6 Wood Discoloration

9.7 Recent Biotechnological Processes and Outlook 251
biodegradability of coal tar oil (creosote) by 16 bacterial species and six fungi
using IR-spectra as an indicator for attack have been unsuccessful, assumably
due to the complex mixture of some hundred toxic compounds in the tar oil
(Schmidt et al. 1991).
Bark extracts of Acacia spp. (wattle or mimosa bark extract) and wood extracts
of Schinopsis spp. (quebracho wood extract) are rich sources of tannins.
Tannins are used for a long time in leather tanning and for the production of
adhesives (Pizzi 2000; Roffael et al. 2002). Copper tannate was tested as a possible
wood preservative (Pizzi 1998). In 1950, worldwide about 300,000 t of
tannin extracts were produced (Herrick and Hergert 1977). Main commercial
producers are Argentina, South Africa, Brazil, Paraguay, Zimbabwe, Indonesia,
Kenya, and Chile. The hot water extract of spruce and larch bark contains a high
amount of carbohydrates and was thus unsuitable for adhesives. The soft-rot
fungus Paecilomyces variotii reduced the carbohydrate content, so that the tannins
were suitable as adhesives (Schmidt et al. 1984; Schmidt and Weißmann
1986). Wagenführ (1989) used a commercial pectinolytic enzyme preparation
to reduce the carbohydrate content.
Despite the massive amount of money and effort devoted over the past
decades to the microbiological or enzymatic conversions/treatments of lignocelluloses,
several of the projects started with enthusiasm have suffered success
or practical utilization or even loss of interest. Oil has remained the premier
raw material for chemicals of all types (Little 1991). However, the foreseeable
limitation of oil resources and thus the probable increase in the cost of
petroleum-derived feedstock will provide the necessary incentive to further
research. But, the development and utilization of alternative processes also
depend on political interests and geographical aspects. As an example for the
latter, the use of biofuels (rapeseed oil methylester, RME) may be a possible
substitute for fossil fuels, which also contribute substantially to the increase in
CO2 in the atmosphere. In Germany, the share of RME on the whole consumption
of diesel fuel however is 4.3% and cannot exceed 7% due to the limited
arable acreage. In the end, economy and subsidization will decide on future
research.
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