Fire resistance of Douglas fir (Pseudotsuga menzieesi) treated with borates and natural extractives Ergun Baysal a, * , Mustafa Altinok b , Mehmet Colak a , S. Kiyoka Ozaki c , Hilmi Toker a a Mugla University, Faculty of Technical Education, Kotekli, Mugla 48000, Turkey b Gazi University, Faculty of Technical Education, Besevler, Ankara 06500, Turkey c University of Sao Paulo-USP-IFSC, P.O. Box 369, Sao Carlos-SP 13560-970, Brazil Received in revised form 14 January 2006; accepted 1 April 2006 Available online 5 July 2006 Abstract The objective of this study was to determine fire resistance of Douglas fir (Pseudotsuga menzieesi (Mirb.) Franco) specimens treated with borate supplemented aqueous solutions of brutia pine bark powder, acorn powder, sumach leaf powder, and gall-nut powder. Boric acid (BA) and borax (BX) were used as borates which are the most commonly used fire retardants in wood preservation industry. Natural extractives (brutia pine bark powder, sumach leaf powder, acorn powder, and gall-nut powder) were also used which have toxic efficiency against insects and fungi due to their tannin contents. A commercial treatment compound Tanalith-CBC (copper-borate-chromate), which is an impregnation chemical, is used for comparison. The fire test method was performed in three stages: flame stage, without flame stage, and glowing stage. Results indicated that the lowest temperature for flame stage, without flame stage, and glowing stage were obtained for specimens treated with BA and BX mixture (7:3; weight:weight). The lowest mass loss was found for the specimens treated with a mixture of BA and BX. Natural extractives did not improve fire resistance of the samples. However, boric acid and borax had excel- lent fire retardant effectiveness over untreated and treated samples with natural extractives. Ó 2006 Elsevier Ltd. All rights reserved. Keywords: Wood; Borates; Natural extractives; Fire retardant; Fire test 1. Introduction Carbon-based cellulosic materials, such as wood- and bio-based composites will combust, pyrolize, or burn when subjected to either radiant energy (as from a fire a short dis- tance away) or sufficient direct heat (as from a flame in direct contact) (Slifka, 1997). For wood ignition, an oxygen flame source and flammable material are necessary. How- ever, wood has excellent natural fire resistance due to its low thermal conductivity. Charring is formed when wood is burned. In order to reduce flammability and provide safety, wood is treated with fire-retardant chemicals. In other words, the combustibility of wood may be reduced with flame-retardant or fire-retardant materials (Nuss- baum, 1988; Ellis and Rowell, 1989; Mitchell, 1993). Borates have several great advantages as wood preserva- tives as well as imparting flame retardancy, providing suf- ficient protection against all forms of wood destroying organisms, have low mammalian toxicity and low volatility, they are moreover colorless and odorless (Hafizoglu et al., 1994; Murphy, 1990; Yalinkilic et al., 1999; Drysdale, 1994; Chen et al., 1997). Boric acid (BA) and borax (BX) are the most common boron compounds which have found many application areas in the wood preservation industry in order to obtain the benefit of their biological effectiveness and fire retar- dancy (Hafizoglu et al., 1994; Baysal, 1994). Boric acid and borax mixtures have some efficacy in retarding flame 0960-8524/$ - see front matter Ó 2006 Elsevier Ltd. All rights reserved. doi:10.1016/j.biortech.2006.04.023 * Corresponding author. Tel.: +90 252 2238612; fax: +90 252 2238511. E-mail address: ergun69@yahoo.com (E. Baysal). Bioresource Technology 98 (2007) 1101–1105