US2054400A - Wood preservation and mode of treatment - Google Patents

Description

Patented Sept. 15, 1936 UNITED STATE woon raEsEavATIoN AND MODE or TREATMENT Robert H. White, Jr.,

Atlanta, 6a., assignors Corporation, Atlanta, Ga.,

and Joseph A. Vaughan,

to Industrial Research a corporation of Georgia No Drawing. Application December 31, 1934, Serial No. 760,049

13 Claims. (01. 21-45) This invention relates to a novel process of applying preservative treatment to wood, timber or forest products. More specifically, it relates to'-a process of treating wood with oil or oily preservatives, such as are used in the wood preserving industry. One important feature of the invention involves the employment of a phosphatide, such as vegetable lecithin, in conjunction with ordi-' nary preserving oil, such as standard creosote, to reduce its viscosity, surface tension and relative interfacial tension without impairing its durability or toxicity, whereby to increase the penetration and improve the distribution of the preservative in the wood. The idea is to reduce the treating temperature heretofore. employed to produce the best penetration. Another aim of the invention is to provide a novel mode of treatment involving the introduction of preserving oil and water in separate stages or in succession, whereby the preserving oil is better distributed throughout the penetrated sapwood and the surface concentration is greatly reduced. The main object of this treatment is to practically eliminate bleeding or exudation of the oil when the preserved products are exposed to the weather and generally to improve the life and appearance of thepoles and thellike.

This application is a continuation in-part of our applications, Ser. No. 612,379, filed May 19, 1932 and Ser. No. 702,096, filed December 12, 1933.

It is to be understood that this invention is applicable to the preservative treatment of wood using known preserving oils, such as creosote, shale oil, coal tar, etc., which may be produced by fractional distillation or otherwise. The practice of the invention will be explained, by way of example, in connection with the introduction of standard creosote, since it has been generally adopted in the wood preserving industry. It is well known that wood treated with creosote or similar oils in accordance with the standard well known practice, is subject to several objections, chief among which are excessive bleeding and checking. Many prior, but unsuccessful, attempts have been made to eliminate both of these objections. It is known that bleeding or exuding of the a preserving oil is caused by exposure of the treated wood to the elements or to solar radiation. It has been found that the amount of.bleeding is dependent very largely upon the temperature difference betweenone side and the other side of the treated product when exposed to the sun. We have found that the greatest amount of bleeding occurs in poles wherein the surface concentration of the creosote is the highest. While the timber loses a portion of' its preservative by evaporation and by leaching with water, we shall concern ourselves chiefly with actual bleeding, which creates the most objectionable condition because the timber remains wet with oil in all its early stages and the public, as well as the workmen, must come in contact with it. In the later stages, this may become, due to evaporation, residual deposit and accumulation of dust and dirt, a. sticky and gummy mass, which is not only unsightly, but also more objectionable than the oil or creosote itself.

Bleeding is caused or accompanied by the movement of air or gas'confined in-the wood;

cavities or cells, the air or gas moving always toward the hottest portion. This movement tends to force the liquid creosote out ofthose cells near the surface where the concentration of oil is usually initially high and the cell cavities as well as the orifices are practically full of oil, leaving no room for thefree flow of the confined air and gas. The high concentration is due largely to the method of treatment and to the necessarily high viscosity of durable oil. After a period of from one to five years in service, the heavy concentration near the surface has been so materially reduced by evaporation, leaching and bleeding, that in most poles, actual bleeding ceases. However, a residual deposit may remain as a soft or hard 'asphaltic mass on the surface. As the lighter fractions of the oil at the surface evaporate, there issome progressive movement of the oil within the wood, which movement maybe considered a slow feeding of constituents from the interior toward the surface to replace those constituents previously lost from the surface oils. Then the oil solution is again volatilized and the process repeated, and, in this manner, the wood becomes progressively weathered.

We have found that the distribution and depth of penetration of durable oil control, to a very great extent, the loss of oil by evaporation, leaching and bleeding. penetration are very largely dependent upon the viscosity of the oil. This invention provides a novel method of practically eliminating bleeding and greatly reduces evaporation losses by producing far better penetration and distribution of the oil. In accordance with the preferred mode of treatment, the viscosity, surface tension and relative interfacial tension of standard, creosote are reduced by the addition of a small quantity "of phosphatide, such as lecithin obtained from soja beans. We have'found that between 25% and 2% by weight of phosphatide, dissolved in Also, the distribution and the creosote, produces good results. This solution is introduced into the wood by either the empty cell or full cell process, preferably by the standard Rueping treatment, but at a slightly lower temperature than that required for introducing creosote alone, the temperature range being preferably between 150? F. and 180 F. The treatment is given after the timber has been properly conditioned by the well known steam conditioning or air drying process. It is subjected to initial air pressure varying between 30 and pounds per square inch in a closed,retort, for a period of not less than 30 minutes. The preservative solution, consisting of a mixture of a small percentage of phosphatide with the preserving oil is then introduced into the retort without loss of pressure until the retort is completely filled. Additional preservative solution containing the phosphatide is pumped into the timber by means of a pressure pump or any other apparatus which will force. the solution into the timber atv a hydrostatic pressure of from pounds to 200 pounds per square inch.

When the timber has absorbed a predetermined and sufiicient amount of the preservative solution, to insure a correct final net retention, we slowly release the hydrostatic pressure and empty the retort or cylinder of all free preservative. After this is done, we create in the cylinder a vacuum of from 22 to 27 inches over a period of from 30 minutes to one hour, in order to further rid the timber of free and excess oil or solution. The vacuum is then broken and air pressure applied to the timber at from 20 pounds to 100 pounds per square inch. The air is then allowed to escape slowly from the timber and the retort and a second vacuum of from 22 inches to 27 inches is created in the retort for a period of approximately one hour, at the end of which time the vacuum is again broken and the cylinder or retort drained of all liquid. After the preserving solution is injected into the timber,

as above described, the second stage of the treatment is applied. This may be identified as the water stage, because water or moisture is introduced into the wood to redistribute the oil and reduce the surface concentration. The water is preferably made slightly alkaline by adding an alkali, such as sodium or potassium hydroxide, to produce a solution of aboutv tenth normal strength. The idea is to produce a slightly basic reaction to neutralize any acid that tends to impair the action of the phosphatide. This water or aqueous solution is injected or introduced'into the timber either by a slight modification of the above described process, or by means of the well known Bethell process. However, it is to be understood that it may be introduced by any suitable method. Thequantity of water introduced will be varied according to the amount of retained moisture in the timber. When the water is injected by the full cell method, it rushes inwardly into the wood cells due to the vacuum drawn and passes through the-cells filled'with the oil solution. It entrains globules of oil, forming a temporary'emulsion or mixture of water and oil, thereby carrying the oil deeper into the .wood. During this stage'of the treatment, the

temperature is preferably maintained at F. to F. In most instances, the moisture content of the wood after treatment exceeds by 10% to 15% the amount of moisture corresponding to fibre saturation of the wood. When the final vacuum is drawn, after the water is injected, and the wood cells near the surface are practically full of the water and oil emulsion or mixture, the water evaporates due to the reduction in pressure and to its temperature; while the oil does not evaporate because of its much higher boiling point. This leaves voids in the wood cells to a substantial depth in the sapwood. The retained oil and moisture adhere to the walls of the cells and in the capillary passages, in the form of more or less uniform films or coatings, thus providing ample spaces through which the air may pass, without forcing oil to the surface when the product is exposed to the elements or to solar radiation.

To give a concrete example of the improved mode of treatment, we shall assume that yellow pine is to be treated with 8 pounds of creosote per cubic foot, by either the empty cell or full cell process. For this treatment, approximately 1% of phosphatide by weight, added to the creosote, gives very satisfactory results. The wood is then impregnated with a sufiicient quantity of this solution to give the desired net retention. Sufficient moisture or aqueous alkaline solution is then introduced to make the total moisture contentof the treated wood slightly greater than that corresponding to" fibre saturation. Inci-' dentally, the quantity of water required to proture content is below 30%. This method is fully disclosed and claimed in our application Ser. No. 693,524, filed October 13, 1933.

From the foregoing description, it will be understood that the illustrative treatment is subject to variations. The quantity of phosphatide used will depend upon the characteristics of the creosote or other preservative oil employed. Furthermore, the method of injection or introduction of the oil and water in the two stages may be varied within wide limits. Further, it must be understood that the two stage treatment is highly advantageous, whether or not phosphatide is used in solution with the oil. Tests of poles treated in accordance with the improved method have shown deeper penetration and far better distribution of the oil than products treated according to the well known methods. 'Moreover, the products present cleanand light colored surfaces, without any oily or greasy feel and do not smear the clothing. Accurate concentration tests have shown that the net retention of oil at the surface of pine poles has been reduced to about two-thirds of that resulting from the ordinary treatment with creosote. It has been shown also that the products having the light color resulting from less surface concentration, do not absorb heat rapidly and are not subject to high temperature differences,

1. The process of treating timber products which is characterized by introducing a phosphatide'in conjunction with a wood-preserving oil into the wood. l l

2. The process of treating timber products weight of phosphatide with a wood-preserving oil;

and introducing it into the wood.

4. The process of treating timber products which is characterized by introducing creosote mixed with a small quantity of lecithin into the wood.

5. In the process of applying preservative treatment to wood, the steps which comprise mixing about one percent by weight of vegetable leci-,

thin with creosote to reduce its viscosity and interfacial tension; and introducing the mixture into the wood.

6. The process of treating wood or timber which is characterized by, first, introducinginto the wood a mineral preserving oil together with a small quantity of phosphatide derived from soja beans to decrease the viscosity, surface tension and interfacial tension of the oil and act as an oil and water emulsifier; and, subsequently, introducing an aqueous solution into the treated wood to combine with and distribute the oil more uniformly throughout the penetrated portion of the wood.

'I. That process of treating wood or timber which is characterized by injecting an oily preservative containing a small percentage of phosphatide into the wood; and introducing water containing a small-amount of alkali.

8. The process of treating timber which is characterized by introducing a wood-preserving 011 containing a small percentage of phosphatide to a substantial depth in the wood; .and then introducing an aqueous alkaline solution into the wood in such quantity as to efiect redistribution and better penetration of the oil solution.

9. The process of treating timber which is characterized by introducing a wood-preserving oil containing a small percentage of phosphatide to a substantial depth in the wood; then introducing an aqueous alkaline solution into the wood in such quantity as to effect redistribution and better penetration of the oil solution; and finally subjecting the treated product to a partial vacuum to evaporate a portion of the introduced moisture.

10. That process of applying preservative treatment to timber products which is characterized by making a solution of durable creosote and approximately 1% byweight of lecithin obtained from soja beans; introducing the solution into the product to a substantial depth; making up an alkaline aqueous solution of approximately tenth normal strength; injecting said solution into the wood in such quantity as to effect redistribution of the oil solution; and finally evaporating a portion of the contained moisture in the wood cells near the surface.

11. That process of applying preservative treatment to timber products which is characterized by making up a preserving oil solution of creosote and approximately 1% of phosphatide;

injecting the desired .quantity of said solution into the-wood by an empty cell treatment; then introducing water into the wood by a full cell treatment in such quantity as to effect redistribution of the oil solution and greatly reduce the surface concentration of the oil in the wood.

12. That process of applying preservative treatment to timber products which is characterized by making up a preserving oil solution of creosote and approximately 1% of phosphatide; injecting the desired quantity of said solution into the wood by the standard Rueping treatment; then introducing water into the wood by the Bethell process' in such quantity as to efiect redistribution of the oil solution and greatly reduce the surface concentration of the oil in the wood.

13. That method of applying preservative treatment to wood which is characterized by introducing creosote, containing a small quantity of phosphatide, into the wood by an empty cell treatment at a temperature ranging between F. and F.; then, introducing a slightly alkaline aqueous solution into the wood by a full cell treatment at a temperature ranging between 150 F. and 178 F. in such quantity as to redistribute the oil in the wood and reduce the concentration of oil at the surface; and, finally, subjecting the treated product to a partial vacuum, whereby to evaporate a portion of the excessmoisture in the wood cells without removing the creosote.

' ROBERT H. Wm. an. JOSEPH A. vapor-rm.