US2365833A - Process of incorporating polychlorophenols in fiberboard - Google Patents

Description

. Patented Dec. 26, 1944 raocess or. moonrona'rrnd POLY- onLoaornENoLs IN r'mEaBoAan Henry L. Moi-rill, Clayton, and John D.-Eleming, St. Louis, Mo., assignors to Monsanto Chemical Company, St. Louis, Mo., a corporation of Delaware - No Drawing. Application September 5, 1939,

Serial No. 293,428

2 Claims. (01. 92-21 'The present invention relates to fiberboard, particularly fiber boards which are made from mechanicallydisintegrated wood, for example, from fibers resulting from the explosive disintegration process, and relates specifically to methods of incorporating toxic polychlorophenols such as pentachlorophenol into such boards.

The principal object of the present invention is to provide a method of incorporating polychlorophenols uniformly in fiber boards.

Wood can be disintegrated to fibers suitable forfeiting and forming boardsby various methods. These methods can be classified generally as chemical disintegration processes or mechanical disintegration processes. In chemical disintegration processes, wood, preferably in the form of chips or in a similar comminuted form, is treated with'chemicals such as sodium sulfite or sodium hydroxide and the resulting fibers are refined, mixed with binding ingredients, if necessary, formed into felts and these felts are then dried and molded into boards. Boards are formed in the mechanical disintegration processes in much the same general manner except that the wood chips are disintegrated into fibers by grinding, explosion, or similar mechanical disintegration methods. The present invention relates particularly to boards and the process of making themfrom fibers produced by the explosion method of mechanical disintegration.

The explosion method of mechanically disintegrating wood and forming boards from the fibers thus produced has been described by W.

.11. Mason in Paper Trade Journal, 1927, vol. 84,

No. 8, pages 131-136 and by Robert M. Boehm in Industrial and Engineering Chemistry, 1930, vol. 22, pages 493-497. -I'he commercial product is known as Masonite andappears in several forms,

differing principally in density as a'result of the molding conditions used in the final forming operation. In the explosion process the wood to be disintegrated is prepared in the form of chips. The types of wood to be used may be varied; since practically no species of wood is unsuitable for manufacture of board by the explosion process. Soft woods such as spruce, as well as hard woods are usable. However,

since the strength of the board is dependent to some extent upon the fibrous structure as well as the proportion-and nature of certain of thewood constituents, long-leaf pine, southern gum and mixtures of the two are preferred because of their availability and desirable characteristics. The wood chips are then placed in metal autoclaves, which are called guns, provided at the bottom with'quick-opening hydraulic 'valves for the release of the loads and with inlets for steam at the top. The load of wood chips in the guns is then subjected tosteam at a pressure of about 350 pounds per square inch, bringing, the chips to a temperature of about 375 F. (190 C.), and is maintained at this temperature for about to 40 seconds. The pressure is then increased to about 1000 pounds per square inch and maintained thereat for about 5 seconds, the temperature reaching about 540 F. (282 C.). While at this high steam pressure the hydraulic discharge valve is opened and the chips pass through a small port in the bottom of the gun where they explode immediately. In the explosion the chip is ruptured as a result of the high to break down the bundles slightly, screened to remove coarse particles and mechanically treated to obtain a suspension of fibers of the desired consistency and uniformity. The fibers may be subjected to one or more refining operations of this type. The stock then passes to a stock chest. The fiber may be treatedwith an emulsion of paraffin or a similar substance to impart to the board a degree of water-repellency. Such sizing operations may, however, be omitted. The fiber suspension from one or more stock chests passes through a head box and is then felted on a machine similar to a Fourdrinier to produce a wet lap of fibers about 2 inches thick. The white water from this operation may be clarified and recirculated. This felting machine is provided with suction boxes and press rolls over which the felt passes and where it isreduced to about inch thickness and is left with a content of about 65 per cent water.

1 then cut in suitable sizes, and subsequently dried pentachlorophenol into fiber boards a number of methods have been tried. To beat up the polychlorophenol in powdered form with the pulp is unsatisfactory because of the difiiculty of grinding the polychlorophenol to a sufiiciently fine form to obtain uniform and intimate distribution of the compound in the fiber suspension. Another meth- 0d consists in incorporating the polychlorophenol The lap isv as a sodium salt inthe pulp or fiber suspension and thereafter precipitating the fibers together with the size, which is usually an alkaline solution of rosin, by the use of alum, for example, in the beater. Much of the polychlorophenol is retained in the white water and this is an economic disadvantage militating against the general use of the process. To overcome this loss in the white water, processes have been described for precipitating the polychlorophenol from its sodium salt in the presence of the pulp in the form of a less soluble metal salt, such as a zinc salt. The cost of the metal precipitating salt is a great obstacle to the use of this process inasmuch as the additional protection afforded by the metal present ploded fibers with about in the resulting polychlorophenol compound'does phenol from its sodium salt in the presence of the pulp or fiber by means of 'an acid, as heretofore applied to various pulps and fiber suspensions, leaves a great proportion of the polychlorophenol in the white water.

It has now been discovered that polychlorophenols can be incorporated uniformly into fiber boards made from exploded fibers during the manufacture of board therefrom by adding the polychlorophenol as the sodium or other watersoluble salt to the exploded fibers contained in the storage chest or stock chest or at the head box in the process briefly outlined hereinbefore for producing fiber board by the explosive disintegration method. This incorporation also results with but a small fraction of the expected losses in the white water and by modifying the process as herein described even these small losses can be drastically reduced.

The solubility of pentachlorophenol in water. in percentages by weight at various temperatures, is given in the table hereinbelow:

Solubility of pentachlorophenol, percent by weight Temperature, C.

The solubility of pentachlorophenol in aqueous acetic acid having a pH of 2.0 is about 0.0040% at 40 0., compared to.0.0025,% in distilled water at the same temperature.

When it is considered that the fiber stock in the production of boards ismaintained at a temperature of 160 'F. (71 C.) during the refining operations and is not substantially cooler during the felting, and it is known that the fiber stock contains acids such as tannic, acetic and formic acids, it was unexpected that the white water losses would not be excessive and much higher than would result from the use of a cold fiber stock suspended in water free from excess acid. Yet such was the discovery that was made when the process was adopted in practice.

It was discovered that the fibers resulting from the explosion process actually removed pentachlorophenoi from an aqueous solution of pentachlorophenol. By stirring up 100 grams of ex- 5,000 grams of a dilute aqueous solution of pentachlorophenol the concentration of the solution dropped from an original concentration of about 23 parts per million to about 2.6 parts per million of pentachlorophenol. This indicates that the-fiber takes up about 0.1% pentachlorophenol directly from an aqueous solution by adsorption or a similar phenomenon. Ordinarily it would be expected that the fibers would take up the solution more or less by absorption or entrainment and no reduction of the concentration of the solution would result. The advantages resulting from operating according to the method of this invention are in part attributable to the characteristics of the fibers obtained by the explosive disintegration of wood and partly to the complex composition of the white water and the nature of its reaction upon the salt of the polychlorophenols.

In the practice of the present invention the process of producing boards by the explosive disintegration of wood is not substantially modified.

.The wood is disintegrated in the usual manner,

the stock is felted in the conventional manner and the water is removed from the felts and the board is pressed between heated platens as heretofore. However, after the fiber is exploded a water-soluble salt of the polychlorophenol is added to the fiber stock in the storage chest, stock chest or head box, that is, the salt is added before or after refining. The proportion of salt of the polychlorophenol, for example, sodium pentachlorophenate, which is added is such that v a sufilcient concentration of the polychlorophenol is left in the board. Generally pentachlorophenol in an amount equivalent to 1% by weight of technical sodium pentachlorophenate (which has an assay of about 90% NaOCsCls) in the finished board is ample. The quantity of sodium pentachlorophenate to be added can be approximated by taking into account the greatest amount of water present in the stock at any point in the process (roughly, the stock will contain from 1 to 2% of fiber and 98 to 99% water) and the solubility of the pentachlorophenol in the water at the particular temperature or at the highest temperature which will be encountered in the process. Since the apparent solubility of the pentachlorophenol in the water in the presence of the fiber will be less than that expected, it will be necessary to add an excess of sodium pentachlorophenate corresponding only to this apparof the fiber, the quantity of sodium pentachlorophenate to be added after the water system is saturated will be simply that required to provide the desired proportion in the board. When polychiorophenols other than pentachlorophenol are to be used, slight variations influenced by the difierent solubility of the polychlorophenol, the

. difference in absorption on the fibers and similar factors must be considered. As an example,'to provide a board containing pentachlorophenol in an amount equivalent to 1% technical sodium pentachlorophenate, 1.2 poundsof 90% sodium pentachlorophenate in the form of an aqueous 14% solution are added to pounds of coated with and entangle or entrain the poly? chlorophenol precipitate as well as take up a large proportion of the polychlorophenol that is not precipitated. This precipitation of polychlorophenol results from the acidity of the fiber stock which has a natural acidity corresponding to'a pH value of approximately 4.5. Contrary to expectations, since addition of sodium pentachlorophenate, for example, to an aqueous solution of acid reduces the initial acidity, there is no substantial reduction of acidity or increase in pH value of the white water associated with the fiber stock on adding small percentages of sodium .pentachlorophenate thereto. The natural constituents of the White Water influence the character of precipitate and the character of the pre cipitate has much to do with its retention on and in the fibrous structure.

The process of producing board fromthestock to which thewater-soluble salt of the polychlorophenol has; been added is then conducted in the usual manner. This consists briefly in preparing the felt on the felting machine and subsequently pressing the felt between heated platens. The white water recovered from the felting operation is then clarified and reused in preparing the fiber stock. Heretofore, in the molding 'of felts containing polychlorophenols, considerable difficulty has been experienced in the polychlorophenol bleeding or concentrating at the surface and being lost by volatilization after remova1 from the press. No such difliculty has been experienced with felts prepared by the improved process of this invention.

The sizing of the fibers to impart water-repellency to the board may be conducted in the conventional manner, that is, by adding an emulsion of paraffin wax to the fiber suspension in the stock chest. With regard-to protective action of the polychlorophenol in the finished board, there is substantially no difference between adding the polychlorophenol before or after the parafiin wax emulsion has been added to the fiber suspension.

The process described herein may'be used for incorporating such polychlorophenols as the various isomeric trichlorophenols and.tetrachlorophenols and ipentachlorophenol into the board. The water-soluble salts which may be used include those of the alkali metals. salts are the most readily obtained commercially and the cheapest, hence are preferred. The 90 technical sodium pentachlorophenate which is referred to herein is the commercially available material that assays 90% NaOC6Cl5, the other constituents of which include water and small proportions of neutral salts and sodium salts of other phenolic bodies.

Fiber board resulting fromthe process cf the invention containing uniformly distributed therethrough from about 1% to 5% or more of a polychlorophenol is resistant to attack by mildew, fungi, insects-particularly termites, and similar pests.

Inasmuch as the foregoing description comprises preferred embodiments of the invention it is to be understood that the invention is not restricted thereto, and that variations and modifications may be made therein without departing substantially from its scope, as defined in the appended claims.

We claim:

1. The process of producing insect and mildewproofed fiber board having uniformly distributed therethrough on the fibers thereof a polychlorophenol selected from the group consisting of trichlorphenol, tetrachlorphenol and pentachlorphenol comprising explosively disintegrating wood, preparing a fiber stock by addition of water to the fibers and the acidic aqueous liquor resulting from said explosive disintegration, adding to said fiber stock a water-soluble salt of a polychlorophenol selected from the group consisting of trichlorphenol, tetrachlorphenol and pentachlorphenol, whereby the said polychlorophenol is precipitated by the water-soluble constituents contained in the aqueous liquor resulting from the explosive disintegration of the wood,

felting the resulting stock, and thereafter moldphenate.

The sodium