Method for treating wood materials with lignosulfonic acids
United States Patent Olson et al.  
 METHOD FOR TREATING WOOD MATERIALS WITH LIGNOSULFONIC ACIDS Inventors: Harry S. Olson, Woodland Rd.,  
 Houghton, Mich. 49931; Bruce A. Haataja, Rt. 1, Box 18, Lake Linden, Mich. 49945 Filed: May 4, 1973 Appl. No.: 357,368  
 Related US. Application Data Continuation of Ser. No. 227,292, Feb. 17, 1972, abandoned, which is a continuation of Ser. No. 886,387, Dec. 18, 1969, abandoned.  
 US. Cl. 427/317; 21/7; 21/58; 260/124 R Int. Cl B27k 3/02; B27k 3/34; B44c1 1/26 Field of Search 21/7, 58; 117/147, 148, 117/149, 57, 59, 116, 62; 260/124 R References Cited UNITED STATES PATENTS 1,057,319 3/1913 Baekeland 117/147 1,075,552 10/1913 117/147 1,165,355 12/1915 117/147 1,291,696 1/1919 Bloom 117/147 OTHER PUBLICATIONS Chemical Abstract, Vol. 47, Col. 10222i. Wood Preservation by Hunt et al., McGraw-Hill Book Co., 1953, pp. 366.  
 Primary ExaminerWi1liam R. Trenor [57] ABSTRACT A process for the conditioning of porous materials, such as wood, with an impregnating agent comprised of an aqueous solution of free or partially free lignosulfonic acids, by treating the material therewith and then subjecting the treated material to elevated temperatures to polymerize the lignosulfonic acid, the treatment adapted to color the material and to improve the physical characteristics.  
 An improved product wherein a porous base material is impregnated with polymerized lignosulfonic acids to define improved product characteristics and uniform coloring of said product.  
 10 Claims, No Drawings METHOD FOR TREATING WOOD MATERIALS WITH LIGNOSULFONIC ACIDS This ia a continuation of application Ser. No. 227,292 filed Feb. 17, 1972 now abandoned which in turn is a continuation of application Ser. No. 886,3 87. filed Dec. 18, 1969 now abandoned.  
  The present invention relates, in part, to a method for the treatment of porous materials, such as wood, and more particularly it relates to a method for treating such material to color it as desired and to modify other physical characteristics of the material.  
  The invention relates also to the provision of an impregnating agent for an improved porous material having a fibrous character wherein the fibers are impregnated and protected with polymerized lignosulfonic acids wherein the product is uniformly colored throughout.  
  Porous materials, such as wood, commonly are treated to preserve them in use by improving the characteristic resistance of the material to decay, insect attack, fire, weathehring humidity, and the like. Such materials also are treated to change their appearance to a form different from its natural form.  
  One of the commonly employed methods of treating wood, for example, resides in applying a paint or varnish to its exterior to protect the wood. This form of protection, however, relies only upon the surface layer of paint or varnish for the protection and appearance of the wood. If the surface layer is removed by scratching, uncoated wood is exposed and the scratched area is unprotected. Also, the scratched area will have the appearance of uncoated wood which will be different in appearance from the surrounding coated areas.  
  The method we have devised for the treatment of wood and the provision of an impregnating agent for an improved wood producr and other porous materials does not solely contemplate the application of a surface coating. The material is exposed to the treating solution to permit penetration of the solution into the material. The treated material then is subjected to heat to polymerize and fix the protective agent with respect to the material.  
  We have developed a method for the treatment of materials which is adapted to change the color of the product, to improve the physical properties, to dimentionally stabilize the material. The method involves the use of an aqueous solution of free or partially free lignosulfonic acids of spent sulphite liquor.  
  The compound which we claim for use in the treatment of porous materials, as defined herein, may be derived from a by-product of the paper making processes.  
  Chemical pulp for makig paper may be prepared by several processes. In these processes wood first is conditioned by removal of the bark. The wood then is further cleaned to remove any remaining bark, pitch or other foreign material.  
  The cleaned wood then is cut into relatively small chips which are screened to remove sawdust (very small wood particles) and dirt. The chips then are cooked in digester tanks with the use of various chemicals.  
  In the sulfite process, for example, sulfur dioxide dissolved in an aqueous solution of calcium bisulfite or magnesium bisulfite is used. In the sulfate, or kraft process, sodium sulfate is reduced by heating with carbonaceous matter to form sodium sulfide which then is used in water solution with soldium hydroxide as the cooking liquor.  
  Lignin and cellulose are the chief constituents of wood. The constitution of lignin has not been clarified but it is suggested as a polymerized coniferyl alcohol.  
  In the manufacture of paper from wood it is necessary to remove the lignin. This often is accomplished by treatment of the wood fibers with such agents as sulfur dioxide calcium bisulfite, sodium sulfate sodium sulfide, or sodium hydroxide.  
  As noted above, the sulfite and neutral sulfite semichemical processes are among the methods used for pulping wood. In these processes wood chips or other lignocellulose are cooked under pressure in sulfite liquor to solubilize the lignin so that it can then be separated from the insoluble cellulose. When separation is affected the liquor resulting from the separation is known as spent sulphite liquor.  
  As used herein, the term spent sulfite liquor refers to liquors derived from calcium, ammonium, magnesium or sodium base sulfite processes, or in the neutral sulfite semichemical process. It will also be used to include sulfonated spent kraft liquor. All of the above noted liquors include lignosulfonic acids or their salts. These spent liquors include, in solution, extracted lignosulfates, hemi-celluloses, wood sugars and their degradation products, and various organic and inorganic compounds.  
  Spent liquor from the well-known kraft process may be sulfonated to give lignosulfonic acids and their salts. Such sulfonated liquor is noted herein as spent sulfite liquor.  
  It is a primary object of the present invention to provide an impregnating agent and a process for the treatment of porous materials to color them.  
  An additional object of the present invention resides in the provision of an improved porous product wherein the product is impregnated with polymerized lignosulfonic acids to define coloring of the product and to protect and preserve the product.  
  Other objects of the present invention reside in the provision of a process for the treatment of porous materials, such as wood, to color the material by means other than the application of a surface coating; to provide coloring agent adapted to penetrate the material to color it to the level of penetration; to provide an economical process for the treatment of wood which may be controlled and which is reproduceable to define means for coloring wood, for example, to a predetermined color level; and to provide an improved porous product impregnated to-uniformly color the product.  
  The novel features which are believed to be characteristic of the present invention are set forth with particularity in the appended claims. The invention itself, however, together with further objects and advantages thereof will be best understood by reference to the following description.  
  Lignosulfonic acids can be obtained by various methods from spent sulphite liquor by removal of the pulping base ion (calcium, ammonium, magnesium and sodium) which releases free acids, especially lignosulfonic acids.  
  In one method, calcium base spent sulphite liquor is treated with sulfuric acid to form insoluble calcium sul fate which may be removed by filtration to obtain lignosulfonic acids. In other methods, the base ion in the lignosulfonates can be removed by ion exchange means or by decomposition of ammonia salts where ammonia base spent sulfite liquor is used. Lignosulfonic acids also can be obtained by electrodializing spent sulphite liquor.  
  Whatever method is used to obtain ligno sulfonic acids, it is important to remove 40% to 100% of the base ion from the spent sulphite liquor to obtain lignosulfonic acids of the greatest utility for the purpose set forth herein. The concentration of the aqueous solution of ligno sulfonic acids used in the treatment of porous material is dependent upon the result desired. If it is desired to color birch (Betula alleghaniensis) veneer onesixteenth inch thick to a pleasing dark brown color, like that in walnut, a solution of approximately 25% spent sulphite liquor from which 95% of the base ion has been removed, by weight, may be used. Dilute solutions will define lighter coloring of the wood while concentrated solutions will give darker colored products. The process and product which we developed involves treating wood, or other porous materials, with an aqueous solution of ligno sulfonic acids and then polymerizing the lignosulfonic acids to impart a water resistant brown color to the wood, or other porous material.  
  To accelerate polymerization and to improve physical properties in some instances, an acid tolerant, liquid phenol formaldehyde resin of the water soluble type (CR 9357 from Ashland Chemical Company, Division of Ashland Oil and Refining Company) may be added.  
  Ordinarily the wood, or other porous material, is saturated by immersing it in a solution of lignosulfonic acids at room temperature or in a solution heated to, and including, nearly boiling temperature e.g., about 200F. This period of immersion can be up to 72 hours or more. We have found that the use of hot solutions will reduce the time needed to get penetration through the material and will give a darker brown color to the solution. The saturated materials may or may not be dried before the polymerization step which involves heat treatment in suitable equipment at a temperature in the range of about 145F to 450F. Generally this heat treatment is carried out for a period of about 2minutes to about 4 hours. When the impregnated material is dried before this heat treatment, it can be dried in air for periods up to 24 hours or longer.  
  In the case of wood veneers one-sixteenth inch thick, about three or four minutes were required to polymerize the lignosulfonic acids in the saturated veneer in a drier at a temperature of approximately 275F. Polymerization also may be accomplished at lower temperatures but at a slower rate or at higher temperatures in less time.  
  The manner in which this invention can be carried out will become apparent from the examples which follow.  
 EXAMPLE 1 A 25% solution of calcium base spent sulphite liquor was calcium ion depleted by adding sulphuric acid in an amount sufficient to react with 95% of the calcium present in the spent sulphite liquor. The calcium sulphate formed by the reaction was removed by filtration and the resulting solution of essentially free lignosulfonic acids was used to color one-sixteenth inch thick birch (Betula alleghaniensis) veneer. l  
  Coloring of the one-sixteenth inch thick birch veneer was accomplished by immersing it overnight in the solution of essentially free lignosulfonic acids. The satu- EXAMPLE 2 A 25% solution of calcium base spent suplhite liquor was calcium ion depleted by adding sulphuric acid in an amount sufficient to react with 95% of the calcium present in the spent sulphite liquor. The calcium sulphate formed by the reaction was removed by filtration. The resulting solution of essentially free lignosulfonic acids then was heated to 200F for 10 minutes to darken the brown color of the solution after which it was used to color one-sixteenth inch thick birch (Betula alleghaniansis) veneer.  
  Coloring of the birch veneer was accomplished by immersing the veneer overnight in the solution of essentially free lignosulfonic acids which solution was maintained at room temperature. The saturated veneer then was dried overnight in air after which it was heated in a press (with no pressure) at 275F for four minutes to polymerize and insolubilize the lignosulfonic acids present in the veneer. The veneer exhibited a darker brown color than that of Example 1. The color extended throughout the veneer, as in Example 1.  
 EXAMPLE 3 A 25% solution of calcium base spent sulphite liquor was calcium ion depleted by adding sulphuric acid in an amount sufficient to react with 95% of the calcium present in the spent sulphite liquor. The calcium sulphate formed by the reaction was removed by filtration. The resulting, essentially free, lignosulfonic acids solution then was used to color one-sixteenth inch thick birch (Betula alleghaniensis) veneer.  
  Coloring the birch veneer was accomplished by immersing the veneer for about 10 minutes in the solution of lignosulfonic acids which solution was heated to a temperature of about 200F. The veneer then was dried momentarily in air after which it was heated to 275F for 4 minutes in a press (with no pressure) to polymerize and insolubilize the lignosufonic acids present in the veneer. A pleasing dark brown color was given to the birch veneer which resembled expensive walnut. The color extended throughout the wood.  
 EXAMPLE 4 A 25% solution of calcium base spent sulphite liquor was treated with sufficient sulphuric acid to react with of the calcium present in the solution. The solution was clarified by filtration and then used to color one-sixteenth inch thick maple (acer saccharum) veneer.  
  The maple veneer was colored by immersing it for about 10 minutes in the solution which had been heated to a temperature of about 200F. The veneer then was dried momentarily in air after which it was heated to about 275F for 4 minutes. The veneer became brown in color throughout.  
 EXAMPLE 5 Although the brown color imparted to wood with the method described in this Example with the use of ammonia base spent sulphite liquor partially decationized with heat is not quite as water resistant as that obtained in wood by methods given in Examples 1, 2, 3 and 4, it nevertheless involves an effective means for coloring wood.  
  Pieces of birch (Betula alleghaniensis) veneer approximately 3 inches X 6 inches X one-sixteenth inch thick were immersed for 72 hours in l2 /2% and 50% solutions of ammonia base spent sulphite liquor. The saturated veneer then was air dried for 24 Hours after which it was heated to about 285F for 4 minutes in a press which polymerized the lignosulfonic acids produced when the heat of the press partially decomposed the ammonia salts in the spent sulphite liquor.  
  The veneer treated as set forth above became a pleasing brown in color. The veneer treated with 50% solution of ammonia base spent sulphite liquor was darker than the veneer treated with the 12 solution.  
 EXAMPLE 6 The use of acid-tolerant, liquid phenol formaldehyde resins of the water soluble type with solutions of ligno sulfonic acids of spent sulphite liquor results in additives for wood and other porous materials which, when polymerized, are especially water resistant and polymerize rapidly.  
  A sufficient quantity of sulphuric acid was added to a 25% solution of calcium base spent sulphite liquor to react with 95% of the calcium in the spent sulphite liquor. The calcium sulphate which formed was removed by filtration. The resulting solution of essentially free lignosulfonic acids then was mixed with an equivalent amount, by weight on a solids basis, of 25% solution of acid-tolerant, liquid phenol formaldehyde resin of the water soluble type (CR 9357 from Ashland Oil and Refining Company).  
  Birch (Betula alleghaniensis) veneer one-sixteenth inch thick was then colored by immersing it in the above mixture of essemtially free lignosulfonic acids and acid tolerant, phenol formaldehyde resing for 24 hours. The saturated veneer was then dried in air overnight after which it was heated in a press to about 275F for approximately 3 minutes. The birch veneer became light brown in color. The color was highly water resistant as indicated by placing the colored birch veneer in boiling water for 10 minutes.  
 EXAMPLE 7 A 25% solution of calcium base spent sulphite liquor was calcium ion depleted by adding sulphuric acid in an amount sufficient to react with 95% of the calcium present in the spent sulphite liquor. The calcium sulphate formed by the reaction was removed by filtration. The resulting solution of substantially free lignosulfonic acids was then adjusted to pH 3.0 with ammonium hydroxide (23-30.0% Nl-l to obtain a less acid, impregnating agent.  
  The impregnating agent was used to color aspen (populus tremuloides) veneer one-sixteenth inch thick by immersing the veneer overnight in the solution after which the saturated veneer was dried at room temperature overnight. The treated veneer was then heated to a temperature of 275F for 4 minutes to polymerize and fix the color in the veneer. The aspen veneer was colored an attractive, medium brown color.  
 EXAMPLE 8 A 25% solution of calcium base spent sulphite liquor was calcium ion depleted by adding sulphuric acid in an amount sufficient to react with 50% of the calcium present in the spent sulphite liquor. The calcium sulphate formed by the reaction was removed by filtration. The resulting solution of partially free lignosulfonic one-twentysixth was then used to impregnate elm (Ulmus thomasi) veneer l-twentysixth inch thick.  
  Coloring of the elm veneer was accomplished by immersing the veneer overnight in the solution of partially free lignosulfonic acids. The saturated veneer then was dried in air overnight after which the lignosulfonic acids in the veneer were polymerized by heating the treated veneer at 300F. for 4 minutes. The veneer was colored throughout with a brown color which was substantially water resistant.  
  We have found that the method of impregnating the porous material with the lignosulfonic acids is not critical. Although the examples specifically set forth a method of treatment of porous materials wherein the materials are immersed in the treating solutions this was done as a matter of convenience in working with the product. It is noted, however, that other means for treating the porous materials may be used. For example, the porous materials may be treated with the lignosulfonic acids by use of vacuum or pressure chambers in which the product would be placed and exposed to the acids. Also, the use of rollers may be employed to impregnate the porous material. Still other methods may be employed which would be equally satisfactory in the impregnation of the material which are not critical to the fact of impregnation as stated herein.  
  We have noted that the characteristics of the veneer, or wood product, are improved with the mode of treatment set forth herein. The improved product is a function of the impregnating of the fibers of the base material with the chain-like polymerized lignosulfonic acids so that the fibers are protected and the coloring is substantially uniform in the fact that the polymerized acids are disposed substantially uniformly in the interstices defined between the-fibers and about the fibers. This provides for a denser product and for uniform coloring. It can be seen that with the product of this invention, if the veneer is scratched (e.g.) bare wood or veneer will not be exposed. Rather, a lower layer of coated fibrous material will be exposed which will be the same color and of the same character as the surface layer surrounding the damaged area. Accordingly, the damage will not be readily detectable and the integrity of the original appearance of the veneer will be maintained.  
  A microscopic examination of the product treated with the chain-like polymerized lignosulfonic acids indicated that there may be some impregnation of or reaction of the acids with the cell walls as well as a filling of the voids. The exact nature of the conditioning is not fully understood at this time but it appears from examination that the coloring occurs in the cell walls as well as from the filling of the voids in and about the cells.  
  While we have shown and described in detail certain characteristics and examples in carrying out the process we have developed it will, of course, be understood that other variations may be used without departing from the true spirit and scope of this invention. We therefore intend by the appended claims to cover all such variations as fall within their true spirit and scope.  
  What we intend to claim and to secure by United States letters patent, is:  
  l. A method for treating wood to impart a color thereto comprising 4 impregnating said wood with an aqueous solution containing a spent sulfite liquor from which 40 to 100% of the base ions have been removed to obtain free lignosulfonic acids; and  
 heating said impregnated wood at a temperature within the range of about 145 to about 450F for a time sufficient to polymerize said lignosulfonic acids and thereby impart a permanent, waterresistant color to said wood.  
  2. A method according to claim 1 wherein said heating is carried out for a time period of about 2 minutes to about 24 hours.  
  3. A method according to claim 1 wherein at least about 95% of the base ions have been removed from said spent sulfite liquor.  
  4. A method according to claim 1 wherein said impregnating step is carried out by immersing said wood in said solution for a time sufficient to substantially saturate said wood with said solution.  
  5. A method according to claim 4 wherein the temperature of said solution during said immersion step is from room temperature to about 200F.  
  6. A method according to claim 5 wherein said wood is immersed in said solution for a time up to about 72 hours.  
  7. A method according to claim 1 wherein said impregnated wood is at least partially dried before said heating step.  
  8. A method according to claim 7 wherein said impregnated wood is dried in air for a time period up to 24 hours before said heating step.  
  9. A method according to claim 5 wherein said solution is at a temperature of about 200F and said wood is immersed in said solution for about 10 minutes.  
  10. A method for treating wood to impart a color thereto comprising immersing said wood for a time period of about 2 minutes to about 24 hours in an aqueous solution containing a spent sulfite liquor from which at least of the base ions have been removed to obtain free lignosulfonic acids, thereby impregnating said wood with said solution;  
 at least partially drying said impregnated wood; and  
 heating said impregnated wood at a temperature within the range of about to about 450F for a time period of about 2 minutes to about 24 hours to thereby impart a permanent, water-resistant color to said wood.