Silicone emulsion
Silicone emulsions are a form of silicone oil. The following is an introduction from two aspects of silicone oil fabric softening agent and silicone oil emulsion type defoamer.
1. Silicone oil fabric softening agent
Silicone emulsion is mainly used as silicone oil fabric softening agent. The first generation of silicone fabric finishes was a mechanical mixture of simethicone and hydrogen silicone (and their derivatives). The second-generation silicone fabric finishing agent is hydroxyl-terminated polydimethylsiloxane emulsion, which is made of octamethylcyclotetrasiloxane monomer, water, emulsifier, catalyst and other raw materials under certain conditions. aggregated. Since the polymerization and emulsification are completed in one step, it has the advantages of short working hours, high work efficiency, simple equipment, and convenient operation. ) can be further reacted to form a film, which is beneficial to improve the application effect of the emulsion, which is beyond the reach of mechanically emulsified silicone oil.
Hydroxy silicone oil emulsions can be divided into cationic, anionic, nonionic, and composite ion emulsions according to the different surfactants used.
1. Cationic hydroxy silicone oil emulsion
The emulsifier used in cationic hydroxyemulsion polymerization is generally quaternary ammonium salt (octadecyltrimethylammonium chloride is reported in foreign literature), and the catalyst is ammonium hydroxide. Cationic hydroxyemulsion can be used in the finishing of various textiles. It has the properties of improving fabric hand feeling, fabric elasticity, smoothness and crispness; its other unique advantage is that it is an ideal waterproofing agent for fabrics, and it can be used together with methyl hydrogen silicone oil emulsion , waterproof performance and waterproof durability can reach a very high level, it can be used as a waterproof agent for vinylon tarpaulin, polyester card cloth, etc.
2. Anionic Hydroxy Silicone Oil Emulsion
Anionic hydroxyl emulsion is characterized by good compatibility in fabric finishing agents and very stable emulsion. In particular, most of the auxiliaries in textile printing and dyeing are anionic. If cationic hydroxyl emulsion is used, it is easy to cause demulsification and floating oil. Anionic hydroxyl emulsion can avoid this disadvantage, so it is more popular with users and has a wide range of uses.
3. Compound ionic hydroxyl silicone oil emulsion
Although cationic hydroxyl emulsion is an excellent fabric softening and finishing agent, this emulsion is not resistant to hard water and cannot be bathed with dimethylol dihydroxyethylene urea resin (2D) resin, catalyst magnesium chloride and anionic brightener Therefore, there are certain limitations in use. In addition, due to the poor stability of the emulsion, silicone polymers are easily separated from the emulsion and float on the liquid surface, commonly known as "floating oil". If cationic and non-ionic emulsifiers are used for compounding in the emulsion polymerization process, the shortcomings of cationic emulsifiers to prepare hydroxyl silicone oil emulsions can be overcome, and the prepared silicone emulsions can withstand hard water and can be compatible with 2D resins, magnesium chloride and The whitening agent VBL is equivalent to bath use, and has good heat resistance and freezing resistance.
4. Nonionic Hydroxy Silicone Oil Emulsion
Non-ionic hydroxyl emulsion has stronger adaptability and better stability than isolated hydroxyl emulsion, so many countries are vigorously researching non-ionic hydroxyl emulsion. For example, UltraX FSA, a new product produced by Ciba-Geigy in Switzerland, is a non-ionic emulsion of hydroxyl-capped polydimethylsiloxane with a molecular weight of more than 200,000. Hydroxyemulsion goes one step further.
5. Silicone finishing agent with other active groups
In order to meet the needs of advanced finishing of various fabrics, improve the oil resistance, antistatic and hydrophilic properties of silicone finishing fabrics, and make chemical fiber fabrics have many advantages of natural fabrics, silicone workers have studied the introduction of other organic silicon molecules. Active groups such as amino, amide, ester, cyano, carboxyl, epoxy, etc. The introduction of these groups makes the silicone fabric finishing agent have special effects. For example, the introduction of amino groups into silicone molecules is suitable for shrink-proof and soft finishing of wool fabrics; the introduction of amide groups is suitable for anti-fouling finishing, and the softness is also greatly improved: introduction The cyano group has good oil resistance, and the copolymer of polyoxyethylene ether and silicone has good antistatic effect; organic fluorine modified silicone has many advantages such as oil repellency, antifouling, antistatic, water repellency, etc.
2. Silicone oil emulsion type defoamer
Silicone oil emulsion defoamers are generally oil-in-water (O/W) emulsions, that is, water is the continuous phase and silicone oil is the discontinuous phase. It is to pre-mix silicone oil, emulsifier and thickener, then gradually add water and stir evenly, and finally grind repeatedly in a colloid mill until the desired emulsion is obtained.
Silicone oil emulsion type defoamer is the most widely used and the largest amount of defoamer among silicone defoamers. It is characterized by being easily dispersed in water systems and can be widely used as a defoamer for water phase systems. When in use, add the emulsion directly into the foaming system to obtain a good defoaming effect. In order to improve the defoaming effect of the emulsion and the accuracy of measurement, it is generally not used directly to use more than 10% concentrated silicone oil emulsion: instead, it is first diluted with cold water or directly with foaming liquid to less than 10% before use. It is taboo to dilute with hot or cold liquid, otherwise it will cause the emulsion to break. The stability of the emulsion will deteriorate after dilution, and stratification (oil floating) may also occur during storage, that is, demulsification. Therefore, the diluted lotion should be used up as soon as possible. Thickeners can be added to increase the stability of the emulsion, if desired. For the batch operation process, the silicone oil emulsion can be added once before the system is running, or it can be added in batches; for the continuous operation process, the silicone oil emulsion should be added continuously or intermittently at the appropriate part of the system.
When using emulsion-type defoamers, special consideration should be given to the temperature of the foaming system and the conditions of acidity and alkalinity, because the silicone oil emulsion is relatively delicate, and if it exceeds its application range, the emulsion will break prematurely and become inefficient or ineffective. (The amount of silicone oil emulsion is generally 10-100 ppm of the weight of the foaming liquid (according to silicone oil). Of course, in special cases, there are also less than 10 ppm and more than 100 ppm. The optimum amount is mainly determined through experiments.
Most of the general silicone oil emulsion defoamers are oil-in-water type. According to the different types of silicone oil, there are several types of silicone oil emulsion defoamers as follows:
1. Silicone oil emulsion based on dimethyl silicone oil
This kind of defoamer is prepared from simethicone plus emulsifier and water, and can be widely used in fermentation, food, papermaking, fiber, pharmaceuticals, synthetic resin, etc.
2. Silicone oil emulsion based on methyl ethoxy silicone oil
This kind of defoamer is made of methyl ethoxy silicone oil and compounding agent.
3. Silicone oil emulsion based on ethyl silicone oil
In recent years, silicone defoamers are developing in the direction of silicone-polyether block copolymerization (or graft copolymerization). This kind of defoamer has the characteristics of both silicone and polyether, so the defoaming power is greatly improved; silicone-polyether copolymerized defoamer can also be called self-emulsifying silicone defoamer, it is Block (or graft) hydrophilic ethylene oxide chain or oxyethylene oxide propylene chain in the silicone molecular chain, so that the hydrophobic siloxane part is combined with the hydrophilic polyether. Such molecules have larger Polarity, as a defoamer, it has a large spreading coefficient, can be uniformly dispersed in the foaming medium, and has high defoaming effect. It is a new type of high-efficiency defoamer. This kind of self-emulsifying silicone oil without the use of emulsifiers, the defoaming effect is quite satisfactory for some systems, it is especially suitable for those occasions where the general silicone oil emulsion is not suitable and the general silicone oil emulsion is difficult to do.
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