US2578695A - Method of making lignin compound and product - Google Patents

Description

' bonding agent.

Patented Dec. 18, 1951 METHOD OF MAKING LIGNIN COMPOUND AND PRODUCT Worth C. Goss, Seattle, Wash, assignor to United States Sheetwood Company, Seattle, Wash., a

corporation of Delaware No Drawing. Application June 26, 1948, Serial No. 35,519

4 Claims.

This inventionrelates to the making of new and useful chemical compounds.

More particularly, the present invention has to do with the making of new chemical compounds, to be used principally as glues, binders and the like, and possessing desirable characteristics and having certain advantages of use over and beyond products heretofore applied to those uses for which the present compounds are to be applied; the present compounds being produced by reactions between certain selected substances of which a chemically depleted form of lignin is one of prime importance.

It is the principal object of my invention to produce new resin compounds that have the following desirable characteristics; They are well adapted for useas glues or bonding agents; they are thermo-setting but only at a relatively high degree of heat, for example, at temperatures over 225 F.; they can be easily and inexpensively manufactured; they are easy to use and are especially suitable for use as a bonding and waterproofin agent in the manufacture of sheet wood products, and the like, whereinthe present compounds are mixed with wood fibers and the mixture compressed and set under the action of heat and mechanically applied pressure.

To impart a better understanding of some of the objects which I desire to attain by and the advantages residing in the present invention, it will here be explained that in a copending application, Serial No. 3,000, filed January 19, 1948, I have described the making of boards, or sheet Wood products, from moist, fiberized, ligno-cellulosic materials and a thermo-setting, plastic More specifically, I have described the making of sheet wood from a mixture of moist wood fibers and a special bonding agent derived by the wet grinding of wood that has decayed to a condition of brown rot; the mixing of materials as described being accomplished by passing the damp wood fibers and the bonding agent, which is of paste-like consistency, together through a mixing machine that operates in such manner as to cause the coatin of the individual fibers with the agent. The coated fibers were then sifted through a series of screens and allowed to fall from suspension in air, to form a pad, the pad then being consolidated in a hot platen press and the fibers thereof coalesced together and the agent set under the action of heat and pressure thus applied.

In my manufacture of sheet wood products according to the above description, I have found it necessary, for the most efiective and quick coalescing and bonding of the fibers, that the mixture should contain a certain amount of moisture to be generated into steam under the heat of the press. However, it is advantageous to fast and economical manufacture, that the moisture content be kept at as low a percentage as practicable without detriment to the finished product.

Where wood fibers, preparatory to the consolidating operation, are formed or felted into sheets by any of the commonly used wet lap processes, the moisture content of the sheet will be extremely high. Because of this, it has been the general practice to pass these sheets as formed by the wet lap process, through squeeze rolls to expel a certain amount of the excess moisture therefrom before the sheet is delivered into the consolidating press. In spite of this squeeze roll pre-pressing operation, the moisture content of the sheets will still remain quite high and by reason of this high moisture content, the pressing time, or drying time required in the press will be prolonged accordingly.

In accordance with the teachings of the previously mentioned copending application, the bondin agent of thin, paste-like consistency, containing a substantial amount of moisture as derived by the wet grinding of brown rotted wood, is mixed with the damp wood fibers in such amount that although each fiber is given a thin coating of the agent, the agent, which is not tacky, is not applied in amount sufficient to cause the adherence of fibers or the balling of the mixture in the mixing operation, or as discharged from the mixer. In fact, the coated fibers may be readily separated by a shaker screen operation to fall from suspension in air for the formation of pads therefrom. However, the mixture, as prepared, still contains approximately of moisture, which is an amount advantageous to the method of mixin which I employ, but considerably more than is required for the production of that amount of steam necessary to insure proper coaelscing of fibers under the effects of heat and pressure as produced by the press. Therefore, I have found it to be quite advantageous for faster pressing operations, to fur- .ther reduce the moisture content of the mixture to approximately 25% by passing it through a suitable dryer before forming it into pads for consolidation.

Heretofore, there has been an objection or disadvantage to this further drying out of the coated fibers, by heat, the objection arising from the fact that under a normal drying heat of around 200 F. to 225 F., the bonding agent, prepared as described in my prior application and applied to the fibers in the form of a thin coating, is subject to pre-setting to more or less amount and thus the finished boards do not have full shear 3 strength. Therefore, the drying of the coated fibers, prior to forming them into pads for consolidation, has not been made a practice. Thus, a faster pressing time with incident decrease of cost has been sacrificed in the interest of additional strength in the finished product.

In view of the foregoing explanation, it has been an object of this invention to produce a series of chemical compounds, designed to replace the bonding agents previously used, which are not only especially effective glues or bonding agents, giving more toughness to the products and increasing shear strength considerably, but also, and most important to the present use, are characterized by the fact that the tendency to pre-set is substantially reduced at the temperatures coming within the range that is desired for the dryin out of excessive moisture from the coated fibers preparatory to forming them into sheets or pads for compression.

The present compounds may be produced by compounding various chemicals with what I have designated as a chemically depleted lignin such as that substance comprising the major portion of wood that has decayed to a condition of brown rot. I find it quite practical to carry out the invention, in one way, by reacting together brown rotted wood, ammonium hydroxide, and a selected phenol; for example, I may use resorcinol, pyrocatechol, carbolic acid, cresylic acid or cresol. Some other compounds that may be used are furfural, furfural alcohol, urea, maleic anhydride, petroleum distillation products higher and lower boiling than cresylic acid, various aldehydes and the higher alcohols such as glycerine.

The term brown rotted wood as herein used, which is one source of chemically depleted lignin, is intended to be descriptive of forest wood that either has decayed to a condition of brown rot by natural process, or has been artificially reduced to that condition by subjecting the wood to the action of certain micro-organisms, such as, for example, those known as polyporous Schweinitzii. Wood that has decayed to the condition of brown rot, either by natural process or by artificially produced conditions, is not to be confused in this instance with other forms of rot, for example the white rot sometimes found in forest wood. Furthermore, brown rotted wood is here understood to be a material which analyzes about 70% or more of lignin by acid analysis; the cellulose of the wood having been removed from the material by the cellulose consuming micro-organisms or fungi. This brown rotted wood is one source of what I have designated as a chemically depleted form of lignin, and by reason of its chemical depletion, this form of lignin has an extreme degree of chemical activity as compared with that of ordinary lignin, such as pulp liquor lignin.

To better explain what I mean by my use of the term chemical depletion, or chemically depleted, it will here be pointed out that lignin from fresh Douglas fir wood analyzes 15.4% methoxyl content, while the lignin extracted from brown rotted Douglas fir wood analyzes only 11.6% methoxyl content. There also is a gradation in chemical depletion in the brown rotted material as indicated by a further analysis which was carried out as follows: Brown rotted wood was added to a solution of ammonium hydroxide at a temperature of 170 F. About 20% of the brown rotted wood was dissolved, forming a very dark colored solution. The solution was separated from the solid portion by filtration, and

the filtrate was acidified with hydro-chloric acid and a brown precipitate appeared. This precipitate, on acid analysis, showed 88% lignin content, and this lignin showed a methoxyl content of only 7.9%.

My definition of depleted lignin as used in the present instance, and regardless of its source, is: A. substance essentially lignin in character but containing less methoxyl content than the lignin of the vegetable substance from which the depleted lignin comes. Black forest soil has a depleted lignin of even lower methoxyl content than that of brown rotted wood, and this is also true of peat. In general, the depleted lignins are acidic in character, and my experiments have shown that the lignin that is most depleted, that is, which has the lowest methoxyl content, has the most vigorous chemical reaction with ammonium hydroxide and any selected phenol or substance used in lieu of a phenol.

Sources of depleted lignin suitable for use in carrying out the present invention are black forest soil, peat, lignite coal, animal manure, artificially produced depleted lignin, and the brown rotted wood previously defined.

A satisfactory method of forming the present product, or chemical compound, is as follows:

Brown rotted wood, in accordance with the previous definition of this material, is wet ground to a very fine, paste-like consistency. Grindmay be very satisfactorily accomplished by use of a Carborundum plate attrition mill. One pound of dry brown rotted wood and five pounds of water can be ground in such a mill to form a paste of very satisfactory consistency for the present uses in the manufacture of pressed wood or sheet wood from wood fibers. The proportions used may be varied to some extent from those above given without detriment to the final product.

To the rotted wood paste thus formed, I then add ammonium hydroxide, while stirring the mixture, until it shows a pH of about 9.2.

Explanatory to the addition of the ammonium hydroxide, it will be here noted that in my previously referred to application, I disclosed the washing of the brown rotted wood with a solution of ammonium. hydroxide in order to neutralize the humic acids contained therein which were detrimental to fiber strength in the finished products. In the present instance, where the base material is a depleted lignin to be obtained from various sources which are, in general,

acidic in character, it is desirable to add the ammonium hydroxide not only because of its neutralizing effect on the acidic content, but primarily in order to bring about the reaction between the various substances used in forming the compounds, for without it, or its equivalent, the proper compounds are not prepared nor are the objects of the invention attained.

After the ammonium hydroxide has been added to the rotted wood paste to the extent above specified, I then add to the mixture twotenths of a pound of a selected phenol, for example, resorcinol, for each pound of dry rotted wood used in making the mixture. The mixture is then stirred thoroughly and is thereby made ready for use.

In the manufacture of this compound, I have also used phenols other than resorcinol with satisfactory results. For example, in lieu of resorcinol, I can use any of those previously named with more or less success. Should the 5; compound be made by use of another phenol. in

lieu of resorcinol, the selected phenol would be used in a like manner and in an amount equivalent to that given above for resorcinol, and when so used, a similar resin compound will result therefrom.

An excellent resin compound may also be produced by the three-way reaction between brown rotted wood, ammonium hydroxide and urea in lieu of a phenol.

Another good resin compound is prepared using furfural in place of urea.

An example of preparing the product by the use of urea is as follows:

For each ten parts by weight or" dry brown rotted wood, I add two parts by weight of urea and sixty parts by weight of water. This mixture is then ground to a smooth, soup-like consistency which will have a pH of about 3.3. Ammonium hydroxide is then added slowly thereto while stirring the mixture, until the pH of the mixture reaches 9.0 or over. The new chemical compound thus produced may be used directly as a heat setting glue. of this glue by weight (dry basis) mixed as previously disclosed with 85% wood fibers, and the mixture dried to a moisture content of from 15 to 75%, may be pressed under a temperature of 250 F. and above to form a strong, hard, split-proof board especially suitable for receiving thin plastic overlay sheets.

Mixing of materials in the instance of use of urea also would preferably be in accordance with the teaching of my copending application previously mentioned. The ammonium hydroxide soluble portion of the brown rotted wood proves to make the best resin. This soluble portion shows a lignin content of 88%, which lignin has a methoxyl content of from 7 to 10%.

It is not the intent that the compounding of the present glue or binder be restricted to use of ammonium hydroxide as the agent for neutralizing the acid content of the brown rotted wood and promoting the reaction between the various substances used. In lieu of ammonium hydroxide, other basis nitrogen compounds such as the amines, or quaternary ammonia bases, might be used with a substantial degree of success.

In the preparation of a product using black forest soil as the source of depleted lignin, I proceed as follows: A quantity of black forest soil is put in a vat together with strong ammonium hydroxide. This is heated at a temperature of about 170 F. for a period of about one hour. I then drain the contents of the vat into a centrifuge and by that means separate the black liquor resulting from the treatment of soil from the sludge. This black liquor, which contains the depleted lignin therein, is concentrated by evaporation and may then be used as the basic material of the present product. The compound is then completed by the addition of a phenol thereto as previously described, or by the addition of urea, or other suitable substance.

To extract depleted lignin from lignite coal, I proceed as follows: The coal is first ground to a fine powder. This powder is boiled in a 1% solution of sodium hydroxide for a period of thirty minutes. The black liquor is then centrifuged from the sludge and the black liquor neutralized with hydrochloric acid, and this results in a dark colored precipitate being formed. The precipitate is separated by centrifuging or filtering and is washed with clear water. This precipitate is constituted principally of depleted lignin and is a very excellent starting material for my new compound. It is used with ammonium hydroxide and urea or ammonium hydroxide and a phenol, as has previously been described.

The present compounds as produced by the reaction between depleted lignin, from any of the mentioned sources, ammonium hydroxide and a phenol, or urea, or other substances, is characterized by the property of giving exceptional toughmess to wood fiber products wherein the compounds are used as bonding agents. It very automatically increases shear strength and increases water'resistance. The same characteristics will be found in products regardless of the source of depleted lignin used therein. However, because of its great abundance, the ease of use and excellency of the product produced therefrom, brown rotted Wood is now the preferred source of depleted lignin.

Having thus described my invention, what I claim as new therein and desire to secure by Letters Patent is:

1. The method of making a high temperature, thermo-setting compound comprising wet grinding brown rotted Wood to a paste, adding thereto ammonium hydroxide until the mixture shows a pH of about 9.2, then reacting the neutralized substance with a phenol selected from the group consisting of resorcinol, pyrocatechol, carbolic acid, cresylic acid, and cresol.

2. The method of making a high temperature, thermo-setting resin comprising wet grinding brown rotted wood to a paste, mixing ammonium hydroxide therewith until the mixture shows a pH of about 9.2, then adding approximately oneiifth pound, for each pound of dry brown rotted wood used in the mixture, of a phenol selected from the group consisting of resorcinol, pyrocatechol, carbolic acid, cresylic acid and cresol.

3. The method of making a high temperature, thermo-setting resin comprising mixing a brown rotted wood with ammonium hydroxide until the mixture shows a pH of about 9.2, then reacting, with the mixture, of a phenol selected from the group consisting of resorcinol, pyrocatechol, carbolic acid, cresylic acid and cresol.

4. A high temperature, thermo-setting binder comprising a mixture of brown rotted wood,

1 ammonium hydroxide and a phenol selected from the group consisting of resorcinol, pyrocatechol, carbolic acid, cresylic acid and cresol.

WORTH C. GOSS.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS OTHER REFERENCES Rose et al.: Journal Ind. Eng. Chem, March 1917, pages 284-287.

Thaysen et al.: The Microbiology of Cellulose, 1927, page 300.

Claims (1)

1. 4. A HIGH TEMPERATURE, THERMO-SETTING BINDER COMPRISING A MIXTURE OF BROWN ROTTED WOOD, AMMINIUM HYDROXIDE AND A PHENOL SELECTED FROM CARBOLIC ACID, CRESYLIC ACID AND CRESOL.