Carbomers are an important class of materials every formulator should get familiar with. They are high molecular weight crosslinked polymers of acrylic acid with molecular weights of up to 3 – 4 billion Daltons. Without the crosslinks, the polymer would be a collection of linear polymer chains, physically intertwined but not chemically bonded. Carbomers are polymerized in ethyl acetate, cyclohexane, and typically used crosslinking agents are Pentaerythritol Polyallylether and Polyallyl Sucrose.
Extensively crosslinked Carbomers are commonly used as super absorbers in disposable diapers. Powdered Carbomers have a dry particle agglomerated size of 2-7 microns (primary particle size 50-200 nm). Dispersions are acidic with a PH of ~3 and when neutralized to a PH of 6-10, the particles swell to around 1000 times their initial volume and the viscosity dramatically increases due to charge repulsion. Salts can decrease viscosity by reducing the charge repulsion. Carbomers can also produce clear gels in water and ethanol due to refractive index matching.
The original synthetic powdered alkali swellable Carbomer was trademarked as Carbopol (US patent 2798503) and commercialized in 1958 by BF Goodrich (now known as Lubrizol). Carbopol 940, 941, and 934 were breakthrough technologies that revolutionized how personal care products are formulated and created new types of products that were previously not possible to make.
- Very efficient water thickening using <1% polymer (no electrolytes).
- Can make aqueous or alcoholic clear gels.
- Very efficient at suspending solids and stabilizing emulsions due to the high yield value of gels.
- Can make emulsifier free oil in water crème gel formulations.
- Can make stable water in oil in water emulsion.
- Excellent skin feel (<.5%) and shear thinning rheology.
Carbomer Formulating Tips
- Carbomers can easily be added to emulsions by addition to the oil phase prior to emulsification.
- Easy to disperse powdered grades are preferred when dispersing directly into water.
- Adding electrolyte or small amounts of acid to the water phase prior to Carbomer addition significantly improves its dispersion by reducing solution viscosity. Up to 5% dispersions of Carbomer in water can typically be made with this approach.
- Use Triisopropanolamine (Dow Chemical) or Neutrol® TE (BASF) to neutralize Carbomer when gelling up to 90% ethanol.
- Use granulated grades to reduce dusting issues during manufacturing.
- Be very careful in qualifying new suppliers for an existing Carbomer. These rarely have the same performance characteristics.
- Carbomers are more sensitive to shear after neutralization than before.
- Carbomers are UV sensitive. You need to incorporate a UV absorber into gels when using clear packaging.
- Ultrez 30 (Carbomer-Lubrizol) has significantly better electrolyte tolerance than other grades of Carbomer. High clarity and good skin feel are also claimed. A 1% dispersion with 1% sodium chloride has a viscosity of 9500-12000 cps.
- Ultrez 10 (Carbomer- Lubrizol) is a universal Carbomer for broad application. It is also one of the best Carbomers for hydrogen peroxide stability. A .5% dispersion has a viscosity of 55K cps. Sumitomo Seika sells an equivalent called Aquapec 505ED
- Anhydrous Oil Gellant Technology
- Let’s Be Clear: Formulating Clear Oil in Water Dispersions
- Solubilizing Oils into Water
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