Improving fire retardancy of unheated and heat-treated fir wood by nano-sepiolite

Abstract

The effects of nano-sepiolite (NS) on fire properties of unheated and heat-treated fir wood were studied using a newly developed apparatus. Separate sets of specimens were prepared to be painted with plain acrylic-latex paint and NS-treated paint as well. Heat treatment of specimens was carried out in a laboratory oven at 185 oC and under atmospheric air pressure. Six fire properties were measured including times to onset of ignition and glowing, as well as back-darkening and back-holing times. Two properties of mass loss and burnt area were measured once the fire was extinguished and the test on each specimen terminated. Results demonstrated significant improvement in fire properties of NS. The improvement was partially attributed to the mineral nature of sepiolite with low chemical reactivity, acting as an insulating layer towards the penetration of fire to the wood substrate. The improvement in fire properties was also partially attributed to the high thermal conductivity coefficient of sepiolite, delaying the accumulation of heat at the point nearest to the piloted fire to reach ignition point. Heat treatment did not significantly affect fire properties in unpainted specimens. However, fire properties in the painted heat-treated specimens (with both plain paint, and NS-treated paint) tended to decrease, though the values were still significantly higher than those of unpainted heat-treated specimens. FTIR spectra illustrated significant alteration in intensities at wave numbers 3100 cm−1 and 1,00 cm−1, related to the hydroxyl groups of cell-wall polymers (mostly hemicelluloses). These alterations had a negative effect on the adhesion of the water-based paint used in this study. It was concluded that nano-sepiolite has a promising future as a fire retardant. However, as cost is of vital importance for paint manufacturers, further studies on the effects of sepiolite at micron-scale available at a lower price should also be carried out.