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Jan 22, 2021
Antifoaming agents are generally composed of multiple components with different functions, that is, main antifoaming agent, auxiliary antifoaming agent, carrier, emulsifier or spreading agent, stabilizer or compounding agent.(1) Main anti-foaming agent: the main active component, usually insoluble particulate matter, such as hydrophobic silica, fatty amine, paraffin, etc. treated with silicone oil.(2) Auxiliary defoamer: It is an active component that plays a regulatory role, improves the surface effect of the main defoamer, and has a synergistic effect on the main defoamer. Such as fatty alcohols, fatty acid esters, etc.(3) Carrier: It supports the main and auxiliary defoamers, and water is the most convenient and economical carrier(4) Emulsifier and spreader: it makes the active components of the defoamer dispersed immediately in the foaming medium, and contact the surface faster and more, thereby improving the spreading efficiency of the defoamer. Commonly used emulsifiers are organic esters and ethyl oxidation products.(5) Stabilizer and compounding agent: It is an additive to improve the stability and storage time of the defoamer. The stabilizer of the water-based defoamer is often a preservative to prevent the product from being destroyed by bacteria during storage. Commonly used compounding agents are oleic acid and hexylene glycol.3 Active components and performance of silicone defoamer:(1) Active component: The main component of silicone defoamer is made of linear polysiloxane (English name: Polysiloxane, Silicones) (also known as silicone oil) that can remain liquid at room temperature as the active agent. Oxanes mainly have
The following types;Polydimethylsiloxane: The molecular formula is as follows:Me3SiO(Me2SiO)nSiMe3Fluorosiloxane: The molecular formula is as follows:Glycol siloxane: the molecular formula is as follows:Silicone oil is a non-volatile oily liquid at room temperature. It is insoluble in water, animal, vegetable, and mineral oil, or has a low solubility. It can withstand high temperatures and low temperatures. The chemical properties are inert, the physical properties are stable, and there is no biological activity.(2) The performance of silicone defoamers: silicone defoamers have three functions: foam breaking, defoaming and foam suppression.(3) The characteristics of silicone defoamers[Appearance] White viscous emulsion【PH value】6-8[Water dilution] 0.5%-5.0% foaming liquid dilution【Volatile】Non-volatile[Stability] 3000 rpm/20 minutes without delamination【Ionic characteristics】Non-ionic[Temperature resistance] 130℃, no demulsification, no oil floating, no delaminationThe advantages of organosilicon defoamers(1) Wide application range: Due to the special chemical structure of silicone oil, it is neither compatible with water or substances containing polar groups, nor with hydrocarbons or organic substances containing hydrocarbon groups. Due to the insolubility of silicone oil to various substances, it has a wide range of applications. It can not only use water system to defoam, but also can be used in oil system.(2) Low surface tension: The surface capacity of silicone oil is generally 20-21 dyne/cm, which is lower than that of water (72 dyne/cm) and general foaming liquids, and has good defoaming performance.(3) Good thermal stability: Taking the commonly used dimethyl silicone oil as an example, it can withstand 150°C for a long time and 300°C for a short time, and its Si-O bond will not decompose. This ensures that the silicone defoamer can be used in a wide temperature range.(4) Good chemical stability: Because the Si-O bond is relatively stable, the chemical stability of silicone oil is very high, and it is difficult to chemically react with other substances. Therefore, as long as the formulation is reasonable, silicone defoamers are allowed to be used in systems containing acids, alkalis and salts.(5) Physiological inertia: Silicone oil has been proven to be non-toxic to humans and animals, and its half-lethal dose is greater than 34 g/kg. Therefore, silicone defoamers (with suitable non-toxic emulsifiers, etc.) can be safely used in the food, medical,
pharmaceutical and cosmetic industries.(6) Strong defoaming power: Silicone defoamer can not only effectively break the foam that has been generated, but also can significantly inhibit the foam and prevent the formation of foam. Its usage is very small, as long as adding one part per million (1ppm) of the foaming medium weight, it can produce defoaming effect. The commonly used range is 1 to 100 ppm. Not only is the cost low, but also does not pollute the defoamed substance.Collapse edit this paragraph polyether modified silicone defoamerPolyether-modified silicone is a polyether-siloxane copolymer (silicon ether copolymer for short) prepared by introducing polyether segments into the siloxane molecule. Polyether modified silicone defoamer is a new type of high-efficiency defoamer that organically combines the advantages of the two. It is selected as the main components of polyether with strong anti-foaming ability and dimethyl silicone oil with strong hydrophobicity and rapid foam breaking, matching the emulsifier, stabilizer and other components that can organically combine silicone oil with polyether. Foaming agent. It has the characteristics of low surface tension, rapid defoaming, long anti-foaming time, low cost, low dosage and wide application range. The polyether modification of organosilicon gives it the advantages of the second-class defoamer, and becomes a defoamer with excellent performance and broad application prospects.In the molecule of the silicone ether copolymer, the siloxane segment is a lipophilic group, and the polyether segment is a hydrophilic group. In the polyether segment, the polyethylene oxide chain saves energy to provide hydrophilicity and foaming, and the polyethylene oxide chain saves energy to provide hydrophobicity and permeability, which has a strong effect on reducing surface tension. The groups at the end of the polyether chain also have a great influence on the properties of the siloxane ether copolymer. Common terminal groups are hydroxyl, alkoxy and so on. Adjusting the relative molecular mass of the siloxane segment in the copolymer can make the copolymer highlight or weaken the characteristics of silicone. Similarly, changing the relative molecular weight of the polyether segment will increase or decrease the proportion of silicone in the molecule, which will also affect the performance of the copolymer.
Polyether modified silicone defoamer is easy to emulsify in water and is also called "self-emulsifying defoamer". Above the cloud point temperature, it loses water solubility and mechanical stability, and is resistant to acids, alkalis and inorganic salts, and can be used for defoaming under severe conditions.In order to improve the lipophilicity for water-based inks, coatings, cutting fluids, etc., part of the methyl groups in the polyether-modified silicone copolymer molecules are replaced with long-chain alkyl groups, which can more effectively exert the defoaming effect. In order to have better defoaming performance below the cloud point temperature, commercial self-emulsifying defoamers are usually equipped with dimethyl silicone oil---silica paste, which is at the cloud point temperature. Polyether modified silicone surfactants can also be used as emulsifiers for dimethyl silicone oil to play a role in dispersing and emulsifying.