Method for the preservation of wood

A method for the preservation of wood is disclosed whereby the wood is treated with an aqueous, alkaline solution of an alkylol group containing phenol.

BACKGROUND OF THE DISCLOSURE 
The rendering of wood less susceptible to fungal and bacterial 
deterioration has been a major concern for many years. The rotting of wood 
by fungal and/or bacterial degradation is a particularly distressing 
problem, especially in relation to the use of wood for construction 
purposes and more especially with respect to the construction of homes. 
Three classes of wood additives have proved to be the main rotproofing 
agents for wood for many years, i.e., creosote compounds, 
pentachlorophenol and arsenic compounds. While being relatively effective 
rotproofing additives, their use commercially has faded because they are 
all potential carcinogens. Not only are those treating the wood to render 
it rotproof exposed to these carcinogens, but in those cases where the 
treated wood is used in buildings, those humans or animals living in those 
buildings may also be in danger. Furthermore, since these additives are 
held in the wood by physical forces only, they oftimes migrate to the 
surface of the wood. Therefore, the inner portions of the wood are usually 
not durably treated--especially in the case of the use of creosote and/or 
pentachlorophenol. 
In order to produce more durable rotproofing, wood has also been treated 
with phenol-formaldehyde precondensates or prepolymers which polymerize or 
cure to resinous products inside the wood. These products, however, also 
have disadvantages. They have a tendency to polymerize in solution before 
and during treatment, especially under conditions which catalyze the 
polymerization of the phenol-formaldehyde within the wood. When the 
molecule of precondensate or prepolymer is sufficiently large, it does not 
readily penetrate through the pores of the wood and especially will not 
penetrate into the core or heartwood. To alleviate this situation and to 
further improve the rotproofing characteristics, pentachlorophenol is 
oftimes added to the aqueous solution of phenol-formaldehyde resin former. 
Not only does this addition further the problem of the carcinogenicity 
because of the pentachlorophenol, but it adds to the cost of treating the 
wood because of the cost of the pentachlorophenol and the solvent for the 
pentachlorophenol which is necessary to make it miscible with the aqueous 
solution of phenol-formaldehyde precondensate. Also, since the 
pentachlorophenol does not react with the phenol-formaldehyde, it can 
leach out of the wood. U.S. Pat. No. 4,399,195 is directed to a 
composition of this type wherein the solvent is methanol, and over which 
this invention is an improvement. 
Much of the rotproofing of wood today entails the use of pressure treatment 
of the wood to force the molecules, if they are small enough, into the 
core or heartwood. See, for example, U.S. Pat. No. 3,968,276, incorporated 
herein by reference. The pressure treatments are carried out in containers 
which are capable of being evacuated as well as pressurized. Oftimes the 
vessels containing the wood are first evacuated to remove air and moisture 
from the interior of the wood. With aqueous solutions of 
phenol-formaldehyde precondensate, green wood can be treated because some 
of the water can be removed, especially with cycles of evacuation to 
permit sufficient phenol-formaldehyde resin solids to be forced into the 
wood by the pressure treatment following the vacuum treatment. 
The vacuum step may be carried out under various pressures for various time 
periods. Normally, vacuum of at least 10 inches of mercury and up to 30 
inches of mercury or even more is used with time periods usually over 10 
to 15 minutes and for longer periods of time especially if green wood is 
being treated. After evacuation the treating solution is added and then 
pressure applied. The pressure and time of treatment also can be varied. 
Normally, at least 100 psi is used and can be increased to as high as 300 
psi or even higher. Times of pressure can vary from one to two minutes up 
to several hours. 
The use of formaldehyde, urea-formaldehyde resins, melamine-formaldehyde 
resins, and resins of formaldehyde and various unsubstituted phenols and 
chlorinated phenols as rotproofing agents for regenerated cellulose, i.e., 
viscose rayon, is taught by Bell et al; J. Soc. Dyers & Colourists 71, 
November 1955; pages 660-667. Similar treatments of cotton are shown by 
Chance et al; Textile Research Journal, July 1959; pages 558-564. 
Cotton and viscose rayon, however, while both being cellulosic in nature, 
are materially different than wood with regard to the size of specimen 
being treated and the difficulty most additives have in penetrating into 
the deepest portions of the wood. The Bell et al article teaches the use 
of many prepolymers which are converted into resins once present in the 
substrate. Although reaction of the prepolymer, i.e., monomer, with the 
cellulose is postulated, reaction of the prepolymer to form a resin still 
requires the availability of the reactive methylol groups capable of 
forming such a resin. Polymerization of phenol-formaldehyde prepolymers 
occurs either between available methylol groups on two different 
prepolymer molecules or between a methylol group and a hydrogen group of 
two different prepolymer molecules. In both instances, methylol groups 
available for reaction with a reactive hydroxy group of cellulose are 
taken up in the resin formation. Thus, reduction in the permanency of the 
resin positioning within the wood may occur. Bell et al further indicate 
that chlorinated phenols, however, fail to form resins when added to rayon 
as prepolymers. 
Chance et al show the use of phenol, hydroxybenzyl alcohol, chlorinated 
phenols, brominated phenols, and fluorinated phenols as additives to 
cotton wherein again a resin is subsequently formed, and as such, the 
products resulting therefrom suffer from the same deficiencies as 
discussed above regarding viscose rayon. Chance, in fact, indicates that 
resin penetration into the cellulosic fiber is very poor, i.e., only a 
surface treatment is achieved. 
DESCRIPTION OF THE INVENTION INCLUDING PREFERRED EMBODIMENTS 
The present invention provides a method for the rotproofing of wood with a 
small moleculed rotproofing agent in an alkaline, aqueous solution wherein 
the rotproofing agent penetrates deep into the heartwood. The alkalinity 
of the treating solution not only opens up the pores of the wood but is a 
catalyst for the chemical reaction of the agent with the wood. Thus, the 
rotproofing agent not only penetrates into the heartwood but covalently 
reacts with the wood and is durably held in the wood. 
The method of the present invention comprises treating the wood to render 
it less susceptible to fungal and/or bacterial deterioration, under 
conditions such as to cause substantially complete impregnation of the 
wood, such as those pressure treatments described above, with an aqueous, 
alkaline solution of a compound having the formula 
##STR1## 
wherein each R is a blocking group, for example, each R is, individually, 
a halogen, alkyl (C.sub.1 or C.sub.2), hydroxy, nitro, nitroso, or alkylol 
(C.sub.1 or C.sub.2) group, with the proviso, however, that at least one R 
group is an alkylol group, and each R.sup.1 is, individually, hydrogen or 
R, and recovering the resultant treated wood. 
A preferred group of compounds falling within the scope of those of Formula 
I are the compounds wherein both R.sup.1 groups are hydrogen, and at least 
one of the remaining R groups is a halogen. 
An even more preferred class of compounds useful herein are those of 
Formula I wherein all the remaining R groups and R.sup.1 groups are 
halogen. 
From about 1% to about 20% by weight, based on the weight of the wood being 
treated, has been found to reduce successfully the rotting of the wood, 
the higher concentrations providing the greatest degree of rotproofing. 
Examples of compounds falling within the scope of those of Formula I 
include 2,4,6-trimethylol phenol; 2-chloro-4,6-dimethylol phenol; 
2,4-dichloro-6-methylol phenol; 4-chloro-2,6-dimethylol phenol; 
2,4,6-triethylol phenol; 2-chloro-4,6-diethylol phenol; 
2-nitro-4,6-dimethylol phenol; 2-hydroxy-4,6-dimethylol phenol; 
3,4,5-trichloro-2,6-dimethylol phenol; 2,3,5,6-tetrachloro-4-methylol 
phenol; and the like. Compounds wherein the chlorine derivatives are 
replaced by their corresponding bromine, fluorine, or iodine derivatives, 
may also be used. 
The compounds of Formula I are well known in the art and may be prepared by 
any known method. One method comprises reaction of the appropriately 
substituted phenol compound with formaldehyde or other alkyl aldehyde of 
up to two carbon atoms to replace a hydrogen with an alkylol group. 
After the alkylolated phenol has been impregnated into the deepest recesses 
of the wood, the wood may be heated to a temperature ranging from about 
80.degree.-250.degree. F. from about 30 minutes to 30 days in order to 
enhance the rotproofing, the time and temperature depending on the species 
of wood. 
While not wishing to be bound by any particular theory with regard to how 
or why the process of the present invention imparts rot-resistance to 
wood, it is thought that because resin formation is depressed under the 
conditions of application because the active positions of the phenol 
compounds, i.e., the 2, 4, and 6 positions, which usually contain a 
reactive hydrogen are blocked by the R substituents under the alkaline 
conditions, the molecule is allowed to remain small and is therefore 
capable of penetrating deeper into the pores of the wood, especially the 
heartwood, and at least one alkylol group of the compound, in the 
meantime, reacts with the available hydroxy groups of the cellulose and 
hemicellulose of the wood. As a result, the cellulosic hydroxyl groups are 
no longer susceptible to attack by the enzymes of fungi. Rotting is 
therefore decreased. 
Normal polymerization of phenol-formaldehyde occurs with a methylol group 
(in the 2, 4, or 6 positions) on one phenol molecule reacting with a 
hydrogen in the 2, 4, or 6 positions of another phenol molecule splitting 
off water. Under acid conditions, a methylol group of one phenol may react 
with a methylol group in another phenol molecule, again splitting off 
water and forming an ether group. Under alkaline conditions, however, this 
reaction between methylol groups is not favored. Instead a methylol group 
on one phenol molecule reacts with a hydrogen in the 2, 4, or 6 positions 
of another phenol molecule. These reactions continue if enough 
formaldehyde is available to form 2,4,6-trimethylol phenol. With this 
invention, however, blockage of the hydrogen groups in the 2, 4, and 6 
positions prevents, or at least slows, the reaction of one phenol molecule 
with another to form a polymer or resin and permits instead the reaction 
of the methylol phenol with the hydroxy groups of the wood. 
As mentioned above, the alkaline treatment of the present invention, i.e., 
at a pH of at least 7.1, also forms part of the unique results of this 
process because, as mentioned above, it swells the wood and further 
enhances penetration of the phenolic compound. It also provides a catalyst 
for the reaction between the alkylol groups of the additive and the 
hydroxy groups of the wood. 
When the preferred compounds of the present invention are used, i.e., those 
containing a halogen group, the halogen groups provide fungicidal 
properties to the phenol molecule besides blocking the active hydrogen 
which normally actively participates in the formation of resinous 
products. 
Mixtures of the compounds represented by Formula I may also be used herein 
and, in fact, may oftimes be preferred such as where a high degree of 
fungicidal activity and cellulose reaction is desired, i.e., a mixture of 
a monoalkylolated, polyhalogenated phenol and a polyalkylolated phenol. 
Oftimes, also commercial procedures for the manufacture of these phenols 
result in the formation of mixtures thereof. 
If, in addition to rotproofing, fire resistance of the wood is desired, any 
number of known fire-retardant products may be added during the process of 
the present invention. The phosphates such as the ammonium phosphates, for 
example, can be used. However, these do not usually provide durable fire 
retardancy by themselves. If the reactive 
tetrakis(hydroxymethyl)phosphonium salts are used, however, durable fire 
retardancy as well as rotproofing can be obtained. 
Furthermore, biocidal properties may be imparted to the wood by including 
in the alkylolated phenol solution such biocides as 
1-[[2-(2,4-dichlorophenyl)-1,3-dioxolan-2-yl]methyl]-1H-1,2,4-triazole; 
chlorpyrifos[O,O-diethyl O-(3,5,6-trichloro-2-pyridyl)phosphorothionate]; 
DOMINEX.RTM. pyrethroid-(C.A. number 67375-30-8). These biocides may be 
used as organic solvent solutions in such solvents as methanol, xylene, 
acetone, etc., usually in combination with an effective emulsifier. 
Any type of wood can be treated in accordance with the process of the 
present invention, with such woods as Douglas-fir, cedar, larch, redwood, 
pine, spruce, maple, chestnut, oak, and the like being exemplary.

The following examples are set forth for purposes of illustration only and 
are not to be construed as limitations on the present invention except as 
set forth in the appended claims. All parts and percentages are by weight 
unless otherwise specified. 
EXAMPLE 1 
A piece of Douglas-fir plywood is rotproofed by exposing it to an alkaline, 
aqueous solution of 2-chloro-4,6-dimethylol phenol (pH 7.5) to deposit 
within the wood 10% solids of the 2-chloro-4,6-dimethylol phenol on the 
dry weight of the wood. The wood impregnated is a piece of 3/8 inch 
Douglas-fir plywood which is placed in a chamber and evacuated under a 
vacuum of 29 inches of mercury. The solution of 2-chloro 4,6-dimethylol 
phenol is drawn into the chamber to totally immerse the plywood. After 20 
minutes of vacuum, pressure is built up to 100 psi and held for 2 minutes. 
The chamber then is drained, evacuated for 10 minutes, and the plywood 
removed and allowed to dry. The treated wood is found to be rotproofed. 
EXAMPLE 2 
A piece of green red oak, 1.times.5.times.30 inches with a moisture content 
of 28%, is placed in a chamber and impregnated with an alkaline, aqueous 
solution of 2,4-dichloro-6-methylol phenol (pH 8.0) to deposit 7.5% solids 
of the 2,4-dichloro-6-methylol phenol on the weight of the dry wood. A 
vacuum of 29 inches of mercury is applied to the wood in the chamber for 
15 minutes. The impregnating solution is then admitted to the chamber to 
cover the sample of wood and the vacuum maintained for 20 minutes. 
Pressure is built up in the chamber to 300 psi and the pump secured until 
the pressure falls to 200 psi. The pressure is then increased again to 300 
psi. This cycle is repeated five times. The solution is then drained and 
the wood removed and dried at room temperature for 72 hours. The wood is 
found to be rotproofed. 
EXAMPLE 3 
A green Douglas-fir 12.times.12-inch timber, 2 feet long, is placed in a 
chamber and the chamber evacuated to 26 inches of mercury. An alkaline, 
aqueous solution of 4-chloro-2,6-dimethylol phenol (pH 7.1) is drawn into 
the chamber until the timber is totally immersed. Vacuum is increased to 
29 inches of mercury and held for 15 minutes. The chamber is vented to the 
atmosphere, closed, and vacuum again applied. The solution is again drawn 
into the chamber until 20% solids of the phenol is deposited on the weight 
of the wood. Pressure is then increased to 300 psi and held for 15 
minutes. The chamber is then drained and the wood removed. The wood is 
then exposed to a temperature of 250.degree. F. for one hour to effect 
further reaction of the halogenated methylol phenol with the wood. 
Rotproofing is again effected. 
EXAMPLE 4 
A piece of red oak (1.times.5.times.30 inches) is placed in a chamber and 
impregnated with an alkaline, aqueous solution (pH 7.6) of 
2-chloro-4,6-dimethylol phenol and tetrakis(hydroxymethyl)phosphonium 
sulphate to deposit within the wood 10% solids of the 
2-chloro-4,6-dimethylol phenol and 15% solids of the 
tetrakis(hydroxymethyl)phosphonium sulphate on the dry weight of the wood 
by evacuation of the chamber with a vacuum at 29 inches of mercury for 10 
minutes and then immersion of the wood in the treating solution. After 20 
minutes of vacuum, the pressure is built up to 100 psi and held for 5 
minutes. The chamber is then drained and the wood heated for 20 minutes at 
250.degree. F. The resultant wood is found to be rotproofed and flame 
resistant. 
EXAMPLE 5 
A 3/8-inch Douglas-fir plywood sample is rotproofed by exposing it to an 
alkaline solution of 2,4,6-trimethylol phenol (pH 7.4) to deposit within 
the wood 8% solids of the rotproofing agent. The wood is placed in a 
chamber which is then evacuated to 28 inches of mercury. The alkaline 
solution is drawn into the chamber to immerse the wood. After 15 minutes 
of vacuum, the pressure is built up to 120 psi and held for 5 minutes. 
After the chamber is drained, the plywood is heated for 2 hours at 
200.degree. F. The plywood is found to be rotproofed. 
EXAMPLE 6 
A piece of red oak (1.times.6.times.36 inches) is placed in a chamber and 
impregnated with an alkaline solution of 2,4-dimethyl-6-methylol phenol 
(pH 8.1) to deposit within the wood 9% solids of the impregnating 
material. The wood is first placed in a chamber and evacuated with a 
vacuum of 29 inches of mercury for 8 minutes and then immersed in the 
treating solution. After 15 minutes of vacuum, the pressure is built up to 
100 psi and held for 10 minutes. The chamber is then drained, the wood 
removed and dried. The wood is rotproofed. 
EXAMPLE 7 
The procedure of Example 1 is again followed except that the phenolic 
compound is 2-chloro-4,6-diethylol phenol. Similar results are obtained. 
EXAMPLES 8-12 
Again following the procedure of Example 1, various compounds falling 
within the scope of those of Formula I, above, are impregnated into the 
fir plywood. In each instance, rotproofing of the plywood occurs. The 
specific compounds employed are listed in Table I, below. 
TABLE I 
______________________________________ 
Example Compound of Formula I 
______________________________________ 
8 2-hydroxy-4,6-dimethylol phenol 
9 3,5-dichloro-2,4,6-trimethylol phenol 
10* 2,6-dinitro-4-methylol phenol 
11 3,5-dibromo-4,6-dimethyl-2-methylol phenol 
12** 3,4,5,6-tetrachloro-2-methylol phenol 
______________________________________ 
*Example 4 followed in lieu of Example 1. 
**The treated wood is heated at 100.degree. F. for 30 days. 
EXAMPLE 13 
Example 1 is again followed in all material detail except that a mixture of 
2-chloro-4,6-dimethylol phenol and 2,4-dichloro-6-methylol phenol (50/50) 
is employed. Similar results are achieved. 
EXAMPLE 14 
Again following the procedure of Example 2 except that the aqueous solution 
also contains 0.5% of 
1-[[2-(2,4-dichlorophenyl)-1,3-dioxolan-2-yl]methyl]-1H-1,2,4-triazole. 
The resultant wood exhibits fungicidal properties in addition to being 
rot-proofed. 
EXAMPLE 15 
The procedure of Example 14 is followed except that the insecticide 
employed is chlorpyrifos[O,O-diethyl 
O-(3,5,6-trichloro-2-pyridyl)phosphorothionate]. Again, excellent results 
are achieved.