Applications of Silicone Defoamers

　　Silicone-based defoamers are characterized by their rapid defoaming performance, facilitating their application in wastewater treatment and in industries such as metalworking. They have attracted widespread attention across numerous sectors, including metal cleaning.

　　Silicone compounds are polysiloxanes, indispensable raw materials in cosmetic formulation; accordingly, silicone‑based defoamers are widely used in the daily‑chemical industry. Moreover, their widespread acceptance across various sectors stems from their outstanding properties—such as chemical inertness, non‑toxicity, and environmental friendliness—ensuring they do not pollute the environment.

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

　　1. Printing and dyeing:

　　(1). Sizing process: Use an emulsion‑type silicone defoamer, such as a silicone polyether, at a dosage of 0.2–0.25 g/L in the sizing bath.

　　(2). Synthetic fiber oil agent: Add a 0.02–0.04% aqueous emulsion‑type defoamer to the synthetic fiber oil agent. The silicone oil should be formulated to include the synthetic fiber oil components.

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

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

　　(5). Dyeing: Silicone emulsion defoamer. Polyether‑silicone is the optimal choice for jet dyeing, providing effective defoaming at high temperatures. It is water‑soluble at low temperatures and does not stain fabrics.

　　2. Petrochemical Industry:

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

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

　　(3) Natural gasoline absorption: Mix dimethyl silicone oil with gasoline to prepare a 2% solution.

　　(4) Oil–gas separation and demulsification:

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

　　B. Demulsification: The oil separated from the gas–oil mixture is typically a fine W/O emulsion; adding 0.2 mg/kg of a suitable defoamer can achieve both demulsification and defoaming.

　　(5) Refining: In vacuum distillation, a defoaming agent is added to improve the color of the fractions and broaden their boiling ranges; a common diesel‑soluble defoamer is silicone oil.

　　(6) High‑energy fuel (internal combustion). Jet fuel. A cyano‑functional polysiloxane is dispersed in a high‑flash‑point gasoline and then added to the high‑energy fuel as a highly effective defoaming agent.

　　(7) Pitch and residual oil: The silicone oil addition level is 0.2×10⁻⁶ to 2.0×10⁻⁶.

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

　　(9) Defoaming drilling fluid: The addition level of a high-viscosity sulfonate (calcium petroleum sulfonate) to siloxane is approximately 100–4,000 × 10⁻⁶ or 5–15 mg/kg; a molar ratio of sulfonate to siloxane close to 1:1 is recommended.

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

　　A. The lubricating oil is poorly soluble and remains in a dispersed state, which facilitates its adsorption onto the bubble film and promotes bubble rupture.

　　B. Alkyl groups similar to those in mineral oil can penetrate the bubble film, weakening intermolecular forces;

　　C. It exhibits low interfacial tension and good permeability. When adsorbed on the bubble film surface, the uneven interfacial tension causes a localized reduction in surface tension, leading to bubble rupture. For heavy oils, a silicone oil with low viscosity is used at an addition level of 1–10 × 10⁻⁶. Additionally, alkyl polyacrylates are also effective, offering excellent gas‑release properties. Branched‑chain amines can be added to crude gasoline, and lubricating oil can be incorporated into naphtha; both serve as defoamers at dosages of 0.05–1%. Such defoamers can be formulated into metalworking fluids.

　　3. Papermaking Industry

　　(1) Papermaking: Silicone emulsion defoamer (90 g/T paper).

　　(2) Coated paper: Paper used for coating with surface coatings and for printing after coating; non-silicone defoamers are typically employed to control foam during the coating process.

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

　　4. Coatings. Ink applications

　　I. Requirements for Defoamers in Coating Production:

　　(1) It exhibits a certain affinity for the surfactants on the foam surface, but the re‑foaming liquid should be insoluble and non‑soluble;

　　(2) The interfacial tension is lower than that of the bubble liquid, and the interfacial tension corresponds to a lower HLB value;

　　(3) The emulsion (latex) shall be stable;

　　(4) After film formation, the coating must not result in undesirable defects such as fish eyes or shrinkage.

　　(5) Defoamers for waterborne coatings: These typically employ water-insoluble substances, such as mineral oil, higher alcohols, and organosilicon resins; among them, organosilicon compounds are the most effective defoaming agents for waterborne paints.

　　Defoamer for non-aqueous coatings: Common substances insoluble in organic solvents, such as lower alcohols. Organosilicon resins (the dosage of organosilicon resin should be moderate; excessive amounts can lead to shrinkage and cracking. Nowadays, modified organosilicon resins or emulsified organosilicon resins are predominantly used).

　　II. Silicone defoamers are recommended for water-based coatings:

　　(1) Silicone oil. Hydrophobic SiO mixture—suitable for: epoxy resins, potting; dosage: 0–0.3%; thermoplastic acrylic resins, spray coating; dosage: 0–0.3%.

　　(2) The polyether–polysilicone and hydrophobic SiO2 blend is suitable for thermosetting alkyd resins, with an immersion coating dosage of 0.3% and a brush‑coating dosage of 0.1%.

　　(3) Hydrophobic SiO2–hydrocarbon–silicone oil mixture: suitable for thermoplastic acrylic resins and printing inks, at a dosage of 0.1%; for air-drying acrylic resins applied by pouring, at a dosage of 0.5%.

　　(4) Suitable for silicone oil–hydrophobic SiO2 mixed emulsions: alkyd-modified styrene–acrylic resin, pour coating, dosage 0.05%.

　　5. Industrial-grade silicone defoamer for the detergent industry

　　As additives for powdered detergents, polysiloxanes and modified sodium tripolyphosphate are formulated by blending a 2–6% (15,000 c.s.) dimethylsilicone oil emulsion with anhydrous sodium tripolyphosphate, with the emulsion content ranging from 10% to 40%, thereby yielding a hydrate‑based 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 dimethyl polysiloxane, with a SiO2 content of less than 15%. When used as an aqueous solution, employ the emulsified product; otherwise, the oil-based formulation may be applied directly, with dosage carefully controlled.