Environmental Engineering Reference
In-Depth Information
O
H
3
CC
O
Wood OH +
O
Wood OC
O
CH
3
+
H
3
C C
H
3
C
C
OH
O
Figure 6.8
Wood acetylation reaction.
Wood
O
O
O
O
R
O
H
R
Wood OH
+
O
O
R'
R'
Figure 6.9
Reaction of wood with alkenyl succinic anhydrides (as in Surfasam treatment [6]).
Despite all the advantages of wood, its use as a material is affected by its durabil-
ity. Softwoods have a limited durability and hardwoods are in general more resist-
ant than softwoods; they both contain excellent nutrients for fungi and xylophagous
insects (termites, longhorn beetle larvae, etc.) however. Consequently, the impreg-
nation of wood with antifungal and insecticide compounds is a current practice.
Among these, soluble salts of copper, chromium and arsenic (CCA) are the most
used. However, human health concerns have forced wood treatment companies to
eliminate the most toxic compounds on the market in certain countries. Products such
as copper, chromium and boron (CCB) and copper and chromium without boron or
arsenic (CCO) have therefore been recently introduced. Due to the Biocides 98/8/CE
directive in Europe, wood treatment chemicals are now regulated to ensure that they
do not present a significant danger to the environment, humans and animals.
In response to these ecological concerns, new industrial methods of preserving
wood have been developed from intensive laboratory and pilot plant research,
including the following.
•
Acetylation
(e.g. Accoya,
http://www.accoya.com/acetylated-wood/
): Wood is
treated with acetic anhydride. Residual acetic acid from the esterification reac-
tion is difficult to eliminate however, and a vinegary odour may remain.
•
Thermal treatment
(e.g. Retiwood,
www.retiwood.com;
WTT,
www.wtt.dk)
:
Wood undergoes partial pyrolysis at high temperatures in the absence of oxygen
or in the presence of steam or reducing compounds. Readily biodegradable
biomolecules are destroyed in the process.
•
Oleothermal treatment
(e.g. Oléobois [5]): Wood is 'fried' in hot vegetable oils,
which create a barrier to aggressors, especially by the cross-linking of triglyc-
erides. The use of siccative oils (linseed, sunflower) increases the efficacy of the
treatment.
