US2571986A - Dry process for making composite products with ph control - Google Patents

Description

E. G. HALLONQUIST DRY PROCESS FOR MAKING COMPOSITE PRODUCTS WITH PH CONTROL Filed NOV. 21, 1948 Oct. 16, 1951 .2; 3:5 6 m Q h 0 h if 833% u w M 3m 6Q 9Q wgwwwkm ut wqbmwkow e Z) -ouaaos9v. 831m INVENTOR Earl G lly/0W0,

A TTDRA/EYS Patented Oct. 16, 1951 DRY PROCESS FOR MAKING COMPOSITE PRODUCTS WITH pH CONTROL Earl G. Hallonquist, Tacoma, Wash., asslgnor to Plywood Research Foundation, Tacoma, Wash., a corporation of Washington Application November 21, 1949, Serial No. 128,665 8 Claims. (01. 18-475) This invention relates to a process for making composition boards and related products by the consolidation of dry or moist sheets or felts composed of pieces of lignocellulose materials, e. g. wood fibers.

The present invention is based upon the discovery that, in the manufacture of consolidated products by the dry process, the pH of the lignocellulose mixture immediately prior to its consolidation, is of controlling importance in determining the water resistance properties of the consolidated products. According to the present invention it has been found that, where such pH of the mixture exceeds a value of about 6.0, the water IBSlSt'Zl'lOG characteristics of the product are aifectec'. adversely, this efiect increasing rapidly with increase in pH values. However, if the pH of the mixture is kept below a value of about 6.0, the water resistance properties of the product are markedly improved.

Hence, broadly stated, the process of the presem; invention comprises producing a consolidated product having desirable properties of water resistance by forming a dry mixture of pieces or particles of wood or related lignocellulose materials with suitable quantities of binder and other additives, adjusting the pH of the mixture to a value of less than about 6.0, and consolidating the resulting mixture of controlled pH by the ap plication of heat and pressure. When this is done, the consolidated products formed uniformly have low water absorption and swelling properties upon exposure to moisture, regardless of the identity of the lignocellulose starting material, the nature and amount of the binder and size incorporated in the mixture, and the initial acidity or alkalinity of the lignocellulose starting material and of the added substances.

Processes for the production of consolidated composition boards, particularly hard board, may be of two general classes. In the wet; process, a low consistency slurry of wood fiber in water containing roughly from 3,000 to 10,000% by weight water (on the basis of the dry fiber) is passed through a screen to form a felt from the suspended fibers. This felt then is consolidated to the desired degree by the application of heat and pressure.

In a dry process, on the other hand, the solid fibers are formed into a felt by mechanical means without suspension in a liquid medium. The flbers are not dry, however, in the literal sense of not containing any moisture. They may contain substantial amounts of moisture, such as, for example, in the order of to 1 such moisture content obtaining because of the moisture content of the wood and of the added materials. It is with a dry process that the present invention is concerned. the words "dry process" and dry forming into a mat being used herein in the accepted sense described above, 1. e., in the sense that the lignocellulose raw material is handled in the form of solid pieces or particles without suspending it in a liquid vehicle, although the lignocellulose mixture, just prior to pressing, may have a substantial moisture content. A suitable dry process in which the process of the present invention is applicable, is described in the copending application of Schubert et al., Serial No. 51,938, filed September 30, 1948.

It is to be understood that the presently described process is applicable to llgnocellulose materials which are substantially unaltered chemically from their native condition and which have not been subjected to the drastic preliminary chemical treatments which are often employed, for example, in preparing lignocellulose material for use in molding procedures. In such preliminary treatments the llgnocellulose material is often extensively degraded, as by hydrolysis.

In the present process, on the other hand, the

lignocellulose material is not subjected to chemical treatment beyond an optional preliminary steaming calculated only to soften the fibers, thereby facilitating their subsequent mechanical separation as described herein. There is no extensive hydrolysis of the lignocellulose material, which therefore is employed in the present process in a relatively non-degraded and nonhydrolyzed condition.

Where the wet process is used, the control of the pH of the felt prior to its consolidation does not present a particular problem since, no matter what the character and pH of the starting material and additives, and the amounts of the latter which are incorporated in the mixture, the excess quantities of either acid materials or basic materials are washed away from the lignocellulose fibers with the very large volumes of water used as the suspending medium. Therefore the pH of the felt prior to its consolidation will not be affected materially by the presence of the additives, but usually will be a value which is substantially determined by the pH of the lignocellulose material and water employed. The situation is otherwise in a dry process, however, where the washing effect of large volumes of water is entirely absent. In this case, any added alkali or acid remains in admixture with the form of their aqueous, alkaline solutions in amounts ranging from about 2% up to as much as about by weight (solids basis) depending upon the properties it is desired to impart to the product. It will be apparent that the larger the quantity of such binders used, the greater the quantity of alkali (usually caustic soda) that will be introduced into the lignocellulose mixture. Furthermore, the alkali content of the resinous binder, itself, is widely variable depending upon such factors as its source, its degree of advancement and the like. For these resasons, unless special precautions are taken to adjust the pH of the mixture of lignocellulose and added binder, the pH of the mixture will be extremely variable from operation to operation. When a large percentage of binder is used, or when a binder is used having a high content of alkali, the pH of the felt will be correspondingly high, while if the reverse is true, the felt pH will be correspondingly low.

Still another complicating factor is the fact that the lignocellulose materials, themselves, are

characterized by widely differing pH values,

Thus whereas hemlock wood has a pH of about 5.4 and the wood of the white fir has a pH of about 5.2, the wood of the Douglas fir is relatively acid and has a pH of about 3.6. Hence if one of the more weakly acid woods such as hemlock is used in combination with a large proportion of a strongly alkaline binder, the result- As has been noted above, variations in the pH of the lignocellulose mixture are reflected markedly in the water resistance qualities of the consolidated products made therefrom. This effect is illustrated in the following examples. In all of the examples, the raw lignocellulose (wood) in the form of chips or hog fuel after a preliminary steam treatment was converted to a fibrous state in a mechanical grinder or fibrator. The resinous binder, and wax size (if employed) in the form of a water solution or emulsion were incorporated by adding them to the chips before grinding, or to the fiber after grindi The resulting fibrous mixture then was felted into a uniform mat by mechanical means and pressed in a conventional hot press to remove the moisture and set or cure the resinous binder. A screen was used on one side of the felt to facilitate moisture removal, and a smooth caul on the other side in order to give a smooth glazed surface to the board. The felts were pressed at the temperatures and pressures and times given in the tables and the resulting consolidated products removed from the press.

The water resistance and other properties of 4 cent increase in weight of the soaked sample over its original weight.

The swelling characteristics were determined by soaking a 1" by 6" sample in water under the same conditions as given above, i. e., at F. for 24 hours, and the increase in thickness of the sample measured after soaking. The swelling property then was calculated in terms of per cent of the original thickness. The pH of the unconsolidated felt (when measuredTwashdetermined by immersing 10 grams of the moist fiber comprising the felt and containhig approximately 60% water based on the oven dry weight of the fiber in ml. of distilled water and then taking the pH of the resulting slurry after a period of from 16 to 20 hours. The pH of the board resulting from consolidation of the felt (when measured) was determined in a similar manner except that the board was pulverized before immersing in water.

The examples of Table I illustrate the effect of adding varying quantities of a given binder on the water resistance of the resulting boards.

Introduced as an alkaline aqueous solution of a thermosetting giggly-formaldehyde resin containing about 40% by weight resin The examples of Table II illustrate the effect of the pH of the lignocellulose raw material on the water resistance properties of the consolidated product.

Table II Example 4 5 0 7 8 9 Felt Composition (per cent by wt. solids basis);

White fir fiber (pH-5.54.0) 05 95 95 Douglas fir fiber (pH=3.6-3.9) 95 95 95 ax 2.5 2.5 2.5 2.5 2.5 2.5 Binder 2.5 2.5 2.5 2.5 2.5 2.5 Pressing Conditions:

Pressure (p. s. i.). 150 200 200 1 500/200 500/200 Temperature 190 l00 100 190 190 Time (Min l5 l5 l5 15 15 Board Properties:

Water Absorption (percent).. 62. 2 28. 4 57. 2 25. 7 32. 6 l9. 0 Thickness Bwelling 28.4 12.8 25.9 12.2 17.1 8.00

I 500 p. s. i. for 36 min; then 200 p. s. i. for 14% min.

The examples of Table III illustrate the effect of adding increased amounts of alkali to a resin binder used in fixed amounts on the water absorption properties of the resulting consolidated products. In this case, the products were made up with a fiber mix consisting of 2 /270 by weight (solids basis) phenol-aldehyde resin, 2/2% wax size, and 95% Douglas fir fiber. The resin originally had a sodium hydroxide content (liquid resin basis) of 2%. Additional sodium hydroxide was added as indicated.

the case of highly acid woods such as Douglas it may be necessary to add acid directly to the Table III Example 10 ll 12 13 14 16 16 17 18 19 20 21 Felt Composition (per cent by wt.

solids basis):

Douglas Fir Fiber 95 95 95 95 95 95 95 95 95 95 95 95 Wax 2. 5 2. 5 2. 5 2. 5 2. 5 2. 5 2.5g 2. 5 2. 5 2. 5 2. 5 2. 5 Binder 1 2. 5 2. 5 2. 5 2. 5 2. 5 2. 5 2. 5 2. 5 2. 5 2. 5 2. 5 2. 5 N aOH Content of binder (per cent) 2 5 7. 5 l0. 2 7. 5 10.0 2 5 7. 5 10. 0 H of Felt 4. 7 5. 5 6. 8 7. 9 4. 7 5. 5 6. 8 7. 9 4. 7 5. 5 6. 8 7. 9 oisture Content of Felt (per cent) 54. 0 57. 0 62. 0 64. 0 54. 0 57. 0 62. 0 64. 0 54. 0 57. 0 62. 0 64. 0 Pressing Conditions:

Pressure (p. s. i.) 150 150 150 150 200 200 200 200 500/200 500/200 500/200 500/200 Temperature (0.) 190 190 190 190 190 190 190 190 190 190 190 190 Time (Min.) 15 15 15 16 15 15 15 Board Properties:

Water Absorption.. 24. 7 29. 6 53.0 19. 0 25.1 44. 6 55. 5 14.1 16.3 33. 2 42.1 Thickness Swelling (per cent) 11. 4 13. 9 23. 5 23. 5 8. 9 12. 5 21. 7 24. 2 6. 4 7. 9 17. 2 22.1

1 Introduced as an alkaline aqueous solution of a thermosetting phenol-formaldehyde resin containing about 40% by weight resin SOlldS.

500 p. s. i. for min.; then 200 p. s. i. for 14% min.

It will be seen clearly from the above examples that consolidated products prepared using increased amounts of binders dissolved in alkaline media, and hence incorporating increased amounts of alkali, have increasingly poor qualities of water resistance. Thus, as shown in Table I, a board made using 2.5% by weight of an alkaline binder has a water absorption of 29.6% while a board made using 7.5% of the same binder has a water absorption of 42.3%.

Similarly it is apparent that employing a fixed amount of alkaline binder with lignocellulose materials of varying acidity results in the formation of consolidated products having increasingly good qualities of water resistance as the acidity of the lignocelulose material increases. Thus, as is shown in Table II, Examples 8 and 9, composition boards made from white fir having a pH of 5.5 to 6.0 have a water absorption of 32.6% and a thickness swelling of 17.1% while boardsmade from the more acid Douglas fir (pH=3.6-3.9) under the same conditions and incorporating the same amount of alkaline binder have a water absorption of only 19.0 and a thickness swelling of only 8.0%.

Still further, as is shown in Table III and in the drawing wherein the data of Table III are plotted, increasing the alkaline content of the binder and hence increasing the pH of the felt containing the same very materially increases the water absorption and thickness swelling properties of the finished boards. It will be apparent, however, that this eifect is greatest at pH values above 6.0, changes in pH below this critical limit having but comparatively little effect on the water resistance properties of the boards.

Hence in the manufacture of consolidated boards from lignocellulose material by the dry process of the present invention, the pH of the lignocellulose mixture just prior to consolidation is adjusted to a level below a pH of about 6.0.

The lower pH limit depends upon such factors as the sensitivity of the particular lignocellulose materials used to acid, and the susceptibility of the press and handling equipment to the corrosive action of acid. Usually no substantial practical advantages result in employin a pH below about 2 while practical results obtain by maintaining a pH in a range of about 2 to 6, a preferred range of pH being about 3 to 5.

The pH of the lignocellulose mixture just prior to pressing, preferably is regulated by controlling the amount of alkali added to the resinous binder. This procedure may be employed, for example, in

'lulose mixture.

lignocellulose material or the lignocellulose mixture. Thus when acid is to be added, it may be added at any suitable point durin the procedure, as by adding the same to the lignocellulose material, either before or after defibering or comminuting, or by adding the same to the resin binder, or by adding the same to the lignocelchloric acid, sulfuric acid, sulfurous acid, and

phosphoric acid. These may be used preferably in the form of their dilute aqueous solutions although in certain instances the acid anhydrides, such as sulfur dioxide, may be employed.

.Acid salts such as aluminum sulfate, ammonium chloride or sodium acid sulfite also may be used. Still further and preferably, there may be used the organic acids such as formic acid, acetic acid, propionic acid, and the like. These various acid materials may be used singly or in combination with each other.

After the regulation of the acidity of the lignocellulose mixture, the latter is formed into a felt by any suitable dry forming means adapted to produce a uniform layer of the desired thickness. The felt then may be consolidated by conventional methods and in conventional equipment under operating conditions calculated to produce a consolidated product of the desired density. Suitable operating conditions, as set forth in the examples, comprise pressing at from to 500 p. s. i. at about 190 C. for a time period of about 15 minutes, or in general at from 100-800 p. s. i. and -200 C. for 10-30 minutes.

In the examples illustrated in the drawing, the moisture content of the mixture just prior to pressing was in the order of 60% (by weight). Generally speaking, such a moisture content of the lignocellulose mixture requires pressing conditions of about 200 p. s. i. for 15 minutes to consolidate a hard board and drive out free moisture without difficulties as to blowing, blistering and spotting. While the curves on said drawing indicate that the water absorption qualities improve with increased pressing pressures, other factors, as the amount of moisture present in the mixture, determine the maximum and desired -practlcal pressing conditions. with pressing pressures of over 200 p. s. i. and with relatively. low moisture content in the mixtures, a pH in the order of 6.0 will produce satisfactory hard boards. In any event, the said curves indicate that the water absorption qualities of boards are improved by controlling the pH of the mixture to below 6 just prior to pressing, regardless of the pressing conditions.

Although the present invention has been described and illustrated in terms of wood and the phenol-formaldehyde binders, it will be under-' stood that no limitation is intended thereby and that the invention is applicable broadly to lignocellulose materials as a class, including the various species of wood as well as annual products such as straw, corn stalks, cane and the like in the form of fiber or other pieces or particles susceptible to dry forming into a mat. Similarly other resinous binders may be employed in lieu of the phenol-formaldehyde resins. Such binders include, for example, thermosetting resinous condensation products of cresol and formaldehyde, xylenol and formaldehyde, acetaldehyde and phenol, furfural and phenol, and the like. Still further comprehended are such other thermosetting resinous materials as the urea formaldehyde resins and their analogues.

Having now described the invention in preferred embodiments, what is claimed is:

1. The process for the manufacture of consolidated lignocellulose products which comprises forming a. mixture of pieces of relatively non-hydrolized lignocellulose, adjusting the pH of the mixture to a value of less than about 6, dry forming the mixture into a mat, and consolidating the mat.

2. The process for the manufacture of consolidated lignocellulose products which comprises forming a mixture of pieces of relatively non-hydrolized lignocellulose, adjusting the pH 01 the mixture to a value of between about 2 and about 6, dry forming the mixture into a mat, and consolidating the mat.

3. The process for the manufacture of consolidated lignocellulose products which comprises forming a mixture of pieces of relatively non-hydrolized lignocellulose, adjusting the pH of the mixture to a value of between about 3 and about 5, dry forming the mixture into a mat, and consolidating the mat.

4. The process for the manufacture of consolidated lignocellulose products which comprises forming a mixture of pieces of relatively non-hydrolized lignocellulose intermixed with a binder therefor, adjusting the pH of the mixture to a value of between about 2 and about 6, and consolidating the resulting mixture;

5. The process for the manufacture of con solidated lignocellulose products which comprises iorming a mixture of pieces of relatively non-hydrolized lignocellulose with a thermosetting binder therefor, adjusting the pH of the mixture to a value oi! between about 2 and about 6, dry forming the mixture into a mat, and consolidating the mat by the application of heat and pressure.

6. The process for the manufacture of consolidated lignocellulose products which comprises forming a mixture of pieces of relatively non-hydrolized llgnocellulose with a thermosetting binder comprising a phenol-aldehyde resin, adjusting the pH of the mixture to a value or between about 2 and about 6, dry forming the mixture into a mat, and consolidating the mat by the application of heat and pressure.

7. The process for the manufacture of consolidated lignocellulose products which comprises forming a mixture of pieces of relatively non-hydrolized lignocellulose with a thermosetting binder comprising an aqueous alkaline solution of a phenol-formaldehyde resin, adjusting the pH of the mixture to a value of between about 2 and about 6, dry forming the mixture into a mat, and consolidating the mat by the application of heat and pressure.

8. The process for the manufacture of consolidated lignocellulose products which comprises forming a mixture of pieces of relatively non-hydrolized lignocellulose and an aqueous alkaline solution of a thermosetting phenol-aldehyde resin, adding an acid material to the said mixture for adjusting the pH of the mixture to a value of between about 2 and about 6, dry forming the mixture into a mat, and consolidating the mat by the application of consolidating temperatures and pressures.

EARL G. HALLONQUISTI REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Goss Sept. 6, 1949

Claims (1)

1. THE PROCESS FOR THE MANUFACTURE OF CONSOLIDATED LIGNOCELLULOSE PRODUCTS WHICH COMPRISES FORMING A MIXTURE OF PIECES OF RELATIVELY NON-HYDROLIZED LIGNOCELLULOSE, ADJUSTING THE PH OF THE MIXTURE TO A VALUE OF LESS THAN ABOUT 6 DRY FORMING THE MIXTURE INTO A MAT, AND CONSOLIDATING THE MAT.

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