Multi-layered approach to determine diffusion coefficients through polymer films: Estimating the biocide release from paints

Biocides – added to facade coatings like paints and renders to reduce microbial growth on the outer surfaces of buildings – are known to leach into the environment, when the facades are getting in contact with rainwater. The leaching process is described as diffusion controlled process. Nevertheless, no comprehensive data on diffusion coefficients is available so far. The present study aimed for determining the diffusion coefficients in paint of eight biocides, applying an easy, reproducible method. The study was performed using a paint closely related to commercially available paints. It suggests a new method to determine diffusion coefficients in paint films by submerging paint films consisting of several layers with water for 1 h intervals over a period of 30 h. By determining the biocide concentrations in the water after the contacting time, the mass flow of biocides across the paint film was calculated. The resulting diffusion coefficients varied from (0.27 ± 0.07)·10⁻¹⁵ m² s⁻¹ for Cybutryn to (11.97 ± 3.14)·10⁻¹⁵ m² s⁻¹ for Diuron.