[Federal Register Volume 62, Number 54 (Thursday, March 20, 1997)]
[Pages 13363-13364]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 97-7084]


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. 
    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 
    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 
    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,
[FR Doc. 97-7084 Filed 3-19-97; 8:45 am]