Application of fumed silica in defoamer
The fumed silica is a kind of high-purity, fine, amorphous nanometer silica powder.
The specific surface area is 150 ~ 380m2 / g, the primary particle size is between 7 ~ 40 nm, the aggregate particle size is about 200-500nm, the agglomerate particle size is about 5 ~ 20μm, and SiO2 ≥99.5%. Functional additives. In addition to being widely used in silicone rubber, coatings, inks, paints, plastics and other fields, it is also an important component in high-efficiency silicone oil defoamers, which plays a role of dispersion, adsorption, thickening and anti-settling.
Vapor-phase process carbon black generally has two types of hydrophilic and hydrophobic products. The hydrophobic products are obtained by surface treatment of hydrophilic products. As an important auxiliary in the industry, the defoamer has a small amount but is indispensable. It is widely used in various fields such as textile, papermaking, petroleum, food, pharmaceutical and so on. The defoaming agent is targeted and specific, because the foaming mechanism and process conditions of each foaming system are different, and different foaming systems require different defoaming agents. It can be broadly divided into non-silicon based and silicon based defoamers. Non-silicone series such as higher alcohols, acids, hydrocarbons, polyethers, esters, phosphate esters, etc., they are used in large amounts and have little applicability; silicon-based defoamers are silicone oil / silica black silicone paste and modified silicone oil as defoamers The main component is the most widely used and most effective type of defoamer. Compared with other types of defoamers, it has several outstanding features:
- small solubility, solubility parameters are very different from other organic substances, and will not occur with water, compounds containing polar groups and hydrocarbon compounds with different SP values Associate. It can be used in both water system and oil system, and has defoaming effect on most foaming systems.
- The surface tension is low, its surface tension is 20 ~ 21mN / m, which is much lower than that of water (76mN / m) and general foaming liquid. This is a silicone oil defoamer with a wide application and strong defoaming ability. The main reason is that the general dosage is only 10 ～ 200ul / L of foaming liquid, which will not pollute the system and affect the processing performance of the product.
- Good chemical stability and heat resistance, can adapt to defoaming of weak acid, alkali, salt and high temperature system.
- Physiological inertness, can be used in food, cosmetics and pharmaceutical industries.
- There are many types and models, which can be used for a variety of foaming systems. Except that dispersant (SiO2) -containing systems are not allowed, such as some oily systems, fumed silica is an important component of silicon-based defoamers, and its effect is huge.
The role of fumed silica in defoamers
1.1 Dispersion: An important indicator of the quality of a defoamer is its dispersion effect.
Only substances with low solubility and large dispersibility can become the active ingredients of the antifoaming agent. As the main component of the defoaming agent, dimethyl silicone oil has low solubility and small dispersibility. It must be aided by white carbon black, emulsifiers and other dispersing aids to improve its dispersing effect. Gas phase method carbon black is divided into hydrophilic type and hydrophobic type. The hydrophilic type contains silicon hydroxyl bonds and can form hydrogen bonds with water molecules. It can promote the dispersion and stability of defoamers in water systems. Hydrophobic fumed silica is obtained by surface treatment of hydrophilic silica to reduce the Si-OH number of silica to an appropriate level. It can also be used in water systems to reduce silica in water. The degree of association of the system to achieve the best defoaming effect. The application of fumed silica in the defoamer is to make it and silica gel first to make silica paste, which can improve its wettability with dimethyl silicone oil and dispersibility in silicone oil. The mixing method of silicon paste has certain influence on the stability and defoaming performance of silicon paste. When using hydrophilic silica, due to the low compatibility between inorganic silica and organic silicon oil, in order to achieve the purpose of mixing, put silicone oil and silica in a kneader and mix at 150 ~ 180 ℃. Stir N2 for 2 ~ 7h to improve the wettability of silica and silicone oil. If hydrophobic white carbon black is used, since the surface has been treated with organic matter, its affinity with silicone oil is greatly improved. It can be stirred at 150 ° C for 2 to 5 hours under N2. Silicone paste made of fumed silica is transparent or translucent, and the ratio is generally silicone oil: white carbon black = (90 to 95): (10 to 5), dimethyl silicone oil is generally selected at 25 ° C, 500 to 1000 cp. Silicone oil and white carbon black can be selected with a specific surface area of 200m2 / g or more (BET method). As the active ingredient of silicone oil defoaming agent, silicone ointment can be used directly or diluted with solvent, or self-emulsified with emulsifier or polyether modified silicone oil to achieve the purpose of defoaming. Due to the presence of SiO2 particles, the silicone oil can quickly spread in the foaming liquid, which improves the dispersion efficiency of the silicone oil, thereby improving the defoaming effect. Therefore, fumed silica is a very important dispersant in defoamers.1.2 Adsorption: Gas phase white carbon black plays an important role in defoaming agents.
Due to the small particle size, large specific surface area, high surface energy, and three-dimensional network structure, silica can form a huge force of adsorbing bubbles, which together with silicone oil constitutes a force to attack bubbles, that is, silica adsorbs and impacts. Bubbles cause weak points. Under the action of the low surface tension of silicone oil, the bubbles are broken and the bubbles are broken. Therefore, the gas phase method of white carbon black is equivalent to "needle tip" in the defoamer, with a small amount but a great effect. It and silicone oil, as active ingredients of high-efficiency defoaming agents, have a compound efficient and synergistic defoaming effect.1.3 Thickening and anti-settling effect The important indicators of emulsion type silicone oil defoamer are defoaming effect and storage stability, especially for silicone paste emulsion.
There are many factors that affect the stability of the emulsion, such as the particle size and viscosity of the emulsion. Emulsion particle size is the most important control index for emulsion-type defoamers. Generally, the particle size is required to be less than 10um. Emulsion particle size depends on the choice of emulsifier, emulsification process and particle size. The minimum particle size of gas phase white carbon black can reach about 5um. The silicone oil emulsion particles containing this white carbon black constitute a very small and very large number of basic defoaming units in the foaming liquid, which makes the defoaming agent optimal. Defoaming effect. At the same time, due to the small particle size and large specific surface area, the stable hydrogen-bonded three-dimensional network structure enables the white carbon black particles to be uniformly and stably distributed throughout the system, making the system storage stable. Therefore, as a very good thickening and anti-settling agent in the defoamer, the gas phase method of white carbon black should generally be selected with a specific surface area of 200-300m2 / g. To sum up, the gas phase method of white carbon black silicon paste as a defoaming active in the silicone oil defoamer plays a very important highly effective and synergistic role, which greatly improves the defoaming efficiency of the silicone oil.Silicone oil defoamers can be divided into six types according to the product form: silicone oil type, silicone paste type, solution type, emulsion type, modified silicone oil type and solid type.
In the following, a large amount of emulsion-type defoamer and self-emulsifying polyether defoamer are used as examples to illustrate its application.1. Emulsion type silicone oil defoamer is a general-purpose silicone defoamer. It is a water bag made of emulsified silicone oil / silicone paste with low foaming emulsifiers such as Span, Tween, and polyethylene glycol ether. Oil (O / W) type emulsion. Its characteristics are easy to disperse in water system, and it can be widely used as defoamer in water phase system. It is more sensitive to the temperature, acid, alkali and salt of the foaming liquid, it is easy to cause oil drift or demulsification, and it has dilution stability. And the durability is poor, the dimethyl silicone oil will slowly precipitate out, thus losing the defoaming ability, and the system that can not contain oil will pollute the system.
Example of emulsion defoamer formula: (containing 30% of active substance)
① First make silica paste: (as described in 2.1)25 ℃, 500cp dimethyl silicone oil 45.0g
25 ℃, 1000cp dimethyl silicone oil 45.0g
Gas phase white carbon black (Jibiesi HL-200) 10.0g
Total 100.0g
② Make an emulsion: mix white carbon black silicon paste and composite emulsifier and heat to 60-70 °C, stir for 1 hour, slowly add 50 ° C water under high-speed stirring, continue to stir for about 15 minutes, add thickener to adjust to proper Viscosity, filtered to obtain an emulsion. Silica paste (white carbon black) 30.0g
S-80 6.0g
T—80 2.0g
Polyoxyethylene (20) alkyl alcohol ether 2.0g
Leech 60.0g
Thickener 0.5-1.0g
Total 100.0g
2. Self-emulsifying polyether silicone oil defoaming agent is a self-emulsifying new type of high-efficiency composite organic silicone defoaming agent made of white carbon black silicone ointment and polyether modified silicone oil as active ingredients, supplemented with other auxiliaries. .
Polyether modified silicone oil has a strong emulsifying ability, can emulsify silicone oil and self-emulsifying, making the entire emulsification system very stable; due to both the low surface tension of polysiloxane and the easy dispersibility of polyether, it makes defoaming The agent is easy to spread and spread; it has defoaming property when the temperature is higher than the cloud point, and is dispersed in the foaming liquid when the temperature is lower than the cloud point, which makes the defoaming lasting. Due to the coordination of the components, the applicability of the defoamer is improved. It has the characteristics of high temperature resistance, acid and alkali resistance, mechanical stability, wide application range, low dosage, high efficiency, and long-term defoaming. It is widely used in printing and dyeing. , Papermaking, pharmaceutical, coatings, petroleum, chemical and other fields, especially suitable for harsh foaming liquids that are difficult for general silicone oil emulsions, such as defoaming in high temperature dyeing of polyester fiber fabrics, and defoaming of diethanolamine aqueous solution desulfurization systems, Defoaming of various oils, cutting fluids and antifreeze systems. Example of self-emulsifying polyether defoamer formulation for dyeing: (100% active)Polyether silicone oil: Hydrosilication reaction with low hydrogen-containing silicone oil (0.18%) and single-ended allyl polyether (EO: PO = 4: 6) under the protection of N2 gas, 80 ～ 100 ℃, Pt complex catalyst To get light yellow modified polyether silicone oil. Polyether modified silicone oil tincture 650g
White carbon black silicon paste (same as above) 150g
Allyl polyether (EO: PO = 1: 1) 150g
(25 ℃, 50 ~ 100cp) Low viscosity hydroxy silicone oil 50g
Total 1000g
3 Proportion and application system:
The amount of white carbon black in the defoamer in the gas phase method is generally about 1%, which can be adjusted appropriately according to the application. Gas phase silica can be used in weak acid, weak base, salt, high temperature, shear and other systems, but in high temperature and strong alkali (PH> 13) foaming liquid, hydrophilic white carbon black will gradually dissolve in the system It becomes a water-soluble silicate, which reduces the defoaming effect. The hydrophobic silica has a small amount of Si-OH on the surface, which reduces the degree of association in the water system. It is more difficult to dissolve than the hydrophilic type. In this foaming liquid, the use of hydrophobic silica is better.4 Conclusion:
- Because of its special structure, especially the three-dimensional network structure, gas phase method white carbon black has a strong adsorption rate and causes foam breakage. It is the most important additive in high-efficiency defoamers.
- The gas phase white carbon black with a specific surface area of 200-300m2 / g (BET method) should be selected because it has the best dispersion, adsorption and anti-settling effects.
- In the application of gas phase white carbon black, it must be pre-dispersed so that it is fully wetted and uniform with organic materials such as silicone oil, so as to have better compatibility, stability and defoaming effect in the defoamer.
- Except for systems that do not allow dispersant (SiO2), defoamers containing fumed silica can be widely used in various foaming systems.
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