CA2193370A1 - Lyocell fibre and a process for its manufacture - Google Patents

Abstract

The fibrillation tendency of solvent-spun cellulose fibre can be increased by subjecting the fibre to a treatment which reduces its degree of polymerisation by about 200 units or more. Suitable methods of treatment include severe bleaching, for example application of an aqueous liquor containing 0.1 to 10 percent by weight sodium hypochlorite (as available chlorine) to the fibre followed by steaming. Fibre may be treated in never-dried or previously-dried form. Fibre treated by the process of the invention is useful for example in the manufacture of paper and hydroentangled fabrics. Fibre of increased tendency to fibrillation can be beaten to a Canadian Standard Freeness 400 in the Disintegration Test by 30,000-150,000 disintegrator revolutions and to a Canadian Standard Freeness 200 in the same Test by 50,000-200,000 disintegrator revolutions.

Description

~095l35399 PCTIG~95101439 ' P ~ j 1 2 1 9 3 3 7 0 LrOOELL EIBRE AND A PROCESS FOR ITS MANUFACTURE

Field of the invention This invention relates to a process for manufacturing 5 lyocell fibre with an increased tendency to fibrillation and to lyocell fibre having an increased tendency to fihrill~tion.

It is known that cellulose fibre can be made by extrusion of a solution of cellulose in a suitable solvent 10 into a coagulating bath. This process is referred to as "solvent-spinning~, and the cellulose fibre produced thereby is referred to as "solvent-spun" crll~llose fibre or as lyocell fibre. Lyocell fibre is to be distinguished from c~ll--lose fibre made by other known processes, which rely on 15 the formation of a soluble rh~mir~l derivative of c~l l--lose ~nd its subsequent ~o ~-fiition to regenerate the c~ll--lose, for example the viscose process. Lyocell fibres are known for their impressive textile physical properties, such as tenacity, in ~r; RO~ with fibres such as viscose 20 rayon fibres. One example of a solvent-spinning process is ed in US-A-4,246,221, the contents of which are inco.~uLated herein by way of reference. C~llnlose is dissolved in a solvent such as an aqueous tertiary amine N-oxide, for example N-methylmorpholine N-oxide. The 25 resulting solution is then e~LLuded through a suitable die into an aqueous bath to produce an assembly of filP ts which is washed with water to remove the solvent and is subsequently dried.

Fibres may exhibit a tendency to fibrillate, 30 partirnl~rly when subjected to --h~nir~l stress in the wet state. Fibrillation occurs when fibre ~L.uuLuLe breaks down in the longitudinal direction so that fine fibrils become partially detached from the fibre, giving a hairy ~pp~r~nre to the fibre and to fabric containing it, for example woven 35 or knitted fabric. Such fihrill~tion is believed to be caused by ~hAnic~l abrasion of the fibres during treatment WOg5/35399 PCT1Gs95/0l439 ~ 2 - ~ 93370 in a wet and swollen state. ~igher temperatures and longer times of treatment generally tend to produce greater degrees of f;hr;lliqtion. Lyocell fibre appears to be particularly sensitive to such abrasion and is conse~uently often found 5 to be more susceptible to fibrillation than other types of cellulose fibre. Intenslve e~forts have been made to reduce the fihr;lliqtion of lyocell fibres.

The pl~s~nce of fihrilliqted fibres is advantageous in certain end-uses. For example, filter materials containing 10 f i hr; 1 1 iq ted fibres gr~n~riq 1 1 y have high efficiency.
Fibrillation is induced in paper-making processes by beating the fibres, which is generally known to increase the strength and transparency of the paper. Fibrillation may also be utilised in the manufacture of non-woven fabrics, 15 for example hydroentangled fabrics, to provide improved cohesion, cover and strength. Although the f;hr~ 2tion tendency of lyocell fibres is higher than that of other c~ lose fibres, it is not always as great as may be desired for some end-uses. It is an object of the present 20 invention to provide lyocell fibre with an increased f i hr i 1 1 iq tion tendency.

Disclosure of the invention The present invention provides a process for the manufacture of lyocell fibre with an increased tendency to 25 fihrilliqtionr in~ln~ing the steps of:
(l) dissolving cellulose in a solvent to form a solution, (2) extruding the solution through a die to form a plurality of fili c, and (3) washing the fili Ls to remove the solvent, thereby forming lyocell fibre; and the characterising step of (4) subjecting the lyocell fibre to conditions effective to reduce the Degree of Polymerisation of the cellulose by at least about 200 units.

W095/35399 PCTIGB9~01439 ~ 3 -The solvent preferably comprises a tertiary amine N-oxide, more preferably N-methylmorpholine N-oxide (NMNO), and it generally contains a small proportion of water. ~hen a water-miscible solvent such as ~NO is used, the fil~ ' c 5 are generally washed in step (3) with an aqueous liquor to remove the solvent from the f i 1 i ' ~ .

Lyocell fibre at the end of step (3) is in never-dried form and generally requires to be dried. In one pmho~; t of the invention, the degradation step (4) is performed on lO never-dried fibre which is subsequently dried. In another pmhn~i L of the invention, the fibre is dried between steps (3) and (4)- Use of the degradation step (4) according to the invention on previously-dried fibre may be convenient if batchwise processing or longer treatment times 15 are desired. Previously-dried fibre may be treated in the form of fibre, yarn or fabric, including woven, knitted and non-woven fabric.

Lyocell fibre is pLuduced in the form of tow which is commonly converted into short length staple fibre for 20 further processing, either in the never-dried or dried state. A lyocell tow may be converted into staple fibre either before or after the degradation step (4) and either before or after drying.

The lyocell fibre manufactured by the process of the 25 invention may be nnri~ Pd (bright or ecru) or pigmented, for example incol~oL~ting a matt pigment such as titanium dioxide.

The degree of polymerisation (D.P.) of cellulose is conveniently assessed by viscosimetry of a dilute solution 30 of cPlllllose in a solvent which is an aqueous solution of a metal/amine complex, for example ~ hydroxide solution. A suitable method, based on TAPPI Standard T206, is ~Psrrihpd hereinafter as Test Nethod l. CP1 1111~5e D.P.
is a measure of the number of anhydroglucose units per 4 _ 2 1 9 ~ 3 7 0 molecule. It will be understood that D.P. measured in this manner ls a viscosity-average D.P.

The desired reduction in cellulose D.P. in the degradation step ( 4 ) may be achieved in a number of ways.
5 In one embodiment of the invention, the D.P. is reduced by a hlPArhinr treatment, preferably using a h]PArhinr liquor.
The bleaching liquor may be applied to the fibre by passage through a bath, by padding, or by spraying, for example, particlllArly by spraying the liquor onto a tow of fibre 10 emerging from a nip between rollers.

Bleaching of never-dried fibre may be carried out using an aqueous solution comprising a hyprrhlor;te such as sodium hyporhlorite, for example a solution containing 0.1 to 10, preferably 0.25 to 4, more preferably 0.5 to 2, per cent by 15 weight NaOCl (expressed as available rhlnrinP). The hlPArhinr liquor may optionally contain in addition an alkali such as sodium hydroxide, for example up to about 0.5 or up to about 1 per cent by weight sodium hydroxide.
Alternatively, the pH of the blpArhinr liquor may be 20 controlled in the range from 5.5 to 8, preferably around 6 to 7. Degradation has been found to be relatively rapid in these pH ranges. A hyporhloritp blPArhing liquor may if desired be applied to the fibre at elevated t~, _LUL~I for example about 50~C. Less concentrated bleach liquors may be 25 used in the batchwise treatment of previously-dried lyocell fibre. For example, the hleArhinr liquor may contain 0.1 to 1 per cent by weight available rhl~rinP, and bl~Arhinr conducted at slightly elevated t~ ~LULC, for example 30 to 60 C, for 1 to 3 hours.

Bleaching may alternatively be carried out using an aqueous solution - _ ~ing a peroxide, partir1llAr~y hydrogen peroxide, for example a solution containing 0.5 to 20, pr~fPrAhly 1 to 6, more preferably 1 to 4, per cent by weight hydLuy~ll pPr~ P A pPr~P hlPArhin~ liquor 35 preferably additionally contains an alkali such as sodium _ _ _ _ _ _ . . .. .... . .. . ..

WO95/35399 r~ 43~
~ t ~ 2 1 9 3 3 7 0 hydroxide, for example about 0.05 to about 1.0 per cent by weight sodium hydroxide. The pH of an AlkAl in~ peroxide h]PArhing liquor is preferably in the range from 9 to 13, more preferably 10 to 12. prPfPrAhlyr no peroxide 5 stabiliser is used. Acidic peroxide solutions (pH 1 or less) may alternatively be used. A peroxide bleaching liquor is preferably applied to the fibre at ambient temperature or below to minimise , - ntPd ~PC sition of the peroxide. Peroxide blPArhing liquors have gPnPrAlly 10 been found to be less effective in reducing cellulose D.P.
than hypochlorite hl PArh i ng liquors, and accordingly the latter may be preferred if large reductions in D.P. are desired. The effectiveness of a peroxide treatment may be increased by pretreating the lyocell fibre with a solution 15 of a transition metal ion which catalyses the ~ ~ 6ition of peroxide ions, for example copper or iron cations. It will be appreciated that such pretreatment is preferably ufied in con~unction with a peroxide liquor application technique which does not involve a circulating bath.

The effectiveness of a hlPArhing treatment such as hypochlorite or peroxide hleArhi ng may alternatively be PnhAnrPd by exposure to ultraviolet radiation.

After the fibre has been wetted with a hlPArhinr liquor, it is preferably heated to induce and ArcP]PrAte the 25 degradation reaction during which the D.P. of the cellulose is reduced. For example, a tow of lyocell fibre wetted with hleArhing liquor may be passed through a steam tunnel or heated J-box. Wet or snrPrhPAted steam may be used. The t~ ~ Lu~ in a steam tunnel may be in the approximate 30 range from 80 to 130~C and the rP~i~onre time may be in the range from 10 to 200 or 20 to 60 seconds, although it will be understood that temperature and time are to be chosen having regard to the degree of reduction in cP~ lose D.P.
desired. Other types of equipment such as a J-box or a bed 35 steamer may be used if longer steaming times, for example in the range from 5 to 30 minutes, are desired. Alternatively, WOg5/35399 PCT/GB9S/0l439 fibre wetted with a hypochlorite bl~rhing liquor may be treated with aqueous acid or an acidic or particularly a neutral buffer solution to cause degradation to occur.

Alternatively, previously dried lyocell fibre may be 5 subjected to degradation step (4) accordLng the invention using conventional hl~Arhing equipment for cotton, for example a kier. Further alternatively, never-dried or previously dried lyocell fibre may be subjected in tow or staple form to degradation step ~4) according to the 10 invention utilising conventional equipment for the continuous wet treatment of wet-spun fibres. For example, the lyocell fibre may be laid onto a continuous woven mesh belt and then passed under a series of sprays or other liquor distribution devices alternating with mangle rollers, 15 using the type of equipment generally known for washing newly-spun vLscose rayon. Longer treatment times are more readily obtained using such alternative types of equipment than when a wetted tow is passed through a steam tunnel.

Alternatively, other bleaching treatments known in the 20 art for re1lt-l~fte may be used, for example chlorite bleaching. Aggressive conditions should- grn~r~ 1 1 y be chosen to ensure a signifir~nt reduction in D.P.

In another '~ of the inventLon, cP~ o~e D.P.
is reduced by treatLng the lyocell fibre wLth aqueous acLd.
25 The acLd Ls preferably a mLneral acid, more preferably hydrorhl~ri~ acLd, snlrhl-rLr acid or in particular nitric acid. For example, the fibre may be wetted with a solution containing from about 0.2 to about 4.5 per cent by weight con~ ted nitric acid in water. After wetting with acid, 30 the fibre is preferably heated to cause the desired reduction in D.P., for example by passage through a steam tunnel as ~Srri hed hereinabove with respect to aqueous bleaching processes.

After treatment with a bleaching or acid liquor to W095/3~399 rc~ o~439 ~ 2 1 9 3 3 7 0 reduce rr~ ose D.P., the lyocell fibre is generally washed to remove traces of the ~h~mi,Alc used to induce degradation and any byproducts and is generally then dried in known manner.

Other methods known in the art which reduce the 3.P. of cellulose may also be employed, for example ~UO~ULe to cellulolytic enzymes, electron beam radiation, ozone, ultrasonic vibrations or treatment with peroxy ~ u.lds such as peracetic acid, or persulphate and p~lbol,lte salts.
10 Combinations of two or more methods may be used. Ultrasonic treatment may additionally serve to induce fibrillation in the fibre.

The D.P.-reducing step (4) generally degrades the tensile properties of the lyocell fibres. This would 15 normally be thought to be most undesirable. It has nevertheless been found that fibre produced according to the process of the invention has g~nr~rAlly satisfactory tensile properties for use in the end-uses in which highly fihrillAting fibre is desired, for example the manufacture 20 of paper and non-woven articles.

The D.P. of cellulose used in the manufacture of known lyocell fibre is commonly in the range 400 to 1000, often 400 to 700. The D.P. of ce~ lr~e in lyocell fibre ~luduced by the process of the invention may be below about 250, more 25 preferably below about 200, below about 150 or about 100.
The D.P. of cr~lllllose in lyocell fibre produced by the process of the invention is pr~fr~r~hly at least minus 75, because at lower values than this the fibre tends to disintegrate. (It will be appreciated that, although a 30 negative D.P. is a physical impossibility, the quoted values of D.P. are obtained by applying the standard conversion to solution viscosity measurements in the manner herr~inh~fore ~$,~rih~ and not by direct mea~u~ L.) The D.P. of c~lllllose in lyocell fibre produced by the process of the 35 invention is preferably in the range 0 to 350, further wossr3s3ss PcTIGsssl0l439 2 ~ 9 3 ~ 7 0 ~

preferably 150 to 250, particularly if the D.P. of the lyocell fibre before treatment in the degredation step (4) Ls in the range 500 to 600. The D.P. of the rP~ lose may be reduced by at least about 300 units in the degradation 5 step. The D.P. of the cellulose may be reduced by about 200 to about 500 units, often about 300 to about 400 units in the degradation step. It has surprisingly been found that the fihrill~tion tendency of lyocell fibre ~luduc~d by the process of the invention is markedly higher than that of 10 lyocell fibre of the same D.P. manufactured using low D.P.
cPllnloqe as starting material and omitting the D.P.-reducing step of the invention, for example if the fibre D.P. is about 400.

The titre of the fibre subjected to the degradation step 15 (4 ) ~rcnr~ i ng to the invention may generally be in the ranqe 0.5 to 30 dtex. It has been found that the process of the invention is most effective in increasing the fibrillation tendency of fibres of relatively low titre, for example 1 to 5 dtex or 1 to 3 dtex, perhaps on account of 20 their greater surface to volume ratio.

It has been observed that the f i hri 1 1 ~ti~n tendency of lyocell fibre is directly related to the cP~ se cullu~..LLation of the solution from which it is made. It will be u..d~L~Lo~d that raising the cellulose con~Pntr~tion 25 gPnPr~lly necessitates a reduction in rPll~lloqe D.P. to maintain the viscosity of the solution below the practical maximum working viscosity. The increase in fihrill~tion tendency achievable by use of the process of the invention is gPnPr~lly greater than the increase achievable by raising 30 the cPllnlose co.,r~ Lion of the solution.

Lyocell fibre produced by the process of the invention is useful for example in the manufacture of paper and nonwoven articles, either alone or in blends with other types of fibre, including standard lyocell fibre. A
35 p~p~rr~king slurry containing lyocell fibre produced by the _ _ _ _ _ _ _ . .. . .. . . _ . _ .... _ . ... . . ...

W095/35399 PCTIGB9~l01439 , ~ 2 1 933 7~

process of the invention requires markedly less -hAn;rAl work, for example beating, refining, disintegration or hydrapulping, to reach a chosen degree of freeness than slurry containing standard lyocell fibre. This is a 5 particular advantage of the invention. The process of the invention may reduce the working time required by a high shear device on the resulting fibre to 50 per cent or less, preferably 20 per cent or less, further preferably 10 per cent or less, of that required to achieve a given freeness lO using standard fibre. Nethods which reduce working time to a value in the range from about 20 to about 50 percent, or from about 20 to about 33 percent, of that required ior standard fibre may be preferred. Lyocell fibre produced according to the invention may f i hri 11 Ate in low-shear 15 devices such as hy~rArl-lr~r~, which induce little or no fihri1lAtir,n in conv~ntionAl fibres under usual operating conditions. Lyocell fibre produced according to the process of the invention may have ~nhAnr~d absorbency and wicking properties compared with conv~nti~nAl lyocell fibre, making 20 it useful in the manufacture of Ah50,l.~ articles.

The susceptibility of a fibre to fihrillAtion on ----hAnirAl working may conveniently be assessed by subjecting a dilute slurry of the fibre to -hAni~Al working under standard conditions and measuring the ~rAinAge 25 properties (freeness) of the slurry after various extents of working. The freeness of the slurry falls as the degree of fihrillAtion increases. Prior art lyocell fibre is typically capable of being beaten to ~AnA~iAn Standard Freeness 400, using the Disintegration Test defined hereinafter as Test 30 Method 3, by a number of disintegrator revolutions in the ~ range from about 200,000 to about 250,000 and to rAnA~iAn Standard Freeness 200 by a number of disintegrator revolutions in the range from about 250,000 to about 350,000, although on occasion a greater number of 35 revolutions may be required. The invention further provides lyocell fibre capable of being beaten to CAnA~iAn Standard Freeness ~00 in the Disintegration Test by not more than Wogs/353sg PcT/Gsssl0l439 about 150,000 disintegrator revolutions, in particular by a number of disintegrator revolutions within the range from about 30,000 to about 150,000, often within the range from about 50,000 to about 100,000. The invention yet further 5 provides lyocell fibre capable of being beaten to r~n~ n Standard Ere~n~ss 200 in the ~isLntegration Test by not more than about 200,000 ~;~;n~grator revolutions, in particular by a number of disintegrator revolutions within the range from about 50,000 to about 150,000 or 200,000, often within lO the range from about 75,000 to about 125,000.

Paper made from lyocell fibre according to the invention may be found to have a variety of advantageous properties.
It has g~n~r~lly been found that the opacity of paper cont~ining lyocell fibre increases as the degree of beating 15 is increased. This is opposite to the general experience with paper made from woodpulp. The paper may have high air-pl- ~hility ~r~d with paper made from 100% woodpulp;
this is believed to be a consequence of the generally round cross-section of the lyocell fibres and fibrils. The paper 20 may have good particle-retention when used as a filter.
Blends of lyocell fibre of the invention and woodpulp provide papers with increased opacity, tear strength and air p, -hility compared with 100% woodpulp papers. Relatively long, for example 6 mm long, lyocell fibre may be used in 25 p~r~rr~king compared with conventional woodpulp fibres, yielding paper with good tear strength.

Examples of applications for paper cont~ining lyocell fibre provided ~r~or~ing to the invention include, but are not limited to, capacitor papers, battery separators, 30 stencil papers, papers for filtration including gas, air and smoke filtration and the filtration of liquids such as milk, coffee and other beverages, fuel, oil and blood plasma, security papers, photographic papers, flushable papers and food casing papers, special printing papers and teabags.

It is an advantage of the invention that hydroentangled lV095/35399 PCTIGB95101439 ' ~ r;- -2 ~ 93370 fabrics can be made from lyocell fibre provided according tothe invention at lower entanglement pressures than are required for untreated lyocell fibre for similar fabric properties, at least for short staple lengths (up to about 5 5 or lOmm). This reduces the cost of hydroentanglement.
Alternatively, a greater degree of hydroentanglement can be obtained at a given pressure than with prior art lyocell fibres. A l,ydLoe--Langled fabric made from lyocell fibre provided according to the invention may have better tensile 10 properties than a fabric made from untreated lyocell fibre, although it will be understood that 1~y~Luenl ~ngl ing conditions will need to be optimised by trial and error for the best results in any particular case. A hydroentangled fabric cnnt~ining lyocell fibre provided according to the 15 invention may exhibit high opacity, high particle retention in filtration applications, increased barrier ~nd wetting properties, high opacity, and good properties as a wipe.

r l~s of applications for l,ydLuellLangled fabrics containing lyocell fibre provided according to the invention 20 include, but are not limited to, artificial leather and suede, disposible wipes (inrll7~ing wet, lint-free, clean-room and spectacle wipes) gauzes in~ ing medical gauzes, apparel fabrics, filter fabrics, diskette liners, coverstock, fluid distribution layers or ~hcn~ l covers in 25 absorbent pads, for example diapers, incontinence pads and dressings, surgical and medical barrier fabrics, battery separators, subgtrate8 for coated fabrics and intPrl iningc.

Lyocell fibre provided according to the invention may fihr~ te to some extent during dry processes for .v~"
30 fabric manufacture, for example nPe~lPrllnnhing. Such n~: ~VUII fabrics may exhibit improved filtration PffiriPn~y in -ri con with fabrics containing conventional lyocell fibre.

The fibre provided by the invention is useful in the 35 manufacture of textile articles such as woven or knitted W095/35399 PCT/Gs95/01439 articles, alone or in combination with other types of fibre including prior art lyocell fibre. The presence of the lyocell fibre provided by the invention may be used to provide desirable aesthetic effects such as a peach-skin 5 effect. Fibrillation can be induced in such fabrics by known processes such as brushing and sueding in addition to any f; hri 11 ~tion generated in the wet processing steps normally encountered in fabric manufacture.

Fibre provided ~ecnr~;ng to the invention is useful in the manufacture of teabags, coffee filters and suchlike articles. The fibre may be blended with other fibres in the manufacture of paper and hydroentangled fabrics. The fibre may be blended as a binder with microglass fibre to improve lS the strength of glass fibre paper made therefrom. The fibre may be felted in blend with wool. The fibre may be used in the manufacture of filter boards for the filtration of liquids such as fruit and vegetable juices, wine and beer.
The fibre may be used in the manufacture of filter boards 20 for the filtration of viscous liquids, for example viscose.
The fibre may be made in~o tampons and other absorbent articles with ; ~ d absorbency. Lyocell fibre may f;hr;llate advantageously during dry processing as well as during wet processing, for example during processes such as 25 milling, grinding, sueding, brushing and sanding. Fibrils may be removed from fibrillated lyocell fibre by enzyme finich;ng techniques, for example treatment with c~ cr~c The following proce~1lreS identified as Test Methods l to 4 were used to assess fibre performance:-30 Test Method l - Meas~_ ~ of Cu~ i Solution Viscositv and D.P. (the D.P. Test) This test is based on TAPPI Standard T206 os-63.
C~ 1lose is dissolved in ~,~ inm hydroxide solution containing 15 + O.l g/l copper and 200 + 5 g/l a~mmonia, with 35 nitrous acid content ~ 0.5 gtl, (Shirley Institute standard) ...... = . . .. . ..

'W095/35399 PCTIG~95101439 ~' ~u~ J~ 2193;37o to give a solution of accurately-known cellulose concentration (about 1% by weight). Solution flow time through a Shirley viscometer at 20~C is measured, from which viscosity may be calculated in standard manner. Viscosity-5 average D.P. is det~rmin~d using the empirical equation:
.

D.P. = 412.4285 ln [ lOO(t-k/t) / n.C ] - 348 where t is flow time in seconds, k the gravity constant, C
the tube constant, and n the density of water in g/ml at the t~ _ ~Lure of the test (0.9982 at 20 C).

10 Test Method 2 - Measurement of Fibrillation T. ' y (Sonication) Ten lyocell fibres (20 + 1 mm long) are placed in distilled water (10 ml) contained within a glass phial ~50 mm long x 25 mm ~ r). An ultrasonic probe is inserted 15 into the phial, taking care that the tip of the probe is well-c~ntered and is positioned 5 + 0.5 mm from the bottom of the phial. This distance is critical for reproducibility. The phial is ~uLLuunded with an ice bath, and the ultrA~mnir probe is switched on. After a set time, 20 the probe is switched off, and the fibres are transferred to two drops of water placed on a miu.uscu~e slide. A
photomicrograph is taken under x20 ~-gnifimation of a representative area of the sample. Fibrillation Index (Cf) is assessed by -ri~on with a set of pho~ngrArhic 25 standards graded from 0 (no fil-rillAtion) to 30 (high f~hrillAtion).

Alternatively, Cf may be measured from the photomicrograph using the following formula:

2f = n.x/L

30 where n is the number of fibrils counted, x is the average length of the fibrils in mm, and L is the length in mm of woss/3s399 _ _ ____ _ PCT/GB95l01439 3~ 2~ 9337~ --fibre along which fibrils are counted.

The ultrasonic power level and sonication time (5-15 minutes, standard 8 minutes) required may vary. The calibr~tion of the equipment should be checked using a 5 sample of fibre of known fibrillation tendency (Cf 4-5 by Test Method 2) before use and between every group of ~ive samples.

Test Method 3 - Mea~G ~ of Fibrillation T_ ' ~ (The D'ls~n~-~ratlon Test~

Lyocell fibre (6 g, staple length 5mm) andf;f~m;n~rAl;cf~d water (2 1) are placed in the bowl of the standard disintegrator described in T~PPI Standard T-205 om-88, ~lnd disintegrated (simulating valley beating) until the fibre is well-dispersed. Suitable disintegrators are available from 15 Messmer In~Ll, ~s Limited, Gravesend, Rent, UR and from B~chel van de Korput BV, V~ ~1, Neth~rl~n~c. The f~An~ n Standard Freeness (CSF) of the fibre in the resultlng slurry or stock is measured according to TAPPI
Standard T227 om-94 and recorded in ml. In general, the 20 stock is divided into two 1 1 portions for mea~ul, ~ of CSF and the two results are averaged. Curves of CSF against disintegrator revolutions or disintegration time may then be prepared and the relative degree of disintegration required to reach a given CSF assessed by interpolation. The zero 25 point is defined as that lef~ d~d after 2500 ~;c;ntf~grator revolutions, which serve to ensure dispersion of the fibre in the stock before CSF measurement.

Test Nethod 2 is quick to perform, but it may give variable results because of the small fibre sample. Test 30 Method 3 gives very reproducible results. These factors should be taken into account during assessment of f; hri 11 ~tion tendency.

W095/35399 r~ 01439 Test Method 4 _ T' - ~ L of Fibri~ ion I.~den~Y
(Valley seatinq) Lyocell fibre is tested by beating in accordance with TAPPI data sheet T 200 om-85 except that a stock consistency 5 of 0.9% is used. The beater used is preferably one dedicated to the testing of lyocell fibres. Results are best treated as comparative within each series of r~Yr~r i ~: .

Brief DescriPtion of the Drawinqs Figures 1 and 2 are graphs of the C~n~ n Standard Freeness, expressed in ml, (y-axis) against the beating time, expressed in min, (x-axis) for the samples in ry~mrl~c 1 and 2, respectively.

Eigures 3, 4 and 5 are graphs of the ~n~ n Standard 15 Freeness, expressed in ml, (y-axis) against the number of disintDgr~tor revolution, expresed in thousands of revolutions, (x-axis) for the samples in r lr~ 3, 4 and 5, respectively.

Figures 6 and 7 are grAphs of the ~An~ n Standard 20 Freeness, expressed in ml, (y-axis) against the beating time, expressed in min, (x-axis) for the samples in r 1 7 and 8, respectively.

Figure 8 is a graph of beating time required to achieve C~n~rii~n Standard Ereeness 200, expressed in min, (y-axis) 25 against Fibre D.P. (x-axis) for the samples in Example 9.

The invention is illustrated by the following r ,lr~s, in whlch lyocell fibre was prepared in known manner by spinning a solution of woodpulp cellulose in aqueous N-methylmorpholine N-oxide:-W O95/35399 PCTIGB9~101439 t r ~ 2 1 9 3 3 7 ~ ~

Example 1 Never-dried lyocell fibre tow (1.7 dtex ecru, 300 g samples) was saturated with an aqueous solution containing either hydl~y~n peroxide (1% by volume) or sodium 5 hypochlorite (1% by weight available chlorine), and in both cases sodium hydroxide (0.5~ by weight), and placed in a steamer. The steaming cycle was heating over 7 min., llO C
for 1 min., and cooling under vacuum over 4 min. The steamed fibre was washed and dried, and exhibited the properties 10 shown in Table l:

Table 1 Rc~. D.P. C~ dtex ADT ADE ~ WT WE
cN/tex c~/tex 15 Untrcated 1~ 563 0-2 1.76 40.613.5 36.7 16.0 Peroxidc lB 299 S-15 1~76 34.811.1 23.7 11.6 ~ypn~hl ~rl ~
lC 92 20-30 1.7823.8 6.8 18.0 8.8 (D.P. was measured by Test Method 1. ~ihrillAtinn tendency (Cf) was measured by Test ~ethod 2. ADT = air-dry tenacity, AD~ = air-dry extensibility, WT = wet tenacity, WE = wet extensibility.) The fibre was hand-cut to 5 mm staple, formed lnto a web (n~ in~lly 60 g/m2), and subjected to hydroentanglement using various jet ~s~ Ul~S ~measured in bar). The hy~oellLangled nonwoven lyocell fabric so obtained exhibited the properties shown in Table 2:

'WO 95/35399 PCT1GB95101439 Q ~ 17 - 2 t 9 33 7 0 Table 2 P~f Jet Breaking 1Oad (daN) OVera11 tenaCitY
bar ~.D. ~.D. C.D. C.D. (da~/g) drY Wet drY Wet drY Wet .

5 Untreated 1A 100 3.56 2.54 4.63 2.75 4.13 2.65 160 3.84 3.25 3.74 4.01 3.79 3.65 200 3.48 3.16 PerOXide 1D 75 2.77 1.07 2.63 1.51 3.60 1.75 100 5.00 3.32 3.51 3.55 5.76 4.56 10 UYrn~h1nr;~ 1C 75 4.77 1.12 3.34 - 5.49 100 5.06 1.96 4.44 1.92 4.76 1.94 160 4.24 1.46 2.40 1.08 3.45 1.28 (M.D. = machine direction, C.D. = cross directionj The treated fibre could be converted into ~ LLUI;~1 15 hydroentangled no,..-v~ fabric than the untreated control under suitable conditions. Notably, several fabrics made from treated fibre exhibited higher overall dry tenacity than any of the controls. This is L~ -r~hle in that the treated fibre had inferior tensile properties to the 20 untreated fibre.

The lyocell staple fibre was slnrri~d at stock consistency 0.9% and subjected to valley beating using Test Method 4.
The relat~r~hir between the CSF of the stock and the beating time is shown in Figure l and Table 3. It can be 25 seen that much shorter beating times were required to reach the same degree of freeness with treated than with untreated fibre.

Table 3 Sample Ref.Beating time min. to reach Untreated lA 226 155 Peroxide ls llO 85 ~ypochlorite lC 46 29 WO 95/3S399 _ PCT/GB95/01439 EYamP1e 2 Never-dried lyocell tow (1.7 dtex ecru) was treated as follows: -2A. Untreated control.
2B. On-line bleaching, sodium hypochlorite solution (1%
by weight available chlorine) at 50~C, bath residence time 4 sec, followed by steaming in a tunnel (100~C steam) for 25 sec.
2C. As 2B, but bath residence time 7 sec. and steaming time 50 sec.
2D. As 2B, but off-line, bath residence time 60 sec.
and steaming as described in Example 1.
2E. As 2D, but 2% by weight available rhl nrinP .
2F. As 2D, but using hydrogen peroxide solntinn (1~ by weight).

The treated fibre was washed and dried and cut into 5 mm staple.

The lyocell staple fibre was slurried at stock consistency 0.9~ and subjected to valley beating using Test Method 4.
20 The relatinn~hip between the CSF of the stock and the beating time is shown in Figure 2 and Table 4. It can be seen that much shorter beating times were required to reach the same degree of frepn~ss with treated than with untreated fibre.
Table 4 3eating time min to reach Sample 200 CSF 400 CSF

PCTiGI~95/~ 143g Beaten slurries of samples 2A-2E were made into paper.
The physical properties of all the samples (tear strength, burst index, tensile strength and bulk) were very similar.

The cut staple was formed into webs and hydroentangled as S ~srr;h~d in Example 1 (jet pressure 100 bar). The samples of fabric so obtained had the properties shown in Table 5:

~able S

Fibre Fibre Overall fabric tenacity N~g D.P. tenacity C~/tex Dry Wet 10 2A 524 43.2 18.6 27.9 2B 227 40.9 41.7 62.4 2C 206 36.1 35.2 69.9 2D 159 34.7 45.5 79.6 2E 40 23.3 18.5 49.3 Exam~le 3 Example 2 was repeated, except that the following treatment conditions were used:
3A As 2A.
3B On-line, nitric acid solution (0.72~ by weight concentrated nitric acid) at 50~C, bath r~si~nre time 4 sec, followed by steaming (25 sec).
3C As 3B, but 2.8% nitric acid.
3D As 3B, but 4.25~ nitric acid.

The treated fibre was washed and dried and cut into 5 mm 25 staple. The lyocell staple fibre was suhjected to disintegration using Test Method 3. The r~l~ti~n~ip between the CSF of the stock and the beating time is shown in Figure 3 and Table 6. It can be seen that shorter beating times were required to reach the same degree of freeness with 30 treated than with untreated fibre.

woss/3s3ss PcT/Gsss/0l439 ~ t~;; 2 1 9 3 3 7 0 ~able 6 Disintegration rev. xlOOO to reach Sample 200 CSF 400 CSF

Exam~le 4 Example 2 was repeated, except that~ the following 10 treatment conditions were used:
4A Untreated control.
4B Off-line, sodium hypochlorite solution (0.5~ by weight available chlorine) at 50~C, bath residence time 60 seconds, no steaming.
154C As 4B, except that the treatment bath additionally co~tAin~d 15 g/l sodium birArh~nAte (pH 8.5). No steaming was used.
4D As 4B, except that the treatment bath additionally contained 15 g/l sodium dihydrogen phosphate (pH
206.8). ~No steaming was used.
4E As 4s, except that the treatment bath additionally contained 7.5 g/l citric acid and 7.5 g/l sodium dihy~lvyen citrate (pH 5.5). No steaming was used.
4F As 2D.

25The treated fibre was washed and dried and cut into 5 mm staple. The lyocell staple fibre was assessed using Test Method 3. The relationship between the CSF of the stock and the beating time is shown in Figure 4 and Table 7. It can be seen that the addition of hirArhonAte or phosphate buffer 30 reduced the beating time required to reach any particular degree of freeness.

W095~5399 r~ r0l439 s 21:93370 Table 7 Disintegration rev. xlO00 to reach Sample 200 CSF 400 CSF

5 4s 254 221 ~xam~le S

Example 2 was repeated, except that the following treatment conditions were used:

SA Untreated control.
5B Hydrogen peroxide solution (1.0% by weight) at 50~C, on-line at line speed 6 m~min (bath residence 7 sec), followed by steaming for 50 seconds.
5C As 5B, except that the treatment bath additionally cnnt~;nr~d 0.5~ by weight sodium hydroxide.
5D As 5C, except that the treatment bath contained sodium hypor~l nri te (1% by weight available n~lnrinr~) instead of hy~lOy_ll peroxide.

The treated fibre was washed and dried and cut into 5 mm staple. The lyocell staple fibre was assessed using Test ~ethod 3. The relar;nn~ir between the CSF of the stock and 25 disintegrator revolutions is shown in Figure 5 and Table 8.
It ca~ be seen that addition of sodium hydroxide reduced the beating time required to reach any particular degree of freeness when hydrogen peroxide was employed as bl e~rh i nrJ
agent.

W095/35399 pcTGs95lol439 Table 8 Disinteyration re~. x lO00 to reach Sample 200 CSF 400 CSF

ExamPle 6 Lyocell fibre was bleached using the treatment 10 bath liquors d~A~rihed in Example 4 under reference codes 4B, 4C, 4D and 4E at 25 and 50~C. The results shown in Table 9 were obtained:

Table 9 Liquor Temp ~C pH D.P. dtex Tenacity ~Yt~nAi~n cN/tex None - - 548 2.0 37.7 15 4B 25 11.46 524 1.9 37.7 15 4B 50 10.71 406 l.9 37.1 14 4C 25 8.65 489 1.8 35.9 14 20 4C 50 8.64 376 1.8 33.4 13 4D 25 6.73 298 2.0 28.7 10 4D 50 6.69 308 1.9 24.7 7 4E 25 5.67 526 1.9 37.8 14 The samples treated at 50 C were those of Example 4.

ExamPle 7 An nnri~_ ed solution of cell..1ose in aqueous N-methylmorpholine N-oxide was extruded through a plurality of spinnerettes (spinning speed 37 m/min) and washed with water. The titre of the individual fil~ ~ A was 1.7 dtex 30 and the titre of the c~ ~in~d tow was 64 ktex. The tow was then passed firstly through a bath containing aqueous sodium hypochlorite solution (temperature 76-80~C, steam sparges, . . _ ~

WO95/35399 PCT~GB95iOI439 ,r~ 21 q3370 residence time 60 sec) and secondly through a circulating bath to which sulphuric acid was continuously added (temperature 67~C, pH 8, resi~nre time approx 5 sec). The tow was then washed with cold water and dried. The 5 fihr;ll~tinn tendency of the fibre was assessed by Test Nethod 4. Hypochlorite cuncel.Ll~tion in the treatment bath and experimental results are shown in Figure 6 and Table 10.

Table 10 Ref. Avallable chlorine Beating time min. to reach 0 ~ by weight 400 CSF200 CSF
7A Control 187 240 73 0.2 153 204 7C 0.3 120 170 7D 0.47 109 Example 3 Example 7 was repeated, except that matt fibre (pi~3 L~d with titanium dioxide) was used. IIyporhlnrite c~l.c~nLl~tion in the treatment bath and r~rrri- ~1 results are shown in Figure 7 and Table 11.

Table 11 Ref. Available r~lnrinr Beating time min. to reach % by weight400 CSF 200 CSF
8A Control 143 197 8B 0.2 122 174 25 8C 0.45 114 167 8D 0.65 87 126 Example 9 Lyocell fibre was ~gra~rd according to the invention under various conditions, and its D.P. and beating 30 performance assessed using Test Nethods 1 and 4 ~095/35399 PCT/GB95/01439 respectively. The relationship between the beating tLme to 200 CSF and the fibre D.P. is shown in Figure 8. (The data plotted with a cross are factory trials and the data plotted with a filled square are laboratory trials.) The three 5 samples with D.P. above 500 are untreated controls.

Example lO

Lyocell fibre was spun from a solution in aqueous N-methylmorpholine N-oxide of "V;~r~kra~t~' (Trade Nark of International Paper Co., USA) pulp of nominal D.P. 600 with 10 nominal c~ lose concentration 15~, washed, saturated with solutions of various reagents (bath t~ ,~ aLuLt 50~C, residence time 60 seconds), steamed in the manner of Example 1 for 60 seconds, and dried. The D.P. and Fibrillation Index C~ of the fibre were assessed by Test Nethods 1 and 2. The 15 results shown in Table 12 were obtained:
Table 12 Re~gents Stea~ t~mp~C D.P. Cr Untreated control - 565 1.3 8erles 1 20 o.s% NaOH 110 567 0.7 O.05~ NaOCl 110 548 2.1 0.25~ NaOC1 110 427 1.8 O.5% NaOCl 110 306 3.7 1.0% NaOCl 110 .178ll.C
25 2.0% NaOCl 110 44 30.0 Seri-s 2 1.0% NaOC1 + 0.5% NaO~ - 508 1.1 Beries 3 1.0~ NaOCl + 0.5% NaO~ 100-120 169-176 8.7-11.0 30 1.05 NaOC1 + 0.05% NaO~ 110 109 20.3 1.0~ NaOC1 + 0.25% NaO~ 110 139 18.4 1.0~ NaOC1 + O.S~ NaO~ 110 155 20.0 1.0% NaOC1 + 1.0% NaOE 110 168 15.1 1.0% NaOC1 + 2.0% NaO~ 110 194 7.3 PCTIG~95101439 ? 5~ 1 9 3 3 7 0 NaOCl concentration is expressed in terms of per cent by weight of available chlorine. NaOH concentration is expressed in terms of per cent by weight. It will be observed that the bleached samples of low D.P. had markedly 5 higher fihril1~tion indices than any of the nnhlr~rh~d samples. It will also be recognised that solutions of c~lllllnse whose D.P. is below about 200 cannot readily be spun into fibre by solvent-spinning processes.

ExamPle 11 Never-dried lyocell tow was passed through a bleach bath containing 0.5% by weight NaOH and a hl~rhing agent, steamed (steam temperature 100~C), washed and dried. The D.P. and Fibrillation Index C, of the dried fibre were assessed. ~Yp~ri Lal cnn~1tinnf. and results are shown in 15 Table 13, Cf being quoted as the observed range between i f f~r~nt photographs.

Table 13 Bleach Bath Steaming Time D.P. Cf Agent Temp~C Time sec sec Control - - - 532 1-2 1.0% H2O~ 60 50 25 426 3-5 1.11% NaOCl 40 50 50 205 4-12 1.11% NaOCl 40 25 25 249 2-8 1.10% NaOCl 60 50 50 203 4-16 1.10% NaOCl 60 25 25 227 7-14 0.98% NaOCl 70 50 50 221 4-10 0.98% NaOCl 70 25 25 251 2-10 1.00~ NaOCl 60 50 25 235 6-8 (% NaOCl is % by weight available chlorine, % H20. is ~ by weight) An appreciable increase in f i hri 1 1 ~tion tendency was observed in all cases.

Example 12 Previously-dried 1.7 dtex 5 mm bright lyocell fibre (200 kg) was bleached in aqueous sodium hypochlorite (3 g/l available chlorine) at 40°C for 75 minutes, soaked in aqueous sodium metabisulphite (1 g/l) as antichlor for 30 minutes, washed with dilute acetic acid to return fibre pH
to neutral, and dried. The nominal D.P. of the cellulose from which the fibre was made was 600 and the average D.P.
of the treated fibre was 217 (range 177-230, six samples).
Disintegration Test results for the treated sample and for an untreated control sample are shown in Table 14.

Table 14 Disintegrator revolutions 0 100,000 150,000 Control sample CSF 650 620 510 Treated sample CSF 656 400 80 Example 13 A 8 ktex tow of never-dried 1.7 dtex lyocell fibre was passed through a first aqueous bath containing copper (II) sulphate (0.1% w/w) and a second aqueous bath containing hydrogen peroxide (4% w/w) and sodium hydroxide (0.5% w/w). The temperature of each bath was 20-25% °C, and the residence times in the baths were 10 and 131 seconds respectively. The tow was then passed through a steam tunnel at 100°C with residence time 120 seconds, rinsed and dried.
A sample treated as above, but with the omission of the copper sulphate bath, and an untreated control sample were also prepared. Disintegration Test results are given in Table 15.

~~ 95135399 - - - PCTIGP95I0l439 ~ 27 - 3 7 ~
Table 15 Dicint~r~t~r revolutions x 1000 0 50 75 100 175 200 ~ntreated ~ontrol sample CSF697 - - 672 - 611 Treated sample (no CuS04)715 - - 491 66 Treated sample (with CuS04)702335 124 A dash indicates that no mea~uL, L was made.

FYA~le 14 A 5.3 ktex tow of 1.7 dtex bright lyocell fibre was passed through an aqueous bath c~nt~ining sodium hypoe~lorite (17-20 C, residence time 42 sec.), next through a steam tunnel (100 C, residence time 120 sec.), rinsed and dried. Fibrillation tendency was measured by Test ~ethod 3 on fibre cut to 5 mm staple, and the number of disintegrator revolutions (in thousands, krev) required to reach 200 CSF
estimated by graphical interpolation. Other ~Yp~ri details and results are shown in Table 16.

Table 16 Bath D.P. dtex Tenacity ~xtcnsion krev to cN/tex ~ 200 CSF

None (control) 5331.88 36.2 11 307 0.1~ A.Cl 4291.85 36.7 11 228 0.3~ A.Cl 3411.69 37.3 11 190 1.0~ A.Cl 1541.68 34.1 1 100 2.0~ A.Cl 49 1.91 22.0 6 61 1.0~ A.Cl + 0.5~ NaO~ 2421.80 37.0 12 140 (A.Cl = available chlorine, ~ ~ per cent by weight) Exam~le 15 A 10.6 ktex tow of 1.7 dtex bright lyocell fibre was passed through an aqueous bath c~nt~ining sodium W095/35399 _ _ ___PCTGB9~!01439 2 1 933 7~ --hypochlorite (16-18-C, residence time 132 sec.), next through a steam tunnel (100-C, residence time 120 sec.), rinsed and dried. Eibrillation tendency was measured as described in Example 14. Other experimental details and results are shown in Table 17.
Table 17 Bath D.P. krev to 2D0 CSF
None (control)501 341 0.5~ H2O~ + 0.5~ NaOH 180 123 1.0% H2O2 + 0.5% NaOH 158 113 2.0% H2Oz + 0.5% NaOH 156 117 3.0% H2O~ + 0.5% NaOH 147 113 4.0% H2O2 + 0.5% NaOH 120 87 (% ~ per cent by weight) Exam~le 16 Never-dried bright lyocell tow (various fibre titres, i.e. dtex) was soaked in an aqueous solution containing sodium hypo~hl~rite ~1% by weight available ~hl~rinG) and sodium hydroxide (0.5% by weight), steamed for 1 minute as ~ rihed in Example 1, washed, dried and cut to 5 mm s~aple lenyth. The D.P. and fihrill~tion tendency (Test Method 3) of the treated fibre and of untreated control samples are reported in Table 18.
~able 18 Fibre Control Treated dtex D.P. CSF D.P. CSF
0 rev 100 krev 0 rev 100 krev 1.7 530 685 656 136 658 179 2.4 540 698 673 140 695 413 3.4 557 705 696 136 705 560 _ =

WOgS/35399 r~ 3~/0~439 ~ ~ ¢ ~ 29 - 2 i 9 3 3 7 0 Exam~le 17 Never-dried bright lyocell tow (1.7 dtex/fili L, 15.4 ktex total) was passed at 6.4 m/min through an application bath containing 4% by weight hY~LIJY~II peroxide and 0.5% by weight sodium hydroxide (t~.~eL~wL~ 17-19 C, residence time 125-130 sec.), then through a steam tunnel (lOO C, residence time 120 sec.), washed and dried. The washing step optionally included a wash with 2% by weight hydrochloric acid. The fibrillation properties of the fibre and of an untreated control (measured by the Disintegration Test) are reported in Table 19.
2able 19 krev to 400 CSP krev to 200 CSF

Control 185 235 Treated (12 samples)75-100 95-120

Claims (17)

1. A process for the manufacture of lyocell fibre with an increased tendency to fibrillation, including the steps of:
(1) dissolving cellulose in a solvent to form a solution, (2) extruding the solution through a die to form a plurality of filaments, and (3) washing the solution to remove the solvent, thereby forming lyocell fibre, characterised by the step of (4) subjecting the lyocell fibre to conditions effective to reduce the Degree of Polymerisation of the cellulose by at least about 200 units.

2. A process according to claim 1, characterised in that the solvent comprises a tertiary amine N-oxide.

3. A process according to claim 2, characterised in that the tertiary amine N-oxide is N-methylmorpholine N-oxide.

4. A process according to any preceding claim, characterised in that the Degree of Polymerisation of the cellulose is reduced in step (4) by at least about 300 units.

5. A process according to any preceding claim, characterised in that the Degree of Polymerisation of the cellulose after step (4) is below about 250 units.

6. A process according to any preceding claim, characterised in that the Degree of Polymerisation is reduced in step (4) by a bleaching treatment.

7. A process according to claim 6, characterised in that the bleaching treatment comprises applying to the fibre a bleaching liquor which is an aqueous solution comprising sodium hypochlorite.

8. A process according to claim 7, characterised in that the concentration of sodium hypochlorite in the bleaching liquor expressed as available chlorine is in the range 0.5 to 2.0 percent by weight.

9. A process according to claim 6, characterised in that the bleaching treatment comprises applying to the fibre a bleaching liquor which is an aqueous solution comprising hydrogen peroxide.

10. A process according to any preceding claim, characterised in that step (4) is performed on never-dried lyocell fibre.

11. A process according to any one of claims 1 to 9, characterised in that step (4) is performed on previously-dried lyocell fibre.

12. Paper comprising lyocell fibre, characterised in that at least some of the lyocell fibre has been manufactured by the process of any one of claims 1 to 11.

13. Hydroentangled fabric comprising lyocell fibre, characterised in that at least some of the lyocell fibre has been manufactured by the process of any one of claims 1 to 11.

14. Lyocell fibre, characterised in that it is capable of being beaten to Canadian Standard Freeness 400 in the Disintegration Test by a number of disintegrator revolutions in the range from about 30,000 to about 150,000.

15. Lyocell fibre according to claim 14, characterised in that it is capable of being beaten to Canadian Standard Freeness 400 in the Disintegration Test by a number of disintegrator revolutions in the range from about 50,000 to about 100,000.

16. Lyocell fibre, characterised in that it is capable of being beaten to Canadian Standard Freeness 200 in the Disintegration Test by a number of disintegrator revolutions in the range from about 50,000 to about 200,000.

17. Lyocell fibre according to claim 16, characterised in that it is capable of being beaten to Canadian Standard Freeness 200 in the Disintegration Test by a number of disintegrator revolutions in the range from about 75,000 to about 125,000.