Defoaming agents are substances that can reduce the surface tension of water, solutions, suspensions, etc., prevent the formation of foam, or reduce or eliminate the original foam.

The defoaming agent should have the following properties: ① Strong defoaming power and low dosage; ② Adding to the foaming system does not affect the basic properties of the system, that is, it does not react with the system being defoamed; ③ The surface tension is small; ④ It interacts with the surface Good balance; ⑤ Good heat resistance; ⑥ Good diffusion and permeability, high positive spreading coefficient; ⑦ Chemical stability, strong oxidation resistance; ⑧ Good gas solubility and permeability; ⑨ Foaming property The solubility in the solution is small; ⑩ has no physiological activity and is highly safe.
Defoaming agents are widely used in food industry, paper industry, water treatment, oil production industry, printing and dyeing industry, coating industry, detergent industry, rubber latex industry, aerosol industry, daily chemical industry, pharmaceutical industry, dairy industry, etc. 

Divided by ingredients

1. Natural oils (i.e. soybean oil, corn oil, etc.)
Advantages: easy source, low price, simple to use;
Disadvantages: If not stored well, it will easily deteriorate and increase the acid value.
2. Polyether defoaming agent
There are many types, the main ones are as follows:
a. GP type defoaming agent
It is made by addition polymerization of propylene oxide or a mixture of ethylene oxide and propylene oxide using glycerin as the starting agent.
GP type defoaming agent has poor hydrophilicity and low solubility in the foaming medium, so it should be used in thin fermentation broth. Its foam-suppressing ability is superior to its defoaming ability, and it is suitable to be added to the basic culture medium to inhibit the generation of foam during the entire fermentation process.
b.GPE type defoaming agent is foaming enemy
Add ethylene oxide to the end of the polypropylene glycol chain of the GP type defoamer to form polyoxyethylene oxypropylene glycerin with a hydrophilic group at the chain end, also known as polyoxyethylene oxypropylene glycerin. According to the ethylene oxide addition amount of 10%, 20%,...50%, they are called GPE10, GPE20,...GPE50 respectively.
GPE-type defoaming agent has good hydrophilicity, is easy to spread in the foaming medium, and has strong defoaming ability, but its solubility is also large and the defoaming activity is short-lived, so it is more effective when used in viscous fermentation broth.
c.GPES defoamer

 There is a new polyether defoamer. The ends of the GPE defoamer chain are capped with hydrophobic stearate to form a hydrophobic chain at both ends with a hydrophilic gap in the middle. chain block copolymer. Molecules of this structure tend to lie flat and gather at the air-liquid interface, so they have strong surface activity and high defoaming efficiency.
3. High carbon alcohol
High-carbon alcohols are linear molecules that are strongly hydrophobic and weakly hydrophilic. They are effective defoaming agents in water systems. In the early 1970s, former Soviet scholars conducted experiments in aqueous solutions of anionic, cationic, and nonionic surfactants and proposed that the defoaming effect of alcohol is related to its solubility and diffusion degree in the foaming liquid. C7~C9 alcohols are the most effective defoaming agents.
C12~C22 high-carbon alcohols are formulated with appropriate emulsifiers into water emulsions with a particle size of 4~9μm and a content of 20~50%, which are defoaming agents for water systems.
There are also some esters, such as phenylethyl oleate and lauryl phenylacetate, which have defoaming effects in penicillin fermentation, and the latter can also be used as precursors.
Tributyl phosphate (CAS: 126-73-8), as an ancient defoaming agent, is still widely used in the industry because of its extremely low surface tension (27.79 25℃) and extremely low water solubility (0.61 25 ℃, the solvent is soluble in water), and has a significant defoaming effect. However, due to its irritation and certain toxicity, it is mostly used in other industries that are not in contact with food/daily cosmetics.
4. Silicon
The most commonly used is polydimethylsiloxane, also known as dimethicone. It has low surface energy, low surface tension, low solubility in water and general oil, and high activity. Its main chain is a silicon-oxygen bond and it is a non-polar molecule. It has no affinity with the polar solvent water and has little affinity with general oils. It is low-volatility and chemically inert, relatively stable and less toxic. Pure polydimethylsiloxane cannot be used as a defoaming agent without dispersion treatment. This may be due to its high interfacial tension with water and low spreading coefficient, making it difficult to disperse in the foaming medium. Therefore, the composite formed by mixing silicone oil into SiO2 aerosol can be obtained by mixing the hydrophobically treated SiO2 aerosol into dimethyl silicone oil and processing it at a certain temperature and for a certain time.
Silicone defoamer is mechanically emulsified by mechanical emulsification of silicone grease, emulsifier, waterproofing agent, thickener, etc. with an appropriate amount of water. It is characterized by low surface tension, high surface activity, strong defoaming power, low dosage and low cost. It is immiscible with water and most organic matter, and can defoaming most bubble media. It has good thermal stability and can be used in a wide temperature range of 5℃-150℃; it has good chemical stability and is difficult to react with other substances. As long as it is properly configured, it can be used in acid, alkali and salt solutions. , without compromising product quality; it also has physiological inertness LD250g/Kg rat, usually used in the food and pharmaceutical industries. It has foam suppression and foam breaking functions for all bubble systems and belongs to the category of broad-spectrum defoamer. It is widely used for defoaming in the production processes of detergents, papermaking, pulp, sugar, electroplating, fertilizers, additives, wastewater treatment, etc. In the petroleum industry, it is widely used to desulfurize natural gas and accelerate oil and gas separation; it is also used to control or inhibit bubbles in ethylene glycol drying, aromatic hydrocarbon extraction, asphalt processing, lubricating oil dewaxing and other devices. . In the textile industry, it is used for defoaming in processes such as dyeing, scouring, and sizing; in the chemical industry, it is used for defoaming in synthetic resins, latex, coatings, inks, etc.; in the food industry, it is used Used for defoaming in various concentration, fermentation and distillation processes. Silicone grease can be applied to the pot wall, outlet or metal mesh to defoam. Silicone grease is prepared into a solution and can be used for defoaming in oil phase systems. Add silicone grease to low-viscosity silicone oil to form a water emulsion, which can be used for defoaming in a variety of aqueous systems. In medicine, it is usually used to remove bloating from organs or stomach organs before surgery, X-rays and gastroscopy.
Defoaming agents can be roughly divided into two categories: one type can eliminate the generated bubbles, such as ethanol, etc.; the other type can inhibit the formation of bubbles, such as emulsified silicone oil, etc. Defoaming agents approved for use in my country include emulsified silicone oil, high-carbon alcohol fatty acid ester complex, polyoxyethylene polyoxypropylene pentaerythritol ether, polyoxyethylene polyoxypropylene amine ether, polyoxypropylene glyceryl ether and polyoxypropylene.
5. Polyether modified silicon
It combines the advantages of polyether and silicone defoaming agents. It is non-toxic and harmless to bacteria and has a very small amount of addition. It is a cost-effective product.
Polyether modified silicone is a polyether-siloxane copolymer (referred to as silicon ether copolymer) made from polyether segments in the siloxane molecule. Polysiloxane defoamer has the characteristics of rapid defoaming, long foam suppression time and safety and non-toxicity. However, it is difficult to dissolve in water, has high temperature resistance and poor resistance to strong alkali. Polyether defoamer has good water solubility and resistance to strong alkali. It has high temperature resistance and strong alkali resistance, but its defoaming speed and foam suppression time are not ideal. The polyether chain is introduced into the polysiloxane chain through grafting through condensation technology, so that it has the advantages of a second-class defoaming agent. It has become a defoaming agent with excellent performance and wide application prospects. In the molecule of silicon ether copolymer, the siloxane segment is a lipophilic group and the polyether segment is a hydrophilic group. The polyethylene oxide chain in the polyether segment provides hydrophilicity and foaming properties, while the polypropylene oxide chain provides hydrophobicity and permeability, which has a strong effect on reducing surface tension. The polyether end groups also have a strong influence on the properties of silicon ether copolymers. Common end groups include hydroxyl, alkoxy, etc. Adjusting the relative molecular weight of the siloxane segment in the copolymer can make the copolymer highlight or weaken the properties 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 easily emulsified in water, also known as "self-emulsifying defoamer". When the temperature is above its cloud point, it loses its solubility in water and mechanical stability, and is resistant to acids and alkali. and inorganic salts, which can be used for defoaming under harsh conditions and are widely used for defoaming in high-temperature dyeing processes and fermentation processes of polyester fabrics. In addition, it can also be used for defoaming of diethanolamine desulfurization systems and various oils, cutting fluids, antifreezes, water-based inks and other systems. It is also suitable for washing away uncured resin after photosensitive resin plate making in the printing industry. Defoaming is a very representative, excellent performance and widely used silicone defoaming agent. Polysiloxane defoamer is usually composed of two main components: polydimethylsiloxane and silica. The defoamer with polydimethylsiloxane as the base material is one of the defoaming systems. It is an ideal defoaming agent because it is insoluble in water and difficult to emulsify. Polydimethylsiloxane has lower surface properties than carbon chain hydrocarbons, so it has a lower surface tension than surfactants commonly used in the textile industry. Pure polydimethylsiloxane has poor and slow antifoaming performance. The defoaming effect needs to be strengthened by silica particles. The silica particles are brought to the air-water interface of the foam by silicone oil and enter the bubble liquid film due to its hydrophobicity. property, the contact angle with the surfactant foaming droplets is greater than 90°, thus forcing the foaming liquid to drain away from the surface of the solid hydrophobic particles, causing local rapid drainage of the foam and resulting in rupture. In this way, due to the synergistic effect, the two compositions produce a good defoaming effect.
6. New self-emulsifying defoaming agent
Contains specially modified polysiloxane. It has excellent heat resistance, acid and alkali resistance and chemical stability, and can be widely used to eliminate and suppress foam in various harsh systems within a wide temperature range.
7. Polysiloxane defoamer
Polysiloxane defoamer is usually composed of two main components: polydimethylsiloxane and silica. The defoamer with polydimethylsiloxane as the base material is one of the defoaming systems. It is an ideal defoaming agent because it is insoluble in water and difficult to emulsify. Polydimethylsiloxane has lower surface properties than carbon chain hydrocarbons, so it has a lower surface tension than surfactants commonly used in the textile industry. Pure polydimethylsiloxane has poor and slow antifoaming performance. The defoaming effect needs to be strengthened by silica particles. The silica particles are brought to the air-water interface of the foam by silicone oil and enter the bubble liquid film due to its hydrophobicity. property, the contact angle with the surfactant foaming droplets is greater than 90°, thus forcing the foaming liquid to be discharged from the surface of the solid hydrophobic particles, causing local rapid drainage of the foam and resulting in rupture. In this way, due to the synergistic effect, the two compositions The substance produces a good defoaming effect. Due to its excellent defoaming performance and other advantages, polysiloxane defoamer has been widely used in many fields, especially in textile dyeing and finishing processing, where it has developed particularly rapidly. Research has found that polydimethylsiloxane A silicone glycol defoamer based on a copolymer of polyethylene has an ideal defoaming effect in jet dyeing and other textile processing due to its special solubility properties.