Weatherability and combustibility of fire-retardant-impregnated wood after accelerated weathering tests

The weatherability and combustibility of fire-retardant-impregnated wood during accelerated weathering for up to 2000 h were evaluated. The ability of coating to retain fire-retardant chemicals against leaching was also examined using four coating systems (water-borne or solvent-borne, pigmented or clear, film-forming or penetrating). Furthermore, the distribution of fire retardants in the specimens was observed by scanning electron microscopy in combination with energy dispersive analysis of X-rays (SEM-EDX). The fire performance of the specimens during weathering depended on the chemical retention, and was maintained at a quasi-noncombustible material level if the chemical retention was above 150 kg/cubic m. The maximum duration of accelerated weathering to keep this retention was 250 h for the uncoated specimens, but increased to over 1000 h for pigmented coatings. SEM-EDX revealed that the fire retardants were accumulated in the cell lumina throughout the wood tissues. However, in the uncoated samples, the leaching of fire retardants occurred for surfaces exposed to light and water, and was observed down to a depth of about 150 micro m after 500 h. The leaching depth extended throughout the specimen after 1000 h. In contrast, the fire retardants still remained in samples finished with a solvent-borne pigmented penetrating coating even after 1000 h due to their relatively high chemical retention.