Carbopol polymers are extremely efficient thickening polymers that are most often used to thicken cleaning formulas for many different applications. Carbopol yields crystal-clear water-based gels that are freeze-thaw stable and will not vary in viscosity with temperature. They will work in nearly any system where these conditions are met:
· A polar media, such as water, is present.
· The pH is 4 - to - 5 or higher.
· Long-term temperatures do not exceed 85°C.
· High levels of soluble salts are not present.
A single particle of a dry, powdered Carbopol resin will wet out very rapidly when placed in water. Like many other powders, Carbopol resins tend to form clumps or particles when haphazardly dispersed in polar solvents. The surfaces of these clumps solvate, forming a layer which prevents rapid wetting of the interior of the clumps. Several guidelines for dispersing Carbopol powders are as follows.
1. Add Carbopol resins slowly to the vortex of an already agitating medium.
2. Add Carbopol polymers as early in a formulation as possible. This allows for the longest possible mixing time which helps insure that the carbopol resin is completely dispersed and hydrated.
3. Neutralize the Carbopol resin, that is, increase the pH, as close to the end of the process as possible. This allows for the complete dispersion of the resin and other formulation ingredients prior to the Carbopol resin providing its highest viscosity.
4. Carbopol polymers do not swell readily in non-polar solvents prior to the addition of a water phase. This insures that the Carbopol resin will be completely dispersed before it begins to swell.
5. When Carbopol polymers are to be added to aqueous systems, make a stock solution of Carbopol resin and water. Additions of the stock solution to individual batches can reduce mixing times per batch.
Carbopol resins must be neutralized in order to achieve their maximum viscosity. Unneutralized, aqueous dispersions of Carbopol resins have an approximate pH range of 2.8 to 3.2 depending on resin concentration. Increasing the pH causes the viscosity of the solution to increase rapidly until the pH reaches approximately 5. At a pH of 5, a plateau viscosity is achieved. The system remains at this viscosity through a pH of 10. Although Carbopol resins will still thicken highly alkaline systems, a loss in thickening efficiency occurs as pH's of greater than 10 are obtained. This is caused by excessive neutralizing ions.