US2454534A - Process for defibering lignocellulose while subjected to steam and alkali-metal hydroxide - Google Patents

Description

Patented Nov. 23,- 1948 PROCESS FOR DEFIBERING LIGNOCELLU- LOSE WHILE SUBJECTED TO STEAM AND ALKALL-METAL HYDROXIDE Henry 1:. Walter, Cloquet, Minn, assignor to Wood Conversion Company, Oloqnet, Minn., a

corporation of Delaware No Drawing. Application August 3, 1940, Serial N0. 351,240

9 Claims. (01.92-63 The present invention relates generally to the production of fiber from lignocellulose, and in particular to the simultaneous subjection of the material to a mechanical defibering action in the presence of strong alkali.

Reference is made to the U. S. patents to Asplund No. 2,008,892, No. 2,145,851, and No. 2,047,170, relating respectively to a process and machine for producing fiber, and to the process using a. fusible size. In general, the machine provides a high pressure steam chamber housing a rotary grinding disk facing a stationary companion disk. Means is provided for introducing lignocellulose material, and particularly wood chips, into the chamber by forming an advancing plug. The material then is conveyed to the grinding disks where, softened by heat, it is readily defi-- bered, for example in the case of jack pine at about 150 lbs. steam pressure at 365 F., or in the case of aspen at about 135 lbs. steam pressure. The formed fiber is discharged through valved orifices, by the differential pressure of the steam chamber and the atmosphere. Raw wood, or wood with absorbed added water, is preferably employed, there being insufficient water to sizepend the wood or fiber, and only sufllcient to discharge a moist fiber.

Such fiber has many uses. Among the uses is the ultimate formation of felts, such as paper, cardboard, insulation board, and hardboard.

These all may involve felting the fibers from.

water suspension in the several well-known methods and machines, such as cylinder and Fourdrinier forming machines. As in the case of chemically cooked fibers so formed into felts, the fiber desirably provides the "paper makers bond. This is obtained through a process of hydration. pends the felt formation, and strength of the ultimate product. Hydration involves mechanical work on wet or water-suspended fiber, at great expenditure of power. Difflcultly hydratable fibers call for more expenditure of power and longer time. Length of time of hydration increases the breakage or reduction in size of the fibers. Such breakage lowers the strength, or increases the density without corresponding gain in strength.

The fibers resulting from the operation of the Asplund machine upon raw lignocellulose material or from other mechanical defibering processes are of course susceptible to the usual operations of hydration, felt-forming and drying to provide papers, boards and the like, but the production of such materials presents problems. To secure adequate hydration considerable power and time are required, accompanied by breakage of fiber. The resulting boards are relatively weak in physi- Upon the degree of hydration decal properties, or outside-the economical strength to density ratio. The presentinvention aims to preserve the desirable advantages of mechanically reducing lignocellulose to fiber, in the Asplund machine or in like useful machines or processes, and to employ simultaneously a chemical efiect upon the material whereby the resulting fibers are improved in their properties pertinent to making felted products.

It is a particular object of the invention to subject wood to mechanical defibratlon at elevated temperatures in a gaseous environment and in the presence of strong alkalis, such as the hydroxides of alkali metals.

It is also an object of the invention to defiber wood mechanically with a substantially simultaneous chemical action, to shorten the time required for hydrating the fiber for felt-formation, thus to minimize the breakage of fibers, and to improve the physical properties of felted products, and particularly of rigid board.

Various other and ancillary objects and advantages of the invention will be apparent from the following description and explanation of the invention.

The invention is more particularly illustrated herein by reference to the use of wood, since wood, compared to straw and grasses, imposes greater burdens .in reducing it mechanically to fiber. Wood and other lignocellulose, isnaturally acid and acid-forming. The fiber discharged from feeding wood or other lignocellulose, through the Asplund machine and process, has a pH considerably lower than '7, depending in part upon the species of wood. It, therefore, follows that in the Asplund process of defibering, the wood is subjected at high temperature to acid conditions,

not by added acid, but by 'its own elements.

Neither high temperature nor acid conditions are favorable to hydration, so that a normal hydration practiced on the resulting fiber is a difficult hydration.

According 'to the present invention, the acid condition during defibration is changed towardor to a neutral to alkaline condition, by adding to the lignocellulose material to be defibered, at least sumcient strong alkali to neutralize some of the acidic elements of the material, but preferably some excess is added as a measure of safety to provide a pH of 7 or over. Based upon the dry weight of wood, such as aspen, a usage of about 4% more or less of caustic soda is required to neutralize the acidic elements. At least such amount of alkali is added to the wood prior to its deflbration, as by adding it with the wood, or introducing it into the machine in advance of the final stage of defibration and at such a point that the defibering action will distribute the alkali onto the material. The alkali may be added as a solid, or as a solution. In using a solution, it is necessary to avoid such dilutions that a fibersuspending amountof water is introduced into the defibering machine.

The discharged partially or wholly neutralized or alkaline fiber may then b leached or washed with water, whereby soluble material, including residual products of the alkali, is extracted. The resulting washed fiber then customarily exhibits a characteristic acid'pH of slightly below '7. Such fiber may then be subjected to hydration in a usual way, as in a Jordan, a beater, a Bauer, or other suitable equipment, which may at the same time refine as well as hydrate, to break down any bundles of fiber to ultimate fibers. Such hydration is preferably carried out in water free from added agents, such as alkali, which are well known to change the rate and character of hydration. However, if desired, such added agents may be present. The refined and hydrated fiber is then ready for felting.

Preliminary to felting, some treatment of the fiber may be desired. It is common in making insulating board to add a wax emulsion to the stock. and to precipitate the wax with-alum. If a paper is to be made, it may be desirable to size th stock by adding a rosin soap or the like, and precipitate with alum. These and other familiar treatments I may be practiced. Fireproofing agents may be present in the stock.

In developing the invention, it has been found that there are several distinct effects resulting from the use of caustic alkalis. The color of the stock is made somewhat darker. The ease of gelatinization increases (this is measured as time necessary to attain a given slowness value). The strength of felted products is increased. These results are all due to the use of caustic alkalis, as distinguished from weaker neutralizing substances. Where an equivalent amount of sodium carbonate is used, the acidity may be destroyed, but the color does not darken, the stock does not hydrate much, if any, easier, and the felted products are not appreciably stronger. The causticity as well as neutralizing capacity plays some part in the functioning of caustic alkalis. The exact reasons are not known, but some explanations are available.

From other development'work, it is known that wood contains, and develops or releases acid under the conditions of the steam environment in the Asplund machine, as it passes through the machine in 40 to 60 seconds more or less. It is thus logical to assume that the caustic alkali is a caustic reagent active on the material at a high temperature for a time period of less than about one minute. This action probably induces some changes in the material which cannot be produced by milder neutralizing alkalis, such as the carbonates, and oxides or hydroxides of metals other than the alkali metals. one effect of the presence of caustic alkalis is to effect a certain amount of, or some preliminary stages of hydration, under the influence of the work done in defibering in the presence of the moisture in the material.

In order to illustrate the nature of the invention, the following results are given. comparing properties, one on untreated aspen wood, and one on like aspen wood treated with a usage of 5% (based on dry wood weight) of caustic soda.

COMPARATIVE ANALYSIS or rm: Frsans Aspen wood, defibered in the Asplund machine,

It is also possible that both untreated and treated with a usage of 5% caustic soda, is extracted at 2% consistency with boiling water for two hours. For reference. fiber similarly produced. but with usage of 5.75% of sodium sulflte and 0.15% of sodium carbonates, is given. The following results obtain on the basis of parts of dry fiber, based upon aspen having 20.7 parts lignin, and 51 parts alpha cellulose:

Parts by Weight NaOH NuzSOJ Untreated Treated Treated Fiber 90. 2 76. 0 8i. 5 Lignln in fiber 16.9 l4. 4 15.1 Solubles 9. 8 24. 0 l8. 5 Carbon drates in solublcs. 0. 0 17. 7 12. 9 Lignin n solubles 3. 8 6. 3 5. 6

Composition of the fiber NaOH NmSOi Untreated Treated Treated Per cent Per cent Per cent Alpha cellulose 56. 6 67 62. 5 In n 18. 7 l9 l8. 5 Carbohydrates not cellulose .24. 7 14 v19. 0

f From the foregoing, it is seen that the presence of alkali, in the defibration and carried with the fiber to the extraction, changes the soluble portion of the fiber from 9.8% to 24%. At the same time the cellulose content is raised and the lignin 7 and carbohydrate content reduced. The residual carbohydrate and lignin may be different, however.

- The term "pH of the fiber is in effect the pH of a water extract of the fiber determined as follows:

A sample of 10 grams of oven-dry fiber, or 10.7 grams of air-dry fiber, is extracted for hour at 50 to 60 C. in 100 cc. of distilled water which has been boiled. The water is separated, stoppered and cooled to room temperature, and its pH is measured.

Compressive Properties" are those of dry bulk unfelted fiber as set forth in the copending application of Anway U. S. Serial No. 313,920, filed January 15, 1940, now U. S. Patent No. 2,325,026, issued July 27, 1943. Briefly, two columns of weighed fibers in cylinders of different diameters are compressed by a moving piston at a slow and standardized rate. The pressures exerted by the columns as a result of the compression are correlated to the density of the columns. From the data the properties are calculated.

Sliding friction indicates the surface character of a mass of fibers to exhibit friction, as it does on the cylinder in compressing.

Free-footage is an extrapolated density value, expressed as a reciprocal density in board-feet per pound of fiber when the fiber is unfelted by pressure other than its own weight. It is akin to flufflness.

Specific elasticity" (Ks) is an indication of the elastic poperties when the fiber being compressed is at an arbitrary reciprocal density of 3.15 board feet per pound.

"Absolute elasticity is an index, or an indicative slope of a line produced in the mathematical solution, on which line the value Ks is read.

Specific felting (Kr) is an indication of the force which felts the fiber as it is being compressed and at 3.15 board feet per pound.

' in Heritage U. S. Serial "Absolute felting (Me) is an index, or an indicative slope of a line produced in the mathematical solution, on which line the value Kr is read.

Coarseness modulus or C. M. is an arbitrary but standardized measure of particle size distribution. The method and apparatus is set forth No. 336,495, filed May 22, 1940, now U. s. Patent No. 2,325,055, issued July 27, 1943. Briefly, a specimen is divided by screening, into fractions according to screen size, and the percents as fractions are weighted in totaling, to give a significant figure, larger as the general coarseness of the fiber increases. Numerous systems different in detail are used to classify fiber, but diiferent systems give correlatable values for conversion from one to another.

EXAMPLE Fiber is produced from peeled aspen by forcing it in chip form into an Asplund defibrator operating at about 135 lbs. steam pressure. In one case a usage of NaOH is added, and in the other case no agent is added. Also, a case is given where usages of 5.75% of NazSOa and 0.15% of mixed sodium carbonates, calculated as NazCOz, has been used for comparison. The stocks are then washed similarly with cold water (60 F.) and refined at about 7.5% consistency with water (40 parts per 3 parts of fiber) in a Sample s-zzs NaOH NazSOa Unnamed Treated Treated 466 467 Before washing 5. 3 7.18 6.15 After washinr. 6. 84 ii. 85 After ball-milling 5. 5 6. 72 5. 90 Minutes to attain Freeness 19 seconds 100 75 115 Coarseness modulus:

Before milling 145 125 1% After milling 81 84 73 Per cent Reduction 0. M.

by milling 44 32. 6 41 MAKING or BOARD The above fibres after hydration, without other treatment, are formed into boards of the character referred to as insulation board. This comprises merely felting a slurry of the fibers on a wire in a suitable manner to provide roughly a board of /2-inch thickness. The wet mat thus formed is pressed to %-inch thickness. It is then dried in several ways. One extreme is to dry the mat without restraint, whereby it may swell or spring back, or shrink, in drying, if it will. Another way is to dry with restraint on the wet mat. This may be by means to maintain constant thickness, or means to maintain constant pressure. The latter-is preferred for comparisons, and is used at 100 lbs. per sq. ft. to obtain the restraint" values given below.

Unrestrained drying NZIOH NaeSOa Untreatbd Treated Treated Dried specimen weight, grams. 30. 4 31.3 29. 7 Dried specimen thickness, inches. 0. 600 0. 532' 0. 544 Pounds per cu. ft 15.4 17.3 16.5 Per cent increase over pressed wet thickness on:

Releasing pressure 72.0 50.0 54. 4 Drying 60. 0 42. 1 45. l

Restrained drying NaOH NazSO: Ummnttd Treated Treated Density, lbs. per cu. ft. (dried board) 17. 23 22. 79 i6. 95 Per cent increase over pressed wet thickness on drying with 100 lbs./sq. it. pressure 34. 7 9. 9 17.3 Board thickness. inches 0. 492 0. 383 0. 417 Property Values in Bending:

Load in lbs. at elastic limit... 14.7 21. 0 12.0 Load inlbs. at point oirupture. 20. 0 31. 6 1 8. 0 Modulus of elasticity 33, 200 77, 200 43, 900 Modulus transverse strength 182 420 207 1 Modulus rupture 248 647 311 2590, and 3390.

COMMERCIAL BOARD A strong board has been obtained wholly from aspen wood as follows: The wood is defibered at about 135 lbs. steam pressure in an Asplund machine with a, usage of 5% added caustic soda.

- The fiber is washed with cold water F.) and hydrated in a Bauer machine. The stock is treated with a wax size by use of wax emulsion and alum. The sized stock is run on a mat forming machine, the mat pressed, and dried in a drier under pressure of lbs. per sq. ft. All the steps and equipment of the process beginning with the hydration are standard for a commercial prior art board, the variation being a change from a wood mixture to all aspen, and substitution of the continuous mechanical defibration with caustic soda for the batchwise chemical cooking of chips followed by mechanical action. The stock in the case of the new board has a. coarseness modulus comparable to that used for the commercial prior art board. The new board and process evaluates in the laboratory as follows:

Specimen dried unrestrained:

Volume increase after wet pressing,

percent 33.3 Volume increase, dry board over wet pressed, percent 16,9 Density board dried unrestrained lbs/cu. ft 19.4

Specimen dried under restraint of Commercial magnitude:

Modulus of rupture in bending, lbs./sq. in

PAPER Aspen fibers untreated and treated with a usage formed to paper sheets on a screen, and dried directly from formation, without pressing and without restraint.

The following data concerns the two samples referred to, and also a sample similarly treated with a usage of sodium sulfite in place of 5% caustic soda.

Sample 3-226 NaOH NBzSOa ggg Treated Treated Before washing 5. 25 7. 6. 05 After washing- 6. 50 6. 60 After ball-milling 5. 86 5. 90 6. 35 Minutes to attain slowness of 300 seconds 255 170 210 Coarseness Modulus: I

Before boll-milling. 135 108 125 After ball-milling 29 55 57 Per cent Reduction in C. M. by ball-milling..." 78 49 55 Paper:

Thickness in inches 0. 017 0. 014 0.016 \Veight in lbs/M. sq. ft 12.13 12. 58 11. 66 Weight in lbs/ream (480 sheets 24 x 36 in.) 34. 92 36. 22 33. 31 Apparent density (lbs.

ream weight per oint) 2. 06 2:59 2. 08 Tear (16 sheets) grams- Elmendorf)... 12 36 24 Mullen burst less than 2 3. 0 less than 2 Mullen factor. 0. 08

From the foregoing, it will be appreciated that the treatment with caustic soda, shortens the time for hydration, reduces the breakage of the fiber in hydration, and improves the properties for forming paper, and the paper. Without the treatment it is not possible to make a paper permitting a Mullen test to be made.

The invention is not limited to the use of amounts of caustic alkali suflicient to prepare a neutral or alkaline fiber, as above described. Smaller amounts may be used for the purpose of making a less drastic change in the fiber. Thus, fiber made from wood chips using 1% of NaOH based on dry wood content, and dried directly from the machine, is compared to fiber made in the same operation of the machine at substantially the same time. and similarly dried.

Sample l8-190 Untreated Treated Sliding friction 0. 524. 0. s15 Free-footage 8. 42 8. 12 Specific elasticity (1b).. 235 235 A solute elasticity (ME) 0.608 0. 892 Specific felting (Kr 41.1 47. 1 Absolute felting (Mr) 0.315 0. 333

The efiect of the treatment with a usage of 1% 8 NaOH is" to change physical and chemical qualities of the fiber.

The term caustic alkali as used herein signifies the hydroxides of alkali metals, as solid, or as solution. Solutions at 50% concentration may be mixed with wood chips entering the defibering process. Reference is made to my copending generic application U. S. Serial No. 351.239, filed August 3. 1940, to which this application is specific.

The mechanical defiberin may be accomplished in various machines which operate also to distribute chemicals or solutions. Machines or processes, like that of Asplund, but not operating at above 212 F. in a steam atmosphere are shown in British Patent No. 15,105 of 1911, and Schouten U. S. No. 1,367,895. The Banbury apparatus, (see Robinson U. S. No. 2,142,334 referring to abandoned application Serial No. 101,014, filed September 16, 1936), also described in U. S. No. 1,523,387, and the Respats apparatus and process of Respess U. S. No.'1.976,297 are all useful. In the latter, wood as chips is steamed and thus softened, and the softer chips are defibered by pressure from heavy rolls. Chemicals present at 1 this stage are effective according to the present invention. The rolling process takes longer than the Asplund process, and this is a compensation for its lower temperature. g

It is of course to be understood that the hydration in water, and the felting from water, are merely convenient test procedures, and do not limit the invention. Hydration may be effected with moist fiber in the absence of suspending water, and felting ma be done from suspension inother liquids, or gases, to formboards and papers, or other forms of felted structures.

The invention not only contemplates the treatment of the fiber, but various uses thereof as ex--v pressed in the appended claims.

I claim:

1. The method of treating lignocellulose which comprises heating lignocellulose in the absence of suspending liquid and in an atmosphere of steam at an elevated temperature above 212 F. at which the lignocellulose is rendered plastic, and simultaneously defibering the plastic lignocellulose and incorporating alkali-metal hydroxide substantially uniformly throughout the lignocellulose, whereby to produce chemically treated fibers without substantial loss of constituents of the original lignocellulose. t

2. The method of producing fiber which comprises supplying undefibered lignocellulose to a mechanical defibering device, supplying to said -device'alkali-metal hydroxide, mechanically delignocellulose as the latter is being defibered and while reacting said hydroxide with said lignocellulose thereby to effect an elevation of the pH of the resulting lignocellulose, whereby to produce a fiber of chemically modified lignocellulose, said fiber containing substantially all the solid content of the original lignocellulose.

3. The method of producing fiber which comprises supplying undefibered lignocellulose to a mechanical defibering device, supplying to said device alkali-metal hydroxide, mechanically defibering said lignocellulose in the absence of suspending water in an atmosphere of steam at an metal elevated temperature above 212 F. and at which the lignocellulose softens to a plastic state, said defibering being effected by operation of said device while rubbing and pressing said plastic lignocellulose and while distributing said alkalihydroxide substantially uniformly throughout the lignocellulose as the latter is being defibered and while reacting said hydroxide with said lignocellulose thereby to effect an elevation of the pH of the resulting lignocellulose, whereby to produce a fiber of chemicall modified lignocellulose, said fiber containing substantially all the solid conent of the original lignocellulose.

4. The method of producing fiber which comprises supplying undefibered lignocellulose to a mechanical defibering device, supplying to said device alkali-metal hydroxide in quantity from 1 to 10 parts by weight for 100 parts by weight of dry lignocellulose, mechanically defibering said lignocellulose in the absence of suspending water and in the presence of moisture in a gaseous environment by operation of said device while rubbing and pressing said lignocellulose, while distributing said alkali-metal hydroxide substantially uniformly throughout the lignocellulose as the latter is being defibered and while reacting said hydroxide with said lignocellulose, thereby to efiect elevation of the pH of the resulting lignocellulose including neutralization of at least a part of the acidity available therein, whereby to produce a fiber of chemically modified lignocellulose, said fiber containing substantially all the solid content of the original lignocellulose.

5. The method of producing fiber which comprises supplying undefibered wood to a mechanical defibering device, supplying to said device alkali-metal hydroxide, mechanically defibering said wood in the absence of suspending water and in the presence of moisture in a gaseous environment by operation of said device while rubbing and pressing'said wood, while distributing said alkali-metal hydroxide substantially uniformly throughout the wood as the latter is being defibered and while reacting saidhydroxide with said wood, said hydroxide being supplied in quantity to provide fibers having a pH of at least '7, thereby to effect modification of the lignocellulose of the wood and the provision of non-acid fibers containing substantially all the solid content of the original wood.

6. The method of producing fiber which comprises supplying undefibered wood to a mechani cal defibering device, supplying to said device alkali-metal hydroxide, mechanically defibering said wood in the absence of suspending water in an atmosphere of steam at an elevated temperature above 212 F. and at which the lignocellulose of the wood softens to a plastic state, said defibering being effected by operation of said device while rubbing and pressing said plastic li nocellulose and while distributing said hydroxide substantially uniformly throughout the plastic lignocellulose as the latter is being defibered and while reacting said hydroxide with said lignocellulose thereby to efiect an elevation of the pH of the resulting lignocellulose by neutralization of at least a part of the acidity available therein, whereby to produce a fiber of chemically modified lignocellulose, said fiber containing substantially all the solid content of the original lignocellulose.

7. The method of producing fiber which comprises supplying undefibered aspen wood to a mechanical deflbering device, supplying to said Number Number device alkali-metal hydroxide in quality equivalent to 5 parts by weight of caustic soda to parts of dry aspen wood, mechanically defibering said wood in the absence of suspending water in an atmosphere of steam at an elevated temperature above 212 F. and at which the lignocellulose of the wood softens to a plastic state, said defiber-- tity to provide substantially neutral fibers having a pH of about 7, thereby to effect modification of the lignocellulose and the provision of fibers containing substantially all the solid content of the original lignocellulose.

8. The process ofclaim 2 in which suflicient alkali-metal hydroxide is employed to provide fibers having a pH of at least 7, followed by refining and hydrating said fibers in the presence of water, by felting the resulting hydrated fibers to a felted fiber body, and by drying said felted body while binding the fibers by the product of hydration.

9. The process of claim 7, followed by refining and hydrating said fibers in the presence of water, by felting the said felted body while binding the fibers by the product of hydration.

HENRY E. WALTER.

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

UNITED STATES PATENTS Name Date Herron Sept. 14, 1875 Pond Apr. 15, 1884 Reed Dec. 17, 1889 Schorger May 26, 1925 Wells Jan. 3, 1928 Ellis Dec. 16, 1930 Hatch Feb. 24, 1931 Mason Aug. 23, 1932 McMillan June 13, 1933 Wollenberg Nov. 27, 1934 Asplund July 23, 1935 Asplund July 14, 1936 Robinson Mar. 2, 1937 Mason May"11, 1937 Asplund Feb. 7, 1939 Offermanns June 27, 1939 Feldman Jan. 14, 1941 Morgan Mar. 11, 1941 Basler Dec. 9, 1941 Kressman Mar. 30, 1943 FOREIGN PATENTS Country Date Australia Apr. 10, 1933 Germany June 10,-1886 Australia Apr. 28, 1938 Great Britain June 1, 1933 OTHER REFERENCES Paper Trade Journal, Oct. 15, 1925, pp. 57-59.

Der Papier-Fabrikant, g. 36, 1938, Tell I, pp. 519-531.

Verein der Zellstofi und Papier-Chemiker und Ingenieure, g. 17, 1936, pp. 313-319.