US3085927A - Process for preparation of fibers having differing characteristics - Google Patents

Description

A. W. PESCH PROCESS FOR PREPARATION OF FIBERS HAVING April 16, 1963 DIFFERING CHARACTERISTICS 2 Sheets-Sheet l Filed Nov. 16, 1960 ,.igi22.2% Mge@ ligmr D g FIG.|

INVENTOR ANTHONY W. PESCH 'BY/(Mu M ATTORNEY FIG.2

Aprll 16, 1963 A. w. PEscH 3,085,927

PROCESS FOR PREPARATION OF' F' IBERS HAVING s DIFFERING CHARACTERISTICS Flled Nov. 16, 1960 2 Sheets-Sheet 2 MEDI UM SPRINGWOOD I8 f ORIGINAL PULP Is-r Isn-r MEDIUM suMMERwooD HIGH suMMERwooD FIG.5

INVENTOR. ANTHONY W. PES CH BMI M ATTORNEY tates This invention relates t-o the manufacture of oellulosic pulp, and more particularly to a process for separation of the pulp libers into fractions having differing characteristics.

It is known that the ditferences between the characteristics of springwood (also called early wood) and of summerwood (also called late wood) produce marked differences in the properties of paper made from wood pulp in accordance with the variation in the proportion of springwood and summerwood in the pulp logs being used as the raw stock for the pulp.

Every tree, at least in the non-.tropical zones, has annual rings which are distinctive increments of annual growth. Each annual ring consists of a portion of springwood which is that part of the annual growth which occurs early in the growing season, and a portion of summerwood which is that portion of the growth which occurs later in the season.

Generally speaking, the Woods of the Northern States and Canada, particularly the softwoods lor lconiferous woods, have a comparatively larger [amount of springwood and a comparatively smaller amount of summerwood because ot the long northern winters and comparatively short summers, while the trees of the Southern States have a higher proportion of summerwood because of the longer growing season of the warmer climate.

For a given species of tree the proportions of springwood and summerwood may vary to such an extent under diiferent growing conditions that the variation in the characteristics Iand properties of the paper produced from the tree is greater under identical manufacturing conditions than the variation in papers produced from two ditferent species under different manufacturing conditions. A paper produced from a northern tree having a comparatively low Aamount of summerwood usually has markedly different properties from a paper produced from a southern tree of the same species or genus having la comparatively high propontion of summerwood. Likewise, papers produced from species having a higher springwood content vary from those produced from `different species having a higher summerwood content. These dierences are demonstrable by standard ltest procedures.

Such papers may, for convenience herein, be designated :and distinguished as springwood papers and sununerwood papers. Springw-ood pulps and papers, other things being equal, have less freeness, bulk, rtear strength, air permeability (Le. higher densometer of porosity test reading) and greater bursting strength (Mullen test), smoothness, fold, tensile strength and p-rintability than summerwood paper, while the latter for many purposes has desirably greater bulk and tear strength.

While in general these facts have been known, no one, as far as known, has l'been able to take advantage of the differences in characteristics between springwood and summerwood of the same or different species of trees to produce papers having predetermined characteristics under commercial conditions by precisely controlling the proportions Iand manner of application of pulp from springwood and summerwood libers. The best that has been done prior to this invention is Ito determine roughly that pulp logs from given tree species growth under given conditions in particular locations have respectively greater 3,085,927 Patented Apr. 16, 1963 BCC 2 or lesser proportions of springwood and summerwood, and to try to schedule the llow of pulp logs into and from the wood yard accordingly.

The rdiiculty inherent in separation and use of springwood and summerwood iibers from a given log is that since the components are thin and alternate, it is commercially impractical to separately remove the alternate thin springwood :and summerwood layers from the log. This has -been ydone if at al1 only :on a laboratory basis and in minute quantities. Nevertheless it is highly desirable to be able to separate the springwood fibers from the surnmerwood bers of a given batch of raw stock, land to handle and apply them separately or in combination in predetermined proportions inthe paper making operation.

My invention accordingly consists in the appreciation of the advantages to be gained in the paper making art by using springwood and summerwood fibers in predetermined proportions and also separately, in the concept that this can be achieved by separating the two types of fiber from each other in the pulp or in the formation of the pulp, either virgin stock Isuch as from logs and `chips or re-pulped stock from waste paper and the like, in the perception of certain `differing properties, among others, of springwood and summerwood fibers which can be used for such separation, and in the discovery of a process and means which makes use `of these differing properties and characteristics for such separation economically on a commercial scale, as more fully hereinafter set forth in connection with the drawings, in which:

FIG. l is a photomicrograph of la `cross section of la rtree or pulp log of Ia typical coniferous wood or softwood, taken at the junction of two annual growth rings showing some of the differences in the characteristics of .the springwood and the summerwood;

FIG. 2 is a photomicrograph showing the fibers in a typical example of softwood kraft pulp; and

FIG. 3 isa schematic drawing of one type of apparatus which may be used in the separa-tion of cellulosic springlWood and summerwood liber-s.

In the drawings, FIG. l is a microscopic sample of a piece of softwood 1, =in this case yellow pine, which may normally be used in making cellulosic pulp for the manufacture of paperland of cellulose derivatives. It shows that any such piece of Wood which may be, for instance, a chip used in making chemical pulp, contains springwood bers 2 and summerwood tibers 3y with a clearly distinguishable line of demarkation 4 between them at lthe junction of two annual growth rings. Both types of i'lbers are generally tubular and hollow. The springwood fibers 2 have comparatively thinner walls 5 and comparatively larger openings called lumens 6, and the summer-wood libers 3 have comparatively thicker walls 7 and comparatively smaller lumens 8.

In FIG. 2 the springwood libers 2 and the summerwood fibers 3 are shown intermixed in a Water pulp slurry after the wood has been digested as by cooking with the sulphate or kraft process and the iibers have been separated so that they are interspersed helter skelter. It can be seen that the summerwood libers 3 have a more condensed appearance and structure as the result of the thicker walls 7 and smaller lumens 8, giving the dark thin appearance, while the springwood fibers 2f appear wider, with thinner walls and are lighter in appearance. The flattened appearance of the springwood bers 2 in FIG. 2 is due to the fact that in some of the later stages of pulping due to beating and the like, these bers have, to some extent, collapsed and become llatter in section, nevertheless retaining the essential characteristics above described.

The material of the walls 5 and 7 of both the springwood and the summerwood fibers 2 and 3 is relatively pure cellulose which has an actual specific gravity of approximately 1.6. But after the wood has been deiiberized into pulp with the bers suspended in water in typical pulp stock, the lumens or openings 6 and 8 of both types of ber become at least partially lled lwith water and in this condition the springwood fibers 2 have an apparent specific gravity which is less than the apparent specific gravity of the summerwood iibers 3. That is to say, they are lighter when in water.

I have discovered that the differences in apparent spe- -cie gravities of the sprngwoods and summerwoods are suihcient so that starting with any typical pulp stock after digestion, the mixture of the types of fibers under discussion can be separated into fractions consisting essentially of springwood having a comparatively lower apparent specific gravity and summerwood having a comparatively higher apparent specitic gravity.

I have also discovered that the fractionation process is favorably influenced by the fact that due to the less compact shape of the springwood fibers they tend to sink more slowly in water than the summerwood ii'oers which have a more compact shape, as previously described.

There are various -ways to accomplish the separation by taking advantage of these differences in apparent specie gravity and sinking rate.

One example of a preferred type of apparatus is diagrammatically illustrated in FIG. 3. It consists of at least one hydrocyclone of the general type used for separation of ore components of different specilic gravities, as described in United States Patent No. 2,648,433 and as also used for separation of dirt from pulp, as shown in United States Patent No. 2,878,934. Such a hydrocyclone may be particularly adapted and improved for the particular purpose of eflicient pulp fractionation according to the present invention, but the details of such adaptation are not herein particularly described and claimed since the scope of the invention, as presently claimed, includes the practice of the process by any one of several types of apparatus.

A typical hydrocyclone 15 has a hollow, at least partly conical, chamber 16 having a base end 18 and an apex end 20. Generally speaking, the material to be separated is pumped in slurry form tangentially through a line 2.2 into the chamber 16 thereafter spiralling toward the apex end 2t) of the conical chamber 16 in circles of decreasing diameter and with increasing angular velocity. As a result,

two concentric vortices form creating a central air column.

The heavier constituent of the slurry is thrown by centrifugal force into the outer vortex and the lighter constituents are forced into the inner vortex. The lighter constituents travel upwardly along the inner vortex and -leave the chamber 16 through a line 24 connected to an orifice at the base end 18 while the heavier constituents travel downwardly in the outer vortex and leave the chamber 16 through a line 26 from the apex end 2t), thereby classifying the different constituents. In FIG. 3 the original pulp to be fractionated according to the invention is tangentially introduced to the chamber y16 through the line 22, and in accordance with the above summarized principle of operation the component having more than the original proportion of springwood leaves the chamber through the line 24 while the component having more than the original proportion of summerwood leaves the chamber through the line 26.

For many purposes in the practice of the invention, the use of a single hydrocyclone 15 is sufficient. As long as the proportions of springwood and summerwood fibers produced in the lines 24 and 26 respectively are measurably higher than they were in the original pulp slurry introduced in the line 22, the fractionation thereby achieved for use in paper making in predetermined amounts or proportions is within the scope of the claims.

Since complete separation into fractions containing only springwood and only summerwood respectively is probably only theoretical, the degree of separation to be achieved is primarily a matter of mechanical efficiency.

In some cases the use of one hydrocyclone 16 may not achieve the desired degree of efficiency for the purposes intended and in such instances more than one hydrocyclone may be used as illustrated. In such case the pulp slurry containing the higher proportion of springwood in the line 24 is introduced at 28 into the hydrocyclone 15a and the fraction leaving the latter through the line 30 contains a still higher proportion of springwood.

The slurry containing the higher proportion of summer'- wood in the line 26 may be introduced tangentially through the line 32 to another hydrocyclone 15b and the pulp slurry leaving the latter through the line 34 contains a still higher proportion of summenwood. Further reiinement of the fractionation may be carried out by the use of additional hydrocyclones in series, and the slurries leaving the hydrocyclones 15a and 15b through the lines 36 and 33 respectively may be used separately on separate paper machines, applied separately through separate headboxes on the same paper machine, combined in predetermined proportions and used on a paper machine, recycled to the system, or used in any other manner in which the fractionation of the invention is advantageous.

The hydrocyclones used as described either singly or in series may also be connected in parallel batteries to increase the volume for fractionation in commercial quantities as for use in preparing pulp for large paper machines or for a number of paper machines.

Other fractionation systems can be used, for instance, quiet and tiow settlement system tanks or sluice boxes which are well known for use in the separation of components of materials such as ores having different specific gravities and other characteristics which influence sinking or settlement time.

The pulp fractions of springwood and summerwood fibers can be combined and proportioned in a predetermined rnanner to combine desirable properties and characteristics and to reduce undesirable properties and characteristics in the paper to be produced for the purposes intended.

One specific example of the application of the invention is in the production of kraft liner board for use in making the face sheets between which the corrugated medium is sandwiched in the production of sheet stock for corrugated containers. Such a liner board is improved if it has good bulk and tear resistance as produced by summerwood fibers and at the same time a better appearance, a smoother surface and increased printability as produced by springwood bers. These characteristics can all be achieved by my invention in connection with the use of two head boxes on a paper machine. Pulp consisting essentially of summerwood bers is run through the primary head box to produce the body of the paper, and pulp consisting essentially of springwood fibers is run through the secondary head box to lay the springwood fibers on the surface of the paper being formed on the Fourdrinier wire, thereby achieving the combination of desired results.

Other applications and advantages may be achieved by fractionating the pulp according to the invention and using the separated fractions separately to make paper of differing grades on separate paper machines in the paper mill. Still other advantages may be achieved as by combining the fractions in predetermined proportions to make paper of a predetermined grade under controlled conditions.

It is obvious that much greater control of paper grade and characteristics can be achieved with decreased necessity for selection and control of the pulpwood used to make the pulp.

The practice of the present invention may be carried on with pulp at various consistencies and the consistency is not critical.

The fractionation is accomplished on the pulp after 'the pulp wood has been de-berized and thereby prepared in the pulp slurry state. The process is applicablecto'c-l *i pulp de-oerized in any manner, including the chemical, semi-chemical and groundwood processes.

Specific examples of a process according to the inven- The results in Table I show that a deiinite separation with respect to ber characteristics was obtained. The accepted pulp had the characteristics normally attributed to springwood fibers and the rejected pulp resembled tion, including the operative conditions and test results thick Walled Summerwoed hers Compared to the (High are as follows: XA E nal pulp, the accepted pulp had 17% higher mullen and E MPL I 42% lower tear and the rejected pulp had 14% lower A sample of pine kraft pulp was diluted to 0.10% mullen and 39% higher tear. In addition, the accepted consistency and pumped through a 3inch Bauer centripulp had higher apparent density, smoothness, air resist- Cleaner 21h20 gallons P61 mmm@ W1.l}40 P-S-I1161I?IS 10 ance reading, fold and tensile than the rejected pulp. Spr@ and Zero Outlet pressure. Am11111 numS12ed. 14 mch Further, fiber classifications showed that the accepted tip was used at the reject (bottom) discharge. The iirst puh) had about more long fibers (14 and 30 mesh) ftog foduced 40% accepted (OP) Pull) and 60% than the rejected pulp. Both fractions had more long 1 u P- fibers than the err irrai i ir ir b b1 d t A 15 g pupw 1c wasproa y ue o Th accepted and reiectm Pulps were each then pumped some loss of short ber on the collecting screens and through the cleaner two more times under the same condudu dehuurinu ditions as previously. In the second and third passes, g c' the undesirable portions (rejects in the `accepted pulp and accepts in the rejected pulp) were discarded. The EXAMPLE H linal reject portion was defloured by pumping onto a 60 y to 40 mesh screen which was the same that had been U Ddumg S? Wolhcoveled bydExanple I remzgkably used to collect the accepted pulp. The approximate OO @par lon o e Sprmgwoo 12in sunimerwoo com' amounts of pulp obtained in each fraction after the pcncms of p mc kraft Pulp was .rca lzcd usmg a thrccmch three passes are as fellows: Bauer centricleaner and multiple passes at 0.1% con- Orgiml sistency. Pulps with widely different strength characteristics were developed. However, such work showed that, Weight, lbs. centrifuged 78 lbs. (approx.) if the same conditions were used on a paper mill scale, the power requirements for pumping would be Very large. l i Consequently, further work was conducted to determine First Pass Accepts Rejects the degree of separation that could be obtained at higher Weight lbs' centrifuged 31 47 consistencies and fewer passes. The data collected in this Percent 40 60 work are set forth in Table II.

` The sample investigated was unbleached pine kraft l-Fl pulp, portions of which were diluted to the selected consistencies (0.1% to 0.5%) and pumped only once through second pass Acccpts Rclccts Accepts Rclccts a three-inch Bauer centricleaner at 20 gallons per minute Weight, um centrifuged 22 9 10 37 with 40 p.s.i. inlet pressure and zero outlet pressure and gfcnt 71 29 21 79 'zero outlet pressure. A minimum sized, one-eighth inch I crcent of original 28 48 40. tip was used at the reject (bottom discharge). The centri- .cleaner separated pulp at a consistency of 0.1% to give i i l i 49% accepted pulp (top, springwood fraction) and 51% 'r1-.irri pass Accepts* Rejects Accepts Rejects* 'rejected pulp (bottom, summerwood fraction). At a 45 consistency of 0.5%, the accepted portion was 74% v geeiclritlbs' lmfuged sg i 1i gg and the rejected portion was 26%. These and other data Perec original 24 43 collected during this work are included in Table II, infra, The ,hhah asterisked accepted and rejected portions and, from them, it has been calculated that the pumping were evaluated for strength and ber classifications in leflulemfl'lts f of 100 AD tous 0f Whole Pulp Per day comparison withthe original pulp. Table I shows the 50 at 0.1% consistency would be 15,000 gallons per minute data obtained to vbe as follows: with a head of at least p.s.i.

Table l Sample Original Accepts*l Rejects* Permanganate numb 21. 4 21.2 21.0 Initial Ireeness 733 727 758 o.s.frccrress 500 400 300 500 400 300 500 400 300 Power-,factor (kg.inin./cc.) 1. 43 1.18 0.99 1.79 1.42 1.11 1.49 1. 24 1.09 Beating factor (kg-min). 320 371 4 360 413 473 364 430 494 Muiierr (percent, pt./ib.).. 145 149 151 167 173 179 120 127 134 'icer factor A Y 141 136 133 82 s0 79 199 192 181 Apparent density (lu/pt.) 10.4 10.5 10.6 12.2 12.5 12.7 9.9 10.1 10.3 Smoothness (see/5 cc.). 33 39 45 66 76 85 20 27 33 Air resistance (seo/100 0o.). 14 54 108 439 986 3030 5 l0 82 M.i.fr.fe1d 664 699 765 689 l720 7s9 450 539 607 'rcrrsi1e(1b./iirr.mdt1r 31.8 33. :34.3 40.6 42. 43.6 28.1 29.7 30.7 Breckingiength (meters) 9, 820 i0. 200 10,700 12, 500 12,900 13,300 s, 590 9, 030 9,350 Gurney stiuness (mg.) 12 119 11 104 10 10i 13s 137 131 Fiber classifications, percent retained on:

i4 mesh 50. 9 74. 6 56. 0 30 mesh 31. 6 17.8 2s. 4 mesh 10. 2 6. 2 11. 0 mesh 3.7 1.0 3. 6 Percent fines 3.6 1. 4 1.0

mullen and lower tear, while the rejected pulp, desig- 45 nated R in the columns of Table II had 7% lower mullen and 16% higher tear. At 0.5% consistency, the

accepted pulp (A) had 3% higher mullen and the same tear as the original pulp, while the rejected pulp (R) had 3% lower mullen and 5% higher tear. In every case, 50 the'accepted pulp had higher apparent density, smoothness, air resistance, fold,` and tensile than the rejected pulp. When the consistency was increased, the difference in the tow fractions became less. There was no difference in the brightness of accepted and rejected pulp, but fiber classification showed that the accepted pulp had up to 10% more long fibers (14 and 30 mesh) than the rejected pulp.

I claim:

1. The process which comprises de-fiberizing wood into cellulosic pulp as an aqueous slurry containing a heterogeneous mixture of springwood and summerwood fibers, separating the mixture into fiber fractions respectively containing predominantly springwood and summerwood fibers by subjecting the slurry to forces which cause the fibers having a comparatively lower apparent specific gravity to separate from the fibers which have a comparatively higher apparent specifie gravity, then making a paper-like sheet from at least one of the fiber fractions.

Table Il COIESSGDCY Feed. percent 0,1 0 2 0 3 6 4 0 5 Welht 0109811131 pulp, g 2,999 2,993 3,272 3,654 3,826

Sample original .4. R. A. R. A. R. A. R A. R Weleht 0f Separated pulp, g. 1, 469 1, 536 1, 876 1, 663 2,183 1, 689 2,129 925 2, 839 981 Pel'ceut 0f 0"?11121 Pulp--- 49 51 64 36 67 33 76 36 74 26 BrlshtueSS. percent G.E- 17.8 17.5 17. 3 18.1 17. 6 18. 1 18.1 18. 6 18. 2 17.8 18. 1 Initial CS reeneSS, ce 722 679 749 712 746 713 723 723 747 718 732 Power factor (k3-111111799.) 566 1. 36 1. 21 1. 68 1.31 1. 36 1.46 1. 59 1. 58 1. 62 1. 64 1. 55 366 6. 83 6. 80 6.31 6. 89 6. 97 6. 97 6. 97 1. 61 1. 62 1. 62 1. 66 Beetlng leetor (1185111111.) 566 267 212 243 1 296 284 366 315 331 331 316 366 366 297 351 351 466 386 462 426 437 419 427 Mullen (percent. pt/lb.) 566 146 156 136 155 129 152 137 151 136 146 137 366 153 165 143 162 141 161 147 157 144 158 116 Tear factor 566 128 166 152 117 153 128 143 129 140 130 137 306 121 97 146 111 139 1.23 131 123 129 121 127 Apparent density (1h/pt.) 566 11.1 11.7 16. 4 11.2 10. 6 11. 1 16.6 11.2 16.6 16 16. 6 366 11.3 12. 6 16 7 11.4 16.8 11. 4 16 9 11 6 16.9 11 1 16.9 smoothness (Sec-l5 ce.) 566 46 54 28 44 18 43 27 39 31 47 39 366 59 84 38 57 41 58 36 51 45 54 63 Air reSlStanee (see/ ce.) 500 37 64 16 55 36 41 28 62 28 54 37 366 341 619 94 435 252 383 233 542 252 389 297 M-LT. feld 506 513 356 472 561 473 526 467 717 568 469 469 366 641 446 518 482 631 657 557 591 577 563 542 Tensile (1b-l1 111. Width) 509 35.6 39. 7 31. 6 35. 7 32. 3 38.6 32.6 34. 6 33.3 36.8 32.2 366 37.6 41. 9 34. 6 36.4 34. 3 39. 4 35.6 36.9 36.1 36.8 34. 9 Breaking lengths (meters) 500 16, 286 11,726 l9. 326 16, 776 9,476 11,616 9, 636 16, 476 16,666 16, 766 6, 586 366 11,626 12, 656 16,396 11,316 9, 986 11,476 16, 716 11,166 16,876 11,656 16,556 Gurley stitness (mg.) 566 134 126 133 114 138 144 136 117 118 146 130 366 126 117 128 166 131 136 126 116 119 126 118 Fiber classifications, percent retained on:

14 mesh 51. 4 53.1 45. 8 52. 6 41.7 52.8 46. 6 52.3 41.3 51.2 46. 6 36 mesu 36. 8 29. 5 35. 6 32.2 37. 6 32.8 37.6 31. 6 38. 2 32.6 37.8 56 mesh 16. 4 9. 2 11.9 16.6 12. 5 16.3 12.8 9. 7 13. 6 16.2 13. 4 166 mesh.- 3. 6 3. 3 4. 5 3. 5 4. 8 3. 2 5.1 3. 3 5. 2 3. 8 5. 4 Percent fines 3. 8 4. 9 2. 8 1. 7 4.6 6.9 4. 5 3. 2 2. 3 2. 2 2. 8

2. The process as set forth in claim 1 in which the slurry is subjected to centrifugal forces by treatment in a centrifugal separator.

3. The process as set forth in claim 1 in which the slurry is subjected to forces which cause the fibers to separate by sedimentation.

4. The process which comprises de-iiberizing wood into cellulosic pulp as an aqueous slurry containing a heterogeneous mixture of springwood and summerwood fibers, treating the slurry in a centrifugal separator to separate the mixture into fiber fractions respectively containing predominantly spring wood and summerwood fibers of comparatively lower and higher apparent specific gravity, then making a paper-like sheet by re-combining the pulp fractions in apredetermined manner.

5. The process which comprises de-fiberizing wood into cellulosic pulp as an original aqueous slurry containing a heterogeneous mixture of springwood and summerwood fibers, separating the slurry into at least two intermediate fractions the fibers of which respectively have predominantly higher and lower apparent specific gravities than the -average specific gravity of the fibers in the original slurry and repeating at least once the said separation with respect to at least one of the intermediate fractions and forming a paper-like sheet from at least one of the end fractions thereby obtained.

References Cited in the file of this patent UNITED STATES PATENTS 1,500,208 Shaw Iuly 8, 1924 1,818,897 Kumagawa Aug. 11, 1931 1,927,361 Edge Sept. 19, 1933 1,951,017 Hatch Mar. 13, 1934 2,972,171 Heritage Feb. 21, 1961

Claims (1)

1. THE PROCESS WHICH COMPRISES DE-FIBERIZING WOOD INTO CELLULOSE PULP AS AN AQUEOUS SLURRY CONTAINING A HETEROGENEOUS MIXTURE OF SPRINGWOOD AND SUMMERWOOD FIBERS, SEPARATING THE MIXTURE INTO FIBER FRACTIONS RESPECTIVELY CONTAINING PREDOMINANTLY SPRINGWOOD AND SUMMERWOOD FIBERS BY SUBJECTING THE SLURRY TO FORCES WHICH CAUSE THE FIBERS HAVING A COM GRAVITY TO SEPARATE FROM THE FIBERS WHICH HAVE A COMPRATIVELY HIGHER APPARENT SPECITFIC GRAVITY, THEN MAKING A PAPER-LIKE SHEET FROM AT LEAST ONE OF THE FIBER FRACTIONS.

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