In the past few years, the coating industry has started to explore the possibilities of replacing fossil based with bio based raw materials, and this slow shift is also happening in applications such as exterior wood coatings. With the change to bio based materials, there often occurs a reduction in the mechanical properties of the coating. Although mechanical properties are only one of the important factors in exterior wood coatings, it is possible that new types of reinforcements can become a suitable method to retain or even improve the resilience of exterior wood coatings to mechanical deformation.

The present work centers on the reinforcement of alkyd binders emulsified in water and used in exterior wood coatings with nano silica. Raman spectroscopy was used throughout the study to maintain the reproducibility of results as it was found that colloidal nano silica can increase or decrease the speed of alkyd curing affecting the tested mechanical properties. Hydrophilic, colloidal nano silica was seen to have limited effect in improving the mechanical properties due to problems in properly dispersing and attaining good surface interactions with the hydrophobic alkyd polymer. Efforts in increasing the interactions with the alkyd polymer while keeping the nano filler stable in the water phase did not show further improvements of mechanical properties. The best results in respect to mechanical properties, as measured under static and dynamic loading, were obtained with the use of hexamethyldisilazane treated nano silica which was incorporated in the pure alkyd and then subsequently emulsified.

When the change in the coating formulation increases the stiffness of the exterior wood coating, as happens with the addition of nano particles, there is a concern for the long term performance due to possibility of premature cracking. In this study we have shown that increased stiffness in the first stage of coating lifetime is just one of the parameters and that behavior during the aging needs to be taken into account before drawing conclusions.