Note: Descriptions are shown in the official language in which they were submitted.
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TITLE OF INVENTION
MATERIALS AND METHODS FOR TREATING LUMBER AND WOOD PRODUCTS
CROSS-REFERENCE TO OTHER APPLICATIONS
This application is a continuation-in-part of application no. 09/965,740,
filed September 9, 2001,
pending, and is also a continuation-in-part of application no. 60/374,543,
filed April 21, 2002,
the priority of both of which is claimed under 35 USC ~ 120, and whose
teachings are
incorporated by reference. .
BACKGROUND OF THE INVENTION
One of the most effective and widely used treatments for the preservation of
lumber and other
wood products against fungal decay and insect attack is a system based on
chromated copper
arsenate (CCA). However, the use of CCA as a wood treatment has been shown to
have
negative health and environmental effects (Kluger, J. "Toxic Playgrounds:
Forts and Castles
Made ofArsenic-treated Wood Last for Years, but Should Kids Be Playing oh
Them?" Time
158 2 p48-49 (2001); Brooks, Kenneth M. (2000). Assessment of the
Environmental Effects
Associated with Wooden Bridges Preserved with Creosote, Perctachloropher~ol,
or Chromated
Copper Arsenate. Madison, WI : U.S. Department of Agriculture, Forest Service,
Forest
Products Laboratory. (FPL-RP-587); Hingston JA, Collins CD, Murphy RJ, Lester
JN.
"Leaching of Chromated Copper Arsenate Wood Preservatives A Review".
Environmental
Pollution 111 ( 1 ), 53-66. (2001 ); Long, Cheryl "Arsenic Again Showr~ to
Leach From Pressure
Tr°eated Wood". Ore~anic Gardening, 44(4), 18, (1997).) As a result,
the US Environmental
Protection Agency (EPA) has asked lumber manufacturers to undertake a
voluntary phase-out of
CCA usage (see: "Manufacturers to Use New Wood Preservatives, Replacing Most
Residential
Uses of CCA" (http://www.ep~ov/pesticides/citizenslcca transition.htm). The
primary toxic
effects of CCA are associated with arsenic; however, it is known that chromium
and copper salts
also have adverse effects on environmental and human health (Timothy Townsend,
et al.
"Leaching and Toxicity of CCA-Treated and Alternative-Treated Wood Products,
Florida Center
for Solid and Hazardous Waste Management Report # O1-XX (2001), see
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httn://www.floridacenter.org/publications/Altchem final draft.pdf). Exposure
to these toxic
compounds can occur through direct contact during manufacture, shipping, or
construction; or by
incidental contact such as inhalation of sawdust or vapors released upon
burning. Leaching of
these toxic metals into the soil or groundwater is also a problem.
U.S. Patent Application No. 09/965,740 teaches the use of quaternary ammonium-
containing
polymers grafted onto cellulose substrates as absorbent antimicrobial
surfaces. Cellulose is one
of the principal components of wood. The method described in the above patent
application is
applicable to the treatment of wood in order to render it resistant to
microbial attack. Evidence
for the efficacy of this method for the prevention of decay by wood-destroying
fungi is presented
herein. It has also been found (unexpectedly) that wood treated in this manner
is also resistant to
destruction by termites.
Preservative treatment of wood is usually done by using pressure to force the
liquid preservative
solution into the pores of the wood. A vacuum may be applied prior to
introduction of the
treatment solution in order to increase penetration. The active agents (such
as CCA) are
generally dissolved in a solvent. The solutions are generally of low viscosity
in order to
facilitate penetration of the treatment. Treatments may be classified as
waterborne, or oilborne.
A useful summary of the various chemical systems, application methods,
efficacy, and other
considerations related to wood preservation is given in: Forest Products
Laboratory. 1999.
Wood handbook- Wood as an engineering material. Gen. Tech. Rep. FPL-GTR-113.
Madison,
WI: U.S. Department of Agriculture, Forest Service, Forest Products
Laboratory. 463 p.
Arsenic-containing formulations, such as CCA, are waterborne treatments.
Although most of the
toxic chemical is retained in the treated wood for a long period of time, some
leaching does
occur since the toxic agents are water-soluble. Waterborne systems are
generally preferable to
solvent based (oilborne) preservative systems for economic reasons, but also
because the oil-
based solvent themselves must be considered as pollutants.
One of the most common oilborne wood preservative treatments is the coal-tar
creosote system.
This system is generally used for railroad crossties, dock pilings, and
utility poles. Most people
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are familiar with the dark appearance and unpleasant odor of wood treated in
this manner.
Creosote vapor photosensitizes exposed skin. Timbers treated in this manner
cannot be
satisfactorily painted. Creosote is an EPA restricted-use pesticide. Toxic
chemicals are released
when this type of wood is burned.
Pentachlorophenol (penta) is another common oilborne preservative. It is
applied to wood using
petroleum-based solvents. It is an EPA restricted-use pesticide. It is toxic,
and should not be
used where human, plant, or animal contact is likely.
Copper napthenate is another oilborne preservative, and although it is not a
restricted-use
pesticide, it is toxic and should be handled accordingly.
Bis(tri-n-butyltin) oxide is another oilborne preservative. Organotin
compounds are known to be
highly toxic, and their use in marine applications has been banned.
Waterborne preservatives, other than arsenic-containing systems, have also
been used for wood
preservation. Many of these systems rely on the antimicrobial activity of
metals such as
chromium or copper. Chromium is known to be an extremely toxic pollutant, and
it use is
undesirable. Copper is a metal found in natural deposits and widely used in
household plumbing
materials. Copper is an essential nutrient, required by the body in very small
amounts.
However, if the level of contamination is above the MCL in water or food
supply, then people
exposed to it can be affected by stomach and intestinal distress, liver and
kidney damage and
anemia. (see, for instance: Toxicological Profile for Copper, December 1990
Update, Agency
for Toxic Substances and Disease Registry, United States Public Health
Service). Most of the
contamination is due to copper mining and smelting operations and municipal
incineration. As
such, the use of copper in treated wood should be discouraged.
Didecyldimethylammonium chloride (DDAC), also called alkyl ammonium compound
(AAC),
is a water (and solvent)-soluble antimicrobial effective against fungi and
insects. Unfortunately,
it is water soluble, and thus will leach from treated lumber unless fixated by
a stabilization
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method. It is used as a component of the ammoniacal copper quat (ACQ)
preservative system.
That system is undesirable for the reasons discussed above.
Grafting of various monomers onto wood to form wood-polymer composites is
known (Robert
M. Rowell, Robert Moisuk; John A. Meyer, "Wood Polymer Composites: Cell Wall
Grafting
With Alkyleue Oxides and Lumen Treatments with Methyl Methacrylate ", Wood
Science, Vol 15,
No 2, 90-96 (October 1982)). Grafting occurs not just on the exterior of the
wood, but also in the
interior sections, onto the cell walls of the internal voids, or lumen. An
alternative approach is
bulk polymerization of nongrafted polymer within the internal lumen spaces.
Rowell studied
both these methods. Grafting was performed using propylene oxide and alkaline
catalysis.
Interlumenal bulk polymerization was carried out using crosslinked poly(methyl
methacrylate),
which led to a general improvement of the mechanical properties of the wood.
Neither of these
approaches was intended to prevent decay by insect or fungal attack.
Ibach and Rowell (Rebecca E. Ibach and Roger M. Rowell, "Wood Preservation
Based oh In situ
Polymerizatiofz of Bioactive Mouome~s: Past 1. Synthesis of Bioactive
Monomers, Wood
Treatmev~ts and Microscopic Analysis'; Holzforschun~, Vol 55, No 4, 358-364
(2001))
investigated in situ polymerization of bioactive monomers within the cell
voids of wood.
Various compounds were studied including pentachlorophenolyl acrylate (PCPA),
tributyl tin
acrylate (TBTA), 8-hydroxyquinolyl acrylate (HQA). Some of these compounds
afforded a
moderate degree of fungal resistance; however, some of these monomers are
quite toxic (PCPA
and TBTA), none are commonly available (and thus expensive), and all require
the use of
organic solvents such as alcohol or acetone for pressure treatment. Since the
polymers formed
are insoluble in water, they should not leach from the wood under normal
conditions; however, a
high percentage of residual (toxic) monomer was found to be present, which
could potentially
migrate to the surface of the product. This required an additional processing
step (leaching with
acetone) to remove. The composites prepaxed by that method are not expected to
be covalently
bonded graft copolymers formed between wood and the bioactive monomer
(polymer).
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SUMMARY OF THE INVENTION
The subject invention is based on the formation of composite or graft
copolymer materials
formed between wood and polymers that contain quaternary ammonium groups. In
this process,
an aqueous solution of quaternary monomer, catalyst or polymerization
initiator, and (optionally)
crosslinking agent is impregnated into the pores of the wood. Preferably, the
wood or wood-
containing product becomes fully saturated with said solution. Reaction of the
catalyst causes
polymerization of the monomer along with grafting to form covalently bonded
wood/quaternary
composites. The addition of crosslinking agent serves to increase the degree
of branching of the
polymer, thus providing additional bioactive function. Preferably, the
impregnation of the wood
to be treated is assisted by the appropriate application of vacuum and/or
pressure. Heating may
optionally be applied to the system in order to increase the rate of the
polymerization reaction. A
washing step may be employed after polymerization in order to remove soluble
components such
as quaternary homopolymer. Alternatively, or in addition, pre-formed
antimicrobial polymer
may be infused into the lumber to confer resistance to termite infestation,
wood rot, microbial
decay, or to confer other beneficial properties on the lumber. Conference of
resistance to
termites and microbes may also be produced by the presence of antimicrobial
groups within the
interstices of the wood without necessarily being bound to the wood structure.
The monomers used in the practice of this invention preferably contain
polymerizable vinyl or
allyl groups that can be polymerized by free radical polymerization. The
monomers also contain
quaternary ammonium groups in order to provide an antimicr~bial effect.
Quaternary
ammonium compounds are known to show an antimicrobial effect against a wide
variety of
microorganisms including fungi, bacteria, and some viruses. It may not be
expected that
quaternary ammonium compounds would be toxic to termites and other wood-
destroying insects.
It is known, however, that the digestive process of termites relies heavily on
the action of
numerous microorganisms found in the termite gut.
The quaternary polymers utilized in the practice of this invention are of low
toxicity. They also
pose a very low risk for pollution and environmental concerns. Many of the
polymers useful in
the practice of this invention are widely used as flocculating agents in
wastewater treatment.
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Examples of some monomers useful in the practice of this invention are
disclosed in application
no. 09/965,740. Some catalysts that are useful in the practice of this
invention include peroxides,
azo compounds, and cerium (IV) salts, preferably those compounds that are
soluble in aqueous
solutions. Examples of some of these catalysts are: (2,2'-azobis(2-
methylpropionamidine)
dihydrochloride (V-50), hydrogen peroxide, sodium persulfate, and cerium(IV)
ammonium
nitrate.
It will be understood from this disclosure that wood in the form of lumber,
wood-pulp, and
wood-derived products may be treated to confer resistance to microbes,
including but not limited
to fungi, bacteria and the like, as well as to certain insects, such as
termites, which may depend
on the action of microbes in their digestion of wood-based foodstuffs. It will
further be
understood from the present disclosure that quaternary amine containing
polymers may be
formed in-situ, by provision of appropriate conditions for quaternary amine
monomers to
polymerize after being impregnated into the wood. Alternatively, or in
addition, pre-formed
quaternary amine containing polymer may be infused into the interstices of the
wood.
Where formed in-situ, the polymer is at least partially bonded to the
cellulosic substrate of the
wood. Where pre-formed, the polymer will take substantially longer to diffuse
out of the wood
than if quaternary amine monomers are used to protect the wood. Furthermore,
other compounds
may be included with the polymer in formulating an optimal composition for
protecting wood.
Inclusion of copper, chromium, organic antimicrobials and the like may be used
to advantage in
combination with the methods and products taught according to this invention.
Utilization of
this invention in combination with a product such as CCA may permit effective
control of
lumber decay, while at the same time vastly decreasing the amount of CCA
needed to provide
the same level of lumber protection heretofore only achievable using much
higher levels of
CCA.
Treatment of wood and lumber products according to this invention will provide
significant
protection against wood-destroying fungi and insects. It is also likely that
mechanical properties
of the wood will also be improved, particularly at high grafting levels.
Representative examples
of methods used in the practice of this invention are given below, along with
supporting data to
confirm anti-fungal and anti-termite efficacy.
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Example 1:
Yellow pine sapwood, and poplar boards were purchased at a local building
supply store and cut
into 3/4 inch cubes. Growth ring density of the pine was approximately 4 to 6
rings per
centimeter. Wood was stored indoors at room temperature for several days prior
to treatment.
Wood samples were dried to constant weight under vacuum to establish baseline
conditions. The
average weight of the pine blocks was 4.2 grams per block, while the average
weight of the
poplar blocks was 3.6 grams per block.
Approximately 42 blocks were treated in each run. For each run the blocks were
placed into a
750 mL aluminum pressure vessel and evacuated for approximately 20 minutes.
The,treatment
solution was introduced under vacuum and the blocks were allowed to soak for
approximately 10
minutes. An overpressure of 200 psi of argon gas was applied to the vessel,
held for several
minutes, and then released slowly. The pressurization step was then repeated.
The vessel was
slowly vented, opened, and contents of the vessel were then transferred to a
one-quart mason jar.
The liquid in the jar was sparged with argon gas, and the jar was then sealed
with an argon
atmosphere inside. The jar was then placed into an oven at 70°C
overnight (approximately 18
hours).
After heating overnight, the jars were cooled, opened, and the blocks were
removed and washed.
Samples prepared using crosslinking agent had to be physically removed from
the surrounding
gelled polymer. Samples were washed in warm tap water for several days in
order to remove
any residual monomer or soluble quaternary homopolymer. This step is not a
necessary part of
this invention, but it was undertaken in order to allow an evaluation of the
antimicrobial activity
of the grafted copolymer without interference from soluble components. After
washing, the
samples were air-dried at room temperature overnight, and then dried with
heating under vacuum
until constant weight was obtained. The average weight of the blocks was
calculated. The
composition of the treatment solutions and the average weights of the treated
blocks are
presented in Table 1.
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8
The monomer used was Ageflex FM1Q75MC ([2-
(methacroyloxy)ethyl]trimethylammonium
chloride, 75 wt% solution in water, Ciba Specialty Chemicals Corporation),
also abbreviated as
TMMC. Catalysts were either CAN (ammonium cerium(IV) nitrate), SPS (sodium
persulfate),
or V-50. Crosslinking agents were either SR344 (polyethylene glycol
diacrylate, Sartomer
Company), glycerol, or ethoxylatedls trimethylolpropane triacrylate (SR 9035 -
Sartomer
Company).
Table 1
# wood type monomer catalyst crosslinker water weight
1 A pine 100 mL 5 g CAN none 400mL 4.4 g
1 B poplar 100 mL 4 g CAN none 400 mL 3.4 g
2A pine 100 mL 4 g CAN 5 g SR344 +
2 g glycerol 400 mL 4.5 g
2B poplar 100 mL 4 g CAN 5 g SR344 +
2 g glycerol 400 mL 3.9 g
3A pine 150 mL 5 g SPS 20 g SR344 330 mL 5.5 g
3B poplar 150 mL 5 g SPS 20 g SR344 330 mL 4.8g
4A pine 50 mL 3 g CAN 4 g SR344 +
2 g glycerol 450 mL 4.3 g
4B poplar 50 mL 3 g CAN 4 g SR344 +
2 g glycerol 450 mL 3.6 g
Example 2:
Samples of wood treated as taught in Example 1 were inoculated with a white-
rot wood
destroying fungus, along with untreated controls. After 10 days incubation,
the surface of
untreated blocks was greater than 90% covered with a layer of fungal growth.
The treated blocks
were virtually free of any visible fungal growth. Photographs were taken of
these samples in
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order to provide a permanent verification these experimental results. Samples
of wood treated
according to the above formulations were sent to The Mississippi Forest
Products Laboratory at
Mississippi State University for testing according to the AWPA Standard E10-91
"Standard
Method of Testing Wood Preservatives by Laboratory Soil-Block Cultures". .The
average
weight loss of the treated wood blocks (4 different treatment levels), after
exposure to four
different wood-destroying fungi is summarized below:
SPECIES SAMPLE Avg. Wei ht
loss
G. t~~abeum Untreated -44.48%
" Ret 1 -37.71
" Ret 2 -37.32%
" Ret 3 -0.86%
" Ret 4 -13.25%
P. placenta Untreated -40.07%
" Ret 1 -27.12%
" Ret 2 -26.90%
" Ret 3 -20.36%
" Ret 4 -0.26%%
T. lilacino-gilvaUntreated -54.21
" Ret 1 -44.64%
" Ret 2 -44.40%
" Ret 3 -52.63%
" Ret 4 -0.91
T. ver~sicolor~Untreated -73.88%
" Ret 1 -3.32%
" Ret 2 -16.02%
" Ret 3 -18.63%
" Ret 4 -0.45%
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The above data clearly indicates that the treatments were quite effective in
reducing destruction
of wood by fungi.
Example 3:
Samples of wood treated in the manner described Example 1 were subjected to a
modified
version of the AWPA Standard E1-97, "Standard Method for the Laboratory
Evaluation to
Dete_~-mine Resistance to Subterranean Termites". Five jars containing pine
blocks treated by the
above process, and five jaxs containing untreated pine blocks were tested
against termites
(Reticulitermes flavipes). After 10 days, significant destruction of the
untreated wood by insect
activity was observed; whereas, the treated samples were completely intact
with no evidence of
insect activity. Samples of wood treated according to the above formulations
were sent to The
Mississippi Forest Products Laboratory at Mississippi State University for
testing according of
the AWPA Standard El-97, "Standard Method for the Laboratory Evaluation to
Determine
Resistance to Subterranean Termites". These results are summarized below.
Termite s ep ties SAMPLE# Weight loss
Reticulitermes T-1 0.00%
spp.
" T-2 -0.07%
" T-3 -0.28%
" T-4 -1.31
" Untreated -23.09
Coptotermes for~mosanusT-1 -0.12%
" T-2 -0.80%
" T-3 -0.73
" T-4 -0.83
" Untreated -16.42%
It can be seen that all four formulations were very effective in protecting
wood against
destruction by termites.
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11
EXAMPLE 4
1N-SITU POLYMERIZATION AND CROSSLINI~ING TREATMENT OF SOUTHERN PINE
FOR FIELD TESTING
The objective of this study was to evaluate the field performance of wood
treated with several
polymer systems disclosed and claimed herein.
MATERIALS
Monomer - [2-(methacryloyloxy)ethyl]trimethyl ammonium chloride (TMMC);
Initiators - 2,2'-
Azobis(2-methylpropionamidine)dihydrochloride (AZO) and sodium persulfate
(SPS),
Crosslinker - Ethoxylated trimethylolpropane triacrylate esters (SR9035)
PREPARATION OF TREATING SOLUTION
Treating solutions were prepared by adding the monomer, initiator and
crosslinker (in this order)
into water. Special care was taken to ensure that each ingredient was
completely dissolved before
the next ingredient was added. Argon (Ar) gas was sparged into the solution to
purge oxygen
during the whole solubilization process. For each formulation, 3500 grams of
solution were
prepared. The components of each system are given in the following table.
SUMMARY OF THE MONOMER, INITIATOR AND CROSSLINKER
IN THE TREATING SOLUTIONS
Sample TMMC AZO/SPS SR9035 Water
#
1 154.0 AZO:15.0 39.0 3292.0
2 215.0 AZO:15.0 43.0 3227.0
3 312.0 AZO:15.0 52.0 3121.0
4 154.0 SPS:15.0 39.0 3292.0
215.0 SPS:15.0 43.0 3227.0
6 312.0 SPS:15.0 52.0 3121.0
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TREATMENT
Thirty Fahlstrom stakes (0.16" x 1.5" x 10") were vacuum-pressure treated
using l5minutes of
27" Hg vacuum, vacuum fill, followed by 5 minutes of 100 psi pressure of Ar
gas. Retentions
were calculated based upon solution concentrations and weights before and
after treatment.
After treatments, samples were split into two groups. One group was placed
into a plastic bag
pre-purged with Ar gas and sealed. The other group was placed in a plastic bag
without Ar
purging and sealed. Both groups were stored overnight in an oven preset at
70°C. The treated
samples were then taken out, air-dried and the ten stakes closest to the
desired retention were
selected and labeled for field exposure. Stakes were placed into ground
contact exposure in
Gainesville, Florida and inspected annually for extent of fungal decay and/or
termite attack
following the procedure in AWPA Standard E7-O1.
EVALUATION OF THE SOLUTION STABILITY
The solutions before and after treatment were sampled and placed in the lab at
room temperature
for stability evaluation. It was found that all solutions were cured and
gelled after two days.
RESULTS:
Average results for decay and termite infestation were determined after
approximately eight
months in the ground. A perfect wood stake is firm and the corners are square.
Minor softening
in eaxly wood corners or other trace decay and isolated shallow termite
grazing is ignored. A
decay grade of 10 = sound, minimal decay; 9 = trace decay to 3% of cross
section; 8 = 3-10%
decay; 7 = 10-30% decay; 6 = 30-50% decay; 4 = 50-75% decay; 0 = failure. For
termites: 10=
sound, 1-2 small nibbles; 9 = slight feeding -3% of cross section; 8 = 3-10%
of cross section; 7 =
attach of 10-30% of cross section; 6 = 30-50%; 4 = 50-75% cross section
attacked; 0 = failure.
Averages were taken for ten stakes per treatment:
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SAMPLE RETENTION AVERAGE AVERAGE
# DECAY TERMITE DECAY TERMITE
AIR CURED ARGON CURED
1 5.5 10 8.1 9.7 7.7
2 7.4 9.9 8.7 10 9.9
3 10.4 10 9.9 10 9.7
4 5.5 9.9 7.1 9.9 7.0
7.4 10 9.1 10 8.4
6 10.4 9.9 9.5 10 9.7
CONTROL 0 8.8 5.0 8.8 5.0
As can be seen, all treated samples improved resistance to termite attack as
well as to decay. The
degree of protection appeared to be correlated with the retention levels.
The teachings of all cited references are incorporated by reference to the
extent they are not
inconsistent with the teachings herein. It should be understood that the
examples and
embodiments described herein are for illustrative purposes only and that
various modifications or
changes in light thereof will be suggested to persons skilled in the art and
are to be included
within the spirit and purview of this application and the scope of the
appended claims.
