The Rural Voice, 2019-01, Page 54 I belong to a couple of online
woodworking discussion groups.
Recently another member asked if
anyone had knowledge of, or
experience with, Accoya lumber. I
had never heard of it, so of course
that piqued my interest and started
me on a circuitous path to learn
more.
I learned Accoya is acetylated
wood, i.e. lumber that has been
treated with acetic anhydride at
temperatures between 100 and 120
degrees Celsius. Accoya is actually a
trade name for the lumber product of
a company based in the Netherlands.
It is a fairly new product, only
commercially available for about 10
years and apparently commonly used
in Europe; however, it is also
available but not commonly used in
North America (lumber wholesaler
Upper Canada Forest Products lists it
on their web site).
Wood acetylation is described in
an article by George I. Mantanis in
the North Carolina State University
Bio Resources Journal as, “The
reaction of acetic anhydride with
wood polymers resulting in the
esterification of the accessible
hydroxyl groups in the cell wall, with
the formation of a by-product, acetic
acid.”
Whew! I think what Mr. Mantanis
is saying is the wood is chemically
modified by rearranging the Carbon,
Oxygen and Hydrogen molecules
already found in the wood, with the
only by-product of the process being
vinegar (acetic acid). The modified
wood is less interested in absorbing
water, thus more dimensionally
stable (i.e. very limited swelling,
shrinkage or warping) so good for
uses where that could be a problem,
such as windows and doors and
meaning paint or other coatings
should last longer. It is also less
hospitable to fungi or enzymes that
cause wood degradation, so the wood
is much more durable. In Europe the
wood is used for outdoor windows
and doors, decks, siding, general
construction and even in-ground
applications. Acetylated wood
apparently maintains its original
strength and machinability, but is
slightly heavier. Since there is no
chemical added, just a rearranging of
elements already in the wood, there
is no added toxicity and it can be
disposed of by burning or
conventional landfill.
Accoya uses mostly radiata pine
(also known as Monterey pine) a
species that originated in California
but is now one of the most
commonly used plantation conifers
around the world due to its very rapid
growth. A drawback is its higher cost
in comparison to some other
products. Also, stainless steel
fasteners must be used due to the
increased acidity of the wood.
Thermally modified wood is an
alternative durable wood for exterior
siding or decking. As the name
implies, the internal wood chemistry
has been modified though a heat
treatment process. There are several
types of treatments used by
manufacturers, including heat, or
heat and steam, both in absence of
oxygen at up to 180 or 200 degrees
Celsius. Absence of oxygen is of
course critical, or the wood would
combust at those temperatures.
Thermally modified wood has
improved dimensional stability (i.e.
reduced shrinkage or warping) and is
much more durable (i.e. decay
resistant) so can be used in outdoor
applications such as siding or
decking. Thermally modified wood
generally becomes darker in colour,
e.g. white ash looks more like black
walnut. I wonder if the dimensional
stability and darker colours may also
make it attractive to woodworkers or
wood turners for various projects.
Apparently it is already preferred by
some musical instrument makers. As
it has no chemicals added, there is no
increased toxicity and waste can be
50 The Rural Voice
Accoya: A
modified wood
that swells less
Steve Bowers
is a forester,
forest owner
and member of
the Ontario
Woodlot Assoc.
Woodlots
197 Dinsley Street, Blyth, Ontario
www.hotellux.ca
519-450-8589
Watch for spring tree order forms
at abca.ca or call us at
519-235-2610
or toll-free 1-888-286-2610
Also, nominate a person
GBSN
CVTJOFTT
PSgroup you know for the
annual conservationist award!
Automobile, Residential, Farm & Commercial Properties
507 Main St. S., Exeter
519-235-0350
www.usborneandhibbert.ca