Natural weathering of spruce wood chemically modified by re-used ε-caprolactone solution

Increasing environmental pressures over the last few years have led to attention for non-biocide treatments in the wood protection field. The ε-caprolactone modification of wood by substitution or blocking of hydroxyl groups with hydrophobic poly(ε-caprolactone) (PCL) is one of the novel modification methods developed in recent years. In this study, ring-opening polymerisation of ε-caprolactone in wood cell walls was evaluated by the third and sixth re-use of recovered monomer and by oven-curing method. Spruce samples were modified by re-used ε-caprolactone and exposed to the natural weathering agents for 12 months. After weathering, the colour change, surface roughness measurements, and macroscopic and ultra-microscopic observations revealed that the modified wood had better surface properties than reference wood. Fourier-transform infrared (FTIR) analysis proved that PCL could be found on the weathered surface up to the sixth month, but very little amount was detected on the surfaces with a longer weathering period. The results clearly showed that the efficiency of PCL modification with re-use of the monomer solution was sufficient during the initial weathering periods, but efficiency was reduced after a prolonged exposure period.