In many industries (such as printing and dyeing, fermentation, paper, coatings, pharmaceuticals, food processing, oilfield mining, water treatment, industrial applications, chemical processing, etc.) In the wide range of industrial processes, mixing, vibration, boiling, and other operations often produce a large number of foam, the foam will bring a lot of trouble to the production, such as affecting the normal conduct of production, reducing the amount of equipment payload, resulting in product quality and production capacity decline. In order to eliminate and control the surface foam, the most effective and most economical, and simple method is to add a defoamer.
Silicone defoamer, also known as an anti-foam agent or silicone antifoam, can be divided into oil, emulsion, solid and paste, etc. According to the state; The chemical composition can be divided into alcohols, fatty acids, amides, phosphates, polyethers (The product is an excellent defoamer for metalworking fluids, pulp and paper, and paints, etc.) polysiloxanes (customarily also called silicone), etc. Siloxane agents and processing aids can meet a wide variety of processing requirements. Typically, defoamers are formulated around a carrier fluid, which can be silicone oil, vegetable oil, synthetic polymer, etc. Compared with non-silicone defoamer, silicone defoamer has good defoaming and foam inhibition effect, and it reduces the stress on the motor and reduces labor costs by eliminating the need to continuously empty the recovery tank, low VOC, prevents surface defects such as shrinkage, fish eyes, pinholes and weak spots in the paint after drying renewable food contact certification and other characteristics of various industries are concerned.
The following is a brief description of the factors affecting the performance of the defoamer.
Each of these influencing factors will be described in detail next.
- The effect of viscosity and dosage of methyl silicone oil
- The effect of silicon dioxide selection and dosage
- Effect of polyether silicone oil dosage
- The effect of the compounding of emulsifiers and their dosage
- The effect of thickening agents
1. The effect of viscosity and dosage of methyl silicone oil on the performance of silicone defoamer
Methyl silicone oils have low surface tension, strong defoaming ability, good thermal stability, chemical and physiological inertness, plus insoluble in water, and have excellent defoaming performance for most foaming media, this property can be used as a hot tub defoamer and spa chemicals. Therefore, we choose methyl silicone oil as the main component of silicone defoamers. Fixed other conditions, to examine the impact of changes in the viscosity of methyl silicone oil on the performance of the defoamer, the experimental results: with the increase in viscosity of methyl silicone oil, the defoamer defoaming time was first reduced after a slight increase in the trend, but the time of foam inhibition is always increasing. This is because the low viscosity of methyl silicone oil surface tension is small and easy to disperse in the foaming solution to play the role of antifoaming, but the solubility of large, easily dispersed, short foam inhibition time; and viscosity of methyl silicone oil solubility is small, long foam inhibition time, but emulsification difficulties, Poor existing control foam effect.
In addition, the content of methyl silicone oil in the emulsion should be moderate, if the dosage is too low, the defoaming effect is poor, in order to achieve the expected defoaming effect, the amount of defoamer emulsion must be added, prevent existing foam, but this will affect product quality; if the dosage is too high, it is not easy to emulsify. With highly demanding applications, experiments show that the appropriate content of methyl silicone oil in the emulsion is 16%-17%.
2 . The effect of silicon dioxide selection and dosage
(1) Can be used for methyl silicone oil defoamer silica are:
Fumed silica, precipitated silica, silica gel, silica sol, quartz powder, etc. Because the fumed silica-specific surface area is large, small in density, and easy to disperse, without hydrophobic treatment is hydrophilic, in the organic phase is difficult to infiltrate and dispersion, after hydrophobic treatment of the surface by the base content is reduced, the aggregation tendency is weakened, from hydrophilic to hydrophobic, and the organic phase of the infiltration, dispersion is improved, help to enhance the dispersion of silicone oil in the foaming system, increase the emulsion stability of the emulsion! Therefore, We chose to compound fumed silica with polydimethylsiloxane oil to improve the effectiveness of the polydimethylsiloxane oil in eliminating more unwanted foam.
(2) Experimental conclusion
The effect of different amounts of silica on the defoaming performance of the silicone defoamer was investigated under the same conditions, and the experimental results are shown. With the increase in the amount of hydrophobic silica and the control of foam, the stability of the resulting defoamer emulsion became worse. Relative to 100 g of methyl silicone oil, when the amount of silica is lower than 8 g (equivalent to 1.300 in the emulsion), the defoamer defoaming performance is enhanced with the increase of the amount of silica, but when the amount of silica is higher than 89, the defoaming performance basically does not change with the increase of the amount of silica. Comprehensive consideration, we believe that the most applicable amount of silica in the defoamer should be about 1.3%.
3 . Effect of polyether silicone oil dosage
Polyether silicone oil itself has defoaming and foam inhibition properties, and can produce synergistic effects with methyl silicone oil/modified silica. Fixed other conditions, adding polyether silicone oil and changing its dosage, observing the defoaming performance of the defoamer, the experimental results: simple methyl silicone oil/silica emulsion defoaming effect is not the best. After adding polyether silicone oil, in a certain dosage range, with its dosage increases, the defoamer defoaming time becomes shorter and is conducive to extending the time of foam inhibition.
In addition, the stability of the silicone emulsion and its dispersion in water with the increase in the amount of polyether silicone oil become better. This is due to the addition of polyether silicone oil, polyether silicone oil white body can be white emulsification, and the use of a synergistic effect between the components and the defoamer defoaming effect improved significantly. But when the amount of polyether silicone oil is more than 20 g (10% of the total mass fraction of the emulsion), will lead to a large increase in the hydrophilicity of defoamer components, easy to disperse in the foaming solution and reduce the foam control, so the proper concentration of polyether silicone oil is about 10%.
4 . The effect of the compounding of emulsifiers and their dosage
(1) Compounding of emulsifiers
Emulsifier is one of the key factors in the preparation of emulsion-type silicone anti-foaming agent methyl silicone oil is difficult to emulsify in order to make the emulsifier can play a good role in emulsification and dispersion, the first should consider the HLB value of the emulsifier and silicone oil HLB value (about 8—11) is close, followed by consideration of the emulsifier foaming force to be small, in addition to considering the emulsified system (non-aqueous systems) and the emulsifier water-repellent base of the affinity. Usually, ionic emulsifiers such as solvents, sulfate esters, etc. Have varying degrees of foam, while Span and Tween class non-leaving type emulsifiers and methyl silicone oil's affinity are better, and have low foaming performance, so this study selected Span-80 and Tween-80 for compounding. It can be seen that the defoaming performance, centrifugal stability, and dispersion of the defoamer in water are better when the HLB value of the emulsifier is about 10.
(2) Experimental conclusion
Fixed other conditions and emulsifier Span-80 and Tween-80 ratio are unchanged, to examine the impact of changes in the amount of compound emulsifier on the performance of defoamer, the experimental results: the amount of emulsifier is too small, defoamer emulsion is not stable, easy to delamination. The amount of emulsifier is too large, defoamer emulsion stability, but the defoaming effect decreased. This is caused by two factors: First, the amount of emulsifier is too much and entrained air, resulting in emulsion particles being too small, which reduces the speed of defoaming; Second, the amount of emulsifier is too much, increasing the stability of the emulsion, the loss of defoaming performance. When the amount of compound emulsifier is less than 6%, at low concentrations, the stability of the defoamer emulsion with the number of compound emulsifiers increases, and the defoaming performance is enhanced; when the amount of compound emulsifier is greater than 6%, the stability of the defoamer does not change with the amount of change, but the defoaming performance is reduced. Experiments have proved that the amount of compound emulsifier is about 6%, when the defoamer defoaming effect is better, curbing more foam.
5 . The effect of thickening agents oil on the performance of silicone defoamer
In order to improve the stability of emulsions, adding thickeners is an effective way. Commonly used thickeners include sodium cunning methyl cellulose, ethyl cellulose, polyethylene glycol, sodium alginate, etc.
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