Problems and Pitfalls in the Evaluation and Design of New Biocides for Plastics Applications*

Abstract

Many factors need to be considered in the design of new biocides for use in plastics applications. In Europe, biocides are now becoming more tightly regulated under the Biocidal Products Directive (BPD), and a significant data package needs to be provided not only for the registration of new actives, but also for existing biocides and biocidal formulations. A novel biocide must be compatible with the polymer matrix and must not adversely affect its physical properties. Once the issue of compatibility has been overcome, the antimicrobial efficacy of the biocide in the substrate should be established. Before selecting a test method to demonstrate such efficacy, it is necessary to consider whether the substrate should be pre-conditioned to simulate end use conditions, e.g. by leaching or artificial weathering. The final use of the product can also dictate the test protocol, e.g. a building membrane for ground contact should be evaluated using a soil burial test. Historically, biocides have been added to plastics to prevent their spoilage by fungal attack. Latterly, plastics with antibacterial effects have aroused much public interest. Advantages and disadvantages of traditional test methods will be discussed, and an alternative method for the evaluation of biocidal performance that is thought to be more representative of end use conditions will be presented.