Understanding the influence of wood substrates on the permeability of coatings
The shift towards waterborne coatings makes coatings more sensitive to water. As a consequence, the durability of both wood and coatings can be negatively affected. The aim of a study was to elucidate the influence of wooden substrates on the water permeability of the coating applied to it.
Pine sapwood, oak and teak were selected as the wood types, covering a whole range of low to high density wood.
Permeability is determined by water solubility
Three types of coatings were formulated: a solventborne alkyd, a waterborne alkyd and a waterborne acrylic. For all wood-coating combinations water transport appeared to be externally (i.e. coating) limited. The loss of bound water started only after evacuation of free water, which showed a local thermodynamic equilibrium associated with bound and free water. The researchers furthermore compared water permeability of free films and wood supported films to understand the influence of the wood-coating interactions. They found that the interaction of the coating with the wood has no influence on the water permeability for the considered combinations. Furthermore, the permeability is largely determined by the water solubility.
The study is published in: Progress in Organic Coatings, Vol. 114, Januar 2018.
