INFLUENCE OF TEMPERATURE ON THE DEGRADATION OF ISOTHIAZOLONE BIOCIDESIN AQUEOUS-MEDIA AND IN A METALWORKING FLUID CONCENTRATE

The degradation of the active component of two isothiazolone biocides has been monitored at 24-degrees, 40-degrees, and 60-degrees-C by reve rsed-phase liquid chromatography. The first-order rate constants are m easured, and temperature-dependent kinetic data are used to show that the rate of degradation is doubled if the temperature is increased by 5-degrees-C and 6-degrees-C in aqueous media of pH 8.5 and 9.6, respec tively. At pH 5.5, the active component is found to be stable at 24-de grees and 40-degrees-C, and its depletion at 60-degrees-C is about 10 percent over a period of three and one-half months. An estimated half- life of the active component in a metalworking fluid concentrate is si x months at 24-degrees-C. However, at both 40-degrees and 60-degrees-C , its degradation appears to be a two-step process. Initially, the con centration remains invariant or decreases slowly. This is followed by a rapid, first-order kinetic process. The overall times required for 5 0 percent loss of the active component are 12.2 and 1.6 days at 40-deg rees and 60-degrees-C, respectively.