non‑corrosive, compatible with most base fluids and surfactant systems.
• Mechanism of Action: When added to a foaming system at concentrations as low as 1–100 ppm, dimethylpolysiloxane migrates to the gas‑liquid interface and penetrates the foam‑stabilising surfactant layer. Its very low surface tension creates an imbalance in the foam lamella, causing rapid rupture of foam bubbles and preventing re‑formation.
• Thermal and Chemical Stability: The product is thermally stable, maintaining defoaming performance across a broad temperature range (typically –50°C to +200°C for neat grades) and across pH 2–12 for emulsion grades. It is resistant to oxidation, hydrolysis, and microbial degradation.

2. Applications:

Textile Industry:

• Textile Printing and Dyeing: Dimethylpolysiloxane defoamer emulsion (e.g., BWF 160) is widely used as a foam control agent in textile processing and other surfactant systems. It eliminates surface foam and entrained air bubbles in printing pastes and dye baths, preventing print defects, ensuring sharp pattern definition, uniform colour transfer, and reducing fabric reject rates.
• Sizing and Finishing Baths: Added to sizing and finishing baths to prevent foam interference and ensure uniform application of chemical auxiliaries, improving fabric hand feel and processing efficiency.

Water & Wastewater Treatment:

• Industrial Water Treatment: The dimethylpolysiloxane emulsion is an effective antifoaming agent for industry water treatment, cooling towers, and effluent treatment systems. It knocks down persistent foam in aeration tanks, clarifiers, sludge holding tanks, and final effluent channels, preventing overflow and accelerating solids settling.
• Sewage Treatment Plants: Used in municipal and industrial sewage treatment facilities to control foam caused by surfactants and organic loading, improving operational stability and reducing maintenance costs.

Papermaking Industry:

• Paper Coating and Paper Machine White Water Systems: Silicone defoamer emulsion is applied in papermaking to control foam in paper coating formulations and paper machine wet ends. Foam‑free white water circulation reduces sheet defects, improves drainage, increases machine speed, and enhances paper quality.

Paints, Coatings & Inks:

• Water‑Based Paints and Coatings: Dimethylpolysiloxane silicone resin defoamers (e.g., DOWSIL™ 8628 Additive, XIAMETER™ AFE-0700 Antifoam Emulsion) act as defoaming and anti‑foaming agents in water‑borne coating systems, acrylic wood paints, trims, varnishes, water‑based wood stains, and water‑borne UV‑curable inks. These additives have limited impact on surface appearance, excellent foam control persistence, and outstanding dilution stability in tap and demineralised water.
• Industrial Coatings: Methyl phenyl group‑containing silicone resins (e.g., SILRES® SY 409, SILRES® REN 80) used in automotive and industrial coatings offer very good hydrophobicity, heat resistance, and corrosion resistance while functioning as anti‑foaming agents.
• Solvent‑Based Paints: High‑molecular‑weight silicone resins (e.g., KP‑326, KP‑330, KP‑391, KP‑650 by Shin‑Etsu) act as levelling and defoaming agents in solvent‑based paints and epoxy systems, preventing convection and eliminating flaws in painted film including flooding, floating, orange peel, and cratering.

Fermentation & Bioprocessing:

• Microbial Fermentation Antifoam: Dimethylpolysiloxane is the primary component of simethicone, a silicone‑based antifoaming agent used in microbial fermentation and bioprocessing. It reduces surface tension at the gas‑liquid interface within the fermentation broth, destabilising foam bubbles and preventing excessive foam buildup that can lead to reduced oxygen transfer (kᴸa), contamination, and culture volume loss.
• Recommended Dosage: Concentrations as low as 1–10 ppm can be effective, with optimal dosage determined by strain‑specific titration. For CHO cell cultures, a simethicone emulsion (EX‑Cell) is used at an initial concentration of 30 ppm.
• Specialised Blends: Aqueous compositions of polydimethylsiloxane with EO/PO block copolymers and silicone/silica blends are employed for defoaming alcoholic fermentations.

Metalworking Fluids (MWF):

• Cutting, Grinding and Rolling Emulsions: Dimethylpolysiloxane defoamer is incorporated into soluble oils, semi‑synthetic, and synthetic metalworking fluids to suppress foam build‑up that would otherwise reduce cooling, lubrication and chip‑settling efficiency. It extends fluid service life and prevents microbiological contamination.
• Hydraulic Fluids and Industrial Lubricants: Used as a foam suppressant in petroleum lubricating oils and hydraulic fluids to prevent pump cavitation and component wear.

Oilfield Chemicals:

• Drilling Fluids and Fracturing Fluids: Dimethylpolysiloxane silicone defoamer is added to water‑based drilling muds and hydraulic fracturing fluids for oil and gas operations to eliminate foam that would reduce pump efficiency, decrease penetration rates, and cause circulation loss.
• Oilfield Production and Cementing: Controls foam during crude oil separation, produced water treatment, and well cementing operations.

Food & Beverage Processing:

• Food‑Grade Antifoam: Food‑grade dimethylpolysiloxane emulsions approved for food contact are used as antifoaming agents in edible oil refining, fruit juice concentration, potato processing, poultry scalding, and meat processing wash water to control foam and improve hygiene.

Chemical Manufacturing & Detergents:

• Process Foam Control: Added to polymerisation reactors, solvent recovery columns, distillation units and other process vessels to control foam that reduces throughput, carries over product, and causes process instability.
• Detergent and Cleaning Formulations: Used as a foam suppressant in liquid laundry detergents, automatic dishwashing rinse aids, and industrial cleaners to improve rinsing efficiency and reduce water consumption.
• Concrete and Construction Additives: Functions as a defoamer in concrete admixtures, preventing entrained air voids that weaken final concrete strength.

Printing Inks:

• Water‑Based and UV‑Curable Inks: Dimethylpolysiloxane additive defoamers (e.g., DOWSIL™ 8628) are suitable for use in low pigment volume concentration water‑borne UV‑curable inks and PVC inks, preventing air entrapment during ink mixing and printing to ensure consistent print quality.

Other Industrial Applications:

• Rubber and Tire Manufacturing: Used as a processing aid and antifoam additive in rubber compounding and molded goods production.
• Mold Release Agent: Silicone oil grade (e.g., 四海 brand model 205) functions as an effective release agent and lubricity enhancer with good hydrophobicity for moulding applications.
• Adhesives, Pigment Dispersions and Paper Coatings: Provides foam control in water‑based adhesives, pigment pastes, filler slurries, and paper coatings.

3. Preparation Method:

• Laboratory Method: Dimethylpolysiloxane is not synthesised in the laboratory for defoamer applications but can be prepared by ring‑opening polymerisation of cyclic siloxanes (octamethylcyclotetrasiloxane, D₄) using an acid or base catalyst. The molecular weight and viscosity are controlled by the ratio of monomer to chain‑terminating agent.
• Industrial Process: Industrial production of dimethylpolysiloxane silicone defoamer follows a large‑scale continuous process:
  1. Polymerisation: Cyclic siloxane monomers (mainly octamethylcyclotetrasiloxane, D₄) and a chain terminator are reacted in the presence of an acid or base catalyst at 100–160°C in a stirred reactor, yielding a linear PDMS polymer of controlled viscosity.
  2. Emulsification (for emulsion grades): The PDMS oil is emulsified in water using non‑ionic and/or anionic surfactants under high‑shear mixing to produce a stable, white, aqueous emulsion with active contents ranging from 10% to 60% (e.g., BWF 160, XIAMETER™ AFE-0700). Critical emulsion parameters include: appearance: white emulsion (water base); water miscibility: forms a good dispersion; viscosity: ≤1000 cPs at 20°C (DIN 53019, 100 rpm); cleanliness: no particles after screening through a 400‑micron aperture screen; emulsion particle size: 90% less than 100 microns; water content: not greater than 85%.
  3. Formulation (for neat oil grades): High‑viscosity PDMS may be compounded with hydrophobic silica particles (treated fumed silica) to enhance defoaming performance in aggressive foaming systems; this blend is known as simethicone (PDMS + hydrated silica gel) for fermentation and pharmaceutical applications.
  4. Quality Control: Key specifications analysed include active content (by loss on drying), viscosity (rotational viscometer), pH, emulsion stability (centrifuge test), particle size distribution, flash point, density, surface tension, and residual monomer content.
  5. Packaging: The final product is packaged in 25 kg drums, 200 kg drums, 1000 kg IBC totes, or bulk road tankers for shipment. Recommended storage is in closed containers, with avoidance of extremes of low temperature (freezing) to preserve emulsion stability.

4. Safety Information:

• Hazard Classification: Dimethylpolysiloxane silicone defoamer is generally classified as a low‑hazard or non‑hazardous product under GHS/CLP Regulation (EC) No 1272/2008. The product is not classified as dangerous for transport (UN number not assigned for most grades) and is not flammable under standard conditions. However, the neat oil is classified as a combustible liquid with flash point >140°C. Hazard statement H413 may apply for silicone oils (May cause long‑lasting harmful effects to aquatic life). Some formulations carry hazard statement H319 (Causes serious eye irritation). Signal word: Warning (for dusty or eye‑irritant formulations). Hazard pictogram: GHS07 (for certain eye‑irritant grades). For most industrial and food‑grade emulsions, no hazard labelling is applicable.
• Health Hazards:
  • Inhalation: Inhalation of mists or vapours may cause mild respiratory tract irritation, coughing, or throat discomfort in sensitive individuals. The neat oil has a high flash point and negligible vapour pressure at room temperature.
  • Skin Contact: Generally non‑irritating to intact skin; prolonged or repeated contact may cause mild mechanical irritation or slight dermatitis in sensitive individuals. Emulsion grades may contain surfactants that can cause mild irritation upon prolonged exposure.
  • Eye Contact: May cause mild transient mechanical irritation; direct contact with eye‑irritant formulations (carrying H319) may cause more pronounced irritation. Rinse thoroughly with water.
  • Ingestion: Low acute oral toxicity (LD₅₀ > 5,000 mg/kg). Ingestion of large amounts may cause mild gastrointestinal discomfort (diarrhoea, bloating). PDMS is not absorbed systemically from the gastrointestinal tract and is generally regarded as safe (GRAS) for food‑contact applications.
• First Aid Measures:
  • Eye Contact: Rinse cautiously with plenty of water for several minutes. Remove contact lenses if present and easy to do. If eye irritation persists, seek medical attention.
  • Skin Contact: Wash skin with plenty of soap and water. Remove contaminated clothing. Seek medical advice if skin irritation develops.
  • Inhalation: Move person to fresh air. Keep at rest in a position comfortable for breathing. If symptoms (coughing, throat irritation) persist, seek medical advice.
  • Ingestion: Rinse mouth immediately. Do NOT induce vomiting. Drink water to dilute if conscious and able to swallow. Seek medical attention if a large amount is ingested or if symptoms develop.
• Fire & Explosion Hazards: Dimethylpolysiloxane neat oil is not classified as flammable but is combustible. In case of fire, thermal decomposition may release irritating and toxic fumes including carbon monoxide (CO), carbon dioxide (CO₂), and silicon oxides (SiOₓ). Use water spray, foam, dry powder, or CO₂ as extinguishing media. Prevent fire extinguishing water from contaminating surface water or groundwater systems.
• Personal Protective Equipment (PPE):
  • Respiratory protection: Not normally required under good ventilation. In poorly ventilated areas or during handling of mist‑producing operations, use a dust/mist respirator (N95 or P2).
  • Eye protection: Safety glasses or chemical splash goggles (recommended, especially for eye‑irritant formulations).
  • Skin protection: Protective gloves (nitrile, neoprene) to minimise skin contact and reduce risk of mild irritation from surfactants in emulsion grades.
  • General hygiene: Wash hands thoroughly after handling. Do not eat, drink, or smoke in work areas.
• Environmental Precautions: Dimethylpolysiloxane is a silicone polymer that is not readily biodegradable but does not bioaccumulate. Avoid large‑scale release into natural water bodies, drains, or soil. Comply with local environmental regulations for disposal.
• Storage & Stability: Store in tightly closed, moisture‑proof containers in a cool, dry, well‑ventilated area away from direct sunlight, heat sources, and strong oxidising agents. For emulsion grades: store in closed containers; avoid extremes of low temperature (freezing) as this may destabilise the emulsion (shelf life: 6 months minimum). For neat oil grades: stable for 12–36 months under recommended storage conditions.
• Regulatory Compliance: Dimethylpolysiloxane (CAS#63148-53-8) is listed on EINECS, TSCA, DSL, AICS, NZIoC, ENCS, KECI, and other regional chemical inventories. Food‑grade silicone antifoam emulsions comply with FDA regulations for food contact substances (21 CFR 173.340). The product is approved for use in potable water treatment (NSF/ANSI 60 certification may be required). For use in fermentation, pharmaceutical, and cosmetic applications, additional regulatory approvals may be required depending on the jurisdiction. Always consult the Safety Data Sheet (SDS) and local regulations for complete safety, environmental, and regulatory information specific to each product grade and application jurisdiction.