The microbial resistance of polymer dispersions and the efficacy of polymer dispersion biocides – A statistically validated method

• There is no standard test method for evaluating biocides in polymer dispersions.
• A model polymer dispersion was tested for resistance to 7 mixed Gram −ve bacteria.
• Statistically significant variability between nine laboratories did not invalidate results.
• The triple challenge test developed was robust, repeatable and reproducible.
• It is suitable for use as a Standard Test Method for polymer dispersions and biocides.

The biodeterioration of water-based manufactured formulations, such as polymer dispersions, is a major problem for the producing companies and the users of such products. Industrial preservatives, also known as biocides, are therefore used to protect these and similar products from the effects of microorganisms, predominantly bacteria and yeasts. In the absence of internationally recognised standard methods for determining the resistance of polymer dispersions to microbial growth and the efficacy of biocides used in them, protocols for testing other products, e.g., paints, have been adapted, and other methods produced by manufacturing companies, test laboratories, and academic institutions have been used. Often these do not take into account the specific nature of the materials being tested, the types of organism commonly causing contamination, and the conditions that the polymer dispersions will be exposed to during manufacture, storage, and use. By conducting a series of round-robin, collaborative tests, the member organisations of the International Biodeterioration Research Group Polymer Dispersion Working Group have identified the bacteria that commonly infect polymer dispersions, defined the main parameters necessary for a standard method of test, and developed a protocol that is robust, repeatable, and reproducible. The recommended test involves three repeat inoculations of the material with a previously determined mix of seven Gram-negative bacteria and evaluation of living cells by a simple plating technique. The work reported here, carried out by nine participating laboratories, is a final statistical validation and suggests that the method is eminently suitable as a standard test method.