Kauri-butanol

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The Kauri-butanol value is a standardized measure of solvent power for a hydrocarbon solvent, and is governed by an ASTM standardized test, ASTM D1133. The result of this test is a scaleless index, usually referred to as the "Kb value." A higher Kb value means the cleaner is more aggressive or active. Mild cleaners have low scores in the tens and twenties; powerful cleaners like the old chlorinated solvents have ratings in the low hundreds.

This contrasts with the cleaning "horsepower" measurement of water-based cleaners and degreasers, which is the pH and which is the concentration of hydrogen ions in such a solution. But since solvent-based cleaners do not use water, they cannot have a pH. So they are commonly classified by their Kb value.

In terms of the test itself, the kauri-butanol value (Kb) of a chemical shows the maximum amount of the hydrocarbon that can be added to a solution of kauri resin (a thick, gum-like material) in butyl alcohol without causing cloudiness. Since kauri resin is readily soluble in butyl alcohol but not in most hydrocarbon solvents, the resin solution will tolerate only a certain amount of dilution. "Stronger" solvents such as benzene can be added in a greater amount (and thus have a higher Kb value) than "weaker" solvents like mineral spirits.