Silica aerogel-encapsulated biocide crystals for low-loading antifouling coatings: rheology, water absorption, hardness, and biofouling protection

To protect surfaces against marine biofouling, the continuous leaching of biocides, such as cuprous oxide (Cu2O) and copper pyrithione (CuPT), from antifouling coatings is a widespread and effective method. However, from an environmental and economic perspective (costs of raw materials), a high biocide loading of formulations is not sustainable. Silica aerogel-encapsulated CuPT is a promising approach to reduce Cu2O and CuPT loadings without compromising the mechanical properties and antifouling performance of the coating. In the present study, silica aerogels, with varying CuPT loadings, were incorporated into model coating formulations, and selected coating properties, i.e., rheology, water absorption, and hardness, were measured and evaluated. Furthermore, to demonstrate antifouling performance, static exposure testing with the aerogel-containing coatings was performed. The level of CuPT loading of the silica aerogels did not have a significant influence on neither the water absorption nor the rheology of the coating. However, an increase in the CuPT loading of the aerogel from 0 to 80 wt% reduced the coating's pendulum hardness from 61 to 37 s. Additionally, compared to a reference coating with nonencapsulated CuPT, results demonstrate that a coating containing silica aerogel-encapsulated CuPT provides a 17% higher antifouling resistance when evaluated according to guidance from The European Chemicals Agency.