屋外に１，２，３，７および１５年暴露した難燃合板の耐久性

Abstract

Fire-retardant plywood panels of lauan (Shorea negrosensis Fox) were pressure treated with a phosphoric acid containing melamine-formaldehyde condensate as a leach-resistant fire retardant and with diammonium hydrogen phosphate, guanidine phosphate, minalith and pyresote as non-leach resistant fire retardants. Their fire retarding efficiency and bending strength were measured after 1, 2, 3, 7 and 15-year outdoor exposure at the experimental field of the Wood Research Institute, Kyoto University, Uji, Kyoto.The fire retarding efficiency and burning behaviors of the fire retardant plywood in comparison with those of the non-treated ones were evaluated while being subjected to a fire test under a high radiation furnace. The burning behaviors such as: the ignition time and time-temperature of the fire-exposed surface; the time at which the unexposed surface reached the critical temperature of 260°C; the afterflame; and the afterglow of the specimens, as indications of fire retarding efficiency, were measured. The relationships between the modulus of rupture and/or modulus of elasticity of the specimen plywood and the exposure period were also discussed.The fire retarding efficiency of the fire retardant plywood decreased proportionately with longer exposure time. The fire retardant effectiveness of the plywood treated with inorganic fire retardants, such as diammonium hydrogen phosphate, guanidine phosphate, pyresote and minalith, was almost negligible after a year of exposure. However, the fire retardant effectiveness of those treated with phosphoric acid containing melamine-formaldehyde condensate was slightly remarkable even after seven years of outdoor exposure.The durability of the fire retardants was in the order of pyresote, diammonium hydrogen phosphate, guanidine phosphate, minalith and phosphoric acid containing melamine-formaldehyde condensate. The percentage loss in the bending strength were 10-20%, 40-65% and 50-70% after 1, 7 and 15-year exposure period, respectively.