Water-Repellent Aqueous Wood-Treating Solutions

The present invention is related to solutions that provide increased water repellency for wood and other cellulose products. More particularly, the invention is related to aqueous cellulose-treating solutions of hexavalent chromium and, optionally, copper or copper-arsenic mixtures with aluminum halohydrates in an acid medium. In accordance with the invention it has been discovered that when aluminum halohydrates are incorporated into a solution of hexavalent chromium and, optionally, copper or copper-arsenic mixtures, a superior wood-treating solution is produced. The solution can be used to treat paper, cardboard, and cellulose products generally, but for convenience, the disclosure describes the treatment of wood.

Copper, chromium and arsenic can be supplied to the solution by compounds such as those contained in aqueous wood-preserving solutions known as Acid Copper Chromate (ACC) and Chromated Copper Arsenate (CCA). Compounds are preferably selected, however, that will not release more than trace amounts of sulfate ions in the aqueous wood-treating solution. Suitable compounds include basic copper carbonate, copper sulfamate, copper nitrate, copper fluosilicate, copper fluoborate, cupric oxide or hydroxide, potassium or sodium dichromate, chromium trioxide, arsenic pentoxide, arsenic acid, sodium arsenate or pyroarsenate. Sulfate ions are undesirable because the aluminum halohydrate is incompatible with an aqueous solution containing more than a trace or minor amount of sulfate ion and tends to precipitate out of solution.

To insure the solubility of the aluminum halohydrate in the aqueous solution, the amount of chromium, copper and arsenic on an oxide basis should not exceed about 45 weight percent of the solution. The lower limit, however, can be as small as about 0.5 but is preferably between about 0.8 and about 14 percent by weight. The amount of aluminum halohydrate employed will depend upon the concentration of oxides of copper, chromium and arsenic, but generally from about 0.5 and about 25 percent aluminum halohydrate is employed and preferably from about 0.7 to about 6 percent by weight of the solution. For best results, the amount of oxides of copper, chromium and arsenic present in the solution is determined by the standards promulgated by the American Wood Preservers Association in standard no. P5-77 for acid copper chromate and chromated copper arsenate solutions.

Aluminum halohydrates which can be employed include aluminum chlorohydrate, aluminum iodohydrate, aluminum bromohydrate and aluminum fluorohydrate.

Depending on the compounds employed, it may be necessary to add a strong acid in order to solubilize the components of ACC and CCA Type B solutions and may, in addition, be employed to provide the desired pH for the final solution. Generally, the pH must be between about 0.1 and about 5.0, and is preferably between about 1.2 and 4.3. Typical acids that can be employed to provide the desired pH include sulfamic acid, nitric acid, fluorosilicic acid, fluoroboric acid or a mixture of any of these acids with a minor amount of about 2 percent of phosphoric acid. In order to prepare the solutions of the invention, it is preferred that the compounds added to form the oxides and/or aluminum halohydrate be diluted before mixing as the use of concentrated solutions tends to inhibit the solubilization of the components. Generally it is sufficient to dilute the additive mixtures to about 0.5 to 14 percent oxides containing 0.7 to 6 percent aluminum halohydrate.

The aluminum halohydrates useful in the invention can be represented by the formula: Al.sub.x (OH).sub.y X.sub.z, wherein X is a halogen such as chlorine, bromine, fluorine or iodine and x and y are integers of from 1 to 4 and z is an integer of from 5 to 1. The aluminum halohydrates are usually polymeric in nature and thus the above formula should not be considered restrictive. Typical non-limiting examples of the aluminum halohydrate that can be used in the present invention are: Al.sub.3 OH.sub.5 Cl.sub.4, Al.sub.4 OH.sub.10 Cl.sub.2, Al.sub.4 OH.sub.9 Cl.sub.3 and Al.sub.2 OH.sub.4 Cl.sub.2.

Any method of treating wood with aqueous treating solutions can be used when wood is treated with the aqueous wood-treating solutions of the present invention. These methods include treating wood by injection of the aqueous wood-treating solution under pressure in closed vessels or dipping in open vessels or by brush or spray painting of the solution. Also, in the method of treating wood with the aqueous wood-treating solution of the present invention, the wood may be end-sealed in any manner known to those skilled in the art to enhance the water repellent effect of the aqueous wood-treating solution.

The following description is directed to several alternative embodiments of the aqueous wood-treating solution of the present invention. In these embodiments the preferred aluminum halohydrate used is aluminum chlorohydrate in a 50 percent aqueous solution. Nonlimiting examples of such solutions that are commercially available are Wickenol 303 solution, Wickenol 305 solution, and Wickenol 306 solution, all available from Wickhen Products Inc., Huguenot, New York. The Wickenol 303 solution is an aqueous 50 percent aluminum chlorohydrate which has an atomic ratio of two aluminum atoms to one chlorine atom.

For non drug use, Wickenol 303 is now known as Wicklor 904--Al complex 56,

Wicklor 305 is now known as Wicklor 906--Al complex 23, and

Wickenol 306 is now known as Wicklor 905--Al complex 34.

Other products which have ratios of one aluminum atom to one chlorine atom and intermediate ratios between one and two aluminum atoms to one chlorine atom may also be used. The diluted Wickenol solutions did not appear to exhibit high inherent water repellency when applied to wood by itself, but when used in the aqueous wood-treating solutions of the present invention a synergistic effect is obtained, resulting in an increased water repellency in treated wood.

The following examples will serve to illustrate preferred embodiments of the invention. All parts and percentages in said examples and elsewhere in the specification and claims are by weight unless otherwise specified.

The following solutions were prepared.

Sulfamic acid was added to the solution to prevent the arsenic acid from reacting with part of the copper oxide.

The three solutions alone and with 3 percent of a Wickenol aluminum chlorohydrate were used to treat southern pine sapwood wafers to assess water repellency. The wafers were vacuum treated with the solution, allowed to air dry and conditioned at 65.+-.5 percent relative humidity and 75.degree.-80.degree. F. for ten days, whereupon the water repellencies were determined by 30 minute immersion in deionized water at room temperature by the general procedure of the National Wood Manufacturers Association swellometer test. The results are shown in the following table.

From the data it can be seen that the water repellency is considerably increased with the compositions of the invention as compared with a standard type solution or one with an aluminum halohydrate alone.

An additional unexpected property imparted to the dilutions from CCA Type C 50% oxide liquid concentrate by the addition of the aluminum halohydrates is that compatible mixtures inhibit the formation of insoluble green sludge when in contact with wood, especially at the 1 to 2 percent oxide level normally used in timber treating. Tests were initiated in which four Douglas fir heartwood blocks, each 3/4".times.1.5" were placed in 8 oz. cylindrical bottles with their long axes vertical. Aqueous test dilutions were added to float the blocks but were kept immersed by the constriction in the bottles below the screw caps as the bottles were completely filled. The tightly capped test units were kept at 80.degree. F. The results of observations from preparation, at which time all test dilutions were of a transparent yellow orange color, are tabulated below.

The yellow orange dilution of 1.0 and 2.0% CCA alone became cloudy after three days in contact with the wood and visible light green precipitates were evident after one week covering the bottom of the containers. After seven months the precipitate covered the top surfaces and sides of the Douglas fir blocks as well as the bottom of the bottles in tests number 7 and 8. No visible precipitate was noted on the remaining test blocks or green precipitates on the bottom of the containers up to seven months in tests number 1 through 6.

The tests were repeated using 1 percent CCA Type C oxides alone and with 3 percent of Wickenol 303, 305 and 306, but at 140.degree. F. The 1 percent oxides alone was found to be unstable after overnight heating to form a green precipitate on the top and edges of the wooden blocks. The remaining tests solutions remained stable with a brown amber color at the end of the 72-hour test period at 140.degree. F.

The action of the aluminum halohydrate appears to be solubilization of the sludge as it is formed by the reduction of hexavalent chromium in contact with the wood.

Similar tests were performed with an ACC type solution of the following composition.

Aqueous solutions of 5 percent or 2 percent oxide concentrations alone and with the inclusion of varying amounts of aluminum chlorohydrate were used for the swellometer test. The southern pine sapwood wafers with a 42.2 pcf density at 11-12 percent M.C. took up an average of 38.9 pcf of solution on vacuum treating at room temperature. A ten-minute vacuum near 28 inches of Hg was impressed on the wafers, followed by filling at room temperature and ten additional minutes of wafer immersion at ambient conditions. Water repellency data was then obtained on 30-minute water immersion using the vacuum treated wafers after seven days of air drying.

From the data reported in the table it can be seen that compositions of the invention are considerably superior to the ACC type solution alone.

Solutions of 5.08% sodium dichromate dihydrate (3.41% CrO.sub.3) and 3.41 percent chromium trioxide (3.41% CrO.sub.3) were tested alone and with 3 percent of several different aluminum chlorohydrates. Solutions 1-4 reported below were used to treat southern pine sapwood wafers, and solutions 5-8 were used to treat Ponderosa pine sapwood wafers. The improvement in reduction of tangential swell for the chromium-aluminum chlorohydrate solutions was from about 2 to many times as shown in the following Table III.

While the invention has been illustrated by several preferred embodiments, it will be obvious to one of ordinary skill that numerous variations can be made without departing from the scope of the invention and, accordingly, the invention is intended to be limited only by the appended claims.