Impact of impregnation with boron compounds on combustion properties of oriental beech (Fagus orientalis Lipsky) and varnishes

This study examined the impacts of varnishing after impregnation with boron compounds on combustion properties of oriental beech. The test samples prepared from oriental beech (Fagus orientalis Lipsky) wood were impregnated according to ASTM D 1413-76-99 with boric acid (Ba) or borax (Bx) using a vacuum technique. After impregnation, one of six varnishes (cellulosic (Cv), synthetic (Sn), polyurethane (Pu), water-based (Wb), acrylic (Ac) or acid-hardening (Ah) was applied in accordance with ASTM D 3023 coated surfaces. After treating, varnishing and conditioning, the combustion properties of samples were determined according to ASTM E 160-50. Combustion temperatures for Bx and Wb were highest when testing without flame source combustion (WFSC), while Ba and Pu exhibited the lowest temperature when testing for flame source combustion (FSC). For the combination of combustion type, impregnation material and varnish type, combustion temperature was the highest for WFSC + boric acid + water-based varnish, but the lowest for WFSC + boric acid + synthetic varnish. As a result, the tested varnishes showed an increasing impact, but boron compounds (Ba and Bx) showed a decreasing impact on the combustion properties of beech. In conclusion, for usage areas having a high risk of fire, impregnation of wood material with boron compounds before varnishing will decrease combustion temperature and provide some degree of security.