Polyether modified silicone oil, also known as polyether modified polysiloxane, is the most produced and widely used type of modified silicone oil in the organosilicon industry. Because its molecular structure contains both hydrophobic and hydrophilic groups, polyether modified silicone oil exhibits surfactant properties.
Structural types of polyether silicone oil
(1) Side chain type (the most common type)
(2) Two-end type
(3) Side chain, two-end type
(4) One-end type
In the polyether unit C2H4O)a(C3H6O)bR, there is a balance between hydrophilicity and hydrophobicity between a and b.
To maintain its surface activity, the ratio of b/(a+b) is generally controlled between 0.2 and 0.8. That is, when b/(a+b) is less than 0.2, the hydrophilicity is strong, and the hydrophilic-lipophilic balance (HLB) value is large; when b/(a+b) is greater than 0.8, the hydrophobicity is strong, and the HLB value is small. The average molar mass of the polyether segments is generally controlled between 500 and 5000 g·mol⁻¹. Below 500 g·mol⁻¹, the surface activity cannot be fully realized, while above 5000 g·mol⁻¹, the viscosity is too high, leading to poor dispersibility.
Application areas of polyether silicone oil
One. Polyurethane foam stabilizer
Also known as a foam leveler.
In the formulation of polyurethane foam materials, the addition amount is 0.5%~2.0% of the polyol. It has four functions:
1. It acts as an emulsifier during the mixing of the compound.
The main raw material, polyether polyol, has poor compatibility with isocyanate. The hydrophobic groups of the polyether-modified silicone oil are soluble in isocyanate, while the hydrophilic groups are soluble in polyether polyol, thus aiding in the mixing and emulsification of the two components. This allows the reaction to begin simultaneously throughout the entire system.
2. This facilitates bubble formation and homogenization.
It lowers the surface tension of the reaction system, allowing air to disperse in the system as uniform, fine bubbles, forming tiny bubble nuclei. The carbon dioxide produced in the reaction system and the gas generated by the foaming agent easily enter the bubble nuclei to form bubbles, and the low surface tension of the system at this time is conducive to bubble growth.
3. It stabilizes the bubbles.
Before the system viscosity reaches a certain level, the formed bubble nucleus-liquid film is very thin. Due to drainage, coalescence, and mechanical impact, the bubble walls can rupture. At this point, polyether-modified silicone oil can stabilize the bubble nuclei through the Gibbs-Marangoni effect, effectively reducing leakage from the bubble walls and preventing bubble coalescence. Furthermore, the nonionic nature of polyether-modified silicone oil can reduce the van der Waals forces between the two film surfaces at the gas-liquid interface, also contributing to bubble stability.
4. The final stage of polyurethane flexible foam formation is the interconnection of the bubble cores.
Before the bubble cores have fully expanded, they are closed polyhedra in the reaction system. Just before gelation occurs, the rising temperature and increased internal pressure can cause the bubble core walls to rupture and open up pores. The role of polyether-modified silicone oil is to stabilize the wall film during the low viscosity phase and to allow the film to reach the critical thickness for opening pores, thus creating conditions for the final opening.
Polyether-modified silicone oil is the most effective stabilizer in the one-step production of polyurethane flexible foam.
The polyether-modified silicone oil used in rigid foam materials has a lower molar mass than that used in flexible foam materials, a larger C2H4O to C3H6O ratio in the polyether segments, and a higher cloud point.
Rigid foam materials use a wide variety of raw materials, including polyether polyols and isocyanates, resulting in diverse foaming formulations. Furthermore, to enable on-site foaming, they are typically produced in a two-component blend form, requiring long-term storage. Therefore, the foam stabilizer must be a non-ionic polyether-modified silicone oil, generally added at a ratio of 0.5 to 1.5 parts polyether polyol to 100 parts polyether polyol. The foaming formulation is adjusted according to the foaming conditions.
In semi-rigid foam materials, stabilizers prevent bubble shrinkage and regulate bubble size.
High-resilience polyurethane foams have high viscosity and low crosslinking degree due to the use of highly reactive α-hydroxy polyols and lower curing temperatures, making the bubbles easily stabilized. Therefore, stabilizers with lower molecular weights and less stabilizing effects should be selected, such as low-molecular-weight polyether-modified silicone oils. Using general-purpose flexible foam polyether-modified silicone oils can lead to excessive foam stabilization, reduced foam connectivity, and ultimately, foam shrinkage.
Polyether-modified silicone oil is used as a stabilizer for polyurethane foam. It is very important that it is free of Si-H groups, as the presence of residual Si-H groups will affect the micropore size and uniformity of the foam.
Two. Cosmetic Raw Materials
Polyether-modified silicone oil is readily soluble in alcohols and water, and is also easily compatible with other cosmetic ingredients.
When added at 0.15% to 5%, it can reduce the surface tension of cosmetic formulations, promoting the diffusion of cosmetics onto the skin or hair surface.
It is widely used in shampoos, conditioners, mousses, skin care products, shaving products, antiperspirants, perfumes, soaps, and color cosmetics. Adding a small amount of polyether-modified silicone oil to hair formulations can impart shine, manageability, smoothness, antistatic properties, and a pleasant feel to the hair.
Polyether-modified varieties with lower HLB values can be used as emulsifiers in silicone oil complex systems. For example, in skin care cream formulations, using polyether-modified silicone oil as an emulsifier can emulsify low-viscosity methyl silicone oil with water to form a stable dispersion system. This formulation is non-irritating to the skin and safe to use.
This type of polyether-modified silicone oil can be prepared by hydrosilylation reaction of dimethyl silicone oil with a Si-H terminal group and an allyl-terminated polyether.
Three. Coating additives
1. Defoamers
Polyether-modified silicone oil readily emulsifies in water and is a major component of self-emulsifying defoamers. Polyether-modified silicone oil loses its water solubility and exhibits defoaming properties above its cloud point temperature.
Defoamers formulated with polyether-modified silicone oil exhibit good heat resistance and mechanical stability, and are resistant to acids, alkalis, and inorganic salts, making them suitable for defoaming under harsh conditions.
Examples of defoaming include high-temperature dyeing processes for polyester fabrics, defoaming in diethanolamine aqueous solution desulfurization systems, and defoaming in various oils, cutting fluids, antifreeze, and other systems.
Especially in the printing industry, after photosensitive resin plate making, a strong aqueous solution containing inorganic alkaline salts such as sodium borate and surfactants is used to wash away the uncured resin. The foam generated by the washing solution under high shear force severely affects the cleaning efficiency. Polyether-modified silicone oil is a very suitable defoamer. If a defoamer formulated with ordinary dimethyl silicone oil is used, its defoaming effect will decrease under prolonged shear force, promoting foaming and leaving dimethyl silicone oil residue on the plate, thus affecting the quality of the plate.
2. Polyether-modified silicone oil is a major leveling agent and slip agent in water-based coatings.
3. Polyether-modified silicone oils with epoxy groups at the ends of the polyether chain can improve the recoatability of the same coating and enhance the coating's resistance to hot water, steam, and scratches. They can be prepared by hydrosilylation reaction of polyethers with allyl groups at one end and epoxy groups at the other with Si-H-containing polyorganosiloxanes.
Four. Pesticide Wetting Agents
Low molar mass polyether-modified silicone oil can significantly reduce the surface tension of its aqueous solution. When used as a pesticide wetting agent, it can improve the adhesion of pesticides to plant leaves in rainy weather and reduce the amount of pesticide used.
Five. Resin Modifier
The polyether segments in polyether-modified silicone oil molecules can improve its compatibility with resins, form a uniform dispersion in the resin, improve the fluidity of the resin during melting, enhance the lubricity between metals and plastics, and significantly improve the extrudability of plastics.
It can also promote the formation of micro-dispersions of inorganic materials in plastics, especially the dispersion effect of titanium dioxide, calcium carbonate, etc.
However, conventional polyether-modified silicone oils typically contain 1% to 20% residual polyether compounds by mass, which can affect the mechanical strength and solvent swelling properties of the modified resin. A solution is to use a single-terminated allyl polyether with a smaller molar mass to undergo a hydrosilylation reaction with methyl hydrogen-containing silicone oil, and then evaporate the unreacted polyether from the resulting polyether-modified silicone oil under high vacuum.
Six. Fabric finishing agents
Textiles made of synthetic fibers or cotton exhibit strong hydrophobicity after resin processing, while finishing with polyether-modified silicone oil can impart hydrophilicity, sweat absorption, and antistatic properties.
When durability is required, the hydrophobic segments of the polyether-modified silicone oil molecule can be replaced with Si-H groups or alkoxy groups.
When softness and smoothness are required, the hydrophobic segment can be replaced with epoxy-modified or amino-modified organosilicon groups.
Seven. Used in the formulation of water-based release agents
Aqueous dispersions of polyether-modified silicone oil with a cloud point of 25℃~50℃ can be used as release agents for polyurethane foam molding and injection molding.
Aqueous dispersions of polyether-modified silicone oil and perfluoroalkyl phosphoric acid can be used as release agents for epoxy resin molding.
Aqueous dispersions of polyether-modified silicone oil and dimethyl silicone oil can be used as release agents for the molding and processing of plastics, rubber, paper products, and metal products.
EIGHT. Latex heat sensitizer
Latex heat sensitizers are gelling agents suitable for use with latex.
When this gelling agent is added to latex, it is relatively stable at room temperature; however, when the temperature rises to a certain value, the latex quickly solidifies, and this type of latex is called heat-sensitized latex.
Using polyether-modified silicone oil as a heat sensitizer for both natural and synthetic rubber latexes results in very stable latex below its cloud point temperature, providing a long shelf life; when heated to the cloud point temperature, the latex solidifies rapidly with a small temperature range, and the solidified gel exhibits excellent properties.
Heat-sensitized latexes formulated with polyether-modified silicone oil are widely used as adhesives for non-woven fabrics and artificial leather base fabrics.
