BORON EFFECT ON DECAY RESISTANCE OF SOME FIRE-RETARDANT COATINGS APPLIED ON PLYWOOD SURFACE

Boron effect on decay resistance of some fire-retardant coatings appli ed on plywood surface was studied. Boric acid (B) was mixed into aqueo us trimethylol melamine (TM) solution to increase the fixation in wood . To reveal the decay resistance of boric acid-added formulations, coa tings were applied over radiata pine plywood surface as 100 g/m(2) amo unts. Phosphoric acid (P) and dicyandiamide (D) were also used alone o r in mixtures as reference coatings for comparison. Coated specimens w ere exposed to weathering according to Japanese Industrial Standard JI S A 9201 (1991) as severe leaching for 10 cycles, prior to decay test. Non-leached and leached specimens, then, were inoculated with a brown -rot fungus Tyromyces palustris and a white-rot fungus Coriolus versic olor. Extent of the fungal attack was determined by mass loss of the s pecimens after 12 weeks incubation and microscopic examinations by 6 x magnification. Results indicated that TMB and TMDB coatings imparted the panels complete decay resistance despite severe weathering conditi ons and were proved superior over all other alone and mixture coatings . Although other combinations and alone treatments used in the study w ere also effective to inhibit the fungal damage before weathering, lea ching greatly reduced their protective efficacy. Surface characteristi cs of decayed specimens were consistent with the determined values of mass losses caused by fungal attack. TMB and TMDB coatings were remark ably effective in maintaining sound surface properties after exposure to weathering and decay fungi.