US2929756A - Production of bamboo pulp and paper - Google Patents

Description

March 22, 1960 C, H SCHUH 2,929,756

PRODUCTION OF' BAMBOO PULP AND PAPER Filed Jan. 23, 1958 nited States atent i PRODUCTION OF BAMBOO PULP AND PAPER v Charles Herman Schuh, Tampa, Fla., asslgnor to the Government of Burma Application VJanuary 23, 1958, Serial No. 710,809

6 Claims. (Cl. 162-26) This invention relates to an improved method and apparatus for the production of bamboopulp and paper products, and more particularly, to an improved method and apparatus for modified mechanical pulping of bamboo.

It has been stated in the literature and by various research investigators that mechanical pulping of bamboo is not practical or feasible. For example, after an extensive investigation by the Herty Foundation, it was reported that Most of the known methods of pulping have been applied to bamboo. Least promising of the conventional methods is mechanical pulping.

U.S. Patent No. 1,376,789 describes a machine for shredding bamboo based on a combined .cutting and splitting action for producing slivers of bamboo for use in brooms or the like. A machine has also been proposed for shredding bamboo for paper and pulp production which involves shredding of pieces of bamboo by rubbing apart and cutting across the fibers with saw teeth and the like. There is a general reduction of the pieces to a comminuted mass. These and other devices have been proposed but each has left much to be desired for practical use with bamboo.

The present invention avoids the problems and drawbacks of conventional mechanical pulping, as applied to bamboo. The instant invention makes it possible not only to successfully and economically produce mechanical bamboo pulp but also to produce a pulp that is superior to mechanical wood pulp. In addition, the instant invention produces a mechanical bamboo pulp at lower cost than that required for producing mechanical wood pulp. The superiority of the instant bamboo pulp results from a much greater average fiber length, a higher ratio of fiber length to liber diameter and improved ease of hydra'.-V tion of the fiber.

In the practice ofthe instant invention it is possible to individualize the bers by a bearing and combing out of the pith between the bers. The instant invention diifers from the usual or conventional carding process which employs relatively thin teeth spaced closely together for literally combing out the liber. In contrast, in order to achieve the desired result of the instant invention, it is necessary to provide a rotating drum of certain size, with teeth of a detinite size and shape, spaced in a particular manner and with a definite speed of rotation, using a deiinite speed and manner of feeding the bamboo culms against the rotating drum. The action against the culms resulting in the practice of the instant invention is a combination of impact, attrition, and combing.

It is, therefore, an important object of the Ainstant invention to provide an improved method and apparatus for producing bamboo pulp and paper.

Another important object of the instant invention is to provide an improved apparatus Yfor producing bamboo pulp comprising a rotary drum, means for rotating said drum, a myriad of short dull closely spaced teeth projecting radially from the drum surface, and means for feeding bamboo culms against the teeth on the rotating drum surface generally tangentially to the drum surface.

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Still another important object of the instant invention is to provide an improved process of producing bamboo pulp comprising the step of subjecting bamboo culms having a moisture content in excess of 40%l to a shredding action produced by 8,000 to 12,000 longitudinal tooth strokes per inch width per inch feed of bamboo to individualize the fiber and cut it into lengths averaging largelybetween 3A: inch and 1 inch.

Other and further features, objects and advantages of the present invention will become apparent to those skilled in thepart from the following detailed disclosurethereof and the drawing attached hereto and made a part hereof.

On the drawings:

Figure 1 is an essentially diagrammatic elevational view showing the device of the instant invention;

Figure 2 is a detail view of an individual tooth in the device of the instant invention; and

Figure 3 is a view in perspective of the drum employed in the instant device, with certain associated parts.

As shown on the drawings:

The device of the invention, indicated generally at 10 in Figure 1, comprises a rotary drum 11, a motor indicated diagrammatically at 11b for rotating the drum 11, a myriad of short dull closely spaced teeth 12 projecting radially from the. drum surface, and means (indicated at 13) for feeding bamboo culms B against the teeth 12 on the rotating drum surface generally tangentially to the drum surface. Such means 13 being indicated here has a motor 13a driving a worm gear 13b which moves a screw 13e axially and the screw 1 3c mounts a backing member 13d at oneend thereof for urging the bamboo culm B against the teeth 12 at a predetermined rate.

As indicated in Figure 2, each tooth 12 has an average radial dimension R of 1/2 inch to 1 inch, the radial dimen-` sion here shown being of an inch. Each tooth 12 has an average dimension d at its base of 1/5 inch to 1A inch; and the tooth 12 here shown has a diameter of e inch. The tooth 12 is tapered at its outer extremity 12e to give relatively dull knife edges 12b.

Referring to Figure 3, it will be seen that the drum 11 has a relatively large diameter of 2 to 3 feet and there is a relatively high density of teeth 12 on the peripheral surface 11a of the' drum 11. The teeth 12 are shown in full view near the top of the drum 11 in Figure 3, but for the sake of simplicity the remaining teeth on the surface'lla are omitted in Figure'3 and dots 12a are shown indicating the location of the centers of each of such other teeth. The dots 12a bring out more clearly the nature of the density of the teeth, which is herein defined as the number of teeth in a given area on the peripheral drum surface 11a. For example, the dotted lines 14a and 14b on the peripheral drum surface 11a represent circumferences which are spaced apart l inch (longitudinally of the drum 11) and thus define a peripheral area A 1 inch in width on the drum surface. This peripheral area has an average tooth density of 128 to 256. In other words, the total number of teeth 12 whose centers lie within the peripheral area A may range from 128 to 256. The teeth 12 have a generally random arrangement, except for the fact that certain tooth densitieshave been found to be important. The actual tooth density for the peripheral area A in the instant drum is 192 teeth. Expressed in other terms, if circumferences (such as the circumferences 14a and 14b) are drawn on the drum surface 1,64 inch apart, there will be three teeth centered on each such circumference, when a 3 foot diameter drum is used, such as the instant 3 foot diameter drum. Actually, an average of from 1 to 4 teeth may be centered ou each such circumference, but

this will require less advantageous rotating speeds for amarte surface speed of 2,000 to 2,500 feet per minute'. The best results are obtained using a surface speed of 2,200 feet per minute which is 250 revolutions per minute with a 3 foot drum. Such are the operating conditions here used.

The bamboo culm B is fed against; the' teethY '12 on 'the drum 11 generally tangentially to the drum 1'1 ata predetermined rate of about 4 inches to about 6 inches 'per minute. A certain number of tooth strokes fora given area of bamboo are required. Rotating 'the' 3 foot diameter drum 11 at 250 r.p'.'m., it will be appreci` ated that in the peripheral area A, `which is lv inch in width, there are 48,000 tooth strokes per minute. These tooth strokes are, in etect, longitudinal ofV the bamboo culm. If the culm is fed at a rateof 6 inchesper minute then each inch of bamboo fed receives 8,000 longitu'dlarea a of only 1 square inch, theavrage tooth density is 2. Two tooth centers 12a, 12a are' shown in theinch square peripheral area a of Figure 3. The tooth `density per square inch may vary from l to 3 teeth, but 2 teeth is the preferred tooth density, and this is the" tooth density on the drum 11 here shown. Of particular importance, is the actual drum surface speed ot 220 feet per minute. As the drum diameter is varied the tooth densities are varied to effect the desired number -of tooth strokes at the drum surface speed of about 220 feet per minute.

It has been found that the instant shredding arrange'- ment is carried 'preferably with bamboo culms having a moisture content of Vabove 40 (weight) percent, and the best results are obtained using culms with a moisture content of at least 50%. Bamboo culms having a moisture content of less than 40% are irst soaked in water to obtain the desired moisture content. Y

Under the instant shredding conditions superior re sults are obtained in, the form of highly individualized iiber masses containing a minimum of powered material and having an optimum average ber length with very remarkably low power consumption. The percentage of powdered material (largely pith)` is weil below 10%. The average fiber length will be in the rangeof inch to 1 inch, with Vrelatively small amounts above2 inches and below 1A inch. The power consumption vis inthe" order-of to 20 lhorsepower per ton of bamboo per day Y(dry basis). This is only a small fraction of the power consumed in the conventional mechanical pulping of wood, which is about 60 to 100 horsepower per ton of Wood ground per day.

It has `further been found that the products of the instant shredding process can readily be converted to paper pulp stock by beating in the conventional type beater with certain precautions. `The loading of the drum should be relatively light as the iibers cut easily. If the pH is held above 12 during beating it has been Since the instant shredder product cuts relatively easily the beating or pulping is carried out in a tank with high speed mixing. Fiber is reduced in length and further individualized and hydrated, as in the beater. In this instance, the pH may be conveniently maintained even higher than 12.5 with no harmful effects to the equipment, for example, by the addition of caustic upY to 2%. The caustic soda thus used may 'range from 1/2 to 2%;

For a crude type of pulp, useful in hard board production, the shredded .product is simply pulped in the beater for about to 40 minutes to condition it, and then formed into sheets and hot pressed in the usual manner. A similar processing will be found suitable for some types of cardboard and the like. In this instance, the time of pulping may be extended somewhat and the pH raised to above 12. Other additions may be made in line with the usual 'practice Vfor this type of product. In the case -of finer grades of pulp and paper stock, it is advantageous to iirsft screen the shredded product'to remove the powdered portion which is largely'pith and nontbrous node particles. The non-fibrous powdered portion is rless than 10% and it may be regarded merely as ller, if itis left in the shredded product.

found that a sheet of greatly increased strength is obv tained. For example, after 60 minutes of ybeatingat'a conventional pH of about 7, the breaking length ofa test sheet was found to be 1.37 kilometers, 'whereas the 'same heating operation at a of 12.5 vgives a 'test sheet having a breaking length of 2.70 kilometers, which is a gain of over 100% in strength. Also, the burst factor of sheets made from pulp using the conventional pI-I of 7 during beating was 0.20, whereas the kburst factor for sheets made from pulp wherein thepH of 12.5 Was maintained during beating'is` 0.44; ThisV also represents a 100% gain in strength. It will be appreciated that these test sheets were made without any additions.

If a particularly line grade of pulp is desired, it is aclv'antageous to 'raise 'the caustic content during pulping vand to carryr out this step at elevated temperatures with direct steam heating. It is not necessary to use pressure cooking with all its expensive problems and drawbacks. Open steel-tanks with open coil direct steam heating and high speedK agitators are suicient. As previously indicated, comparatively low concentrations of caustic will suffice for most purposes (within the range of I/2% to 2%). The chemical treatment, pulping, and conditionin'g for individualzation of the iiber and partial hydration and 'reduction of fiber length are all accomplished at the same time with the simplest kind of 4equipment at aA min` 'irnumof power consumption. Excess 'unused caustic is recovered by'wa'shing the fiber in the usual manner.

The washed fiber may be screened in the usual manner to obtain high vvquality pulp,l which may also be sub- 1jected toa bleaching action using, for example, zinc hydrosulphite, as inthe `case of mechanical wood pulp. The instant pulp stock may be given' a final beater treatmentito more completelyhydrolyze the fiber and to make thel usual'fsizing and loading additions forspecic types of paper. Sheetv formation is carried out inthe conventional m'anner 'forwoo'd pulp;

The shreddecl product of th'einstant invention 'is unique in that it may be used inconventional wood pulp beating, conditioning, and 'the 4like operations including sheet formation. The instant pulp is advantageously' suggested to pulpingv and beating at a pH of l2 or more. v

It will be uuderstood'th'at'modifications and variations maybe effected without departing from the spirit and 'scope ofthe novel concepts of the present invention.

I'y claim as my invention:

`l. The process 'of producing bamboo pulp and paper productscomprising'subjecting bamboo culms having a moistureV content in excess of 40% vto' a shredding action produced by 8,000 to 12,000 longitudinal tooth strokes per inch width `per inchfeed of bamboo to individualize the fiber and. cut it into lengths averaging largely between 3/5; inch and l inch, said teethhaving an average height of l/z to.-1'-inchV and an average diameter of Vs to el/ inch, and producing lessthan 10% of Vpowdered material .of -rnesh then subjecting'tlie shredded product to a mechanical pulping'actionina water suspension offpH in excess of l2, followedV by sheet for- -mation yfrom the pulp suspension by dew'atering and felting-and 'pressing and drying-to form 'finished sheets.

l2.Thep'roces's'asclaimed in claim 1, inv which the Y 'shredded product is screened before pulping, in order to remove the powdered nonabrous material.

3. 'Ifh'eprocesstaselaimett''inelain f1, in'which the pulping step is carried out using a suspension containing 1/2% to 2% caustic soda.

4. The process as claimed in claim 1 in which the shredded product is screened to remove powdered nonfibrous material before pulping and in which the pulping step is carried out in a suspension containing up to 2% of caustic soda, and in which the pulped fiber is washed and screened to remove excess caustic and any undesirable particles still remaining prior to sheet formation.

5. The process as claimed in claim 4, in which the washed and screened pulp is given a bleaching treatment with zinc hydrosulphite prior to sheet formation.

6. The process as claimed in claim 5, in which the washed, screened and bleached pulp is given a second beater treatment to more completely hydrolyze the ber and this is followed by making various sizing and loading additions prior to sheet formation.

UNITED STATES PATENTS Guest Mar. 14,

Fritz Oct. 24,

McMillan June 22,

Barnes Aug. 11,

Leyst Aug. 27, McQuiston July 7, Williams Feb. 23,

FOREIGN PATENTS Italy Dec. 9, Great Britain July 13,

Claims (1)

1. THE PROCESS OF PRODUCING BAMBO PULP AND PAPER PRODUCTS COMPRISING SUBJECTING BAMBOO CULMS HAVING A MOISTURE CONTENT IN EXCESS OF 40% TO A SHREDDING ACTION PRODUCED BY 8,000 TO 12,000 LONGITUDINAL TOOTH STROKES PER INCH WIDTH PER INCH FEED OF BAMBOO TO INDIVIDUALIZE THE FIBER AND CUT IT INTO LENGTHS AVERAGING LARGELY BETWEEN 3/8 INCH AND 1 INCH, SAID TEETH HAVING AN AVERAGE HEIGHT OF 1/2 TO 1 INCH AND AN AVERAGE DIAMETER OF 1/8 TO 1/4 INCH, AND PRODUCING LESS THAN 10% OF POWDERED MATERIAL OF -100 MESH, THEN SUBJECTING THE SHREDDED PRODUCT TO A MECHANICAL PULPING ACTION IN A WATER SUSPENSION OF PH IN EXCESS OF 12, FOLLOWED BY SHEET FORMATION FROM THE PULP SUSPENSION BY DEWATERING AND FELTING AND PRESSING AND DRYING TO FORM FINISHED SHEETS.

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