Silicone-based defoamers, owing to their rapid defoaming properties, have garnered widespread attention across numerous industries—including wastewater treatment, metalworking, and metal cleaning—and are extensively applied.

　　Silicones are composed of polysiloxanes, which are indispensable raw materials in cosmetic formulations; therefore, silicone‑based defoamers are widely used in the personal care and household products industries. Moreover, their broad appeal across various sectors stems from their outstanding properties: they exhibit chemical and physical inertness, are non‑toxic and environmentally friendly, and do not contribute to environmental pollution.

　　Today, we’ll introduce the six major applications of silicone defoamers:

　　1. Textile Printing and Dyeing:

　　(1) Sizing process: Water-emulsion‑type silicone defoamer, such as silicone polyether; add 0.2–0.25 g/L to the sizing bath.

　　(2) Synthetic fiber oil agent: Add 0.02–0.04% of an emulsion‑type defoamer to the synthetic fiber oil agent. The formulation of the synthetic fiber oil agent should contain silicone oil.

　　(3) Desizing and refining: Use a formulation containing polyether‑silicone.

　　(4) Bleaching: Highly acidic, silicone-based defoamer.

　　(5) Dyeing: Silicone emulsion defoamer. For jet dyeing, polyether‑silicone is preferred, offering excellent defoaming at high temperatures and water solubility at low temperatures, while remaining non‑staining to fabrics.

　　2. Petrochemical Industry:

　　(1) Drilling: Ethyl silicone oil (or methyl silicone oil emulsion) is used as a mud additive.

　　(2) Oil production: oil–gas separation, defoaming rod. Its melting point is 2.8–13.9°C higher than the foam temperature at the wellhead.

　　(3) Natural gasoline absorption: Prepare a 2% solution of dimethyl silicone oil using gasoline.

　　(4) Oil–gas separation and demulsification:

　　A. Oil–gas separation: Adding 0.025 to 0.0065 mg/kg to crude oil can enhance production capacity.

　　B. Demulsification: Crude oil after oil–gas separation typically exists as a weak W/O emulsion; adding an appropriate defoamer at approximately 0.2 mg/kg can achieve effective demulsification and defoaming.

　　(5) Refining: Vacuum distillation with the addition of a defoaming agent improves the color of the fractions and broadens their boiling ranges; a common practice involves using a diesel solution containing silicone oil.

　　(6) Cyanated polysiloxanes are dispersed in high‑flash‑point kerosene for use as high‑performance antifoaming agents in high‑energy fuels (internal‑combustion, jet, and aviation fuels), and then added to the fuels.

　　(7) Asphalt and residual oil: The amount of silicone oil added is 0.2×10⁻⁶ to 2.0×10⁻⁶.

　　(8) Delayed coking, coke removal, and scale inhibition: Recommended dosage of defoamer: 0.05–100 × 10⁻⁶

　　(9) Defoaming drilling fluid: high-viscosity sulfonated metal salts (calcium petroleum sulfonate:sodium sulfonated asphalt = 1:1), with a siloxane addition of approximately 100–400 × 10⁻⁶ or 5–15 mg/kg; a molar ratio of sulfonate to siloxane close to 1:1 is preferred.

　　(10) Lubricants: such as internal‑combustion engine oils, automotive lubricants, metalworking fluids, and compressor oils. When silicone oil is added as an antifoaming agent, it offers the following advantages:

　　A. Poorly soluble in lubricating oil and exists in a dispersed state, which facilitates its adsorption onto the bubble film to promote bubble rupture.

　　B. It contains alkyl groups similar to those in mineral oil, which can penetrate the bubble film and weaken intermolecular forces;

　　C. It has low surface tension and excellent penetration; when adsorbed on the bubble film, it reduces local surface tension, leading to bubble rupture due to uneven surface tension across the film. For heavy oils, a low-viscosity silicone oil is recommended, with an addition level of 1–10 × 10⁻⁶. Additionally, alkyl polyacrylates are also effective, offering good gas‑release properties. Branched-chain amines can be added to crude gasoline or naphtha and then incorporated into lubricating oils as defoamers, at dosages of 0.05–1%. Such defoamers are also suitable for use in metalworking fluids.

　　3. Paper Industry

　　(1) Pulping: Silicone emulsion defoamer (90 g/ton of paper).

　　(2) Coated paper: A type of paper coated with a coating formulation and calendered, used for printing posters and other applications; non-silicone defoamers are typically employed to control foam during the coating process.

　　(3) Wastewater treatment: water-in-emulsion-type silicone defoamer.

　　4. Applications in Coatings and Inks

　　I. Requirements for defoamers in paint production:

　　(1) It exhibits a certain affinity for the surfactants on the foam surface, but should be poorly soluble or insoluble in the bubble‑forming liquid.

　　(2) It has a surface tension lower than that of the bubble liquid and a relatively low HLB value;

　　(3) The emulsion (latex) should be stabilized;

　　(4) After film formation, the coating must not cause undesirable defects such as fish eyes or craters.

　　(5) Defoamers for waterborne coatings: These typically employ substances that are poorly soluble in water, such as mineral oil, higher alcohols, and organosilicon resins; among them, organosilicon compounds are the most effective defoamers for waterborne coatings.

　　Defoamers for non-aqueous coatings: Commonly used are substances that are poorly soluble in organic solvents, such as lower alcohols and organosilicon resins (the dosage of organosilicon resin should be moderate; excessive amounts can lead to shrinkage cracks and pinholes. Nowadays, modified organosilicon resins or emulsified organosilicon resins are more widely employed).

　　II. Recommended silicone-based defoamers for waterborne coatings:

　　(1) Silicone oil–hydrophobic SiO2 blend: suitable for epoxy resins, applied by potting at 0.3%; for thermoplastic acrylic resins, applied by spraying at 0.3%.

　　(2) Polyether–polysiloxane/silica hydrophobic composite: suitable for thermosetting alkyd resins; application rate of 0.3% for dip coating and 0.1% for brush coating.

　　(3) A mixture of hydrophobic SiO2, hydrocarbons, and silicone oil is suitable for thermoplastic acrylic resins and printing inks, at a dosage of 0.1%; and for air-drying acrylic resins used in casting, at a dosage of 0.5%.

　　(4) Emulsion of silicone oil and hydrophobic SiO2: suitable for alkyd-modified styrene–acrylic resin; applied by pouring, at a dosage of 0.5%.

　　5. Silicone-based defoamer for the detergent industry

　　Polysiloxanes and modified sodium tripolyphosphate are used as additives in powdered detergents. A dimethylsilicone oil (1500 cSt) emulsion containing 2–6% SiO₂ is blended with anhydrous sodium tripolyphosphate, with the emulsion accounting for 10–40% of the formulation, to produce a hydrated compound serving as the additive.

　　Metal cleaning solution, requiring alkali resistance; ideally, it should remain clear and exhibit defoaming activity when liquid additives are incorporated.

　　6. Silicone antifoaming agent for the food industry

　　Food-grade polysiloxane resin: Primarily composed of dimethylpolysiloxane, with less than 15% SiO2. When used in aqueous solutions, the product should be emulsified; for other applications, the oil-based formulation may be applied directly, with dosage carefully controlled.