The Forgotten Additives, 2003 Spring Technical Conference Proceedings

Many coating components are not treated with a biocide; potential microbial growth could lead to the loss of pH and viscosity change of a coating color. Monitoring the coating additives for aerobic and anaerobic populations should detect the source(s) of high microbiological activity and thus the appropriate treatment can be determined.

Two mills, one coated publications and the other coated packaging, were experiencing severe pH drops and loss of viscosity in the coating colors. Microbiological surveys of various coating components were initiated to determine the sources of high microbiological activity. Samples were serial diluted for most enumeration techniques. Aerobic and anaerobic counts were determined via traditional plating methods. API medium was utilized to determine the presence of sulfate-reducing bacteria and Reinforced Clostridial Medium to detect Clostridium species. Additives were heated to 80° C for 10 minutes, serial diluted and plated to detect aerobic spore-formers. All test samples were incubated for 48 hours at 37° C and then read. Results indicated that at both mills, clays not preserved on site had high aerobic counts. At one mill, high anaerobic numbers were detected in the TiO2. Coating components, such as latex, protein, and insolubilizers, were also sources of high microbial activity.