Transport and transformation of biocides in construction materials

Biocides are used to protect polymer based polish and paint against attack of fungi and algae. Both leaching processes and degradation control how much biocidal products are leached to the environment. 

In relation to paint, the transport passes through diffusion through the polymer, while there are different possibilities when it comes to plaster: diffusion through the polymer, the minerals or the water-filled pores; or adventitious transport through the watery pores. In this project, tests were performed on various wet and dry cycles, which gave insight into the transport process from the deeper layers to the surface. 

Degradation routes of biocides terbutryn and N-octylisothiazolione were investigated. Decomposition products were identified and subsequently analyzed in leachate and environmental samples. The mass balance for terbutryn was fully described when photon degradation products were taken into account. There are several possible reasons for the lack of a large part in the mass of N-octylisothiazolinone: several unknown decomposition products, mineralization or loss to the atmosphere. All in all, photon degradation products constitute a major part of the final mass balance of biocides in plaster. It is important to add that a large proportion of the products - even if they are formed on the surface - remain in the material and are not washed out immediately. 

As different pigments show different degradation patterns, the light-pigment biocidal interaction is evident and should be considered for future product development. 

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