Carbomer (inci)

Polyacrylic acid, called "carbomer" in the INCI nomenclature, is a synthetically produced chemical compound of high molecular polymers of acrylic acid, cross-linked with polyalkene ethers of sugars or polyalcohols. Polyacrylic acid occurs in different degrees of polymerisation. Depending on the degree of polymerization (molar mass) the carbomer gels differ in their viscosity and thus also in their cosmetic, pharmaceutical and technical application.

Carbomer is available as a hygroscopic, odorless white powder. Carbomer (polyacrylic acid) swells in water and other polar solutions after dispersion. 1% aqueous polyacrylic acid suspensions have a pH value of 2.5 to 3.2. The carboxy groups form linear colloids which enclose the water. By adding alkali hydroxides, sodium carbonate and diisopropanolamine, the free carboxyl groups of the acrylic acid polymer react with a strong cross-linking. A gel structure is formed.

However, the strong increase in viscosity is limited to a pH range between 3-6. An increase in pH >10 in turn leads to a decrease in viscosity. The gel structure collapses. The gel structures are also sensitive to strong acids. Even low cation concentrations can liquefy the gel.

Depending on the carbomer type, carbomers are used in pharmaceutical and cosmetic preparations as thickening agents, suspending agents (quasiemulsifiers - carbomer 35,000), humectants and binders.

Carbomer 50,000 (Carbopol®980) is an easily spreadable gel for cutaneous application.

Carbomer 35,000 (Carbopol® 974P) can be used on skin and mucous membranes). Carbomers are frequently used in tear substitutes.

Carbomers are also suitable, for example, for the production of adhesive gels in the mucous membrane area. A trick is used for this purpose: carbomer is incorporated in high concentration into viscous (anhydrous) kerosene; only after the mixture has been applied to moist mucous membranes does the gel, which has high adhesive properties, form due to water absorption.

Technical areas: Used in paints, lubricants and other technical products.

The highly purified carbomers used in the pharmaceutical and cosmetic sector are non-toxic. The previously existing restrictions on the use of polyacrylic acids were based on residues of toxic solvents such as benzene, as residues from the synthesis process. Today, grades are manufactured almost benzene-free (maximum benzene content 2 ppm). The proportion of non-polymerized, monomeric acrylic acid is also limited to 0.25 %. On the other hand, technically used carbomers generally contain residual benzene.

Ammon HPT et al. (2014) Hunnius Pharmaceutical Dictionary 11th Edition Walter de Gruyter Berlin-New York S. 343-344