An emulsion is a stable and homogeneous mixture of two insoluble or very slightly compatible liquids. Generally, one of them is water, and the other is a water-insoluble liquid, such as mineral or vegetable oil or silicone.
When these two incompatible liquids are mixed, they form two phases. With vigorous stirring, they can be mixed, but once the stirring stops, they separate quickly, resulting in the recovery of the two initial phases. Under these conditions, we would refer to it as an unstable and heterogeneous mixture.
Silicone emulsions are chemical formulations composed of silicone, usually in the form of silicone oil, water, and the necessary emulsifying systems to achieve a stable emulsion.
From a chemical perspective, silicone consists of a finite chain of silicon and oxygen atoms bonded together. In addition to these bonds, silicone itself has two additional bonds to organic groups. In most cases, these organic groups are methyl (CH3) groups that give silicone oil its semi-organic characteristics.
Silicone oils are inert substances, stable in the presence of water, air, oxygen, and metals. They only decompose at high temperatures and in the presence of strong mineral acids, bases, and strong oxidizing agents.
In this document, we will explore the technical characteristics of silicone emulsions, as well as the different families that exist. After providing this general framework, we will focus on the characteristics of Concentrol’s silicone emulsions, as well as their sectors and applications.
Technical characteristics of silicone emulsions
Silicone emulsions allow for easy use of a silicone, allowing for better processing and better efficacy of the final product. The most important parameters in a silicone emulsion are:
- pH
The pH of silicone emulsions is generally not a critical parameter, since non-ionic emulsifiers are commonly used. Variations in pH do not destabilize the emulsion, but they can impact the final formulation where the emulsion is incorporated. To avoid the need for adjustments in the final product, silicone emulsions are typically adjusted to a neutral pH.
- Viscosity
Viscosity measures the fluidity of a silicone emulsion. Silicone emulsions made with silicone fluids have low or very low viscosities, typically below 1000cps, making them highly fluid products. A low viscosity is indicative of a well-emulsified product with small particle sizes.
- Dry extract
Dry extract, also known as solids, refers to the percentage of non-evaporative material in the emulsion after the drying process. The dry extract of a silicone emulsion is related to the quantity of the silicone content, which is the active component of this type of product. In general, silicone emulsions are formulated with a dry extract ranging between 20% and 60%.
- Filtration
Due to their low viscosity, silicone emulsions can be filtered through fine meshes, typically 250 microns or 100 microns. This characteristic allows for easy formulation in products like adhesives, varnishes, paints, or coatings without altering their desired properties.
- Stability
Well-manufactured silicone emulsions are stable products that can be stored for extended periods without separation or instability.
Certain silicone emulsions are capable of withstanding freeze-thaw cycles, making them suitable for use in very cold climates.
- Preservatives
Preservatives such as isothiazolinones (BIT, MIT and/or CMIT), formaldehyde releasers and other additives like bronopol are commonly used in silicone emulsions. Food preservatives such as sorbates and benzoates may be used in specific versions of silicone emulsions, resulting in an acidic pH.
- Particle size
Silicone emulsions typically have small particle sizes, which is directly linked to their stability. The smaller the particle size, the more stable the emulsion tends to be.
- Free monomer
Some silicone emulsions may contain free silicone monomers, which are volatile or semi-volatile compounds. These monomers can be analyzed using gas chromatography.
- Wetting
Silicones can sometimes cause wetting issues due to their inherent properties. When used in coatings, they may lead to uneven coverage or surface defects.
- Toxicity
Silicone oil, the main component of silicone emulsions, is not considered toxic or dangerous. Discharging silicone emulsions into wastewater typically does not pose significant problems, as the silicone settles with the purification sludge, resulting in non-classified residue.
Emulsion families
Silicone emulsions are classified into two groups based on particle size: silicone macroemulsions and silicone microemulsions.
Silicone macroemulsions, also referred to as ES-type silicone emulsions, exhibit the following characteristics:
- They have a whitish appearance and remain stable during storage. They are formulated with preservatives that ensure microbiological stability for over 6 months. The silicone content can vary.
- The average particle size ranges from 0.1 to 1 micron.
- These emulsions can contain up to 60% silicone.
- Various viscosities of silicone oil can be used in their formulation, with 350 cps and 1000 cps being the most common. A typical formulation has a dry extract of 35%, although a higher dry extract of 65% is also common.
- After application, once the water evaporates, the silicone remains on the external surface, offering benefits such as reducing the coefficient of dynamic friction and providing a lubricating effect.
Silicone microemulsions, also known as EMPOL-type silicone emulsions, possess the following characteristics:
- They have a translucent appearance and exhibit high stability, even in extreme conditions. They are formulated with preservatives that ensure microbiological stability for more than 6 months.
- These emulsions have a very small mean particle diameter, typically ranging from 0.5 to 0.2 microns.
- Silicone oil used in microemulsions generally has a very high viscosity, exceeding 100,000 cps. The dry extract is around 40%.
Concentrol silicone emulsions
Concentrol silicone emulsions offer several advantages when used as components in other chemical formulations. These advantages include:
- Good thermal and dilution stability.
- Compatible with soaps or anionic and non-ionic surfactants. Easy application, does not yellow after time.
- Good surface wetting characteristics.
- High brightness and color intensity.
- Good slip characteristics and improves abrasion resistance.
- Provides a natural finish to the textile fiber.
- It can be used as a lubricant in sewing machines to reduce needle temperature, thus improving wear resistance and minimizing thread breakage.
Sectors and applications of Concentrol’s references
Concentrol solutions can be used in different professional sectors, such as:
- Textile and leather
- Adhesive Manufacturers
- Paper manufacturers
- Inks
- Pressure sensitive adhesives
- Paintings
Silicone emulsions find various applications in different professional sectors, including:
- Polishing Additives
Silicone emulsions are used as additives in polish formulations. The high gloss and light-reflecting properties of silicone oils contribute to an enhanced shine on smooth surfaces. Emulsions are easily incorporated into formulations, and even in small dosages (<1%), they significantly increase the shine of the final polish product.
This characteristic is used in formulations such as metal polishes, where products such as EMULTROL ES-115-60 and EMULTROL ES-115-35 can be used.
- Anti-Seize Additives and Lubricants
Silicone oils’ non-stick properties make them suitable as anti-seize additives and lubricants. They can be used as mold release agents for plastics and polymers, such as rubber and polyurethane shoe soles or tires. Prior testing is recommended to ensure compatibility with the specific materials.
Silicone oils are also employed as lubricants to reduce friction and minimize heat generation between materials in prolonged and intense contact. They are commonly used in conveyor belts as lubricating and anti-adherent agents, ensuring minimal silicone residue remains on the belt.
- Hydrophobic Additives
Silicone emulsions can increase the hydrophobicity of a product due to the insolubility of silicones in water. Incorporating silicone into a formulation enhances its resistance to water. However, it’s important to note that the hydrophobic character provided by silicone emulsions is temporary, as it depends on the balance between the silicone oil’s hydrophobicity and the hydrophilicity of the emulsifiers used.
- Additives in Textile Formulations and Skin Treatment
Silicone emulsions are utilized to achieve various characteristics in textiles and skin treatments, including wear resistance, hydrophobicity, gloss enhancement, and softness. They provide an elastomeric finish to textile fibers, imparting a natural and soft touch. In oven-cured fabrics, silicone emulsions increase resistance to elongation. They are also employed in high dilution for ironing facilitation, thanks to their softening and lubricating effects. In leather treatment, silicone emulsions with high thermal stability enhance abrasion resistance and provide shine in final aqueous formulations. They are also used to improve slip and create a greasy finish in leather treatment without leaving residue or staining.
Concentrol ranges EMULTROL ES and EMULTROL PS are commonly used in these applications.
- Additives in Adhesive Formulations, Particularly Pressure-Sensitive Adhesives:
Silicone emulsions find use in adhesive formulations, particularly in the production of self-adhesive paper. The small particle size of silicone emulsions allows for good wetting of the liquid adhesive when applied to paper. This is crucial in industrial-scale processes where a minimal amount of adhesive is applied at high speed with low thickness. Good wetting ensures high process efficiency.
EMULTROL PS and EMULTROL ES emulsion references are commonly employed in adhesive applications.
Concentrol is a company dedicated to innovation in chemistry, aiming to create value and ensure the well-being of society both now and in the future. The professionals at Concentrol are committed to continuous improvement, constantly working to enhance their existing products and develop new ones that address the real needs of various professional sectors.
