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.