[Federal Register Volume 62, Number 54 (Thursday, March 20, 1997)]
[Notices]
[Pages 13363-13364]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 97-7084]
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DEPARTMENT OF AGRICULTURE
Forest Service
Commonality of the Chemistries Involved in Moisture, Biological,
Ultraviolet, and Thermal Degradations of Wood; Notice of Intent To Form
a Consortium
Program Description--Purpose. The USDA, Forest Service, Forest
Products Laboratory (FPL) is seeking industrial partners to form a
Consortium dedicated to understanding the commonality of the
chemistries involved in moisture, biological, ultraviolet, and thermal
degradations of wood, and developing basic approaches to protecting
wood from degradation without loss of other basic properties, under the
authority of the Federal Technology Transfer Act of 1986 (15 U.S.C.
3710a).
An industrial partner may be a Federal Agency, university, private
business, nonprofit organization, research or engineering entity, or
combination of the above.
A summary of the current status of preventing wood degradation is
as follows:
(a) Wood is a three-dimensional, polymeric composite made up
primarily of cellulose, hemicelluloses, and lignin. These polymers,
along with extractives and inorganics, and the matrix they are in, make
up the cell wall and are responsible for the characteristics,
properties and performance of wood.
When considering wood as a long term engineering material it must
be remembered that wood is a hygroscopic resource that was designed to
perform, in nature, in a wet environment and that nature is programmed
to recycle wood in a timely way through biological, thermal, aqueous,
photochemical, chemical, and mechanical degradations.
There are four basic chemical reactions involved in all the
degradation reactions of wood: Oxidation, hydrolsis, reduction, and
dehydration. Because of the similarities in degradation chemistry, all
these degradation reactions will be studied together.
Cell wall polymers are responsible for the properties of wood. Wood
changes dimension with changing moisture content because the cell wall
polymers contain hydroxyl and other oxygen-containing groups that
attract moisture through hydrogen bonding. The hemicelluloses are
mainly responsible for moisture sorption, but the accessible cellulose,
noncrystalline cellulose, lignin, and surface of crystalline cellulose
also play minor parts to major roles. Moisture swells the cell wall and
the wood expands until the cell wall is saturated with water (fiber
saturation point (FSP)). Beyond this saturation point, moisture exists
as free water in the void structure and does not contribute to further
expansion. The process is reversible and the wood shrinks as it loses
moisture below the FSP.
Wood exposed to moisture frequently is not a equilibrium and has
wet areas and drier areas. This exacerbates the moisture problem
resulting in differential swelling followed by cracking and/or
compression set. Over the long term, wood undergoes cyclic swelling and
shrinking as moisture levels change resulting in more severe moisture
effects than those encountered under steady moisture conditions.
Wood is degraded biologically because organisms recognize the
carbohydrate polymers (mainly the hemicelluloses) in the cell wall and
have both specific and non-specific chemical and specific enzyme
systems capable of hydrolyzing these polymers into digestible units.
Biodegradation of both the matrix and the high molecular weight
cellulose weakens the fiber cell wall. Strength is lost as the matrix
and cellulose polymer undergo degradation through oxidation,
hydrolysis, and dehydration reactions. As degradation continues,
removal of cell wall content results in weight loss.
Wood exposed outdoors undergoes photochemical degradation caused by
ultraviolet radiation. This degradation takes place primarily in the
lignin component, which is responsible for the characteristic color
changes. The surface becomes richer in cellulose content as the lignin
degrades. In comparison to lignin, cellulose is much less susceptible
to ultraviolet radiation degradation. After the lignin has been
degraded, the poorly bonded carbohydrate-rich fibers erode easily from
the surface, which exposes new lignin to further degradative reactions.
In time, the ``weathering'' process causes the surface of the composite
to become rough and can account for a significant loss in surface
fibers.
Wood burns because the cell wall polymers undergo pyrolysis
reactions with increasing temperature to give off volatile, flammable
gasses. The hemicelluloses and cellulose polymers are degraded by heat
much before the lignin. The lignin and carbohydrate components
contribute to char formation, and the charred layer helps insulate the
composite from further thermal degradation.
The idea of protecting wood in adverse environments dates back to
early human history. Perhaps the earliest reference is in the Old
Testament (Genesis 6:14) when God instructed Noah to build an ark of
gopher wood (a naturally durable and hard wood) and cover it inside and
outside with pitch (for both water repellency and decay protection).
Ancient civilization in Burma, China, Greece, and Italy used
various animal, vegetable and mineral oils, tars, pitches or charring
to preserve wood. Sometime during the second half of the eighteenth
century, the science of wood preservation started with a search for
toxic chemicals that could be used to treat wood to stop decay. The
time line might include: mercuric chloride first used in 1705, patented
in 1832; copper sulfate first introduced in 1767, patented in 1839;
zinc chloride first used in 1815; creosote first used in 1836; copper,
chromium and arsenic salts introduced in the early 1900's; and
pentachlorophenol first introduced in
[[Page 13364]]
the 1930's. All of these treatments were based on broad spectra
toxicity with little concern for environmental implications.
The earliest references to treating wood for fire retardancy dates
back to the first century AD when the Romans used alum and vinegar to
protect boats against fire. The science of fire retardancy started in
the first half of the nineteenth century. In 1820 Gay-Lussac used
ammonium phosphates and borax as fire retardants. Most of the inorganic
fire retardants used today were developed between 1800 and 1870.
Protecting wood from moisture damage also dates back into
antiquity. Waxes, oils, resins, paints, and coatings have been used to
help exclude moisture since shortly after wood was first used by
humans.
Protecting wood from damage caused by weathering also dates from
the early use of wood. Stains and coatings have been used to cover wood
from the degradation caused both by water and ultraviolet radiation.
The process of protecting wood from one type of degradation can
cause another type of degradation to take place. For example, in fire
retardant formulations involving free phosphoric acid, treated wood has
been shown to lose strength. While the wood is very effectively treated
for fire retardancy, service life is shortened by the loss in strength.
Similarly, wood decking treated with chromated-copper-arsenate (CCA),
while having excellent anti-fungal properties, is being replaced after
a few years due to cracking and splitting caused by moisture damage.
Since there are only four basic chemistries involved in the
degradation mechanisms of wood (hydrolysis, oxidation, dehydration, and
reduction), there are many similarities in the degradation pathways
regardless of the source of the degradation. Through a better
understanding of these common degradation chemistries, it should be
possible to protect wood in a more holistic way. That is, controlling
one degradation chemistry can lead to the protection of another
degradation mechanism. This leads to the idea of combined treatments to
control several degradation pathways.
The Forest Products Laboratory is requesting support for this
project. The support is in the form of membership in the consortium and
funding in the amount of $15,000.00 per year for the three-year
proposed duration of the Consortium.
An informational and organizational meeting of the Consortium will
be held beginning May 5, 1997, 1 p.m. and ending May 6, 1997, at 12
Noon, at the USDA, Forest Service, Forest Products Laboratory, One
Gifford Pinchot Drive, Madison, Wisconsin 53705-2398.
Technical questions may be directed to Roger M. Rowell at the above
address, by fax at (608) 231-9262, or by phone at (608) 231-9416.
Questions of a business or legal nature may be directed to John G.
Bachhuber at the above address, by fax at (608) 231-9585, or by phone
at (608) 231-9282.
A copy of the proposed Cooperative Research and Development
Agreement to be executed by consortium members may be obtained by
writing Joanne M. Bosch at the above address, by faxing her at (608)
231-9585, or by phoning her at (608) 231-9205.
Done at Madison, WI, on March 11, 1997.
Thomas E. Hamilton,
Director.
[FR Doc. 97-7084 Filed 3-19-97; 8:45 am]
BILLING CODE 3410-11-M