Silicone oil, a linear polysiloxane product that is liquid at room temperature, is colorless (or light yellow), odorless, non-toxic and non-volatile. It is insoluble in water, methanol and ethylene glycol, but is miscible with substances such as benzene, dimethyl ether, carbon tetrachloride and kerosene, and is also slightly soluble in acetone, dioxane, ethanol and butanol.
Silicone oil can be divided into many types according to its chemical structure, including methyl silicone oil, ethyl silicone oil, etc. At the same time, it also has many applications, such as damping silicone oil, diffusion pump silicone oil, hydraulic oil, etc. In addition, according to the processing conditions, silicone oil can be divided into primary products and secondary products. The former mainly refers to silicone oil products before processing, while the latter is a product such as grease, emulsion and solution made from silicone oil as raw material through a specific process.
In the market, silicone oil usually appears in three basic forms: pure silicone oil, solution or emulsion. They are often not used alone, but combined with other ingredients through special formulas to produce specific application effects.
○ 100% pure silicone oil
Pure silicone oil is known for its excellent stability. It is heat-resistant and frost-resistant, has excellent storage performance, and has high flash point and fire point, which greatly reduces the safety risks during storage and transportation.
○ Solution
Although silicone oil solutions usually need to be diluted before use, users may face some difficulties in preparing solutions by themselves. In this case, adding active auxiliary agents (such as catalysts, cross-linking agents, etc.) can improve its storage and use performance. When selecting solvents, aliphatic, aromatic or chlorinated hydrocarbon solvents are usually preferred, but other types of solvents may also be used in special cases. It is worth noting that the concentration of high molecular weight polysiloxane solution should not be too high, otherwise it may cause excessive viscosity.
○ Emulsion
Emulsion is a common form of silicone oil or silicone oil-containing products. Compared with solvent silicone oil, silicone oil emulsion has the advantages of low price, non-flammable and harmless to health. All silicone emulsions are "oil-in-water" (O/W) heterogeneous systems, in which silicone oil is dispersed in the aqueous phase in the form of extremely fine droplets, making the emulsion easy to dilute with water to the desired concentration. The stability of this emulsion can be achieved by reducing the droplet size and utilizing the stabilizing effect of the emulsifier.
In addition, silicone oil has many unique properties, such as good heat resistance, good oxidation stability and weather resistance, good electrical insulation, good hydrophobicity, low viscosity-temperature coefficient and high compression resistance. These properties make silicone oil perform well in many applications, such as damping equipment, hydraulic oil and cosmetics.
Due to the helical structure of silicone oil molecules and the relatively large distance between molecules, silicone oil has excellent compression resistance. Based on this property, silicone oil is cleverly used as a liquid spring, and its volume can be significantly reduced compared to traditional mechanical springs.
○ Low surface tension
Silicone oil has the characteristics of low surface tension, which makes it have excellent defoaming and anti-foaming properties, isolation properties from other substances, and lubrication properties.
○ Non-toxic, odorless and physiologically inert
From a physiological point of view, siloxane polymers are one of the least active known compounds. Dimethyl silicone oil is inert to organisms and has no rejection reaction with animal bodies, so it is widely used in surgery, internal medicine, medicine, food and cosmetics.
○ Excellent lubricity
Silicone oil has many advantages as a lubricant, such as high flash point, low freezing point, thermal stability, viscosity stability, no corrosion to metals, and no adverse effects on rubber, plastics, coatings and organic paint films. In addition, its low surface tension and good spreading properties on metal surfaces further enhance its lubrication effect.
○ Chemical properties
Although silicone oil is relatively inert overall, the Si-C bond is not stable under certain conditions (such as reaction with strong oxidants at high temperatures). At the same time, silicone oil reacts violently with chlorine, especially methyl silicone oil, and sometimes even explosive reactions occur. On the other hand, Si-O bonds are susceptible to chain scission by strong bases or acids. Under the action of concentrated sulfuric acid, siloxane chains break and attach to them. However, silicone oils with high alkane groups and phenyl groups show relative stability in this regard.
Regeneration of silicone oil
After long-term use, silicone oil may deteriorate due to oxidation and impurity intrusion. Since silicone oil is expensive, it needs to be recovered and regenerated separately. Waste silicone oil is usually regenerated by two methods: one is adsorption refining treatment, which is suitable for waste silicone oil in electrical equipment; the other is vacuum degassing or nitrogen stripping at a certain temperature to purify the regenerated silicone oil.
Another treatment method is to use solvent vapor to treat liquid waste silicone oil. In this process, the solvent will produce a dissolving effect when condensed, thereby dissolving and extracting impurities in the waste silicone oil, and then forming another liquid phase that is immiscible with the silicone oil. This method is particularly effective and can be used to dissolve and remove harmful substances such as polychlorinated polycyclic aromatic hydrocarbons (PCBs) in waste silicone oil. Subsequently, trace amounts of solvent that may remain in the treated silicone oil can be further removed by vacuum drying. In this process, commonly used solvents include hydrocarbon solvents and chlorinated hydrocarbon solvents.
