US2169473A - Method of producing cellulose pulp - Google Patents

Description

' terial originally present may Patented Aug. 15, 1939 UNITED STATES PATENT OFFICE METHOD OF PRODUCING CELLULOSE PULP Fredrich Olsen, East Alton, Ill.,'as'signor to The Cellulose Research Corporation, a corporation of Delaware No Drawing. Application February 8, 1935, Serial No. 5,582-

- 3'Claims. (CI. 92-13) vorable conditions with respect to minimum re- This invention relates to the production of fibrous materials from wood and other cellulosic substances.

The object of this invention is to provide paper, boxboard or the like composed of uniformly .softened cellulose fibers and a relatively large other forms and combining with the cellulose fibers a treated or reacted form 'of the noncellulosic ingredients of the original material.

A further object of the invention is to provide a process adapted to soften interfiber material of the wood so as to preserve and at the same time release the fibers for recombination with the softened ingredients in any desired proportions.

The object of the system of. this invention is to provide 'a mass of softened-flexible wood fibers or fiber bundles capable of being felted and bonded into sheet or board form, intimately associated with the original incrusting material of the wood. All or nearly all of the noncellulosic mabe retained and in modified form redistributed uniformly and intimately throughout the mass of softened fibers and in combination with these fibers constitute a pulp product in which substantially all of the original constituents of the wood are utilized. The fibrous mass may comprise a preponderance of bundles of a few dozen fibers each, or of completely separated fibers; But regardless of the extent of the defiberization, the pulp is distinguished by the flexibility of the individual members of the fibrous mass and of the mass itself, and the high yield of pulp material capable of being milled in a Hollander or other type of beater or apparatus for the purpose of developing the qualities conducive to good sheet or board strength properties and with less mutilation of the fibers than usually results with the milling of conventional pulps. Such material is particularly suitable for boxboard, wrapping and other non-cultural paper purposes.

Another object of this invention is to produce an intermediate pulp product comprising softened, flexible fibers or small flexible bundles of fibers or both with which remain associated substantially all of the original noncellulosic material of the wood in modified form dispersed uniformly throughout the fibrous mass and capable of being readily delignified to any desired extentby means of any type of reagent under most faaction upon the cellulose itself. The ease with which delignification of this new pulp product may be accomplished is due to the accessibility of the noncellulosic component to chemical reagents arising from the vastly increased surface area exposed to the treating liquors by reason of the largely or completely defibered condition of the pulp product.

A further object of the invention is to provide a process for the production of said material which will be simple and economical and readily adaptable to a wide variety of products ofdifferent properties.

Inprior practice the ligneous materials of the. wood have been in a large part removed to free the cellulosic fibers, and where any considerable amount of incrusting materials was retained the resulting'partially treated material has been of non-uniform .composition with respect to the character and distribution of the residual lignin and has therefore required more drastic me- .chanical action to break down the less treated portion of the woody structure. Such processes are expensive in use and also tend to degrade the cellulose, destroy the strength properties of the fibers, reduce the yield, or lead to objectionable complications resulting from the operations required to separate the fibers and the noncellulosic material or both. The prior attempts to utilize the naturalbinding material associated with the cellulose fibers in the wood have been deficient because of the inadequacy of the treatment either to effect a uniform softening to a sufilcient degree, or uniformly to efiect the solution or alteration of a sufficient amount of the incrusting material to permit separation of the fibers without serious detriment to or destruction of the physical properties of the fibers.

In the process of this invention the woody material is subjected to a uniform lime softening treatment, which without appreciable degradation of the cellulose renders all of the material easily defiberable to pulp form with the retention of a nearly full content of ligneous material and without objectionable destruction of the strength characteristics of the fibers themselves.

I have found that wood chips or the like boiled in a lime solution for a sufilcient' time to remove the air willon raising of the temperature to the after sufilcient time, seven hours for instance,

with ordinary chips, the reaction will penetrate to the innermost interstices of the wood and uniagent for this purpose, such as calcium sulfide or point of permitting ciently-long not only to remove the air by penetration with water, one half hour, but may be continued sumciently long after the addition of lime, e. g., three hours, to distribute the lime uniformly throughout the chip.

Calcium hydroxide is an especially effective re-v milk of magnesia may be used. Lime on account of its limited dissolving action and low at 100 C.), may be added tothe treating liquor in an amount in excess of that which will so I into the solution, which has the resulting important and desirable elect of maintaining the strength of the throughout the cook. Thus the ligneous or incrusting material is subjected to the action of a fixed effective concentration of reagent for any desired treating period, with the result that the entire woody substance is so modified as to become quite softened, while the cellulose fibers I themselves are uninjured and are rendered flexso regulated that substantially no free lime is according to the material being the required lble even when occurring in small bundles of, for example, two or more fibers in thickness and four or more fibers in length. Due to the fact that most of the compounds which lime forms with the incrustingsubstances of wood are large ly insoluble in lime solutions, a large part of the modified nonfibrous components of the. wood (calcium lignates) remain associated with the mass of flexible fibers, with the result that overall yields of useful pulp material of and even by weight of the original oven dried wood are readily attainable by Procedure of the following. types:

Procedure A.--Wood chips or flakes are submerged in boiling milk of lime solution in a freely vented condition for approximately one half hour to remove the gas content of the wood from the interstices, after which the container is closed and the temperature raised to C. or more.

The container is maintained at this temperature for a suflicient time to thoroughly soften thewood throughout the entire mass. At 135 C. the time of the treatment will vary from eight hours,

treated. Sumcient lime is present to supply the treating liquor with the desired amount of dissolved lime to give softening. This involve using an amount of slime which maintains a. saturated solution throughout the cook, or the lime may be present at the end of the digestion. vAny desired intermediate condition may be used.

Procedure B.--The wood chips or flakes are submerged in lime water and boiled for approximately \three hours until there is a complete penetration of the entire woody structure by the lime. After this three hour boiling at 100 C., the container is closed without exposure to re-entry of air and thetemperatureraised,forinstance, C. or over, for a period of time suflicient to soften the chips to desired degree. This time will vary from four to five hours depending upon the kind of wood being treated. Throughout the entire process the treating solution maybe reinforced with lime to maintain it saturated, or this saturated condition may be maintained for only ,a part of the cooking period depending subsequent digestion isquite though other. substances,

softening of the chip is solubility in water v(0.08%

treating solution constant on the degree of softening desired.

A point of fundamental importance is the thorough impregnation'of the wood bythe reagent with the concomitant displacement of air. It is also to be emphasized that the action of the lime during this impregnation and in the unique since its re.- sults cannot be paralleled by the use of any concentration of the usual alkalies, for example,

caustic soda. If very small amountsof caustic soda are used such as will permit high yields in excess of 85%, experience shows that similar not attained. The dilute caustic soda solution behaves as it it reacted with .the lignin immediately accessible, and as if the caustic which started prevented from through the depletion of the reactive chemicals from the entering liquors. It is also quite possible that the well known behavior of caustic soda in promoting swelling of polysaccharides may have effectively blocked up the minute passages to infiltration of the caustic solution. a

In contrast with this behavior of caustic soda is the action of'lime which either because of its very low concentration even in saturated solutions, or because of its lower tendency to promote swelling, or because of its'formation of insoluble calcium compounds, (or whichever one or combination of these principles may be involved) the lime behaves as the wood and softening or reacting with thelignin perhaps primarily of the middle lamella, so that to. penetrate the chip was subsequent mechanical action is capable of effecting any. desired degree of defibering.

Another advantage of lime in the softening of woodymaterial follows from its rather high degree of insolubility which permits the maintenance of a suitable supply of reagent held in suspension in all reservoirs of liquid from which the active reagent can be drawn whenever chemical action or adsorption or other action removes the reagent from solution. From an economic standpoint theycry low cost of lime permits its use in such chemical ratios as will perform the desired degree of 'deligniflcation or softening -without requiring that recovery systems. Even if lime were as expensive as caustic soda it would probablygbe still the most suitable reagent for use in pr ucing high yield pulps of uniform defiberabili' if it were uniformly penetrating we resort to the use of further traveling into the chip because of its property of low solubility, low reactivity at 100 C;

and low capacity for swelling wood.

The pulp product of this invention is the cheapest form of defibered pulp attainable since substantially lignin there is attached ani'etalllic ion, calcium,-

all the lignin is retained and to the in the form of aninsoluble calcium lignin'complex. This ligneous material remains an essential'part of the pulp in the subsequentformation of the paper or board.

The softened material resulting from any of unit, and the material in bending flexes each 71 except as they are softened. by the alkaline treat" ment and as some of them are cut and frayed in the chipping or other unit-forming operation prior to the softening treatment and in the following defibering operation.

The softened chips or other units may, if desired, be defibered only to the extent required to obtain a mixture of small bundles of fibers and completely separated fibers. The bundles may be three or more fibers in thickness, but are pref- 0 erably not more than three; they may be three or more fibers in width and four or more fibers in length. These small bundles, as well as the completely separated fibers, are soft and flexible and are especially well suited to form the structural elements of a network for a new type of coarse sheet in which the single fibers may in part form r the filler. By my invention the fibers or other units are so conditioned vand the mechanical treatment controlled so that the small bundles as well as the completely defibered component of the pulp will be properly fibrillated, hydrated and otherwise favorably conditioned for felting and bonding and at the same time ligneous compounds will be swollen and so softened that when the pulp is felted and an appropriate pressure applied, the gelatinous materials associated with the mass of bundles andiridividual fibers and the'ligneous compounds which itself may be in a gelatinous state, are spread on and into the 40 network of fiber bundles and fibers, a strong -sheet results which is useful for a wide variety of purposes, especihlly of a non-cultural character such as boxboard, wrapping papers and other kraft-like sheets not specificallyintended for writing or magazine stock.

The pulp which results from the system of his invention is a new product possessing properties hitherto unattainable, and capable of forming a strong sheet of coarser texture which is in 59 itself a new product. As distinguished from my invention it is necessary in the current practice of paper making to completely separate the hard incompletely cooked bundles of fibers or shives from the individual fibers in the pulp by screenmg before beating or other milling operations, since in all attempts heretofore to utilize such material, unsatisfactory. sheets have resulted due to the fact that such fiber bundles or shives consist largely of hard, brittle splinters which are 60 incapable of flexing and being fibrillated, hydrated and otherwise conditioned for felting and bonding with the consequence that the sheets are lacking in strength, homogeneity, softness, pliability or other necessary properties.

B5 Attempts in the past to produce strength qualities from the larger building units such as those employed by my invention have been unsuccessin] due to the inability to produce the larger elements for the network of the sheets with the '0 requisite flexibility and capability of being fibrillated, hydrated and otherwise conditioned for felting and bonding. The treated wood when discharged from the digester upon completion of the lime treatment retains in large part the orig- 5 inal form it had before treatment, i. e., the form- The cellulose fibers themgroans 3 g of flakes or chips, but these are quite soft, flexible and may be readily separated into small bundles or slivers, or into individual fibers with relatively little effort. To illustrate the" readiness with which the defibering may be'eifected, the largest 5 or thickest treated chips may be easily torn into small bundles or slivers between the fingers. Combined with these softened fibers the pulp contains a large proportion of softened lig'nin embodying calcium lisnatesdnsoluble both in milk 10 of lime and water. The cellulose fibers in addition to being ,undergraded are largely uncut, unbroken and otherwise unmutilated; consequently their strength is unimpaired.

The new sheet producible by my invention combines much of the desirable strength qualities of kraft pulp with a lower cost of production.

Whereas commercial kraft pulps are produced from coniferous woods such as southern pine, hemlock and the like, the system of my invention is also particularly applicable to deciduous woods which in many sections of the country are relatively cheaper than the coniferous species, examples being cottonwood, soft maple, willow, poplar, birch, and gum. The natural 25 color of the treated wood pulp is a brownish tan, sometimes it maybe of a more or less reddish hue. The strength of sheets and board made from the pulp of this invention is many times that which can be made from thepulps used in 30 large quantities of boxboard (wastepaper stock).

As an example of such increased strength, sheets of pulp made from lime treated wood of this invention have shown a..Mullen test considerably higher than that for comparable sheets made 35 from waste paper.

The material from the defibering operation may be further beaten to expand and hydrate the individual cellulose fibers developing fibrillation, which greatly increases the surface area of 49 the'cellulose for redistribution of the lignin, and by proper control in this beater action full strength of the material will be developed for felting of-"the mass in sheet form in the subsequent milling. 45

Where desired the softened material either before or after defibering may be subjected to a treatment, for instance, with usual digesting liquors in desired strength to reduce the lignin content to any proportion required in the final 50 product. or'to eliminate the lignin altogether. I The softened material in defibered form is in condition for treatment with chlorine or other chemicals for delignification and color control.

The process of this invention is simple in opera- 5 tion and makes use of existing apparatus. The softening treatment only requires preliminary boiling and subsequent heating treatment at pressures well within the range of the usual digesting apparatus available in strawboard or so paper mills.-- The draining of the softened material and the washing of such material also corresponds to usual operations in paper mill practiceso that the system of this invention may be readily installed by slight changes in procedure as and by substitution of the new chemical treatments involved. The softening action is economical in its use of chemicals. For instance, it requires only a mild lime treatment usingsmall quantities of the material, which itself is very cheap so that there will be little, if any, advantage in recovery of the lime from the waste liquors; The costs involved in the operation of this process are substantially less than those of any known process of pulp production, even in- 7s practice, the final pulp of the system of this. invention may give calculated yields of over 100% indicating that the lime or lime compounds --remaining in the material exceeds the woody compounds removed during the softening process, ivh'ich often retains over 95% of the materials originally present in the wood. For many purposes the presence of this lime in thepulp is not objectionable, and due to its low cost there is no occasion to remove it for recovery.

The process of this invention is not only inexpensive in operation but also very effective in the i use of the raw materials to which it is applied.

Instead of going to the expense of removing the ligneous components of the wood, it retains these components with corresponding increase in yield,

and at the same time avoiding the cost of the removal and the objectionable effect of such re moval on the remaining cellulose. Even where the ultimate product requires the removal of Y lignin, the system of this invention conditions the material most advantageously for such removal effectively and without undesirable degradation of the cellulose and at a minimum of expense.

I claim: S 1

l. The process of treating woody material to form pulp comprising supplying the wood in subdivisions of chip size or smaller, replacing the air in the wood with a solution of a. compound of the group calcium hydroxide, calcium sulphide' and magnesium hydroxide, raising the temperature and maintaining said raised temperature for a sufficient time uniformly tor nodify the noncellulosic content of the wood throughout its entire mass while maintaining the strength of the treating solution by continuously replacing 3 the reagent removed from solution by the wood,

and dcfibering the treated wood while maintaining the fibers substantially unaffected from their natural condition in the wood to give a wood pulp product composed of such fibers having uniformly dispersed through the fibrous mass most of the original noncelluloses uniformly softened and.

modified. 7

2. The process of treating woody material to form pulp comprising supplying the wood in subdivisions of chip size or smaller, submerging said subdivisionsin a boiling solution of calcium hydroxide and continuing the boiling to replace the air in the wood, then raising the temperature to 135 C. or over and maintaining said raised temperature for a sufllcient time uniformly to modify the noncellulosic content of the wood of each wood subdivision throughout its entire mass while at the same time maintaining the alkalinity of the treating solution with an excess of calcium hydroxide, and subsequently defibering the treated wood while maintaining the fibers substantially unaffected from their vnatural condi-' tion in the wood to give a wood pulp product composed of such fibers having uniformly dispersed through the fibrous mass most of the original noncelluloses uniformly softenedand modifled as a flexible complex of ligneous material and calcium hydroxide.

3. The process of treating woody material to form a pulp having a large proportion of the original noncelluloses uniformly softened, modified and dispersed throughout the fibrous mass, comprising supplying the wood in subdivisions of chip size or smaller, replacing the air in the wood with a solution of a reagent of the group calcium hydroxide, calcium sulphide and magnesium hydroxide, raising the temperature to the point of active reaction and maintaining the concentration of the reagent in said solution constant by supplying an amount of reagent-in excess of its solubility while maintaining said raised tempera-' ture for a sufficient time to modify uniformly the noncellulosic content of the wood throughout its entire mass, and defibering the treated wood while maintaining the fibers substantially unaffected from their natural condition in the wood. I

' FREDRICH OLSEN.