An Analysis of Knowledge on Silicone Oil and Low-Hydrogen Silicone Oil

　　Commonly used silicone oils feature entirely methyl organic groups and are therefore referred to as methyl silicone oils. However, other organic groups can also replace部分 of the methyl groups to enhance specific properties of the silicone oil, making it suitable for a broader range of applications. Popular alternative organic groups include hydrogen, ethyl, phenyl, chlorophenyl, and trifluoropropyl. In recent years, organically modified silicone oils have seen rapid advancements, leading to the development of many specialty silicone oils with unique and improved performance characteristics.
　　Anionic hydroxyl emulsions are distinguished by their excellent compatibility with fabric finishing agents and their highly stable emulsion properties. Notably, most auxiliaries used in textile printing and dyeing are anionic in nature; however, when cationic hydroxyl emulsions are employed, they often lead to emulsion breakdown and oil floating—a common issue that can be effectively prevented with anionic hydroxyl emulsions. As a result, anionic hydroxyl emulsions have become increasingly popular among users and are now finding applications across a wide range of industries.
　　Silicone oil is typically a colorless (or pale yellow) liquid that is odorless, non-toxic, and highly resistant to evaporation. It is insoluble in water, methanol, glycols, and ethoxyethanol, but readily miscible with solvents such as benzene, dimethyl ether, methyl ethyl ketone, carbon tetrachloride, or kerosene. It exhibits very low vapor pressure, along with high flash and ignition points, and a relatively low freezing point. As the number of chain segments (n) varies, the molecular weight increases, leading to a corresponding rise in viscosity. This allows silicone oil to be formulated across a wide range of viscosities—ranging from as low as 0.65 centistokes all the way up to over one million centistokes. To produce low-viscosity silicone oil, an acidic white clay can be used as a catalyst, followed by polycondensation at 180°C. Alternatively, sulfuric acid can serve as the catalyst for polycondensation at lower temperatures, enabling the synthesis of higher-viscosity oils or even viscous materials.
　　Silicone oils, classified by their chemical structure, include methyl silicone oil, ethyl silicone oil, phenyl silicone oil, methyl hydrogen silicone oil, methylphenyl silicone oil, methyl chlorophenyl silicone oil, methyl ethoxy silicone oil, methyl trifluoropropyl silicone oil, methyl vinyl silicone oil, methyl hydroxy silicone oil, ethyl hydrogen silicone oil, hydroxy hydrogen silicone oil, cyano-containing silicone oil, and low-hydrogen silicone oil, among others. When categorized by application, they encompass damping silicone oil, diffusion pump silicone oil, hydraulic oil, insulating oil, heat-transfer oil, brake fluid, and more.
　　Silicone oil boasts exceptional heat resistance, electrical insulation, weatherability, hydrophobicity, physiological inertness, and low surface tension. Additionally, it exhibits a low viscosity-temperature coefficient and high compressibility—some grades even offer radiation resistance.
　　Jiangxi Huahao Chemical Co., Ltd. is located in Xinghuo Industrial Park. Established in November 2011, the company occupies over 30 mu of land. The first-phase project, completed and put into operation in 2014, has an annual production capacity of 4,500 tons of organic silicon products, including hydroxyl silicone oil, dimethyl silicone oil, low-hydrogen silicone oil, polyether-modified silicone oil, and 107 adhesive. In 2017, the company expanded its downstream organic product portfolio by introducing vinyl silicone oil, amino silicone oil, and various silane derivatives, such as methyl trimethoxy silane, methyl triethoxy silane, and methyl silicate. At the same time, it further diversified its hydrogen-containing silicone offerings, adding not only side-hydrogen products but also enhancing its lineup with end-hydrogen and other advanced hydrogenated structures. Currently, the company is actively exploring high-boiling silicone oils that can partially replace traditional methyl silicone oil. In 2018, the third phase of the facility began operations, producing a range of innovative products, including heptamethyl trisiloxane, polyether-modified silicone oil, silazanes, silicone ethers, and dimethyldiethoxy silane.
　　Silicone emulsion
　　Silicone emulsions are a form of silicone oil. Below, we’ll explore their applications as both silicone oil-based fabric softeners and silicone oil emulsion-type defoamers.
　　I. Silicone Oil Fabric Softening Agent
　　Silicone emulsions are primarily used as silicone oil-based softening agents for fabric finishing. The first-generation silicone fabric finishers were mechanically mixed formulations of dimethyl silicone oil and hydrogen-containing silicone oils (along with their derivatives). In contrast, the second-generation silicone fabric finishers consist of hydroxyl-terminated polydimethylsiloxane emulsions, produced via emulsion polymerization under specific conditions using raw materials such as octamethylcyclotetrasiloxane monomer, water, emulsifiers, and catalysts. Because this polymerization and emulsification process is completed in a single step, it offers significant advantages, including shorter processing times, higher efficiency, simpler equipment requirements, and easier operation. Moreover, the resulting emulsion is highly stable, with uniformly sized particles. Importantly, the polymers produced feature reactive hydroxyl groups at both ends, enabling them to further crosslink into a film—a capability that surpasses what can be achieved with conventionally mechanically emulsified silicone oils.
　　Hydroxy silicone oil emulsions can be further classified into several types—such as cationic, anionic, non-ionic, and complex ionic—depending on the surfactant used.
　　1. Cationic Hydroxy Silicone Oil Emulsion
　　The emulsifiers typically used in cationic hydro-emulsion polymerization are quaternary ammonium salts (with overseas literature citing octadecyltrimethylammonium chloride as the preferred choice), while ammonium hydroxide serves as the catalyst. Cationic hydro-emulsions are widely applied in the post-treatment of various textiles, offering benefits such as enhanced fabric hand feel, improved elasticity, and superior smoothness and crispness. Additionally, these emulsions boast a unique advantage: they act as an ideal waterproofing agent for fabrics. When combined with methylhydrogen silicone oil emulsions, the resulting treatment delivers exceptionally high levels of both water repellency and long-lasting waterproof performance. This makes them particularly suitable for use as waterproofing agents in applications like vinyl-covered canvas tarps or polyester-cotton blend fabrics.
　　2. Anionic Hydroxyl Silicone Oil Emulsion
　　Anionic hydroxyl emulsions are characterized by their excellent compatibility in fabric finishing agents and their highly stable emulsion properties. Notably, most auxiliaries used in textile printing and dyeing are anionic in nature; however, when阳离子型羟乳 is employed, it often leads to emulsion breakdown and oil floating—a common issue that can be effectively avoided with anionic hydroxyl emulsions. As a result, anionic hydroxyl emulsions have become increasingly popular among users and find applications across a wide range of industries.
　　3. Composite Ionic Hydroxyl Silicone Oil Emulsion
　　Although cationic hydroxy emulsions are excellent fabric softening agents, they are incompatible with hard water and cannot be used in the same bath as 2D resin (dimethylol dimethyl hydantoin), magnesium chloride catalysts, or anionic optical brighteners. This limits their practical applications to some extent. Additionally, due to poor emulsion stability, silicone polymers tend to separate from the formulation, floating on the liquid surface—a phenomenon commonly known as "oil floating." However, by carefully blending cationic and non-ionic emulsifiers during the emulsion polymerization process, it’s possible to overcome the drawbacks of using solely cationic emulsifiers to produce hydroxysilicone oil emulsions. The resulting silicone emulsion not only remains stable in hard water but also allows for seamless compatibility with 2D resins, magnesium chloride, and optical brightener VBL, while maintaining outstanding heat resistance and freeze-thaw stability.
　　4. Non-ionic Hydroxy Silicone Oil Emulsion
　　Non-ionic hydroxyl emulsions are more versatile and exhibit superior stability compared to ionic hydroxyl emulsions, which is why many countries are actively investing in research related to non-ionic formulations. For instance, Switzerland has introduced a new product called UltrateX FSA—a non-ionic emulsion based on hydroxyl-terminated polydimethylsiloxane with a molecular weight exceeding 200,000—marking a significant advancement over the anionic hydroxyl emulsion Dc-1111 developed by the U.S.
　　5. Other Active-Group Silicone Finishes
　　To meet the demands of advanced finishing for various types of fabrics, silicone researchers have been exploring ways to enhance the oil-repellent, antistatic, and hydrophilic properties of silicone-treated textiles. Additionally, they aim to equip synthetic fibers with many of the desirable qualities found in natural fabrics. To achieve these goals, silicone chemists have introduced other reactive functional groups—such as amino, amide, ester, cyano, carboxyl, and epoxy groups—into silicone molecules. The incorporation of these functional groups imparts unique performance characteristics to silicone-based fabric finishes. For instance, introducing amino groups into silicone molecules is particularly effective for shrinkage control and softening treatments of woolen fabrics. Meanwhile, adding amide groups not only enhances stain resistance but also significantly improves the fabric’s softness. The inclusion of cyano groups boosts oil repellency, while copolymers combining polyethylene oxide ether with silicone deliver outstanding antistatic performance. Moreover, organosilicon compounds modified with organic fluorine exhibit exceptional advantages, including oil and stain resistance, antistatic properties, and water-repellent capabilities.
　　II. Silicone Oil Emulsion-Type Defoamer
　　Silicone oil emulsion-type defoamers are typically oil-in-water (O/W) emulsions, where water serves as the continuous phase and silicone oil is the dispersed phase. The process begins with pre-mixing silicone oil, emulsifiers, and thickening agents, followed by gradually adding water while continuously stirring. The mixture is then repeatedly refined in a colloid mill until an emulsion meeting the desired specifications is achieved.
　　Silicone oil emulsion-based defoamers are among the most widely used and heavily applied types of silicone defoamers. They are characterized by their ease of dispersion in aqueous systems, making them ideal for use as defoamers in water-based applications. To achieve optimal defoaming performance, simply add the emulsion directly to the foaming system. To enhance the defoaming efficiency of the emulsion and ensure precise dosing, it’s generally recommended not to use concentrated silicone oil emulsions with a solids content exceeding 10%. Instead, dilute the emulsion with cool water or the actual foaming liquid itself until the concentration drops below 10% before adding it to the system. Avoid using excessively hot or cold liquids for dilution, as this can lead to emulsion breakdown and phase separation (also known as "oil floating"). Once diluted, the emulsion tends to become less stable, potentially resulting in layering or even complete demulsification during storage. Therefore, it’s best to use the diluted emulsion as soon as possible. If necessary, a thickening agent can be added to improve the emulsion’s stability. For intermittent processes, silicone oil emulsions can either be added all at once before the system starts operating or replenished gradually in batches. In continuous operations, however, the emulsion should be introduced steadily—or intermittently—at an appropriate point within the system to maintain consistent defoaming performance.
　　When using emulsion-type defoamers, it’s especially important to consider the temperature and pH conditions of the foaming system, as silicone oil emulsions are quite sensitive. If these conditions exceed the emulsion’s recommended range, the emulsion may prematurely break down, rendering it ineffective or even useless. (Typically, the dosage of silicone oil emulsion ranges from 10 to 100 ppm by weight of the foaming liquid—calculated based on the silicone oil content.) Of course, in special cases, concentrations may fall below 10 ppm or exceed 100 ppm. Ultimately, the optimal dosage is best determined through experimentation.
　　Most general silicone oil emulsion-based defoamers are oil-in-water types. Depending on the specific type of silicone oil used, silicone oil emulsion defoamers can be categorized into the following types:
　　1. A silicone oil emulsion based primarily on dimethyl silicone oil
　　This type of defoamer is formulated from dimethyl silicone oil combined with emulsifiers and water, and it can be widely used in applications such as fermentation, food processing, papermaking, textiles, pharmaceuticals, and synthetic resins.
　　2. A silicone oil emulsion based primarily on methyl ethoxy silicone oil
　　This type of defoamer is made from methyl ethoxy silicone oil and compounding agents.
　　3. Silicone oil emulsion with ethyl silicone oil as the main component
　　In recent years, silicone defoamers have been evolving toward a direction that combines silicone with polyether block (or graft) copolymers. These types of defoamers leverage the unique properties of both silicones and polyethers, significantly enhancing their defoaming performance. Silicone-polyether copolymer defoamers, also known as self-emulsifying silicone defoamers, incorporate hydrophilic ethylene oxide or ethylene oxide-propylene oxide chains into the silicone molecular backbone via block (or graft) copolymerization. This clever design seamlessly links the hydrophobic siloxane segment with the hydrophilic polyether chain, resulting in molecules with enhanced polarity. As a result, these defoamers exhibit excellent spreading properties, allowing them to disperse uniformly throughout the foaming medium—leading to superior defoaming efficiency. They represent a new generation of highly effective defoamers. Notably, these self-emulsifying silicone oils eliminate the need for emulsifiers altogether, delivering defoaming performance that is particularly satisfying for certain applications. They are especially well-suited for scenarios where conventional silicone oil emulsions either fail to perform adequately or are simply unsuitable due to process constraints.