Enhanced wood preservative composition

A wood preservative composition comprising a biocide such as a quaternary ammonium compound, e.g., didecyldimethyl ammonium chloride (DDAC), an isothiazolone or an isophthalonitrile, in combination with an antioxidant, which is a flavone or a phenol, is useful as a cost-effective and environmentally safe wood preservative. The invention also provides a method for the use of such composition and compositions so treated.

BACKGROUND OF THE INVENTION 
Hardwoods constitute over one-third of the U.S. timber resource. However, 
with the exception of crossties, hardwoods are rarely treated for exterior 
use applications, and demand for treated hardwood products has until 
recently been low. In view of the projected softwood timber shortage and 
relative abundance of hardwoods, expanded use of treated hardwoods for 
both composite and solid wood products is expected. The problem is that 
replacing softwoods with hardwoods is not straightforward since most wood 
preservatives, including second generation biocides, are considerably less 
effective when used to treat hardwoods. (Nicholas, D. D., Proc. of the 
Northern Hardwood Resource: Management and Potential Conference, Heighten, 
Mich., Aug. 18-20 (1986); Preston, A. F., et al., Proc. Am. Wood 
Preservers' Assn., 79, 207 (1983)). This disparity is attributable to the 
considerably higher toxic threshold values obtained when treated hardwoods 
are attacked by white- and soft-rot fungi as compared to softwoods treated 
with the same biocide and exposed to brown-rot fungi. (Nicholas, supra). 
Accordingly, the object of the present invention is to provide wood 
preservative systems that are effective in protecting hardwoods and 
providing greater efficacy for softwoods. 
An apparent solution to the problem of preserving hardwoods is to use 
substantially higher biocide levels, but this approach leads to higher 
costs and increased environmental risks. A more attractive solution would 
be to increase the efficacy of biocides for treating hardwoods. 
In addition, more environmentally benign preservatives to treat softwoods 
are needed, since all major wood preservatives used today to protect 
softwoods have perceived environmental problems. 
Prior to the present invention, antioxidants have been used in wood 
treatments of various kinds, but never in conjunction with a biocide to 
generate a synergistic and environmentally safe preservative for both 
hardwoods and softwoods. In most previous wood preservatives containing 
antioxidants, their purpose was merely to stabilize the mixture from 
chemical decomposition or as a color stabilizer. For example, U.S. Pat. 
No. 1,168,062 discloses the use of oxidation inhibitors as an additive in 
oil-in-water emulsions for use in wood preservatives which contain 
pentachlorophenol as the active ingredient. U.S. Pat. No. 3,889,020 
provides di-t-butyl cresol (also called butylated hydroxytoluene, or BHT) 
as a stabilizer for pentachlorophenol-based preservatives wherein the 
cresol is intended to improve the surface color of treated poles. 
U.K. Patent Application GB 2,025,769A discloses the use of antioxidants, 
selected from such compound classes as sulfites, hydrosulfides, hydrazines 
and thiosemicarbazides. The purpose of the antioxidant there is to 
stabilize biocides from decomposition. U.S. Pat. No. 3,881,940 describes a 
composition containing an antioxidant stabilizer such as di-t-butylcresol 
in a biocide comprising a heavy metal oxide and pentachlorophenol. The 
antioxidant served to prevent discoloration of wood and to prevent sludge 
formation during treating steps. 
U.S. Pat. No. 4,400,298 teaches the combination of dithiocarbamate and a 
borate with an antioxidant stabilizing agent, e.g., potassium 
metabisulfite, for the prevention of fungal decay in wood. U.S. Pat. No. 
4,783,221 describes wood preservatives containing an isothiazolone and 
metal salts of carboxylic acids, to which various additives are added 
including antioxidants. U.S. Pat. No. 5,462,589 discloses a synergistic 
wood preservative composition comprising copper and organic derivatives, 
of which antioxidants are recited as possible additives. 
Despite these teachings of antioxidants in wood treatment products, usually 
as stabilizers, synergistic enhancement of biocide effectiveness by 
antioxidants was unknown prior to the present invention. Moreover, this 
approach has never before been applied to provide an effective wood 
preservative for hardwoods. 
SUMMARY OF THE INVENTION 
The present invention relates to the unexpected utility of adding free 
radical scavengers (antioxidants) to commercial biocides to protect 
hardwoods from fungal decomposition. Selected antioxidants significantly 
increase the activity and effectiveness of biocides to treat hardwoods. 
Accordingly, the present invention provides a wood preservative composition 
comprising (A) at least one biocide selected from the group consisting of 
a quaternary ammonium compound, an isothiazolone, and an isophthalonitrile 
and (B) at least one antioxidant. The composition is especially effective 
when the antioxidant is a flavonoid or a phenol. 
In addition to being highly effective, the wood preservative composition is 
environmentally safe and inexpensive to apply. Of particular practical 
importance is the discovery that the low-cost antioxidant BHT, which is 
commonly used as a food additive, when combined with a biocide has an 
enhanced and synergistic biocidal effect with minimal environmental 
effects. 
DETAILED DESCRIPTION 
The present invention provides a wood preservative composition comprising: 
A. an effective amount of at least one biocide selected from the group 
consisting of: 
(1) a quaternary ammonium compound having the structure: 
##STR1## 
wherein R.sub.1 is a C.sub.8-12 alkyl group or an aralkyl group, or a 
chloro- or C.sub.1-8 alkyl-substituted aralkyl group; R.sub.2 is a 
C.sub.8-12 alkyl group; R.sub.3 and R.sub.4 are the same or different and 
are a C.sub.1-4 alkyl group, a C.sub.1-4 hydroxyalkyl group, an aralkyl 
group, or a chloro- or C.sub.1-8 alkyl-substituted aralkyl group; and X is 
a halide or an alkylsulfate; 
(2) an isothiazolone having the structure: 
##STR2## 
wherein R.sub.5 is a substituted or unsubstituted C.sub.1-12 alkyl, 
C.sub.3-8 cycloalkyl, alkenyl, alkynyl, aryl or aralkyl group; and R.sub.6 
and R.sub.7 are the same or different and are hydrogen, a halogen or a 
substituted or unsubstituted C.sub.1-12 alkyl, aryl or aralykyl group; and 
(3) an isophthalonitrile having the structure: 
##STR3## 
wherein R.sub.8, R.sub.9, R.sub.10 and R.sub.11 are the same or different 
and are hydrogen, a halogen or a C.sub.1-12 alkyl group; and 
B. an effective amount of at least one antioxidant. 
The present invention also provides a wood preservative composition as 
disclosed above wherein the antioxidant is: 
(1) a flavonoid having the structure: 
##STR4## 
wherein R.sub.12, R.sub.13, R.sub.14, R.sub.15 and R.sub.16 are the same 
or different and are hydrogen, hydroxyl or a C.sub.1-12 alkoxy group; and 
wherein the dashed line represents a single or double bond; or 
(2) a phenol having the structure: 
##STR5## 
wherein R.sub.17, R.sub.18 and R.sub.19 are the same or different and are 
hydrogen, halogen, methoxyl, a C.sub.2-12 alkoxyl or a C.sub.1-12 alkyl 
group. Other antioxidants which may be used include dimers, trimers or 
tetramers of the basic structure above such as 
tetrakismethylene(3,5-di-t-butyl-4-hydroxy hydrocinnamate)! or 
4,4'-methylenebis(2,6-di-t-butylphenol). Additional antioxidants include, 
but are not limited to, natural polymeric phenolic materials, such as 
tannins isolated from the wood or bark of woody plants, and lignins 
isolated from woody plants such as kraft pulping lignin, organosolve 
lignin, autohydrolysis lignin, acid-hydrolyzed lignin, steam-exploded 
lignin and derivatives of isolated lignins. Other classes of antioxidants 
which are useful include phosphites, phosphonites, thio bisphenols, 
alkylidene-bisphenols, hydroxybenzyl compounds, acylaminophenols and 
hydroxyphenylpropionates. 
An unsubstituted alkyl group as used in the invention is intended to 
include straight chain and branched chain alkyl, and when substituted, is 
meant to encompass an alkyl group having one or more of its hydrogen atoms 
replaced by another substituent. Examples of the substituted alkyl groups 
useful in the invention include hydroxyalkyl, haloalkyl, cyanoalkyl, 
alkylaminoalkyl, dialkylaminoalkyl, arylaminoalkyl, carboxyalkyl, 
carboalkoxyalkyl, arylthioalkyl, cycloalkylaminoalkyl (e.g., 
morpholinoalkyl, piperidinoalkyl), alkenyl, haloalkenyl, alkynyl, etc. 
A substituted aralkyl group is meant to encompass an aralkyl group having 
one or more of hydrogen atoms on its aryl ring or alkyl group replaced by 
another substituent group. A substituted aralkyl group is meant to 
encompass an aralkyl group having one or more of the hydrogen atoms on its 
aryl ring or alkyl group replaced by another substituent group. A 
substituted aryl group is meant to encompass an aryl group having one or 
more of the hydrogen atoms on its aryl ring replaced by another 
substituent group. 
The quaternary ammonium salt used in the wood preservative composition 
encompasses compounds wherein R.sub.1 and R.sub.2 may be the same or 
different. Examples of R.sub.1 and R.sub.2 include n-octyl, n-nonyl, 
n-decyl, n-undecyl and n-do decyl. Examples of R.sub.3 include methyl, 
ethyl, n-propyl, isopropyl, n-butyl, sec-butyl, t-butyl, hydroxyethyl, 
benzyl, 3-chlorobenzyl, 1,4-dichlorobenzyl, 1,3-dichlorobenzyl, 
3-methylbenzyl, 4-methyl, 2,4-dimethylbenzyl, and 3-ethylbenzyl. Examples 
of R.sub.4 include methyl, ethyl, iso-propyl, n-propyl, and n-butyl. X may 
be fluoride, chloride, bromide, iodide, or methylsulfate, ethosulfate. In 
preferred embodiments, the quaternary ammonium salt is a compound wherein 
R.sub.1 and R.sub.2 are bomb n-decyl, R.sub.3 and R.sub.4 are both methyl, 
and X is chloride, methosulfate or ethosulfate. 
Examples of these quaternary ammonium compounds include 
didecyldimethylammonium chloride (DDAC), didecyldimethylammonium 
ethosulfate, didecylmethylpropylammonium bromide, 
didecylmethylbutylammonium chloride, benzylhexadecyldimethylammonium 
chloride, didecylmethyl-4-chlorobenzylammonium chloride, 
didecylmethyl-3,4-dichlorobenzylammonium chloride; 
decyloctyldimethylammonium chloride, decyloctylbenzylmethylammonium 
chloride, decyldodecyldimethylammonium chloride, 
decyldodecylethylmethylammonium chloride, dodecylbenzyldimethylammonium 
chloride, tetradecylbenzyldimethylammonium chloride, 
diundecyldimethylammonium chloride, dinonylhydroxyethylmethylammonium 
chloride, didecylhydroxypropylmethylammonium chloride, and 
diundecyldihydroxyethylammonium chloride. Blends of compounds containing 
dioctyl, didodecyl and decyloctyl compounds or didecyl, didodecyl and 
decyldodecyl compounds may also be used. In addition, mixtures of 
C.sub.12,C.sub.14 and/or C.sub.16 alkyldodecylbenzylammonium chlorides are 
useful in practising the invention. 
Examples of the substituted alkyl groups characteristic of 3-isothiazolones 
useful in the invention include hydroxymethyl, hydroxyethyl, 
methoxymethyl, ethoxymethyl, ethyoxyethyl, aminoethyl, 
N-acetylaminomethyl, N-acetylaminoethyl, carboxy, methoxycarbonyl, 
ethoxycarbonyl, trifluoromethyl, trifluoroethyl, pentafluoroethyl, etc. 
Examples of the substituted aralkyl groups characteristic of 
3-isothiazolones useful in the invention include halogen-, lower alkyl- 
and lower alkoxy-aralkyl groups. Examples of substituents for aryl groups 
in 3-isothiazolones useful in practising the invention include halogen, 
nitro, lower alkyl, lower alkyl-acylamino, lower carbalkoxy, sulfamyl, 
etc. 
Specific 3-isothiazolones used as a biocide in the composition include 
compounds wherein R.sub.5 is n-octyl, and R.sub.6 and R.sub.7 are both 
chloride; wherein R.sub.5 is n-decyl, and R.sub.6 and R.sub.7 are both 
chloride; wherein R.sub.5 is n-octyl, and R.sub.6 is hydrogen and R.sub.7 
is chloride; and wherein R.sub.5 is n-octyl, and R.sub.6 is chloride and 
R.sub.7 is phenyl. 
The halogen in the isophthalonitrile used as a biocide in the composition 
may be fluoride, bromide, chloride or iodide. Preferably, the halogen is 
chloride. The alkyl group in the isophthalonitrile may be unsubstituted or 
substituted as described below. 
Specific isophthalonitriles useful in the invention include compounds 
having the above-shown structure wherein R.sub.8, R.sub.9, R.sub.10 and 
R.sub.11 are all chloride (chlorothalonil); wherein R.sub.8 and R.sub.9 
are hydrogen and R.sub.10 and R.sub.11 are both chloride; wherein R.sub.8 
and R.sub.11 are both hydrogen and R.sub.9 is methyl and R.sub.10 are 
chloride; wherein R.sub.9 and R.sub.11 are both hydrogen and R.sub.8 and 
R.sub.10 are both chloride. 
Specific examples of phenols used as antioxidants in the invention include 
the phenol shown above wherein R.sub.17 is methoxyl or methyl and R.sub.18 
and R.sub.19 are both t-butyl (butylated hydroxy toluene (BHT)or butylated 
hydroxy anisole (BHA)); and the phenol wherein R.sub.17 is hydrogen and 
R.sub.18 and R.sub.19 are both t-butyl. Preferably, R.sub.18 and R.sub.19 
are t-butyl. 
The flavonoid used as an antioxidant includes compounds wherein R.sub.12 
and R.sub.14 are both hydroxyl and R.sub.13, R.sub.15 and R.sub.16 are all 
hydrogen, and wherein the dashed line signifies a double bond (quercetin); 
the flavonoid wherein R.sub.12 and R.sub.14 are both hydroxyl and 
R.sub.13, R.sub.15 and R.sub.16 are all hydrogen, and wherein the dashed 
line signifies a double bond. Examples of such flavonoids are, chrysin, 
luteolin, myrcetin, hespertin and rhamnetin. 
The wood preservative composition disclosed herein may further comprise a 
liquid carrier medium selected from the group consisting of a solvent and 
a suspending agent. Preferably, the liquid carrier medium is a solvent 
such as methanol, ethanol, alcohols, water, ethyl acetate, toluene, a 
paraffinic hydrocarbon or di chloromethane. The suspending agent may be a 
foam or gel. The composition may also be applied as a solution in miscible 
mixtures of solvents or as an emulsion in multiphasic media. If desired, 
buffers, water-repellents, insecticides, pigments, odorants, coloring 
agents, surfactants, flame-retardant compositions and other additives may 
be added to the treating solution. The amount of such additives may vary 
over a range from about 0.01% to about 7%. The composition of the 
invention may be provided not only as a diluted solution but also as a 
concentrate comprising an undiluted solution, emulsion or suspension of 
biocide and antioxidant which may be diluted with any of the above-named 
solvents. The composition may also be formulated without added solvent or 
diluent as a powder or pellets. 
The amount of the biocidal composition used in the composition and method 
of the invention is a "biocidal effective amount," i.e., an amount 
effective to inhibit the growth of, or kill, one or more organisms that 
cause wood rot. Such organisms include but are not limited to P. placenta, 
T. versicolor, Irpex lacteus (I. lacteus) and Gloeophyllum trabeum (G. 
trabeum). In the wood preservative composition of the invention, the 
weight ratio of the biocide to the antioxidant is from about 0.10:1 to 
about 3:1, preferably from about 0.50:1 to about 2:1. The biocide may be 
present in an amount of from about 0.01 to about 10% by weight and the 
antioxidant in an amount of from about 0.10 to about 12% by weight. 
In pressure-treating wood with the present compositions, roughly 1 gallon 
of treating solution is used for each board-foot of lumber with about 20% 
to about 50% of the solution being absorbed by the wood. Contact times of 
about 2 hours are typically used. Generally, 1,000 board feet of lumber 
require about 1,000 gallons of treating solution which is administered 
during a contact period of between about 1 and about 6 hours. 
The present invention also provides a method for preserving wood against 
destructive fungi which comprises contacting wood with a biocidally 
effective concentration of the wood preservative composition as defined 
above in a carrier liquid. Accordingly, the method permits preserving wood 
against at least one fungus selected from the group consisting of P. 
placenta, I. lacteus, T. versicolor and G. trabeum. 
The components of the present invention are mixed by conventional means 
known in the art to form an emulsion, such as oil in water microemulsions, 
or they may alternatively be prepared as solutions. Conventional 
additives, such as stabilizers, odorants, surfactants, coloring agents, 
emulsifiers and water repellents, may be added as required for particular 
applications. Typical amounts of such additives vary from about 0.001% to 
about 5% by weight. 
Treatment of wood, e.g. lumber, timber, etc., can be carried out by 
conventional techniques including, but not limited to, dipping, spraying, 
brushing, pressure impregnation, and vacuum treatment. The length of the 
treatment time required will vary according to the treatment conditions, 
the selection of which are well known to those skilled in the art. 
Throughout this application, various references are cited within 
parentheses. These publications are hereby incorporated by reference to 
more fully describe the state of the art to which this invention pertains. 
This invention will be better understood from the Examples which follow. 
However, one skilled in the art will readily appreciate that the specific 
methods and results discussed are merely illustrative of the invention as 
described more fully in the claims which follow thereafter. Unless 
otherwise indicated, all parts and percentages in the Examples and the 
present specification are by weight.

EXAMPLE 1 
Sweetgum sapwood blocks were treated with either didecyldimethylammonium 
chloride (DOAC) or 4,5-dichloro-2-n-octyl-4-isothiazolin-3-one (Kathon 
930.TM.,Rohm & Haas), with and without the antioxidant BHT (Table 1). 
These blocks were exposed to the white-rot fungus Irpex lacteus for eight 
weeks in the agar block test described by Archer, K., et al., For. Prod. 
J., 45(1), 86-89(1995). The average retentions are reported in pounds of 
preservative per cubic foot of wood (pcf), as is normal in the wood 
preservative industry. The biocide effectiveness is determined by % weight 
loss. Average % weight loss was determined for 5 mm.times.14 mm.times.14 
mm sweetgum sapwood samples using the agar-block test. The wood was 
exposed to the white-rot fungus I. lacteus for eight weeks, with five 
replicates per treatment. Methanol was used as the solvent. Five 
replicates and one untreated (control) sample were run in each agar cup. 
The results, presented in Table 1, clearly show that the addition of small 
amounts of BHT produced a substantial increase in the activity of both 
biocides. For example, adding as little as 0.03 pcf BHT reduced the toxic 
threshold values of both DDAC and Kathon 930 by over four-fold. This 
experiment supports the concept that the activity of biocides used as 
hardwood preservatives can be significantly increased by adding 
antioxidants. 
TABLE 1 
______________________________________ 
Summary of average % weight loss for 5 mm .times. 14 mm .times. 14 mm 
sweetgum sapwood samples using the agar-block test. 
Biocide/Average Retention (pcf) 
Avg % Weight Loss .+-. Std.Dev. 
______________________________________ 
BHT/0.11 22.6 .+-. 8.7 
BHT/0.23 23.6 .+-. 5.9 
BHT/0.47 20.8 .+-. 7.1 
BHT/0.75 24.2 .+-. 5.4 
DDAC/0.03 22.8 .+-. 4.0 
DDAC/0.05 21.4 .+-. 2.1 
DDAC/0.17 15.7 .+-. 3.1 
DDAC/0.29 0.10 .+-. 1.1 
BHT/0.03; DDAC/0.03 
0.8 .+-. 0.1 
BHT/0.05; DDAC/0.05 
0.8 .+-. 0.0 
BHT/0.17; DDAC/0.17 
0.9 .+-. 0.1 
BHT/0.20; DDAC/0.20 
1.0 .+-. 0.0 
BHT/0.19; DDAC/0.10 
0.8 .+-. 0.1 
Kathon 930/0.02 15.4 .+-. 3.0 
Kathon 930/0.03 15.9 .+-. 6.4 
Kathon 930/0.07 8.3 .+-. 4.1 
Kathon 930/0.12 3.0 .+-. 1.8 
Kathon 930/0.17 -0.4 .+-. 0.3 
BHT/0.03; Kathon 930/0.03 
0.9 .+-. 0.0 
BHT/0.04; Kathon 930/0.04 
0.9 .+-. 0.0 
BHT/0.10; Kathon 930/0.05 
0.9 .+-. 0.1 
BHT/0.17; Kathon 930/0.09 
1.0 .+-. 0.0 
Controls 22.9 .+-. 7.6 
______________________________________ 
EXAMPLE 2 
To show that free radical scavengers (primary antioxidants) will increase 
the efficacy of commercial biocides used as wood preservatives, two tests 
are performed: (1) soil-block and/or agar-block tests and (2) unsterile 
soft-rot test. 
Three commercial biocides were selected for the soil block experiments: 
DDAC (didecyldimethylammonium chloride), chlorothalonil 
(2,4,5,6-tetrachloroisophthalonitrile), and Kathon 930 
(4,5-dichloro-2-n-octyl-4-isothiazolin-3-one). These three biocides show 
promise as potential wood preservatives (Nicholas, D. D. and T. P. 
Schultz, "Biocides That Have Potential as Wood Preservative--An Overview," 
Forest Prod. Soc. Proc., Wood Preservation in the '90s and Beyond (1995)), 
and are either hydrophilic (DDAC) or hydrophobic. The antioxidants used 
include the commercial hydrophobic antioxidant BHT and the natural 
hydrophilic antioxidant quercetin. 
The agar plate method was used (Behr, "Decay Test Methods," Wood 
Deterioration and Its Prevention by Preservation Treatments I, D. 
Nicholas, ed., Syracuse Univ. Press (1973)). In this method agar nutrient 
solutions with various concentrations of biocides are prepared. A plug of 
agar with actively growing fungus is placed in the center of each plate 
and the relative mycelium growth for the treated agar is compared to the 
untreated (control) agar plate. The plates are placed in an incubator at 
28.degree. C. The minimal concentration of biocide composition which 
totally inhibits fungal growth (MIC) and the concentration at which the 
mycelium radial growth is inhibited by 50% (IC.sub.50) can then be 
calculated. 
The wood used in the agar- or soil-block tests includes sweetgum sapwood 
and southern pine sapwood, selected according to AWPA standard E 10-91. 
The white-rot fungi examined were T. versicolor (ATCC#12679) and I. 
lacteus (ATCC#11245) and the brown-rotters were G. trabeum (ATCC#11539) 
and P. placenta (ATCC#11538). Samples treated with the biocide alone at 
five different retention levels were directly compared with similar 
samples treated with the biocide at the same retention levels plus one of 
the two antioxidants at a single retention level. Untreated samples and 
samples treated only with the antioxidants served as controls. 
There is currently no standard method for evaluating wood preservatives 
against soft-rot fungi, so the soil bed method developed by Nicholas, D. 
D., et al., Effect of Soft-rot Decay on the Static Bending Strength of 
Wood, Intern. Res. Gp. on Wood Pres., Doc. No. IRG/WP/2361 (1991)) was 
used. In this method, thin (3 mm.times.19 mm.times.250 mm; 
t.times.r.times.l) sticks are exposed to unsterile soil maintained at a 
moisture content sufficiently high to favor soft-rot fungi. The degree of 
soft-rot attack is determined by periodically measuring the bending 
stiffness of each specimen. The soft-rot tests were carried out with 
sweetgum sapwood samples treated with the combinations of biocides and 
antioxidants shown in Table 2. This soil bed was maintained at a moisture 
content level that provides a minimum equilibrium moisture content of 
approximately 60% in the test samples. The test samples were removed and 
evaluated for bending stiffness approximately every 60 days. 
TABLE 2 
______________________________________ 
Treatments for Soft-rot and Soil-block Tests. 
Treating Solution Biocide/Additive 
Components Conc. (% a.i.) 
______________________________________ 
DDAC 0.20, 0.50, 0.75, 1.00, 1.50 
DDAC/BHT 0.20/0.50, 0.50/0.50/0.75/0.50, 
1.00/0.50, 1.50/0.50 
DDAC/Quercetin 0.20/0.50, 0.50/0.50/0.75/0.50, 
1.00/0.50, 1.50/0.50 
Chlorothalonil 0.20, 0.40, 0.60, 1.00 
Chlorothalonil/BHT 
0.20/0.50, 0.40/0.50, 0.60/0.50, 
1.00/0.50 
Chlorothalonil/Quercetin 
0.20/0.50, 0.40/0.50, 0.60/0.50, 
1.00/0.50 
Kathon 930 0.05/0.50, 0.10/0.50, 0.20/0.50, 
0.50/0.50 
Kathon 930/BHT 0.05/0.50, 0.10/0.50, 0.20/0.50, 
0.50/0.50 
Kathon 930/Quercetin 
0.05/0.50, 0.10/0.50, 0.20/0.50, 
0.50/0.50 
______________________________________ 
DISCUSSION 
These tests show that the efficacy of biocides to protect hardwoods can be 
significantly enhanced by the method disclosed herein. Specifically, the 
addition of an antioxidant to biocides results in a significantly more 
active wood preservative. 
The present inventors have determined that the preservative system 
disclosed herein can be used for both composite products that utilize 
hardwoods and softwoods as well as solid wood products and, as a result, 
greatly increase the utilization of hardwoods in applications where the 
product is susceptible to biodeterioration. Composite products are of 
particular interest because most of them contain hardwoods. However, for 
ecological and economic reasons, it is desirable to minimize the amount of 
biocide used to achieve a preservative effect. Accordingly, the addition 
of antioxidants in accord with the present invention should reduce the 
preservative retention levels required, and consequently, greatly improve 
the economics of both hardwood and softwood preservative systems, and 
thereby provide a more environmentally benign approach to the preservation 
of wood. 
Variations of the present invention will suggest themselves to those 
skilled in the art, and are within the scope of the following claims.