6 Wood Discoloration

152 7 Wood Rot
allowed for indoor and outdoor wood, especially if it is exposed to leaching,
and also for wood in ground contact, e.g., poles, exterior structures, such as
decks and fences, mine timber (Narayanappa 2005), and wood in permanent
water contact, such as cooling towers and marine works. Chrome copper salts
with the addition of either boron (CCB) or fluorine (CCF) may be used indoors
and outdoors.
Chrome copper arsenic salts (CCA) are restricted to outdoor use and certain
application such as noise barriers (Commission Directive 2003/2/EC 2003).
In the USA and Canada, industry registrants voluntary agreed to withdraw
CCA treatment for use in such residential applications as decks, fences, and
playground components effective as of 2004, although it is still registered for
commercial/industrial products (Bao et al. 2005b). Component leaching from
CCA-treated wood during above-ground exposure was affected by climatic
variables like precipitation and temperature (Taylor and Cooper 2005). Bao
et al. (2005b) showed for CCA, CCB and acid copper chromate (retention about
7kg/m 3 ) fixation times of 8–32 days at 21 ◦ C and between 12 and 48 h at 50 ◦ C.
Treatment of freshly impregnated wood with hot steam of 110 ◦ C for 1 h was
also suitable for sufficient fixation (Peek and Willeitner 1981, 1984; also Cooper
and Ung 1992). Timber treated with water-based fixing salts should thus be
protected from rain, depending on the type of preservative, to avoid leaching of
the not yet fixed components, which would decrease the protection and pollute
the environment. Cookson et al. (1998) evaluated the fungicidal effectiveness
of water-repellent CCAs.
Molybdenum and tungsten have been studied as substitutes for arsenic in
CC-salts (Cowan and Banerjee 2005). Schultz et al. (2005a) used a mixture of
copper(II) and oxine copper for an outdoor ground-contact exposure.
Toxicological aspects have lead to an increased use of chromium-free preservatives
that are just as fixing. These preservatives are based e.g., on ACQ (alkaline
copper quaternary ammonium salts), copper HDO [bis-(N-cyclohexyldiazeniumdioxy)-copper]
and Cu-triazoles. Some of these products also include
boron. Quaternary ammonium compounds are used as N-dimethylalkylbenzylammoniumchloride,
didecylpoly(ethox)ethylammoniumborate (polymeric
Betain), and N,N-didecyl-N-methyl-poly-(oxethyl)-ammoniumpropionate.
Zabielska-Matejuk et al. (2004) showed antifungal activity of bis-quaternary
ammonium and bis-imidazolium chlorides (also Pernak et al. 1998).
Didecyldimethylammoniumtetrafluoroborate inhibited mold and stain (Kartal
et al. 2005a) and decay fungi (Kartal et al. 2005b). Copper(II) octanoate/
ethanolamines were investigated by Humar et al. (2003). Mazela et al. (2005)
used copper monoethanolamine complexes with quaternary ammonium compounds.
The group of triazoles as wood preservatives was treated by Wüstenhöfer
et al. (1993).
Solvent-based preservatives contain e.g., Al-HDO [tris (N-cyclohexyl-diazeniumdioxy)-aluminum]
or triazoles (e.g., tebuconazole, propiconazole) as
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