Exterior wood coatings are exposed to UV light, moisture, temperature changes, etc. Most of them, even if they protect the wood for a certain period of time, will eventually fade, peel and wood will have to be resurfaced and refinished at some point. Water-based acrylic coatings are now standard for exterior wood products. These coatings are cheap, show a good adhesion on most wood substrates and possess a good mechanical resistance. Unfortunately, acrylics contain chemical functions, esters, which are sensitive to UV light and temperature degradation. Strategies have been developed to limit the degradation of acrylics. Until now, none of them have shown exceptional performance.
Polyvinylidene (PVDF)-acrylic coatings are well known for their good chemical resistance and weatherability. They have shown outstanding performance as architectural coatings. They can sustain more than 30 years of outdoor exposure without color or gloss changes. Until now, fluoropolymer coatings have been used only on metal substrates, the reason being that fluoropolymer solvent-based coatings need high baking temperature. Now that water-based PVDF-acrylic coatings can be prepared, these coatings could be used on heat-sensitive substrates, such as wood, as they can be dried at room temperature.
In this project, water-based semi-transparent and opaque PVDF-acrylic coatings have been prepared and applied on white pine and black spruce panels. Accelerated and natural weathering experiments were performed in order to compare the performance of these coatings. Results revealed that PVDF-acrylic coatings show a much better color retention than the acrylics. ATR-FTIR and XPS experiments revealed that chemical degradation is much lower for PVDF-acrylic coatings, which could explain the good color retention.