PEG-90 is the INCI systematic name, i.e. the International Nomenclature of Cosmetic Ingredients, for a chemical substance which is a synthetic polymer, also known as polyethylene glycol. The abbreviation PEG indicates the chemical origin of the substance, i.e. ‘polyethylene glycol’, while the number in the second part of the name tells us the average number of characteristic particles with the semi-structural formula -CH2-CH2-O-. The number 90 therefore means that during the production of this substance, glycerol was oxyethylated with ninety moles of ethylene oxide. PEG-90 is a representative of a large group of synthetic ethylene glycol ethers, polymers with a wide range of applications.

Due to their widespread use, PEGs have been extensively studied, their toxicological profiles are well known, and studies show that they do not have mutagenic or genotoxic effects. The product is not classified according to Regulation (EC) No 1272/2008 [CLP/GHS] and is therefore not considered to pose a risk to human health or the environment. PEG-90 is considered a safe cosmetic ingredient and has been approved by both the European Union and the U.S. Food and Drug Administration (FDA). The CAS global chemical substance identification number for PEG-90 is: 25322-68-3.

Properties

PEG-90 is a water-soluble polymer with a high molecular weight (4000 units, on average) derived from ethylene oxide. The basic properties characteristic for the substance are a boiling point above 200 degrees Celsius and a melting point determined at -50 degrees Celsius. At room temperature, PEG-90 is therefore a clear, colourless liquid with high viscosity. The pH of an aqueous solution of the substance is neutral or slightly acidic, ranging from 5.0 to 7.0 on the 14-point scale used to determine the acidity or alkalinity of aqueous solutions.  As a commercial product, it is available in the form of wax, offered in the form of pastilles. Its colour can be described as white to light yellow.

The freezing point of the product is approximately 55 degrees Celsius. PEG-90 is highly soluble in water and other solvents, such as low aliphatic alcohols, ethyl ether and chloroform. It has many characteristics of an ideal solvent – it is very mild, dissolves perfectly in water, and as a non-ionic polymer, it is also compatible with many commonly used ingredients in cosmetic formulations. It has the ability to attract water molecules, but also to release them when applied to the skin or hair. Due to the large number of reactive particles in its structure, it stabilises many other reactive groups derived from other ingredients in the formulation. This makes PEG-90 an excellent stabilising ingredient.

Preparation

PEG-90 on an industrial scale is synthesised by polymerising ethylene oxide using a catalyst, which is usually an alkali metal hydroxide or alcohol. The process involves the repeated addition of moles of ethylene oxide to form a long chain of repeating units until a polyethylene glycol with ninety moles of this oxide is formed. The synthesis of polyethylene glycol occurs with ring opening, which allows for a wide range of molecular weights and polydispersity, i.e. molecular weight distributions. Production of these substances can take place in various geometries – linear, branched, Y-shaped and multi-armed. PEGs can be activated by replacing the terminal hydroxyl group with various reactive functional end groups that enable cross-linking and conjugation chemistry.

Application

PEG-90 is widely used in the cosmetics industry, mainly due to its excellent emulsifying and surface-active properties and its ability to modify viscosity. In addition, polyethylene glycols are generally well tolerated by the skin, do not cause irritation and are not susceptible to attack by microorganisms, so there is no need to add other preservatives. The versatility of the substance and its high compatibility with other cosmetic ingredients make it a very valuable addition to many skin care formulations and other cosmetics, such as cleansers. To improve texture, lubricity and stability of formulations, it is commonly used in skin care products such as creams, lotions and serums. To significantly improve product uniformity and ease rinsing, PEG-90 is also found in shampoos and conditioners.

Due to its origin, which is not naturally derived from animals, this substance can be used in vegan cosmetics. The substance can be classified as a humectant, i.e. an agent that retains moisture in cosmetic products. It is a surfactant that works in two ways: as an emulsifier and a cleanser. Due to its emulsifying properties, it allows the creation of finely dispersed mixtures of oil and water. Thanks to its cleansing properties, it is ideal for products designed to cleanse the skin, hair and teeth. It is a safe, non-toxic product that does not irritate the skin, which is why it is used as a water-soluble ingredient in hard cosmetics such as lipsticks. In addition, PEG-90 is ideal as a carrier for active substances and as a binding agent, for example in dishwasher tablets, laundry tablets and bath salts.  On an industrial scale, the substance is also a component of lubricants, especially water-soluble synthetic cutting fluids and heat transfer fluids. PEG-90 is also used as an anti-adhesive agent, i.e. a preparation that facilitates the release of manufactured components from the moulds needed for their production. It reduces the adhesion of the material to which it is applied, allowing it to be widely used in the rubber, plastics and elastomer processing industries.

PEG-90 is also used in the textile industry, for example in dyeing and finishing processes. The use of this substance during dyeing promotes the even distribution of the dye used on the material. Its use in fabric finishing allows the desired properties to be achieved, such as softening. The substance can also be used as a component in the manufacture of synthetic fibres. Due to the approval of polyethylene glycol as an indirect food additive and its positive opinion by international organisations such as the FDA, PEG-90 is used as a plasticiser and binding agent in the production of ceramics and polymer-based food packaging. In the vulcanisation process, the substance is used as a zinc white activator in the production of tyres. Due to its preventive properties against drying, this polyoxyethylene glycol is also used in flexographic ink formulations.