Defoamers are widely used, such as food industry, paper industry, water treatment industry, oil production industry, printing and dyeing industry, coating industry, detergent industry, rubber latex industry, aerosol industry, daily chemical industry, pharmaceutical industry, dairy industry and so on. [2]
Chinese name
Eliminate foam
Foreign name
defoamer
classify
Silicone, polyether and polyether modified polysiloxane defoamer.
chemical property
stable
Other names
defoamer
brief introduction
Defoamer is an additive to eliminate foam. In the production and application of coating, textile, medicine, fermentation, paper making, water treatment and petrochemical industries, a large number of foams will be produced, which will affect the product quality and production process. Based on the inhibition and elimination of foam, a specific amount of defoamer is usually added to it in the production process. [3]
Foam formation and stability factors
The study of bubbles can be traced back to Plato's time, but for hundreds of years, people have not formed a unified understanding of the definition of bubbles. American colloid chemist L I Osipow and R F Smith of Dow Corning Company defined foam according to its density. Koichi Ito of Japan defines bubbles from the perspective of bubble structure, but ignores the relationship between bubbles. Professor Zhao Guoxi, a famous surface physicist in China, defines foam as a dispersion system in which gas is dispersed in liquid, gas is a dispersed phase (discontinuous phase) and liquid is a dispersion medium (continuous phase). The bubbles in the liquid rise to the liquid surface, forming a bubble aggregate composed of a small amount of liquid, which is separated by a liquid film. Scholars at home and abroad agree that foam itself is a thermodynamically unstable system. When gas enters the solution containing surfactant, it will form a long-term stable foam system. [4]
Attenuation mechanism of foam
In the presence of gravity and pressure difference, the liquid film of the foam will flow unevenly, and the gas in the bubble will continue to diffuse and penetrate because of the different pressure difference between the two sides of the foam film, so the instability of the foam itself is mainly reflected in dynamics. [4]
The attenuation mechanism mainly includes two aspects: the diffusion of gas through liquid film and the drainage of liquid film. These two properties are inherent in the foam itself and have nothing to do with the presence or absence of surfactants. However, these two attenuation mechanisms only play an obvious role in the initial stage of foam system formation. With the attenuation of foam system, these two effects gradually weaken, which makes the speed of foam attenuation gradually slow down. [4]
Stability factors of foam
The direct cause of foaming is the existence of surfactant, which reduces the surface tension of the solution. Under the joint action of this reason and foam attenuation mechanism, different foam systems show different stability, which is mainly related to the following factors: the surface tension of foam solution, the surface viscosity of foam, the viscosity of solution, the self-repairing effect of surface tension (Gibbs surface elasticity and Marangoni effect), the surface electric double layer repulsion and entropy repulsion of liquid film, the hydrophobic end structure and spatial effect of surfactant, etc. These factors are not independent, and the change of one factor will change other factors. The most important factors affecting the stability of foam are the elasticity of liquid film and the drainage rate. From this point of view, we can see that in different foam systems, the main factors affecting foam stability are different, and sometimes several influencing factors exist at the same time and work together. [4]
In addition to these factors, there are also some factors that will affect the stability of foam, such as the size of foam, the coordination of solute and solvent, temperature, pH value, evaporation rate of solvent, impact degree of foam, adsorption rate of surfactant and so on. [4]
Elimination method of foam
(1) physical method
From the physical point of view, the methods to eliminate foam mainly include placing baffle or filter screen, mechanical stirring, static electricity, freezing, heating, steam, radiation, high-speed centrifugation, pressurization and decompression, high-frequency vibration, instantaneous discharge and ultrasonic (acoustic and hydraulic control). These methods all promote the gas permeability at both ends of the liquid film and the drainage of the bubble film to varying degrees, so that the stability factor of the foam is less than the attenuation factor, and the number of foam is gradually reduced. However, the disadvantages of these methods are that the use is restricted by environmental factors, and the defoaming rate is not high. The advantages are environmental protection and high reuse rate. [4]
(2) Chemical methods
The main methods to eliminate foam from the chemical point of view are chemical reaction and adding defoamer. Chemical reaction method refers to adding some reagents to make them react chemically with foaming agent to generate water-insoluble substances, thus reducing the concentration of surfactant in liquid film and promoting foam rupture. However, this method has some disadvantages, such as uncertain composition of foaming agent, and the production of insoluble matter is harmful to system equipment. At present, the most widely used defoaming method in all walks of life is adding defoamer. The biggest advantage of this method is high defoaming efficiency and convenient use, but finding a suitable and efficient defoamer is the key. [4]
Foam bursting process
Defoaming mechanism of defoamer
At present, there is no unified understanding about the mechanism of defoaming agent. According to the mechanism of defoamer proposed by predecessors, there are roughly the following types: [4]
It has a general defoaming mechanism.
Typical and generalized defoaming mechanisms are Robinson defoaming mechanism and Ross hypothesis. Robinson mechanism is the basis of Ross hypothesis, which mainly emphasizes that defoamer destroys foam drainage and Marangoni effect realizes defoaming; Ross hypothesis is based on the fact that defoamer particles are insoluble droplets, but in fact some defoamers produce defoaming effect in dissolved state, so the defoaming mechanism of Ross hypothesis is not comprehensive. [4]
Action mechanism of polysiloxane defoamer
The typical defoaming mechanisms of polysiloxane mainly include "bridging-spreading" mechanism, "bridging-dehumidification" mechanism and "spreading-entraining" mechanism. The "bridging-spreading" mechanism mainly starts from the basic point that "polysiloxane has low tension and is easy to spread on liquid film", emphasizing that defoamer droplets are easy to deform, but this theory cannot explain the defoaming difference between polysiloxane alone and polysiloxane and solid ion mixture as defoamers. The mechanism of "bridging-dehumidification" is mainly based on the hydrophobicity of polysiloxane itself, but it can not explain the defoaming effect of high viscosity polysiloxane well. The mechanism of "spreading with liquid" cannot be proved, because there are facts that polysiloxane sometimes does not spread on the surface of bubble film, but it can also break bubbles. [4]
Defoaming mechanism of hydrophobic solid particles
In the foam system, hydrophobic solid particles will first attract the hydrophobic end of the surfactant, making the hydrophobic solid particles hydrophilic, thus reducing the concentration of surfactant in the foam film and promoting foam rupture. This defoaming mechanism cannot explain the action mechanism of other defoamers, which is too one-sided. [4] There are also some reasons for foam rupture, such as the expansion of defoamer, the impact of surfactant solubilization, and the breakdown of electric double layer on the surface of liquid film caused by electrolyte disintegration. [4] From the above defoaming mechanism, it can be seen that each defoaming agent has its own emphasis in different foam systems, but it is achieved by destroying the stable factors of foam. [4]
Defoaming mechanism of polyether modified silicone oil
To explain the defoaming process of polyether modified silicone oil as defoamer, the most complete defoaming mechanism is "bridging-stretching" mechanism and "bridging-dehumidification" mechanism. [5]
"Bridging-stretching" mechanism: the surface tension of defoamer is much lower than that of liquid film, and the droplets of defoamer can spread and penetrate on the surface of liquid film, and the local liquid film of foam becomes thinner, eventually forming an oil bridge in the middle of water. The surface tension of oil phase and water phase is far from each other, and the oil phase is constantly pulled by the surrounding water phase. After the deformation exceeds a certain range, the liquid film breaks, leading to the bursting of foam. [5]
"Bridge-dehumidification" mechanism: After adding solid hydrophobic particle defoamer into the foam liquid, the defoamer is immediately distributed in the foam system, and the hydrophobic particles are fixed on the surface of the foam liquid film. When there is enough hydrophobic angle between the solid particles and the liquid film, the solid particles have opposite contact surfaces with the surrounding liquid film, which becomes a bridge between the surrounding liquid films and can finally break through the foam liquid film and enter the foam. [5]
Based on the unique low surface tension of silicone oil, the "bridging-stretching" mechanism points out that defoamer droplets can be deformed in different degrees, but it is difficult to explain the difference between silicone oil and pure silicone oil. The mechanism of "bridging-dehumidification" is based on the lipophilicity of silicone oil, which can explain the mechanism of low viscosity polyether modified silicone oil. Therefore, polyether modified silicone oil defoamer has three characteristics of defoaming: first, it is basically insoluble in foaming liquid (most dissolved silicone oil can help foaming); Secondly, the surface tension is lower than that of foaming liquid; Finally, it can be quickly dispersed in foaming liquid. Only substances with small solubility and large dispersion can become defoamers with good foam breaking and foam suppression ability, so as to maximize its dispersion and achieve the dual effects of foam suppression and foam breaking. [5]
Ross (S S.), an American colloid chemist, has made it clear that no defoaming mechanism can cover all defoaming phenomena, and various defoamers can correspond to various defoaming mechanisms. [5]
Composition of defoamer
Defoamers are mainly composed of active ingredients, emulsifiers, carriers and emulsifying additives, among which the active ingredient is the most important core part, which plays a role in breaking bubbles and reducing surface tension. Emulsifier is to disperse the active ingredients into small particles, so as to better disperse them into oil or water and play a better defoaming effect; Carrier accounts for a large proportion in defoamer, and its surface tension is not high, which mainly plays the role of supporting medium, which is beneficial to foam suppression and defoaming and can reduce the cost. Emulsification AIDS are used to make the emulsification effect better. [3]
Classification of defoamers
Types of defoamers
Defoamers can be classified according to different classification standards. For example, they can be divided into five categories: solid particle type, emulsion type, dispersion type, oil type and paste type. According to the application of defoamer in different industrial production, it can be divided into textile defoamer, paper defoamer, coating defoamer, food defoamer and petroleum defoamer. According to the chemical structure and composition, defoamers can be divided into mineral oil, alcohol, fatty acid and fatty acid ester, amide, phosphate, silicone, polyether and polyether modified polysiloxane defoamers. [4]
Here are four types: non-silicon type, polyether type, silicon type and polyether modified silicon type.
Non-silicon type
Non-silicon defoamers mainly include alcohols, fatty acids, fatty acid esters, phosphate esters, mineral oil, amides and other organic substances [4]. Among amides, monoamides, diamides and other nitrogen-containing compounds, such as trialkylmelamine, cyanuric chloride melamine and fatty amines, are usually used. Phosphates, including monoalkyl phosphates, dialkyl phosphates and fluorinated alkyl phosphates, are usually used for defoaming paint detergent products; Carboxylates include three substances: fatty acids, such as lauric acid and palmitic acid; Fatty acid esters, such as fatty acid glycerides, animal and vegetable oils, etc. ; Fatty acid soaps, such as calcium, aluminum and magnesium soaps of stearic acid and palmitic acid; Fatty alcohols and ethers include straight-chain and branched-chain alcohols and ethers. [6]
This defoamer is cheap and suitable for use under the conditions of small liquid shear force and mild foaming ability of surfactant. Its raw materials are easily available, its environmental protection performance is high, and its production cost is low, but its defoaming efficiency for dense foam is low, and its market share has been shrinking because of its strong specificity. However, in some special industries, such as strong acid and alkali, PTFE and other non-silicon defoamers are needed. [6]
Polyether type
Polyether defoamer is a polymer of ethylene oxide and propylene oxide, which mainly uses its different solubility characteristics at different temperatures to achieve defoaming effect. At low temperature, polyether is dispersed in water. When the temperature increases, the hydrophilicity of polyether decreases gradually until the cloud point, which makes polyether insoluble, thus playing a defoaming role. The cloud point of polyether can be changed by adjusting the kind of polyether and the proportion of raw materials in the preparation process, so it can be used in different industries. [3]
Polyether defoamer has excellent properties such as strong foam suppression ability and high temperature resistance, but its disadvantages are certain toxicity, limited use conditions by temperature, low foam breaking rate and narrow application field. If a large amount of foam is produced, the foam cannot be eliminated quickly, and the defoaming agent must be added again to show the defoaming effect. [3]
Polyether defoamers are mainly divided into GP type, GPE type and GPES type [3]
GP forms can be obtained by polymerizing propylene oxide with ethylene oxide or propylene oxide with glycerol. Its defoaming ability in foam medium is higher than that in defoaming. It is often used as defoamer in the production of biological pesticides, yeast and so on. [3]
GPE defoamer mainly adds ethylene oxide to polypropylene glycol chain end (GP defoamer) to make it become hydrophilic polyoxyethylene propylene glycol chain end. Soluble in medium, with strong defoaming ability, but also with high solubility and poor defoaming performance. In pharmaceutical industry, it is often used as defoamer in antibiotic fermentation. [3]
GPES defoamer is a new polyether defoamer which is esterified with stearic acid at the chain end of GPE defoamer. Because the molecules of this structure have increased lipophilicity and decreased hydrophilicity, they are easy to gather at the gas-liquid interface, so the defoaming efficiency is high. [3]
Silicone resin type
Polydimethylsiloxane (also known as silicone oil) is the main component of defoamer in silicone. Compared with H2O and common oil, the surface tension of silicone oil is smaller, which is suitable for both water-based foaming system and oily foaming system. Among H2O and common oil, silicone oil has high activity and low solubility. Its basic characteristics are stable chemical properties, wide application range, low volatility, non-toxicity and outstanding defoaming ability. Its disadvantage is poor defoaming performance. [3]
This kind of defoamer mainly includes solid, emulsion, solution and oil. [3]
Solid defoamer has the characteristics of good stability, simple process and convenient transportation and use. It is suitable for both oil phase and water phase, and its medium dispersibility is also outstanding, so it is widely used in the field of low (no) foaming washing powder. [3]
Silicone oil in emulsion defoamer has great tension and emulsification difficulty coefficient. Once the emulsifier is not properly selected, the defoamer will be layered and deteriorated in a short time. The stability of emulsion is very important to the quality of defoamer, so the preparation of emulsion silicone defoamer focuses on the choice of emulsifier. At the same time, emulsion defoamer has the characteristics of low price, wide application range and obvious defoaming effect, and it is the most used defoamer in silicone. With the development of formulation technology, emulsion defoamer will have great development. [3]
Solution defoamer is a solution made by dissolving silicone oil in a solvent. The defoaming principle is that silicone oil is carried by solvent and dispersed in foaming solution. In this process, silicone oil will gradually condense into droplets, thus completing defoaming. Silicone oil can be dissolved in non-aqueous organic solution systems, such as polychloroethane and toluene. It can be used as an oily solution to defoam. [3]
Silicone oil can be dissolved in aqueous solution, such as ethylene glycol and glycerol. And can be used as an aqueous solution to defoam. It should be noted that solvents can improve the dispersibility of defoamers, and at the same time, their costs will also increase. If the stirring speed and intensity are insufficient in the preparation process, although the solvent is easy to diffuse, the silicone oil will condense into oil beads with large particle size and poor defoaming activity. [3]
Dimethyl silicone oil with high cost is usually suitable for defoaming oil-soluble solutions. Generally speaking, foam systems with high viscosity choose defoamers with low viscosity, and foam systems with low viscosity choose defoamers with high viscosity. [3]
Polyether modified silicone type
This kind of defoamer is a silicone ether polymer obtained by modifying grafted polyether or polysiloxane segments. It is a new type of high-efficiency defoamer which organically combines the advantages of both, and has the advantages of good dispersibility, strong defoaming ability, stability, non-toxicity, low volatility and strong defoaming effect. [3]
Characteristics of (1) polyether modified silicone defoamer
Anti-solubility: because the molecule contains polyether segments, it has the cloud point characteristics of polyether defoamer, which is convenient to choose the appropriate polysiloxane polyether defoamer according to the temperature requirements of defoaming system. [3]
Self-emulsifying property: Due to the different hydrophobicity and hydrophilicity of siloxane chain and polyether chain to the solvent, when polyether modified silicone defoamer is added to the solvent, the polyether chain extends outward and the polysiloxane chain curls inward to form a dispersed state, which is called "self-emulsifying property". The defoamer can be quickly and evenly dispersed in the foaming liquid under the self-emulsification effect, and its stability is outstanding, which is beneficial to give full play to the function of foam suppression and defoaming. By adjusting the ratio of polyether segment to siloxane segment, defoamer can be applied to foaming solutions with different properties. [3]
(2) Types of polyether modified silicone defoamer.
According to the different internal connection methods, polyether modified silicone defoamer can be divided into the following two categories [3]:
The polymer containing -Si-O-C bond prepared with acid as catalyst is easy to hydrolyze and has poor stability. If there is amine buffer, it can be stored for a long time. However, due to its low price, its development potential is extremely obvious. [3]
The structure of * * polymer bonded by -Si-C bond is relatively stable and can be stored for more than two years under closed conditions. However, due to the use of expensive platinum as catalyst in the production process, this kind of defoamer has not been widely used because of its high production cost. [3]
Advantages and disadvantages of different kinds
Organic defoamer, such as mineral oil, amide, lower alcohol, fatty acid and fatty acid ester, phosphate ester, etc. It was researched and applied earlier, and belongs to the first generation defoamer, which has the advantages of easily available raw materials, high environmental protection performance and low production cost. The disadvantages are low defoaming efficiency, strong specificity and harsh use conditions. [4]
Polyether defoamer is the second generation defoamer, which mainly includes linear polyether, polyether with alcohol or ammonia as initiator and polyether derivatives with terminal esterification. The biggest advantage of polyether defoamer is its strong foam suppression ability. In addition, some polyether defoamers have excellent properties such as high temperature resistance, strong acid and alkali resistance. The disadvantages are that the use conditions are limited by temperature, the use field is narrow, the defoaming ability is poor, and the defoaming rate is low. [4]
Silicone defoamer (the third generation defoamer) has the advantages of strong defoaming performance, fast defoaming ability, low volatility, no toxicity to the environment, no physiological inertia and wide application range, so it has broad application prospects and huge market potential, but its defoaming performance is poor. [4]
Polyether modified polysiloxane defoamer has the advantages of polyether defoamer and silicone defoamer, which is the development direction of defoamer. Sometimes it can be reused according to its anti-solubility, but there are few kinds of defoamers, which are still in the research and development stage and the production cost is high. [4]
Existing problems and development trend
exist problem
After 1970s, China began to engage in the development and application of polyether modified silicone oil, which overcame a difficulty. However, the defoamer industry started late, and the upgrading of domestic defoamers could not keep up with the pace of industrial development. The supply of -Si-C- polyether modified silane in China mainly depends on imported channels, because compared with the research on Si-C polyether modified silicone oil abroad, there is much less research on it in China, and there are basically no new products and new processes. On the one hand, there are few manufacturers that can produce special polyether and special hydrogen-containing silicone oil, and the choice of raw materials for products is limited; On the other hand, because polyether modified silicone oil is still synthesized by traditional synthesis process, the product conversion rate is low, there are many cross-linked products in the product, and the product quality is poor, so its economic benefit is difficult to guarantee. [5]
Polyether modified silicone oil was prepared according to the original synthesis process. In addition, chloroplatinic acid as a catalyst has high cost and harsh reaction conditions. If the amount of catalyst used in the reaction is small, the side reaction is difficult to control, the appearance color of the product will deepen, and the reaction time needs to be extended; The solvents (toluene and isopropanol) in the reaction are harmful to the environment and human body. If the solvent remains, the surface tension of the product will increase. In addition, in order to remove the residual solvent, an additional treatment process is needed and the equipment is complicated. [5]
There are many kinds of defoamers in the market, and most of them have good defoaming effect, but the defoaming effect is not strong, which makes customers spend money, but they can't achieve the desired defoaming effect, so that people are afraid to use them safely or simply give up using them. Usually, many admixtures mixed with concrete have certain air-entraining effect, and the introduced bubbles have certain side effects on the strength of concrete. Adding a good defoamer into concrete can inhibit or eliminate excessive or harmful bubbles in concrete, improve the compactness of concrete, and thus improve the strength of concrete. Therefore, it is undoubtedly very important and urgent to develop a defoamer with excellent performance. [5]
development trends
Polyether modified silicone oil (PESO) is the most widely produced and applied silicone oil, which is polymerized by connecting the main chain or side chain of linear dimethyl silicone oil with polyether chain. PESO is the most widely produced and applied modified silicone oil in the market at present. The oxygen atoms of polyether segments in the molecular structure of this silicone oil can form hydrogen bonds with water and dissolve in aqueous solution; The polysiloxane segment is neither hydrophilic nor lipophilic, and the hydrocarbon group in its main chain is also not hydrophilic. Therefore, polyether segments and polysiloxane segments are connected together through hydrosilylation reaction to form nonionic surfactants with unique properties. Due to the variety of polyethers, a series of polyether modified silicone oils will be produced by changing the introduction mode during the addition reaction, which have different properties and functions and can meet the needs of diversified markets. [5]
Molecular structure of peso defoamer
PESO defoamer combines the water solubility of polyether with the low surface tension of silicone. It contains hydrophilic group EO and hydrophobic group PO in polyether segment. If their proportion is properly adjusted, there will be a strong low surface tension and a strong defoaming ability. [5]
With the continuous development of peso defoamer, many new active defoaming components have appeared, which makes the research on the reaction mechanism and synergistic effect of compound defoamer more in-depth. Therefore, the defoamer with single component and poor economic benefit will be gradually replaced by the multifunctional and efficient compound defoamer, which will be the future development trend of defoamer market. [5]
The introduction of new groups on the basis of the original peso, such as -NH2 (amino), Cn(H2O)m (saccharide), C6H5COC6H5 (benzophenone) and-COOH (carboxyl), can give the peso more reactivity and versatility. With the increasing voice of global cleaner production, the development of new surfactants with high efficiency, green and multi-function has become the leading direction of peso defoamer development. [5]
Precautions for use
Selection considerations
The physical and chemical properties of the ideal defoamer must meet the requirements of the use system. Generally speaking, the following requirements must be considered when selecting defoamers [7]:
(1) has strong defoaming ability, and it can effectively eliminate foam when used in a very small amount;
(2) It has lower surface tension than defoaming system;
(3) The addition of defoaming agent does not affect the basic performance of defoaming system;
(4) Insoluble in defoaming system and not easily dissolved by surfactant in the system;
(5) Good balance of surface tension;
(6) It does not react with defoaming medium, nor is it decomposed and degraded by defoaming medium, so it has good chemical stability;
(7) It has good diffusivity and permeability, positive diffusivity in foam medium and rapid spreading ability on foam surface;
(8) Good heat resistance and no failure at high temperature;
(9) Good gas solubility and permeability;
(10) has high physiological activity and safety in defoaming system, and the defoamer itself is non-toxic or low-toxic;
(1 1) The chemical oxygen demand (COD), biochemical oxygen demand (BOD) and total oxygen demand (TOD) are low;
(12) has good storage stability;
(13) has long-term defoaming effect. Some defoamers can defoam quickly, but they will fail after a long time.
(14) low cost;
(15) does not increase the surface viscosity of surfactant aqueous solution.
It is difficult for defoamer to meet the above requirements at the same time, and its main performance can only meet the requirements of defoaming system. Each defoamer can only be effective for a certain system or several systems, and multiple defoamers can also be selected for the same foam system. Because of this, users should experiment and choose the most effective and economical defoamer. [7]
Turbidity problem
The main components of defoamer are generally hydrophobic particles, silicone oil and emulsifier. Hydrophobic particles adsorb silicone oil, so that silicone oil can achieve maximum effect with as little amount as possible. As the main defoaming medium, silicone oil has small surface tension and is neither lipophilic nor hydrophilic. It is suspended in the system. When defoaming agent exists in the middle of foam wall, it replaces oil-water phase to produce defoaming effect. At the same time, a small amount of silicone oil is consumed. When the silicone oil outside the hydrophobic particles is completely consumed, the foam system becomes turbid. Therefore, the amount and color of hydrophobic particles, silicone oil and emulsifier used in defoamer are different, which leads to different properties of defoamer. When the defoaming agent has good defoaming effect and long defoaming time, the system will not be turbid. [7]
Oil drift problem
Because defoamer is not dissolved in the system, but dispersed in the system, the dispersion uniformity of defoamer in the system is very important. When the defoamer is evenly dispersed in the system, it has little effect on the transparency of the system, and it takes a long time to agglomerate into larger particles, which can be kept in the system for a long time. When defoaming agent is unevenly dispersed in the system, but aggregated into many small particles, on the one hand, it will affect the transparency of the system, on the other hand, it will shorten the time for defoaming agent to aggregate into large particles, resulting in turbidity after adding defoaming agent to the system, and oil will drift the next day. In order to avoid oil slick, the following methods can be adopted: (1) moving the addition order of defoamer forward; Dilution is carried out before adding into the system, and the diluent can be water or a surfactant in the system. [7]
Bubble suppression time problem
The nature of silicone oil in defoamer determines the defoaming time of defoamer, and the content of silicone oil determines the consumption period of defoamer in use. Too little silicone oil will make the defoaming performance of defoamer not reach the required value, and too much silicone oil will affect the performance of defoamer and reduce the defoaming performance of defoamer. The particle size of defoamer determines the filtration resistance of defoamer. Excessive particle size may cause defoamer to be easily filtered, resulting in oil slick, which affects foam suppression. Stirring time is also an important index of defoaming agent's foam suppression ability. Insufficient stirring may lead to turbidity, oil slick, weakened defoaming ability and shortened defoaming time. [7]
Fault problem
Acid-base stability. Silicone oil can destroy the surface tension of liquid and eliminate foam. If the defoamer has poor acid and alkali resistance, it will lead to the decomposition of silicone oil, which will lead to the decrease of defoaming ability or even failure. Adding silicate to the system usually inhibits its decomposition. Solubility of defoamer. Some chemical components make silicone oil dissolve into the system, so defoaming agent no longer plays a defoaming role, but exists in the system as a surfactant, and the foam of the system is higher than that without defoaming agent.