CA2452944C - Use of thinnings and other low specific gravity wood for lyocell products - Google Patents

Abstract

Low specific gravity wood can be used to make lyocell fibers. Low specific gravity wood has a specific gravity less than 0.41. The low specific gravity wood is either thinnings or juvenile wood. The low specific gravity wood can be used to make a pulp, wherein the pulp has a viscosity less than 32 cP, a copper number less than 2, a weighted average fiber length less than 2.7 mm, and a coarseness less than 23 mg/100m. The pulp is used to produce a lyocell product.

Description

USE OF THINNING~S AND OTHER LO~V SPECIFIC GRAVITY WOOD
FOR L'YOCELL PRODUG"TS

FIELD OF TIDE INVENTION
The present invention is directed to pulps useful for making: lyocell-molded bodies, including films, fibers, and non-woven webs, and to methods of making such pulps useful for making ttae lyocell-molded bodies, to the Iyocell-molded' bodies made from the pulps and to the methods for making the lyocell-molded bodies. Iu particular, the present invention is directed to using "young" wood (often characterized as "core wood", °'juvenile wood", "law specific gravity wood" or, in some cases as "thi~~nings".).
EACI~GROUND OF THE INVENTION
Cellulose is a polymer of D-glucose and is a structural component of plant cell walls. These cells are referred to as fibers. Cellulosic fibers are especially abundant in tree trunks from which they are extracted, converted into pulp, and thereafter utilized to manufacture a variety of products.
Rayon is the name given to a fibrous forrn of regenerated cellulose that is extensively used in the textile industry to manufacture articles of clothing.
For over a century, strong fibers of rayon have been produced by the viscose and cuprammonium _1_ processes. The latter process was first patented in 1890 and the viscose process~t~vo~years later. In the viscose process,cellulose is first steeped in a mercerizing strength caustic soda soludon~ to form an alkali cellulose. ~ The cellulose is then reacted with carbon disulfide to form cellulose xanthate, which is then dissolved in dilute caustic soda solution. After filtration and deaeration, the xanthate solution is ~eatruded from.
submerged spinnerets into a regenerating bath of sulfuric acid, sodium ~ suli ate;, and ' zinc sulfate to form continuous filaments. 'The resulting viscose rayon is presently ~ used in textiles and was formerly 'widely used for reinforcing rubber articles such .as tires and drive belts. .
. . Cellulose is also soluble in a solution of, ammonia cappcr o~cic~. v This property forms the basis for production of cuprammonium rayon. The cellulose solution is forced through submerged spinnerets into a solution of 59'o caustic soda or dilute sulfuric acid to form the fibers, which are then decoppered and washed Cuprammoni~~ rayon is available in fibers of very low deniers and is.used atmost exclusively in tractiles.
The foregoing processes for preparing rayon both require that the cellulose be chemically derivatized or compleaed in order to render it soluble and therefore capable of being spun into fibers. In the viscose process, the cellulose is derivatized;
while in the cupra~mmonium~ rayan process, the ' ceDulose is , complexed. Jn either process, the derivatiud or complexed cellulose must be regenerated and the itagents used to solubilize it must be removed. The derivatization and regeneration , sups in ' the production of rayon significantly add to the cost of this form of cellulose fiber:
Consequently,. in recent years. attempts have been made to identify solvents that are capable of dissolving undcrivatizcd cellulose to form a dope of underivatized cellulose from which fibers can be spun.
One class of organic solvents useful for dissolving cellulose are the amine N-oxides, in particular the tertiary amine N-oxides. For 'example, Graenacher, in U.S.
Patent No. 2,179,181, discloses a group of amine oxide materials. suitable as solvents.
Johnson, in U.S. Patent No.3,447,939; describes the use of anhydrous N-methylinorpholine-N-oxide (Nr~ViO) . and other , amine ~ N-oxides as ~
solvents for cellulose and many other natural' and sjrnthetic polymers. Franks et al., in U.S. Patent Nos. 4,145,532 and 4,196,282, deal with the difficulties of dissolving cellulose in amine oxide solvents and of achieving higher concentrations of cellulose.

Lyocell is an accepted generic term for a cellulose fiber precipitated from an organic solution in which no substitution of hydroxyl groups takes place and no chemical intermediates are formed. Several manufacturers presently produce lyocell fibers, principally for use in the textile industry. For example, Acordis, Ltd.
presently 5' manufactures and sells a lyocell fiber called Tencel~ fiber.
Currently available lyocell fibers are produced from wood pulps that have been extensively processed to remove non-cellulose components, especially hemicelluTose.
These highly processed pulps are referred to as dissolving grade or high alpha (or high oc) pulps, where the term alpha (or oc) refers to the percentage of cellulose.
Thus, a high alpha pulp contains a high percentage of cellulose; and a correspondingly Tow percentage of other components, especially hemicellulose. The proeessing required to generate a high alpha pulp significantly adds to the cost of lyocell fibers and products manufactured therefrom.
Since the conventional Kraft process stabilizes residual hemicelluloses against further alkaline attack, it is not possible to obtain acceptable high alpha pulps for lyoeell products, through subsequent treatment of Kraft pulp in the conventional bleaching stages. In order to prepare high alpha pulps by the Kraft process, it is necessary to pretreat the wood chips in an acid phase before the alkaline pulping stage. A
significant amount of material, primarily hemicellulose, on the order of 1~% or greater of the original wood substance, is solubilized in this acid phase pretreatment and thus process yields drop. Under these conditions, the cellulose is largely resistant to attack, but the residual hemicelluloses are degraded to a much shorter chain length and ale therefore removed to a Large extent in the subsequent Kraft cook by a variety of liemicellulose hydrolysis reactions or by dissolution: 'r'he disadvantage of conventional high alpha pulps used for lyocell is the resulting loss of yield by having to eliminate hemicelluloses.
yn view of the expense of producing commercial high alpha pulps, it would be desirable to have alternatives to conventional high alpha pulps for making lyocell products. In addition, manufacturers would Iike to minimize the capital investment necessary to produce such types of pulps by utilizing existing capital plants:
Thus, there is a need for relatively inexpensive, Iow alpha (e.g., hi.gh yield, high hemicelIulose) pulps that have attributes that render them useful in Iyocell-molded body production..
_3_ In commonly owned U.S. Patent No. 6,210,801, low viscosity, high hemicellulose pulp is disclosed that is useful for lyocell-molded body production. The pulp is made by reducing the viscosity of the cellulose without substantially reducing the hemicellulose content. Such processes use an acid, or an acid substitute, or other methods therein described.
While the methods described in the '801 patent are effective at reducing the average degree of polymerization (D.P.) of cellulose without substantially decreasing the hemicellulose content, a further need existed for a process that did not require a separate copper number reducing step and which was readily adaptable to pulp mills that have oxygen reactors, multiple alkaline stages and/or alkaline conditions suitable for substantial D.P. reduction of bleached or semi-bleached pulp. Environmental concerns have also generated a great interest in using bleaching agents that reduce the use of chlorine compounds. In recent years, the use of oxygen as a delignifying agent has occurred on a commercial scale. Examples of equipment and apparatus useful for carrying out an oxygen stage delignification process are described in U.S.
Patent Nos.
4,295,927; 4,295,925; 4,298,426; and 4,295,926. In commonly owned U.S. Patent No.
6,331,554, a high hemicellulose, low viscosity pulp is disclosed that is useful for lyocell-molded body formation. The pulp is made from an alkaline pulp by treating the alkaline pulp with an oxidizing agent in a medium to high consistency reactor to reduce the D.P.
of the cellulose, without substantially reducing the hemicellulose or increasing the copper number.
Further efforts to reduce the cost of making lyocell-molded bodies are described in commonly owned U.S. Patent No. 6,605,359. In the '359 patent, the assignee of the present invention describes pulps made from sawdust and other low fiber length wood using a procedure similar to that of the '554 patent. These pulps are high in hemicellulose and low in viscosity, which makes them especially suitable for lyocell-molded body formation.
The forest industry continues to generate vast quantities of byproducts in the normal course of day-to-day forestry management and wood processing. These byproducts are for the most part underutilized. The need to conserve resources by utilizing wood byproducts in new ways presents a unique opportunity. It would be advantageous to develop a low cost pulp that is useful for making lyocell-molded bodies from all this underutilized wood, namely from the core wood or young or juvenile wood such as thinnings, hereafter referred to as low specific gravity wood. Thus, presenting a low cost alternative to the highly refined high-alpha pulps.
SUMMARY OF THE INVENTION
Accordingly, the present invention provides a lyocell product, comprising: at least 7% hemicellulose by weight; and cellulose, wherein pulp used to make the product has a viscosity less than 32 cP, a copper number less than 2, a weighted average fiber length less than 2.7 mm, and a coarseness less than 23 mg/100m wherein the pulp is derived from a wood material with a specific gravity of less than 0.41.
Lyocell products according to the present invention can be fibers, films, or non-woven webs, for example.
The use of low specific gravity wood can produce a lower brownstock viscosity for a given kappa number target. Using wood with low specific gravity values reduce 1 S the bleach stage temperature and the chemical dose needed in the bleach plant to produce pulp having acceptable lyocell specifications. I,ow specific gravity wood results in very low viscosity levels without increasing the copper number of the pulp or the concentration of carbonyl in the pulp above acceptable levels. The process does not use an acid phase pretreatment prior to pulping, and the subsequent bleaching-eonditions do not result in a substantial decrease in hemicellulose co~atent.
BRTEF DESCRIPTION OF THE DRAWINGS
The foregoing aspects and many of the attendant advantages of this invention yvill become more readily appreciated as the same become better understood by reference to the following detailed description, when taken in conjunction with the accompanying drawings, wherein:
FTGURE 1 is a flowsheet illustrating one embodiment of a method of making a pulp according to the present invention, and FIGURE 2 is a flow sheet illustrating one emlbodiment of a method of making a lyocell-molded' body according to the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIIVVIEhdT
Referring now to I~'IGURE 1, a suitable method to produce a lyocell dissolving pulp from low speciFc gravity wood is illustrated., The method may be considered to include two broad processing areas, pulping depicted as block I26 and bleaching depicted as block 128.
In block 100, low specii~c gravity wood chips are loaded or fed unto a digester.
Specific gravity; according to The Handbook of Pulping and Papermakmg, 2d ed., by Christopher J. Biermann, is the (unit less) ratio of the solid wood density to tlae density of water at the same temperature. As used herein, specific gravity is the average specific gravity of any population of wood feedstock material. The solid wood density may be 2S determined using the green volume, the oven-dry volume, ~r intermediate volumes. The wood chips used in practicing the invention can be made from any cellulose source.
Contrary to conventional thinking, low specific gravity wood has been found to be suitable for use as a source of cellulose for making lyocell-molded bodies. A
suitable range of low specif c gravity wood used for the present invention is any wood material having a specif c gravity about equal or less than 0.41. Low specife gravity wood results in a lower brownstock pulp viscosity, which is believed to reduce the use of bleaching chemicals in the bleach plant. Representative sources of low specific gravity wood may be derived from "thinnings" and "juvenile" wood. Juvenile wood is defined as the first growth rings surrounding the pith, according to Biermann. However; others define it as wood formed near the pith of the tree, often characterised by wine growth rings, lower density, and shorter fibers. However, in some instances the juvenile wood may extend to 5 the 15-ring ~or more. Specific gravity increases viiith the increasing height of the tree, so specific gravity at ,16 feet, 32. feet, or 4$ feet is incrementally greater than at the butt of the tree. In some embodiments, the specific gravity will be less than 0.41, and could be less than 0.38, 0.3~, 0.34, 0.32, or 0.30, or less.
Digesters for use in the present invention can include any digester suitable to pulp 10 low specific gravity wood. One example of a suitable digester. is a continuous digester that is often referred to as a "Kamyr" digester. (It should be noted that KaW
yr i~ tlx name' . .
of a Company that designed and built such digesters and as such, the ~ term Kamyr . is loosely associated with a . continuous digester. Kamyr .no longer exists as a Company:
Such continuous digesters are supplied by Kvaerner.) These digesters have been used in the pulp and paper industry for several years with the first one being installed in Sweden in 1950.: Over the years, the modifications have been made to these digesters to improve their operation. The digester system may be either a single vessel or a two-vessel system.
"Kamyr" digesters are typically used in Kraft or alkaline wood pulping, bnt may also be used in semi-chemical pulping methods. Other continuous digesters, such as the M&D#digester and the Pandia#digester, are also suitable to use in the present invention.
However, the present invention can also be practiced using any batch ~ other continuous digester.
Referring to FIGURE 1, within the pulping process,~block 126, there ate several .
operations, depicted as blocks 100-116. Loading, or feeding chips as discussed above, occurs in block 100. The wood' chips may be presteamed~ prior to cooking, block 102.
Steam at atmospheric ~pressui~e preheats the chips and drives off air so that liquor penetration will be enhanced After. the pre-steaming operation is completed, cooking liquor, referred to as white liquor, containing the pulping, chenveals may be added to the chips, block 104. The white liquor and chips are then fed into . the digester.
In KrafE
pulping, the active chemical compounds are NaOH and. Na2S. Other chemicals may be added to influence or impart desirable effects on the pulping process. These additional chemicals are well known to those of skill in the art. The present invention provides a 'Trade-mark lower brownstock pulp viscosity from relatively lower specific gravity wood as composed with wood having a higher specific gravity, i.e., specific gravity is related to Kappa number.
Impregnation, block 106, is the period during which the chenucals are allowed to S impregnate the low specific gravity wood material. Good liquor penetration helps assure a uniform cooking of the chips.
"Cooking" occurs in blocks 108 and 110. The co-current liquid contact operation, block 108, is followed by the counternt liquid contact operation, block 110.
Cooking of the low specific gravity wood occurs during these two operations.
ID either block 108 or 110, the cooking liquor and chips can be brought to temperature.
Digester washing, block Z 1 Q, is accomplished by introducing wash liquor into the bottom of the digester and having it flow counter current to the cooked 'pulp.
Cooking for' the most part ends when the pulp encounters tyke cooler wash liquor.
Upon completion' of the cook operation, and digester washing, the . digester contents are blown, block 112. Digester blowing involves releasing the wood chips arid liquor at atmospheric pressure. The release occurs with a sufbcient amount of force to cause fiber separation. If desired, the blow tank may be equipped with heat recovery equipment to reduce operating expenses..
1n-block 114, the pulp is sent from the blow tank to external- brownstock pulp washers. The separation of black liquor from the pulp occurs at the brownstock washers, In one embodiment of a method of making a pulp from love specific gravity wood to be used in the manufactime of lyocell-molded bodies, tix time allowed for in~n~egnation in . ..
block 106 is about 35 minutes. The initial percent effective alkali is about 8.5. The percent effective alkali at 5 minutes is about 1.6. The percent sulfidity is about 29.
The liquor ratio i$
2f about.4. The initial temperature is about 110°C. The residual grams pea liter of effective alkali is about 9.63. The residual percent effective alkali is about 3.85. The pH is about 12.77, and the H factor is about 2.
In one embodiment of the co-current operation, block 108, the percent effective alkali is about 4.2. According to Biermann; the effective alkali is the ingredients that will actually produce alkali under pulping conditions. . The percent sulfidity is about 29.
According to Biermann, the sulfidity is the ratio of sodium sulf de to the active alkali, expressed as a percent. The liquor addition time is about 1 minute. The temperatures _g_ may be ramped to the final cooking temperature with a hold at one or more temperatures. .
The first temperature platform is about 154°C. The time to reach the temperature is about 9 minutes and the time at the temperature is about 5 minutes. A second and higher, cooking temperature at the co-current operation i~s provided at 170°C.
' The time to reach the second temperature is about 51 minutes and , the ' tip at tennperature is about 3 minutes. The effective alkali remaining after a cook operation is called ~
the residual alkali. The residual grams per liter of effective alkali is about 9.42, following-the co-current operation. The residual percent effective alkali is about 3.77. .The pH is about 12.92, and the H factor is about 649.
In one embodiment of the counter-current operation,. block 1,10, the percent effective alkali is about 8. The percent sulfidity is about 29.2. Capability also exists for ramping to, two different temperatures iv. the counter-Current step: However, in one embodiment, the first and second ~cooIting temperatures are 'both about 171 °C. The time to reach temperature ~ is about 54 minutes and , the time at the temperature is about ' 162 minutes. The effective alkali grams per liter is about 16Ø The displacement rate is about 93-m1 per minute. The.displacement volume is about 20 liters. The volumes given, here are relatively small;, since the method was tested ~ on a lab-scale bench reactor.
However, with the parameters provided herein, and with no ~und~
experimentation, the ' process can be scaled' to any rate. The residual grams per liter of effective alkali is about 9.95. The residual percent, effective alkali is about 3.98. The pH is about.12.74 and the H~factor is about 38'77 ~. Ix one embodiment, the total time is about 319 minutes and the percent effective alkali for the total cook is about 22.3.
In one embodiment, after , washing, the viscosity of the brownstock pulp is about 153~cP. The total yield on oven dried wood is about 41.04 ~ .
Following the pulping process, generally depicted as reference numera1.126 in FIGURE 1, the brownstock pulp made from low specific gravity wood is. bleached to reduce its viscosity. The bleaching process does not lead to a substantial reduction of the hemicellulose content of the pulp. The method according to the invention produces a bleached dissolving pulp that is'suitable for lyocell-molded.bodyproduction. ~
Bleaching of chemical pulps involves the removal of lignin with an attendant decrease in the pulp fiber length and viscosity. However, the bleaching process does not cause a substantial reduction to the hemicellulose content of the pulp. Bleaching brownstock, pulp made from low specific gravity wood may require fewer chemicals than the conventional highly refined, high-alpha pulps presently being used for lyocell.
In one embodiment, the low specific gravity brownstock pulp made according. to the invention can be treated with various chemicals at different stages in the bleach plant.
The stages are carried out in vessels or towers of conventional design.. One representative bleaching sequence is ODEpD. The operations occurring in the bleaching plant are represented collectively by reference numeral' 128 in FTGURE 1. Other embodiments of post bleaching the pulp after pulping are described in U.S: Patent No.
6,331,354, aad U.S.
Patent No. 6,605,359.
The first stage of bleaching is an O stage, block 116. The O stage comprises bleaching with oxygen. However, according to Biermann, some consider oxygen bleaching to be an extension of the pulping process. Oxygen bleaching is the delignification of pulps using oxygen under pressure. 'lie oxygen is considered to be less specific for the removal of lignin than the chlorine compounds.. Oxygen bleaching takes place in an oxygen reactor. Suitable oxygen reactors capable of carrying out the method of the present invention are described in U.S. Patent Nos:4,295,925;

4,295,926;
4,298,426; and 4,295,927. 1'he reactor can operate at a high consistency, wherein the consistency of the feedstream to the reactor is greater than 20~Xc or it can operate at medium consistency, where the medium consistency ranges between 8% up to 2096. Preferably, if a high consistency oxygen reactor is used, the oxygen pressure can reach the maximum pressure rafting for the reactor, but more preferably is greater than 0 to about 85 psig. In medium consistency reactors, the oxygen can . be present in an amount ranging from greater than 0 to about 100 pounds per ton ' of the pulp, but is more preferably about 50 to about 80 pounds pet ton of pulp. The temperature of the O stage ranges from about 100°C to about 140°C.
In one embodiment of the method to make a pulp suitable to be used ~in making lyocell-molded bodies, a D stage, block 118 follows the O stage, block 116.
The D stage comprises bleaching the pulp coming from the oxygen reactor with chlorine dioxide.
Chlorine dioxide is more selective than oxygen for removing lignin. The amount of chlorine dioxide used in this stage ranges from about 20 to about 30 lb/ton, which may be lower than a conventional bleach plant that processes pulp from wood chips with a specific gravity not within the low specific gravity range of. this ~
invention. The temperature of the D stage ranges from about 50°C to about 85°C.
In one embodiment of the method to make a pulp suitable to be used in making lyocell-molded bodies, an Ep stage, block 120, follows the D stage, block 118.
The Ep .
stage is the hydrogen peroxide reinforced extraction stage where lignin is .removed from the pulp using caustic in an amount ranging fr, om about 20 to about 50 lbhon.
The amount of hydrogen peFOxide ranges from about 20 to about 60 lbhon, which may be lower than a.
conventional .bleach plant that processes pulp from wood chips having a specific gravity not considered within the low specific gravity range of this invention. The temperature of the Ep stage ranges from about ?5 to about 95°C. ' .
In one embodiment, a second D stage, block 122, follows the Ep stage, block 120.
The amount of chlorine dioxide used in this stage ranges from' 10 to about 301b/t~nn;
which may lx lower. than a conventional bleach plant that processes pulp from wood chips having a conventional specific gravity not, considered to be: within the low specific ~ gravity range of this invention. The temperature of the D stage ranges from about 60°C
to.about 90°C.
One embodiment ' of a pulp made from low specific gravity wood has a henvcellulose content of at least ' ?96 hemiccllulose, a pulp viscosity less than 32. eP, a copper number less than 2.0, ~ and in some instances ~ less than 1.3 (TAPPI
T'~30), ~a weighted average fiber length less than 2.? mm, and a coarseness less thaw 23 mg/100m.
Other embodiments of ' pulps made according to the present invention have a combined copper, manganese, and iron content less than 20 ppm, a total . metal load less . than 300 ppm, aid a silicon content less than 50 ppm. Lyocell molded bodies made from the pulps of the invention will have a correspondingly high hemicellulose content of at least ?96 by weight, and cellulose. . .
Hemicellulose is measured by a sugar content assay based on TAPPI standard T249 hm-85:
Methods for measuring pulp viscosity are well known in the art, such as TAPPI
T230. Copper number is a measure of the carboxyl content of pulp. The copper number is an empirical test used to measure the reducing value of cellulose. The copper number is expressed in terms of the number of milligrams of metallic copper, which is reduced from cupric hydroxide to cuprous oxide in an alkaline medium by a specifiai weight of cellulosic material. The degree to which the copper number changes during the bleaching operation is determined by comparing the copper number of the brownstock pulp entering the bleaching plant and the copper number of the bleached pulp after the bleaching plant..
A low copper number is desirable because it is generally believed that a high copper number causes cellulose and solvent degradation during and , after dissolution of the bleached pulp' to form a dope.
The weighted average fiber length (WAFL~ is suitably measured by a FQA
machine, model No. LDA93-89704, , with software version 2.0; made by the Optest Company of Hawkesbury, Ontario, Canafa.
Coarseness is measured using Weyerhaeuser Standard Method WM W FQA. . . ~ .
Transition metals are undesirable in pulp because they accelerate the degradation 'of cellulose and NMMO in the lyocell process. Examples of transition ~tals c~amnonly found in bleached pulps include iron, copper, and manganese. Preferably, the combined metal content of these three metals in the pulps of the invention is less than about 20 ppm by Weyerhaeuser Test No. AMS-PULP-1/6010.
Additionally, pulps of the invention have a total. ~tal load of less than 300 ppm by Weyerhaeuser Test No. AMS-PULP-1/6010. Tlx total metal load refers to the combined amount, expressed in units of parts per million (ppm), of nickel, chromium, manganese, irbn and copper. .
20~ . Once. the pulp has been bleached to reduce its viscosity without substantially increasing its copper number or decreasing the hemiccllulose content, the pulp can either be washed in water and transferred to a bath of organic solvent, such as N-methyl morpholine-N-oxide (NNJbiO), for dissolution prior to lyocell-molded body formation.
Alternatively, the bleached washed pulp can be dried and broken into fragments for storage and/or shipping in a m11, sheet or bale, for example.
In order to make lyocell products from the low specific gravity wood 'pulps, the pulp is first dissolved in an amine oxide, preferably a tertiary amine oxide.
Representative examples of amine oxide solvents useful in the practice of the present invention are set forth in U.S. Patent No. 5,409,532 .
The preferred amine oxide solvent is NMMO. Other representative examples of solvents useful in the practice of the present invention include dimethylsulfoxide (D.M.S.O.), dimethylacetamide (D.M.A.C.), dimethylformamide (D.M.F.) and caprolactan derivatives. The bleached, pulp is dissolved in amine oude solvent by any known means such as ones set -forth in U.S. Patent Nos.

5,534,113;
5,330,567; and 4,246,221 - The pulp solution -is called dope. The dope is used to manufacture lyocell fibers, films, and noawovens or other products, by a variety of techniques, including melt blowing, spun-bonding, centrifugal spinning, dry jet wet, or any other suitable method.
Fasaraples of some of these techniques are described in. U.S. Patent Nos. 6,235,392;

6,306,334;
6,210,802; and 6,331,354. Fatamples of techniques for making fil~ims are set forth in U.S. Patent Nos. 5,401,447; and 5,277,857, Meltblowiag,~ centrifugal spinning and spunbonding used to make lyocell fibers and nonwoven webs are described in U.S. Patent Nos. 6,235,392 and 6,306,334. , ~ . ~y j~
wet techniques are more fully described ' in ' U.S. Patent Nos. 6,235;392;
6,306,334;
6,210,802; 6,331,354; and 4,142,913; 4,144,080; 4,211,574; 4,246,221.
One embodiment of a method for making lyocell products, including fibers, films, .
'and nonwoverl webs from dope derived from pulp is provided, wherein the pulp is made from low specific gravity wood, the pulp having at least 796, hemicellulose, s viscosity .
less than or about 32 cP, a copper number less than or about 2, a weighted average fiber length less than or about 2.7 mm, and a coarseness less than or about 23 mg/100m. The .
method involves extruding the dope through a die to form a plurality of filaments, washing the filaments to remove the solvent, regenerating the filaments with a nonsolvent, including water or alcohol, and drying the filaments.
FIGURE 2 shows a block diagram of one embodiment of a method for forming lyocell fibers from the pulps made 5om low specific gravity wood according to the present invention. Starting with low specific gravity wood pulp in block 200, the pulp is physically broken down, for example by a shredder in block 202. The pulp is dissolved with an amine oxide-water mixture to form a dope, block 204. The pulp can be wetted with a nonsolvent mixture of about 40~ NMMO and 60fo water. The mixture can be mixed in a double arm sigma blade mixer and su~cient water distilled off to leave about 12-14~o based on NMMO so that a cellulose solution ' is formed, block 2 0 6 .
Alternatively, NMMO of appropriate water content may be used initially to.eliminate the need for the vacuum distillation block 208. This is a convenient way to prepare spinning dopes iii the laboratory where commercially available NMMO' of about 40-6096 concentration can be mixed with laboratory reagent NMMO having only abort 396 water to produce a cellulose solvent having 7-1596 water. Moisture normally present in the pulp should be accounted for in adjusting the water present in tlar solvent.
Reference is made to articles by Chancy, H., and A. Peguy, Journal of Polymer Scienca, Polymer Physics Ed 18:1137-1144 (1980), and Navard, P., and J.M. Haudia, British Polyrne~r Journal, p. 174 (Dcc. 1980) for laboratory preparation of cellulose dopes iri NMMO and water solvents.
The dissolved, bleached pulp (now caDed the dope) is forced through extrusion orifices in a process called spinning, block 210, to produce cellulose frlaments that are then regenerated with a non-solvent, block 212. Spinning to form lyocell:
molded bodies, including fibers, films, and nonwovens, may involve meltblowing, centrifugal spinning, spun bonding, and dry jet wet techniques. Finally, the ~lyocell filamenL4 ~
fibers are washed, block 214. ' The solvent can either be disposed of or reused Due to its. ~ high: costs, it is generally undesirable to dispose of the solvent. Regeneration of tlx solvent suffers from the drawback that the regeneration process involves dangerous, potentially eacplosive conditions. ~ .
~ The ~ following examples. merely. illustrate tta; best mode now contemplated for practicing the invention, but should not be construed to liuiit the invention..

A commercial continuous extended delignification process was simulated in the laboratory utilizing a specially built reactor vessel with associated au~ciliary equipment, including circulating pumps, accumulators, and direct heat . exchangers, etc.
Reactor temperatures were controlled by indirect heating and continuous circulation of .cooking liquor. The reactor vessel was charged with a standard quantity of equivalent moisture free wood. An optional atmospheric pre-steaming -step may be carried out prior to cooking. A quantity of cooking liquor, ranging from about 509b to 8096 of the total, was then charged to the digester along with dilution water to achieve the target liquor to wood ratio. The reactor was then brought to impregnation temperature and pressure and.
allowed to remain for the target time. Following the impregnation period, an additional -14- ~ ' . .

portion of the total cooking liquor was added to the reactor vessel, ranging from about 5%
to 15% of the total. The reactor was then brought to cooking temperature and allowed to remain there for the target time period to simulate the co-current porkion of the cook.
Following the co-current portion of the cook, the remainder of the cooking liquor was added to the reactor vessel at a fixed rate. The rate is dependent on the target time period and proportion of cooking liquor used for this step of the cook. The reactor was controlled at a target cooking temperature and allowed to remain there during the simulation of the counter-current portion of the cook. Spent cooking :liquor was withdrawn from the reactor into an external collection container at the same fixed rate.
At the end of the cook, the reactor vessel was slowly depressurized and allowed to cool below the flash point. The reactor vessel was opened and the cooked wood chips were collected, drained of liquor; washed, screened and made ready for testing.
Three cooks of low specific gravity wood chips were prepared, along with three cooks t~f non-low specific gravity wood.
1 S E;~~AN~PL.E 2 PULPING PROCESS PARAMETERS FOR LOW SPEC1FTC GRAV~T'S~ WOOD
One cook for low specific gravity wood chips had the following parameters.

Wood Chi S:G. 0:410 Pre-Steam @ 110 C, minutes 5 Im re nation:

Time, minutes 3S

% Effective Alkali, initial $.$

% EA, second @ 5 minutes lob % sulfidity 29 Li uor ratio 4 Tem rature - degrees C l 1p Residual, GIL EA ~ 9.63 Residual, % EA

PH 12.77 H-factor ~

Pressuie Relief Time, Minutes C~-Current:

% Effective Alkali % sulfidit ~9 1i uor addition time., minutes tem erature - de tees C 15'~

time to; minutes g time at, minutes tern erature - de ees C 17~

time to, minutes ~ 1 time at, minutes ~

residual, G/L EA ~.~~

residual, % EA

PH _ 12.2 H-Factor Counter-Current:

% effective alkali % sulfidit tem erature - dees C 171 time to, minutes 54 time at, minwtes ! 0 tem 171 erature -de ees C

time to, mlnuteS

time at, minutes 162 EA; fi/L - siren 16.0 dis lacement rate, CC/IvI 93 dis lacement volume;, liters 20.00 residual, GIi., EA 9.95 residual, % EA 3-g8 PH 12.74 H-factor 3877 Total Time, Minutes 319 % Effective Alkali - T otal Cook 22.3 Acce ts, % on O.D. Wood X1.01 Ite'ects, % on O.D. Wood 0.03 Total field, % on O.D. Wood 4~ 1-Ka a Number, 10 Minute; 16.8~

EXAMPI~IE 3 BLEACHING PI20CESS FOFZ L,OW SPEC3FIC CpRAVITY WOO17 The pulp made by the process of Example 2 was bleached according to the following procedure.
O_ Stage Inwoods low specific gravity wood chips were pulped into an alkaline Kraft pulp with a kappa number of 16.8 (TAPPI Standard T23~5 cm-85 and a viscosity of 239 cP
(TAPPI T230). The brownstock pulp was treated Wllh oxygen in a pressure vessel with high consistency mixing capabilities. The vessel was preheated to about 12~°C. An amount of sodium hydroxide (I>taOlf~) equivalent to 100 pounds per ton of pulp was added to the alkaline pulp. The reaction vessel was then closed and the pressure was increased to 60 psig by introducing oxygen into the pressure vessel. Water was present in the vessel in an amount sufficient to provide a 10% consistency.
After 45 minutes, the stinting was stopped and the pulp was removed from the pressure vessel and washed. The resulting washed pulp viscosity was 35.3 cP, and had a kappa cumber of 3.8.
DD Staae The D stage treated the pulp processed in the ~D stage by washing it three times with distilled water, pin fluffing the pulp, and then transfernng the pulp to a polypropylene bag. The consistency of the pulp in the polypropylene bag was adjusted to 10% with the addition of water. Chlorine dioxide corresponding to an amount equivalent to 28.4 pounds per ton of pulp was introduced to the diluted pulp by dissolving the chlorine dioxide in the water used to adjust the consistency of the pulp in the bag. The bag was sealed and mixed,a:ad then held at 75°C for 30 minutes in a water batl;~. The pulp was removed. and washed with deionized water.
E S
The washed pulp from the D stage was then placed in a fresh polypa~opylene bag and caustic was introduced with one-half of the amount of water necessary to provide a consistency of 10%. Hydrogen peroxade was mixed with tlae other one-half of the dilution water and added' to the bag. The hydrogen peroxide charge was equivalent xo 40 pounds per ton of pulp_ The bag was sealed and mixed and held for 55~
minutes at 88°C in a water bath. After removing the pulp from the bag and washing it with water, the mat was filtered and then placed back into the polypropylene bag and broken up by hand.
D. Stage Chlorine dioxide was introduced a second time to the pulp in an amount equivalent to 19 pounds .per 'ton of pulp with the dilnztion water necessary to provide a consistency of 10%. The bag was sealed and mixed, and then held for 3 hours at 88°C in a water bath. The treated pulp had a copper number of about 0.9 measured by TAPPI
Standard T430 and had a hemicellulose (xylan and mannan) content of 12.7%..

Low specific gravioy wood having a specific gravity of 0.410 was pulped using the Kraft process, and subsequently, bleached and treated with varying amounts of _1g_ oxygen to reduce its viscosity. Components in the pulps made using Inwoods low specific gravity wood chips are 7.2% xylans and 5.5°k mannans.
Table 2 shows the results for three different cooling conditions. While brownstock pulp WAFL is provided, it is apparent that bleaching the brownstock pulp to reduce its viscosity without substantially reducing the hexnicelluio5e content, in accordance with the condixions of the present invention, will not result in any appreciable increase in the bleached pulp WAFL and may in fact be lower than the brownstock pulp WAFL.

Inwoods chips Inwoods chips Inwoods chips Cook A Cook B Cook C

Chi s S ecific Gravit 0.410 0.410 0.410 Ka a of Brownstock 24.4 2p.1 16;,8 Yield % 43.2 41.4 41.0 Brownstock pulp viscosity 4I4 235 16>3 (cP) Fallin Ball Brownstock pulp WAFL 2.70 2.70 2:~9 ) Brownstock pulp Coarsene:os 18.3 17.9 1'1.6 (m 100rn) 02 pulp viscosity cP 55 34 28 (104 lbs/ton NaOH) 7.6 ka a 6.0 ka a 3.8 ka a 02 pulp viscosity cP 80 63 43 (60 lbs/ton NaOH 6.0 ka a 7.5 ka a S.b ka a Bleached pulp coarseness 32.4 21:8 (m /100 m) Inwoods chips Inwoods chips Inwoods chips , Cook A Cook B' . . Cook C

Bleached u1 fibers/. 4.8 ~ ' 4.6 x 106 Bleached uI viscosi 31.8 ' 29.5 .
cP

Bleached pulp intrinsic4.1 4.2 viscosi ' ' -Bleached pulp 0.6 c0.6 .

Cu m Bleached pulp 12 . 14.3 Fe m Bleached .pulp 1.5 . . 3.6 Bleached pulp . N.4 N.3.

Bleached pulp 41 . 31 .

S1 In COMPARAT,~VE EXAMPLE 5:
PULPING PROCESS P S FOR NON LOW SPECIFIC GRAVITY WOOD
A conventional Tolleson#wood chip made from wood having specific gravity of .
0.495 was pulped using a Kraft process .and subsequently treated with varying amounts of oxygen to reduce its viscosity. Table 3 shows the pulping conditions for one cook of Tolleson wood chips.
TABLE 3 .
Wood Chi S.G. 0.495 Pre-Steam C~ 110 C, minutes 5 #Trade-mark Impregnation:
time, minutes 35 % Effective Alkali, initial ~~5 ' % EA, second C 5 minutes 1.6 3~.5 % sulfidit ._ li uor ratio '1 tem erature - de reel C 1.1 a residual, GIL. EA

residual, % EA 3.67 PH 13.24 H-factor J

Pressure Relief Time, Minutes 2 Co-Current:

% Effective Alkali ~.2 % sulfidit 3~~5 1i uor addition time, minutes 1 tem erature - de eea C 157 time to, minutes . 14 time at, minutes ~

tem rature - de ees C 170 time to, minutes 5'I

time at, minutes residual, G/I; EA x.31 residual, % EA 3.32 _21 _ PH 13.07 H-Factor 6g0 Counter-Current:

% Effective Alkali g % sulfidi 30.0 Tem erature - de ees C ll'~1 'Time to, minutes 5~.

Time at, minutes (1 Tem rature - de ees C 1?1 Time to, minutes (1 Time at, minutes 162 EA, G/L - siren 20_~

Dis lacement rate, CC/M 73 Dis Iacement volume, liters ~ l,~.g7 Residual, G/L EA g72 residual, % EA 3.gg 13.18 H-factor 375 Total Time, Minutes 31 g % Effective Alkali - Total Cook 22.3 Acce ts, % on O.D. Wood x.23 Re'ects, % on O.D. Wood 0.13 Total Yield, % on O.D. Wood ,3~

Ka a Number, 10 Minutes [ 17_7 Table 4 shows the results of three different cooks using a conventional:
Tolleson wood chip made from a non-low specific gravity wood. Components in the pulps made using Tolleson non-low specific gravity wood chips are 6.5% xylose; 6.6%
maranose;
5.7% xylans; and 5.9% mannans.

1'olleson chips Tolleson chips Tolleson chips Cook ~ Cook B Cook t, Chi s S ecific Gravit 0.495 0.495 ~.495 Ka a of Brownstock 2;6.9 20.8 17.8 Yield % x.6.6 46.1 44.4 Brownstock pulp 633 358 243 viscosity (cP) Falling Ball Brownstock pulp WAFL G!..13 4:14 4.19 Brownstock pulp d,6.1 24.4 24.3 Coarseness (m 100m) 02 pulp viscosity cP 96 43 41 (100 lbs/ton NaOH) ~i.4 ka a 6.9 ka a 4.7 ka a 02 pulp viscosity cP 180 88 '70 (60 lbs/t~n NaOH) 8.3 ka a 5.5 ka a 6.2 ka a Bleached pulp coarseness 24.9 27.5 (m 100 m) Bleached pulp ~i.8 2.8 fibers! x 106 TABI~ 4 Tolleson chips Tolleson chips Tolleson chips Cook A C~ok B Cook C

Bleached pulp viscosity 28.5 24.2 (cP) Bleached pulp intrinsic 4.3 4 viscosit Bleached u1 Cu ( m) <0.6 <0.7 Bleached u1 Fe ( m) 11.5 16 Bleached u1 lVln ( m) 5 6 Bleached u1 Cr ( m) e:0.4 0.3 Bleached u1 Si ( m) =1 32 It can be seen that the: viscosity of the pulps made from the Inwoods Iow specific gravity wood chips is Iower than the viscosity of the pulps made from the Tolleson non-low specific gzavity wood chips. , It can be seen that the: viscosity of the pulps made from the ~nwoods low specific gravity wood chips is lower than the viscosity of the pulps made from the Tolleson non-Iow specific gravity wood cha':ps.
While the preferred embodiment of the invention has been illusWated and described, it will be appreciated that various changes can be made therein without departing from the spirit and scope of the invention:

Claims (2)

1. A lyocell product, comprising:
at least 7% hemicellulose by weight; and cellulose, wherein pulp used to make the product has a viscosity less than 32 cP, a copper number less than 2, a weighted average fiber length less than 2.7 mm, and a coarseness less than 23 mg/100m wherein the pulp is derived from a wood material with a specific gravity of less than 0.41.

2. The lyocell product of Claim 1, wherein the product is one of a fiber, a film, or a nonwoven web.