Technical Field

This invention relates to a composition and method for preserving wood and other cellulose based materials such as paper, particle board, textiles, rope, etc.... against destructive organisms responsible for rot and decay, namely fungus and insects. More particularly, this invention re¬ lates to an organometal preservative composition, having in- secticidal and fungicidal properties, in the form of an aqueous solution of a compound of metal ammonium complexes of certain specified dicarboxylic acids or mono, di or tri- carboxylic hydroxy acids.. Background Art

Metal compounds have long been recognized for their fungicidal properties. Copper sulfate was recommended for use in wood preservation as early. as 1767 and patented for that purpose in England in 1937 by Margary. Since its ini¬ tial use in the early 1800's copper sulfate has played a ma¬ jor role in the wood preserving industry. However, the use of copper sulfate as a wood preservative has two major dis- advantages. First, copper sulfate does not become perma¬ nently fixed in the wood and is therefore prone to leach¬ ing. Secondly, copper alone is not an effective preserva¬ tive against all forms of wood destroying organisms.

In the early 1940's, a new generation of water-borne preservatives with superior leach resistance was developed. These new preservative systems were based on copper plus the incorporation of chromium and/or arsenic. These preserva¬ tive systems are known as chromated copper arsenate (CCA)

and ammoniacal copper arsenate (ACA). These systems are ef¬ fective preservatives and are the predominant water borne systems used in the wood preserving industry today.

The use of metal salts and organic acids as wood pre- servatives has been known since the early 1900's. During the creosote shortage of the mid-1940's, mixtures of naph- thenic acids, derived from petroleum by-products, were com¬ bined with metal salts to form a series of compounds for wood preservation. One of these compounds was copper naph- thenate. Copper naphthenate was formed by the reaction of copper salts with a group of organic acids known as cyclo- pentane carboxylic acid. Copper naphthenate is an oil-borne preservative system and while an effective preservative, it has a strong odor and because of its waxy nature, wood treated with this preservative is difficult to paint.

Additional antifungal water-borne preservative sys¬ tems based on metal salts and fatty acids have since been developed. U.S. patent 4,061,500 describes a wood preserva¬ tive effective against blue stain, containing a fatty acid of 6-11 carbon atoms, boric acid and an alkali compound- in stoichiometric excess of the fatty acids. The incorporation of copper salts with straight chain fatty acids and fatty alcohols is described in U.S. patent 4,001,400. Here, cop¬ per, zinc, nickel, cadmium and cobalt are combined with an ammoniacal fatty acid salt to provide a water-borne preser¬ vative system which is claimed to be effective against fungi mould and blue stain. The branched chain fatty acid con¬ tains 6-12 carbon atoms per molecule.

A process for preparing a homogeneous liquid compo- sition comprising a cuprammonium complex of one or more monocarboxylic acids containing 1-4 carbon atoms per mole¬ cule is described in U.S. patent 4,175,090. These parti¬ cular compositions are used as fungicides for treating wood, painting surfaces, fabrics and also to inhibit algal growth. U.S. patent 4,220,661 describes a preservative com-

position useful for preventing the growth of mould, bacteria and fungi comprising an aqueous solution of a complex salt of an ion selected from NH+. and a Group I or Group II metal ion and one or more carboxylic acids selected from saturated and unsaturated aliphatic monocarboxylic acids containing from 2-8 carbon atoms.

U.S. patent 4,193,993 discloses a process for pre¬ paring an aqueous fungicidal preservative solution com¬ prising a compound of a preservative metal, a branched-chain carboxylic acid having 6-20 carbon atoms or a dipentene- monocarboxylic acid or a dipentene-di-carboxylic acid and ammonia and/or an ammonium compound. Similarly, U.S. patent 4,380,561 describes a preservative system comprising branched-chain aliphatic carboxylic acids containing 6-20 carbon atoms or their alkali or ammonium salts. This compo¬ sition is particularly suitable for the short term protec¬ tion of wood against sapstain and mould fungi, but not from attack by insects.

It has long been desirable to produce wood products that are aesthetically acceptable to the public, yet pre¬ served from the destructive agencies of wood. Preserved wood is desirable for the home, and is used in the siding, fencing and decking industry. Un ortunately, many of the fatty acid preservative solutions described above are effec- tive only against fungal and bacterial attack, and do little to protect the wood from attack by insects, and particularly termites. Accordingly, it has now been discovered that by changing the organic acid substituent of prior used preser¬ vative compositions from a normal fatty acid to a dicar- boxylic acid or to a mono, di or tricarboxylic hydroxy acid, the resulting preservative will be effective against both fungal and insect attack. Disclosure of Invention

It is an object of the present invention to provide a composition suitable for use as a wood preservative which is

capable of preventing the deterioration of wood or other cellulose based materials by fungal decay and/or insects.

A further object of this invention is to provide a wood preservative composition having fungicidal and insec- ticidal properties, which is particularly effective against insects such as termites.

A still further object of this invention is to pro¬ vide a method for the treatment of wood and other cellulose based materials which comprises contacting these materials with the aqueous solution of this invention.

In order for a particular chemical system to be an effective long term preservative for wood, it must meet the following criteria:

1) At least one of the components must be an effec- tive biocide against the organisms responsible for the degradation of wood including bacteria, fungus and insects.

2) .The preservative components must be capable of readily penetrating the wood. 3) The components must become permanently fixed in the wood.

It is also desirable that the raw materials be read¬ ily available and that their cost is not prohibitive for commercial application. It is desirable that the preserva- tive be an aqueous based system since water is readily available and is an inexpensive diluent. The resulting treated wood products should also be readily paintable and should not pose a potential fire hazard as do some of the oil borne systems. Accordingly, the present invention provides an aque¬ ous preservative composition for treating cellulose based products such as wood to prevent deterioration of such prod¬ ucts caused by known decay causing organisms and insects comprising:

a) a composition of a preservative metal selected from the group consisting of copper, cobalt, cadmium, nickel, and zinc in a preservative amount; b) an organic acid, also in a preservative amount, selected from the group consisting of aliphatic di¬ carboxylic acids containing 2-10 carbon atoms per molecule, aliphatic mono, di, or tricarboxylic hy¬ droxy acids containing 2-6 carbon atoms per molecule, a mixture of these acids and/or their salts; and c) ammonia and/or an ammonium compound such as am¬ monium carbonate, ammonium hydroxide, ammonium bi¬ carbonate, ammonium sulfate or mixtures thereof in an amount sufficient to solubilize the composition in (a) above and neutralize the organic acid in (b) above.

When cellulose or cellulose by-products such as wood are treated with the above aqueous preservative composition as by dipping, soaking, spraying, brushing, impregnating, etc...., the treated material is effectively protected against both fungal and insect attack. Best Mode For Carrying Out The Invention

The preservative metals suitable for use in this sys¬ tem include copper, cobalt, cadmium, nickel or zinc. Copper is the metal most preferred and may be incorporated into the system as a salt such as copper oxide, copper carbonate, copper sulfate, copper hydroxide or as copper metal, pro¬ vided a suitable oxidizing agent such as air, hydrogen peroxide or nitric acid is present. When cobalt, cadmium, nickel or zinc are used they may be incorporated into the system as a metal compound or metal salt such as a metal oxide, metal hydroxide, metal carbonate, etc.... or as the metal itself provided a suitable oxidizing agent is pres¬ ent. These metal compounds are normally insoluble in water but can be solubilized in the presence of ammonia and/or a - monia containing compounds.

The ratio or organic acid to preservative metal com¬ pound used in this process will generally depend on simple stoichiometrics, i.e. one equivalent of metal per equivalent of acid. It is preferable to have an amount sufficient to react stoichiometrically with the dicarboxylic acid or with the mono, di or tricarboxylic hydroxy acid. However, the ratio of metal to organic acid may be varied to less than or greater than the stoichiometric proportion depending upon the preservative effect desired. Examples of aliphatic dicarboxylic acids suitable for use in this preservative system are oxalic acid, malonic acid, succinic acid-, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid and sebacic acid. Ali¬ phatic dicarboxylic acids containing 2-10 carbon atoms per molecule are preferred, based on solubility considerations. Still more preferred acids are those containing 2-4 carbon atoms per molecule. Branched chain dicarboxylic acids are not considered suitable for use in carrying out the instant process as it is theorized that such compounds do not have sufficient mobility to allow good penetration into the wood. It has been found that only straight chain dicar¬ boxylic acids combined with metal preservatives exhibit both fungicidal and insecticidal properties.

Examples of suitable aliphatic mono, di, or tricar- boxylic hydroxy acids are glycolic acid, lactic acid, alpha hydroxybutyric acid, glyceric acid, malic acid, tartaric acid, mesotartaric acid, and citric acid. It is preferable to have an aliphatic mono, di, or tricarboxylic hydroxy acid containing from 2-6 carbon atoms per molecule. Combinations of two or more organic acids and/or the salts of such acids may be used in carrying out this in¬ vention and it is acceptable to use any known commercially available product. Isomers of these acids or mixtures of iso ers are also usable within the scope of this invention. The presence of ammonia and/or ammonia and carbon di¬ oxide in this system is necessary for the purpose of solu-

bilizing the metal compounds and/or neutralizing the organic acid. The ammonia may be incorporated into the system as ammonia or as an ammonium salt such as ammonium hydroxide, ammonium carbonate, ammonium bicarbonate and/or some com- bination of such a salt and ammonia. It is desirable that the ammonium hydroxide (30% NH,) be at least 1.75 times the weight of the copper expressed as the metal and that the ammonium compounds such as ammonium carbonate and/or am¬ monium bicarbonate if required be at least 0.50 times the weight of the copper expressed as the metal. These ratios may vary, but there must be sufficient ammonia present to fully complex the metal and to completely neutralize the or¬ ganic acid „so that the organic acid will be adequately solu- bilized. If sufficient ammonia is not present the preserva- tive will undergo precipitation during storage or during the treatment process.

The preservative may be prepared by first mixing the organic acid with water and allowing the dissolution to oc¬ cur to the extent possible based on the inherent solubility of the acid. The metal or metal compound is then added to this solution and permitted to react. Reaction may take a few minutes or several hours depending upon the reactivity of the organic acid. The ammonia and/or ammonium compounds are then added to dissolve the product resulting from the reaction between the metal and the organic acid.

It is also permissable to first mix the preservative metal compound with an aqueous solution of the ammonia and/ or ammonia compound. The organic acid may then be added to the solution at any time prior to treatment. In the alter- native the ammonia and/or the ammonia compounds may be ini¬ tially added to the organic acid. Thereafter this solution is mixed with the preservative metal.

As a further alternative, it is also possible to mix the preservative metal (or metal compounds), the organic acid and the ammonia and/or ammonia compounds in a single operation. A still further alternative method of prepara-

tion would permit the substitution of carbon dioxide for the ammonium carbonate and/or ammonium bicarbonate in any of the above described preparation procedures. However, some mini¬ mum amount of ammonia would still be required to insure suf- ficient solubility.

The preservative solution may be formulated over a broad temperature range, although the preferred temperature is between about 60° to 80°F (about 15° to 30°C). The limiting factors for selecting a suitable temperature are the freezing point of the preservative and the loss of ammonia at high temperature due to evaporation. Such am¬ monia loss may be controlled by maintaining the system under suitable pressure.

The treating solution may be applied to wood by dip- ping, soaking, spraying, brushing, or any other, well known means. Vacuum and/or pressure techniques may also be used to impregnate the wood in accord with this invention in¬ cluding both the "Empty Cell" process and the "Full Cell" process which are well known to those skilled in the art. The "Full Cell", or Bethell, process is employed in the creosoting of railway sleepers and marine timbers and is the normal method of treatment of any class of timber with water-borne preservatives, and may be used with the treating solution of the invention. It has been in continuous use since 1838 and consists of first subjecting the timber in a cylinder to a vacuum up to 28 inches for 1/2 to 1 hour, then filling the cylinder with treating solution and applying a pressure of up to 180-200 lbs. per square inch until the re¬ quired amount of treating solution has been injected into the timber. The cylinder is then emptied of treating solu¬ tion and the treated timber optionally subjected to a short final vacuum to clean up the surface of the timber. It is usual to heat the treating solution throughout the treat¬ ment, e.g., to a temperature of 150°-200°F, as penetra-

tion is better when hot. As in all pressure processes the pressure period is by far the most important factor af¬ fecting the amount and depth of impregnation. In practice it is the magnitude and duration of the pressure that gov- erns the absorption of the treating solution by the timber. In the early stages of the pressure period the absorption by the timber is fairly uniform but then it gradually slows down until the absorption is too slow to be readily ob¬ served. When this point is reached the timber is said to have been treated to refusal. The rate of absorption varies greatly with different species, and timbers such as beech or Corsican pine will be completely impregnated in a few min¬ utes while others like Douglas fir, larch or oak heartwood are not completely penetrated even when under pressure for several days.

The "Empty Cell" treatment, using an initial ai ^' r pressure, is also known as the Rueping Process and is the standard method for the creosoting of transmission poles. It is also used for wood paving blocks, fencing, and build- ing timbers, and may be used with the treatment solution of the invention. The treating schedules aim at obtaining com¬ plete penetration of any sapwood present. The Rueping treatment was introduced about 1912 and differs from the full cell method in that the timber is initially subjected to compressed air instead of a vacuum. The cylinder is then filled with the treating solution while maintaining this pressure, and pressure is then increased with a hydraulic pump until the desired amount of treating solution is in¬ jected into the timber. The pressure is then released and the air compressed in the interior of the timber is allowed to escape and in so doing expels the excess liquid, leaving the cell walls coated with treating solution. This method of treatment allows a deep impregnation of the timber with¬ out a heavy absorption. The compression of the air origi- nally in the wood serves to recover a small amount of the

injected treating solution when the pressure is released. A long final vacuum is also used to assist in this.

Before impregnating timber with any wood treating so¬ lution it is essential to season it first until at least all the free water has been removed from the cell spaces. This stage of seasoning represents a moisture content of about 25%-30%, varying slightly with different species. There are two very good reasons for this: first, it is not possible to inject another liquid into wood containing much water, and second, splits developing as the result of the sub¬ sequent drying of the timber would almost certainly expose untreated timber. It is also desirable to carry out all cutting, machining and boring, etc...., of the timber before treatment is applied, as all these operations, if carried out after treatment, would expose untreated wood. Where these.operations cannot be done until after treatment all exposed untreated timber should be given a liberal appli¬ cation of treating solution, and holes preferably treated with a pressure bolt-hole treater. The following examples serve to further illustrate the invention:

EXAMPLE 1 A preservative solution was prepared by dissolving 87 grams of citric acid in 500 grams of water. To this solu- tion 100 grams of basic copper carbonate were added and al¬ lowed to react until the evolution of C0 ₂ was complete. Upon completion of this reaction, 446 grams of 30% ammonium hydroxide were added to solubilize the product. The re¬ sulting solution was diluted to a concentration of 1.5% and used to treat southern yellow pine stakes (1/8" x 1/2" x

10") by the Empty Cell process wherein the wood was exposed to the treatment solution and the system was then pres¬ surized for 30 minutes at a pressure of 110 lbs. per square inch. The resulting stakes were air dried and were found to be resistant to fungal and insect attack.

EXAMPLE 2 A preservative solution was prepared by dissolving 114 grams of oxalic acid in 500 grams of water. Upon dis¬ solution of the oxalic acid, 100 grams of basic copper car- bonate were added to the solution. The solution was then heated to 120 to insure complete reaction of the copper carbonate with the oxalic acid. Upon completion of the re¬ action, 446 grams of 30% ammonium hydroxide were added to solubilize the product. The product was then diluted to a 2% working solution and used to treat southern yellow pine stakes (1/8" x 1/2" x 10") using the Full Cell process wherein the wood was initially placed under a vacuum of 30" Hg for 30 minutes followed by the addition of the treat¬ ing solution. The system was then pressurized for 30 min- utes at a pressure of 110 lbs. per square inch. The re¬ sulting stakes were air dried and found to be resistant to fun-gal and insect attack.

EXAMPLE 3 A preservative solution was prepared by dissolving 45 grams of tartaric acid in 150 grams of water. To this solu¬ tion 38 grams of Cu(0H) ₂ were added, followed by the ad¬ dition of 37 grams of ammonium carbonate and 75 grams of 30% ammonium hydroxide. The solution was then diluted to a 1-1/2% concentration and used to treat southern yellow pine stakes by the Full Cell process. The treated wood was found to be resistant to fungal and insect attack.

EXAMPLE 4 To a mixture of 150 grams of water and 150 grams of 30% ammonium hydroxide were added 30 grams of basic copper carbonate. The solution was agitated until the copper car¬ bonate dissolved, at which time 44 grams of adipic acid were added and agitated until dissolved. The resulting solution was diluted to a concentration of 2.0% and used to treat

southern yellow pine stakes by the Full Cell process. The resulting stakes were air dried and found to be resistant to decay and insect attack.

EXAMPLE 5 A solution was prepared by adding 61 grams of copper metal to 150 grams of water containing 100 grams of 30% am¬ monium hydroxide and 70 grams of ammonium bicarbonate. The mixture was agitated and aerated until all of the copper metal dissolved. A second solution, was prepared by adding 31 grams of malonic acid to 100 grams of water. The second solution was mixed with the first and the resulting product diluted with water to 2.5%. This solution was used to treat southern yellow pine stakes by the Full Cell process. The stakes were then air dried and found to be resistant to de- cay and insect attack.

EXAMPLE 6 To 500 grams of water containing 450 grams of 30% am¬ monium hydroxide were added to 132 grams of basic copper carbonate. Upon dissolution of the copper carbonate, 59 grams of citric acid were added to the solution. The prod¬ uct was agitated until a clear solution was obtained. This solution was then diluted with water to a concentration of 1.5% and used to treat Douglas fir stakes by the Full Cell process. The stakes were oven dried and found to be resis- tant to decay and insect attack.

EXAMPLE 7 A solution was prepared by dissolving 75 grams of ox¬ alic acid in 250 grams of water. To this solution were ad¬ ded 75 grams of zinc carbonate. This mixture was allowed to react until the evolution of CO- was complete. Upon com¬ pletion of the reaction, 200 grams of 30% ammonium hydroxide were added to solubilize the product. This solution was then diluted to 2.0% and used to treat southern yellow pine stakes by the Empty Cell process. The resulting stakes

were air dried and found to be resistant to fungal and in¬ sect attack.

EXAMPLE 8 A preservative solution was prepared by dissolving 54 grams of sodium oxalate in 150 grams of water. A second so¬ lution was prepared by adding 100 grams of copper sulfate pentahydrate to 150 grams of water containing 42 grams of 30% ammonium hydroxide and 29 grams of ammonium bicar¬ bonate. Both solutions were mixed and the resulting product diluted with water to a 1.5% concentration. This solution was used to treat southern yellow pine test stakes by the Full Cell process. The resulting stakes were then air dried and found to be resistant to decay and insect attack.

EXAMPLE 9 Utility Stake Test Data

Southern yellow pine sapwood stakes (1-1/2" x 1/8" x 10") were Impregnated with several preservative solutions using the Full Cell process. Test stakes were preserved with copper naphthenate, copper citrate and copper oxalate at three different retention (concentration) levels measured

3 as pounds per cubic feet (lbs/ft ) or kilograms per cubic

3 meter (kg/m ). Ten stakes were treated with each preser¬ vative at each retention level for a total of ninety treated stakes. Ten untreated stakes were also included as a con- trol. The test plot was located in Florida in an environ¬ ment which provided for accelerated test conditions. The stakes were removed from the ground at 12 month intervals to determine performance. Even at the lowest retention levels, the preservative system according to the present invention performed quite well after 36 months exposure time.

The rating system used to evaluate decay and insect attack is as follows: 10 - sound, 9 - slight attack, 7 - moderate attack, 4 - severe attack, 0 - failure.

As can be seen from the test data presented in Table I, the copper citrate and copper oxalate performed well af¬ ter 36 months exposure, as did the copper naphthenate, which is a well known oil-borne preservative. The untreated con¬ trols exhibited moderate to severe attack after 12 months exposure and complete failure due to termite attack after 24 months exposure.

TABLE I

RATING SALT 12 MONTHS 24 MONTHS 12 MONTHS

SYSTEM lb/ft ³ DECAY TERMITE DECAY TERMITE DECAY TERMITE

Copper 1.09 10 10 9.8 10 9.8 10 Oxalate

Copper 0.71 10 10 10 10 9.8 9.8 Oxalate

Copper 0.43 8.9 10 8.9 9.8 8:7 , 9.8 Oxalate

Copper 1.73 10 10 9.9 9.9 9.9 10 Citrate

Copper 1.13 10 10 10 9.9 10 9.9 Citrate

Copper 0.57 10 8.8 9.7 8.5 9.6 Citrate

Copper 1.52 10 10 10 10 10 10 Naphthenate

Copper 1.04 10 10 10 10 9.9 10 Naphthenate

Copper 0.53 10 10 10 10 9.8 9.9 Naphthenate

Untreated 0.00 6.4 5.5 5.9 0.0 0.0 0.0 Control

In addition, various known additives may be combined with the preservative compositions formulated according to the instant invention without substantially affecting the preservative capacity of the present composition. For in- stance, other preservative compounds including those con¬ taining arsenic may be added to this composition. Coloring agents, waxes, resins, aqueous solutions, various emulsions and other ingredients may be added to the present com¬ position where such additional properties are desirable. A wide variety of woods can be preserved in ac¬ cordance with this invention including hard and/or soft¬ woods. Many other types of cellulose based materials in¬ cluding paper, particle board, textiles, rope and other such well known cellulose by-products may also be treated with this preservative composition, provided the material is ca¬ pable of withstanding the treatment process.

In addition, the aqueous solutions prepared according to the present invention may also be used to treat living plants and seeds to prevent fungal and/or insect attack. For this purpose the treatment solution would most likely be ap¬ plied by spraying, but these solutions may be applied by any method commonly used to apply known insecticides to plants or agricultural crops.

It is fully understood that all of the foregoing Examples are intended to be merely illustrative and not to be construed or interpreted as being restrictive or other¬ wise limiting of the present invention, excepting as set forth and defined in the hereto appended claims.