Characteristics and Application of Silicone Defoamer


There are many kinds of commercial defoamers at home and abroad, and their performances are different. At present, there are roughly three kinds of defoamers commonly used, namely polyether, silicone oil and silicone ether mixtures.


1. Polyether defoamer


Ordinary organic compounds, such as ethers, hydrocarbons, alcohols and phosphate esters, have larger spreading coefficients, so they have strong foam-breaking effect, but poor foam-inhibiting effect. Polyether prepared by ring-opening polymerization of ethylene oxide and propylene oxide is an excellent water-soluble non-ionic surfactant with the typical structure of CnH2n+1O(EO)a(PO)bH. The polyethylene oxide segment is hydrophilic and the polypropylene oxide segment is hydrophobic. When the content of ethylene oxide exceeds 25%, polyether dissolves in water. The cloud point is the index to characterize the water solubility of polyether. By adjusting the ratio of ethylene oxide to propylene oxide, surface active agents with different hydrophilic-lipophilic equilibrium values (HLB) can be prepared, and the desired surface activity can be obtained. By adjusting the EO/PO ratio and relative molecular weight, the water solubility and oil solubility of the foam can be improved, the surface tension of the foam can be greatly reduced, and the foam can be defoamed and restrained. The biggest advantage of polyether defoamer is its strong anti foaming ability, so it is the main defoamer used in the fermentation industry. However, it has a fatal shortcoming that is low bubble breaking rate. Once a large amount of foam is produced, it can not extinguish effectively, but requires a new amount of defoamer to solve the problem slowly.


2. Silicone oil defoamer


Simple organic silicon, such as dimethyl silicone oil, has no defoaming effect. However, after emulsification, the surface tension decreases rapidly, and a very small amount of emulsifier can achieve strong foam breaking and anti-foaming effect, which becomes an important component of defoamer. Silicone oil defoamer generally has high defoaming efficiency, the key to its use is the emulsification of silicone oil. If the emulsification is incomplete, it will be demulsified in use, which will affect its use effect. Organosilicon defoamers are widely used because of their strong defoaming ability. Especially, siloxane has the characteristics of chemical stability, physiological inertia and good high and low temperature performance. Because silicone oil is oil-affinity, the defoaming effect of oil-soluble solution is satisfactory.


Silicone defoamer is a kind of defoamer with low toxicity, strong antioxidant and foam breaking ability, but its anti-foaming ability is poor, its consumption is large, its effect on slightly acidic fermentation is poor, and it also has a certain inhibitory effect on mycelial development. Therefore, the application in fermentation industry is limited to a certain extent; in textile printing and dyeing industry, especially in light-colored fabrics, because silicon spots are not easy to clean and once restricted.

3. Polyether Modified Silicone Defoamer


Polyether modified organosilicon is a Polyether-siloxane copolymer prepared by introducing polyether segments into the siloxane molecule. Polyether modified organosilicon defoamer is a new efficient defoamer which organically combines the advantages of both. It is a defoamer composed of polyether with strong anti-foaming ability and dimethyl silicone oil with strong hydrophobicity and rapid defoaming, emulsifier and stability which can organically combine silicone oil with polyether. It has the characteristics of low surface tension, rapid defoaming, long antifoaming time, low cost, less consumption and wide application. Polyether modification of organosilicon makes it have the advantages of second class defoamer, and becomes a kind of defoamer with excellent performance and wide application prospect.


The siloxane segment is an oleophilic group and the polyether segment is a hydrophilic group in the molecule of the silicone ether copolymer. Polyethylene oxide chain in Polyether Segment provides hydrophilicity and foaming, and polypropylene oxide chain provides hydrophobicity and permeability, which has a strong effect on reducing surface tension. The groups at the end of polyether chain also have a great influence on the properties of silicone ether copolymers. Common terminal groups are carboxyl, alkoxy, etc. By adjusting the relative molecular weight of siloxane segments in copolymers, the physical properties of organosilicon can be highlighted or weakened. Similarly, changing the relative molecular weight of the polyether segment will increase or decrease the proportion of organosilicon in the molecule and affect the properties of the copolymer. Silicone has been used as a defoamer in spray dyeing and has been reported in many literatures. In the old dyeing process, dimethylpolysiloxane defoamer is generally used to achieve satisfactory defoamer effect and ensure uniform dyeing. But the new dyeing process uses high-temperature and high-pressure machinery, in which dyes are sprayed by dye solution and then dyed at the same time. Although the resulting foam can be defoamed by ordinary silicone defoamer, at high temperature and high pressure, the general silicone defoamer will produce thin film precipitates and stain the stain. The application of block copolymers overcomes the above shortcomings, because these defoamer components can be dissolved in cold water, but not in hot water, so they can defoam. However, the defoaming effect of the copolymer defoamer is not satisfactory. If a certain amount of foggy SiO 2 is added to the copolymer, the satisfactory defoaming effect can be achieved and the uniform dyed fabric can be produced. Polyether modified silicone defoamer is easy to emulsify in water, also known as "self-emulsifying defoamer". When the cloud point temperature is above, it loses water solubility and mechanical stability, and can resist acid, alkali and inorganic salt. It can be used for defoaming under harsh conditions. It is widely used in high temperature dyeing and fermentation of polyester fabrics. In addition, it can also be used for defoaming of diethanolamine desulfurization system and various oil agents, cutting fluids, non-freezing liquids, water-based ink systems. It can also be used for defoaming of non-cured resin after photosensitive resin plate-making in printing industry. It is a representative silicone defoamer with excellent performance and wide application. In order to improve the lipophilicity of water-based ink, paint and cutting fluid, long chain alkyl substitution of methyl group in polyether modified silicone copolymer molecule can play a more effective defoaming effect. In order to have better defoaming property below cloud point temperature, commercial self-emulsifying defoamers are usually equipped with dimethyl silicone oil-silica paste. At this time, polyether modified silicone surfactants can also be used as emulsifiers of dimethyl silicone oil to disperse and emulsify.