WO1997023669A1

WO1997023669A1 - Filaments and fibers

Info

Publication number: WO1997023669A1
Application number: PCT/GB1996/003183
Authority: WO
Inventors: Roger Norman Ibbett
Original assignee: Courtaulds Fibres (Holdings) Limited
Priority date: 1995-12-21
Filing date: 1996-12-20
Publication date: 1997-07-03
Also published as: TW353115B; AU1166497A

Abstract

A method is disclosed of reducing fibrillation tendency by providing a skin/core structure to a lyocell filament spun from a solution of cellulose in an amine oxide solvent. Such structure is achieved by passing the filament through a regeneration bath containing a solution containing at least 60 % w/w amine oxide (preferably N-methylmorpholine-N-oxide), and thereafter washing the filament in an aqueous medium (for example water, or a relatively dilute amine oxide solution). The relative degrees of crystallinity of the skin and core elements of the filament may be controlled by varying the concentration of the amine oxide solution, the temperature of the solution and/or the residence time of the filament in the solution, and it is preferred that the skin has a lower degree of crystallinity than the core. Various different embodiments of apparatus for carrying out the method of the invention are also disclosed. In each case, the apparatus comprises filament regeneration means including means for providing a flow of high concentration amine oxide solution, the path of the filament through the apparatus being parallel with at least a portion of the liquid flow path.

Description

FILAMENTS AND FIBERS

This invention concerns lyocell filaments and fibers having resistance to wet abrasion and/or surface fibrillation.

Lyocell filaments and fibers are produced by dissolving cellulose in a suitable solvent such as tertiary amine N- oxide mixed with water. A suitable method of manufacture is described in US-A-4, 416, 698 (McCorsley) . The solution of cellulose in an amine oxide solvent is spun into a regeneration bath and the amine oxide solvent leached into water or dilute aqueous amine oxides to produce a cellulose filament which can then be cut into fibers. Filaments produced by this method have a fibrillar morphology throughout, and they are susceptible to wet abrasion and/or surface fibrillation. In some end uses surface fibrillation is desired, for example in producing fabric having a particular appearance and feel resulting from the fibrillation, or in producing fabric having high absorbency for liquids. However, in some cases, fibrillation can be an undesirable characteristic.

It has been proposed hitherto to reduce the tendency of lyocell filaments to fibrillate by effecting chemical cross¬ linking of at least the outer surface of the filaments. Such a process has the disadvantages of requiring complex equipment, and the use of an expensive additional reagent to effect the cross-linking. Another method of reducing surface fibrillation of lyocell fibers involves passing the spun filaments through a long and highly humid air gap before passing them into the aqueous bath. However, this results in uneconomic reductions in line speed. A further method involves redissolution of the fiber surface in a hot bath of the amine oxide or some other solvent or annealing agent, but this method suffers from the disadvantage that the tensile properties of the filaments are seriously reduced by the treatment process.

The present invention seeks to provide a method of reducing fibrillation and does so by controlling the crystal morphology of the lyocell filament.

According to the present invention, in the manufacture o_f a cellulose body from a solution of cellulose, the crystal morphology of the body is controlled through the concentration of solvent in the regeneration solution.

There is also provided a method of making a lyocell filament in which the filament iε spun from cellulose dissolved in an amine oxide solvent and is provided w th a skin/core structure by passing the filament through a regeneration bath containing an aqueous solution of amine oxide containing at least 60% by weight of an amine oxide, and thereafter washing the filament in an aqueous medium.

Preferably the filament is given a skin of lower crystallinity than the core of the filament.

Passing the spun filament into a relatively concentrated solution of amine oxide in water results in the filament skin having a lower degree of crystallinity than that of the filament core, the subsequent passage of the filament into a relatively low concentration of amine oxide in water serving to produce a crystalline filament core.

The concentration of amine oxide in the relatively concentrated solution, the temperature of the solution, and the residence time of the filaments in the solution, can all affect the structure of the resulting filaments, and more particularly they may affect the relative proportions of the skin and core in the filaments after processing. Higher concentrations of amine oxide often require higher temperatures to be used in order to avoid crystallisation of the amine oxide. Increasing bath temperature tends to lead to the skin layer becoming a relatively greater proportion of the filaments, and also to a less well defined skin/core boundary. Increased residence times also tend to lead to an increase in the skin layer thickness. Using the preferred amine oxide solvent, N- methylmorpholine-N-oxide, the preferred concentration for the relatively highly concentrated solution is at least 60% w/w in water, and more preferably at least 67% w/w, in order 5 to achieve a desired degree of skin/core differentiation in the filaments. It is generally preferred that the concentration of the preferred amine oxide in the relatively highly concentrated solution is not more than 75% w/w, and more preferably not more than 72% w/w.

10 The temperature of the relatively highly concentrated solution of amine oxide will usually be in the range 35 to 45"C.

The residence time of the filaments in the relatively highly concentrated solution is preferably less than 15 600msec, and more preferably lesε than 300msec. However, residence times of at least 100msec will usually be uεed in order to produce a sufficiently thick skin layer.

In order to terminate formation of the skin layer, the filaments are subjected to a treatment with a relatively 0 dilute solution of the amine oxide in water. The concentration for this treatment is preferably less than 25% w/w, and more preferably less than 20% w/w.

Once the filaments have been treated with the relatively dilute solution of the amine oxide in water, they 5 can be processed further in a similar manner to that proposed hitherto for lyocell filaments. For example, they can be washed, dried and cut into staple fibers and/or subjected to a crimping operation.

It is generally preferred that the spun filament is 0 passed through an air gap before entering the relatively highly concentrated solution of amine oxide in water.

According to another aspect of the invention there is provided a lyocell filament in which the filament has a skin having a different physical structure to the core of the filamen .

The skin/core structures can be viewed optically using, for example, transmission electron microscopy on dyed or stained fiber.

Preferably the core has a higher degree of crystallinity than the skin.

The difference in the degree of crystallinity of the cellulose of the skin and the core of the filaments results in the skin layer of the filaments being resistant to abrasion when wet and also being resistant to fibrillation when being processed, for example to form staple fibers.

It is generally preferred that the cellulose of the skin layer is substantially non-crystalline in order to achieve high resistance to wet abrasion and fibrillation. The difference in the degree of crystallinity of the skin and the core of the filaments is usually associated with a difference in the orientation of the filaments in the skin and in the core, the skin usually having a lower degree of orientation than the core.

Filaments in accordance with the present invention can be cut to form fibers using known methods, and fibers having, for example, crimp can be produced by known methods for producing crimp in hitherto proposed lyocell fibers. Filaments and fibers in accordance with the present invention can be processed to form other products therefrom, for example woven and non-woven textiles.

According to yet another aspect of the present invention there is provided apparatus for the production of a lyocell filament having a skin/core structure, the apparatus including filament regeneration means through which spun filament passes in operation, the filament regeneration means including means for providing a liquid flow of a high concentration amine oxide solution in water, the apparatus being arranged so that, in operation, the filament path through the regeneration means is substantially parallel with at least a portion of the liquid flow path.

Preferably the apparatus includes an aqueous wash means which utilises water or a dilute solution of amine oxide in water.

Embodiments of the invention will now be described by way of example only, and with reference to the accompanying illustrations in which:-

Figure 1 is a photograph, taken under high magnification, of a high crystallinity lyocell fiber after fibrillation,-

Figure 2 is a photograph, taken under high magnification, of a lyocell fiber according to the present invention, after fibrillation;

Figure 3 is a graph of percentage crystallinity in lyocell versus percentage amine oxide concentration in water in the regeneration means;

Figure 4 shows Infra-red ATR Absorbance Spectra for standard lyocell and for lyocell according to the present invention;

Figures 5A and 5B are solid state ¹³C CP/MAS/NMR Spectra for, respectively, standard lyocell and lyocell according to the present invention;

Figure 6 is a first embodiment of apparatus for the manufacture of lyocell according to the present invention;

Figure 7 is a second embodiment of apparatus for the manufacture of lyocell according to the present invention,- Figure 8 is a third embodiment of apparatus for the manufacture of lyocell also according to the present invention,- and

Figure 9 is an X-ray scattering curve of a sample of lyocell, showing the method by which the degree of crystallinity is assessed.

Various embodiments of apparatus for producing lyocell filaments in accordance with the present invention will now be described with reference to Figures 6 to 8 the accompanying diagrammatic drawings.

Referring to Figure 6, a flume of relatively highly concentrated solution of the amine oxide m water (70% w/w) is created in an inclined trough 55 by feeding the solution at a high flow rate trough conduits 56 into an upper region of the trough 55, the trough 55 being inclined at an angle A of approximately 30' to the horizontal.

As described in WO 94/28212 a cellulose solution or dope including 15% w/w of cellulose, 76% w/w N- methylmorpholine-N-oxide and 9% w/w water is forced under pressure through a spmnerette 51. The cellulose has a degree of polymerisation of between 400 and 1000. The dope forms a multi-filament tow 52 which first passes through a minimal air gap 53 and then into the flume in the inclined trough 55, the tow 52 being kept in contact with the relatively highly concentrated solution as it is passed down the trough 55.

At a position approximately half way down the length of the trough 55, a flow of water is introduced nto the trough 55 from a conduit 57 to dilute the aqueous solution of amine oxide entering the trough from the conduit 56. The position of entry of the flow of water from the conduit 57, and the rate of flow of water entering via the conduit 57, control the period of residence of the tow 52 in the relatively highly concentrated amine oxide solution. The flow of water dilutes the relatively highly concentrated amine oxide solution to a concentration of less than 20% w/w in water.

The tow 52 is then passed around a roller 54, and it is thereafter treated in conventional manner as if it were a tow of conventional lyocell filaments.

The tow 52 tends to be relatively weak when compared with filament tows produced by pulling extruded solutions of cellulose in amine oxide solvents through an air gap and then into a bath of water of a relatively dilute solution of amine oxide in water. However, it is under these latter conditions that lyocell filaments are produced which have a tendency to fibrillate.

With reference now to Figure 7, there is illustrated a second apparatus for producing lyocell filaments in accordance with the present invention. As before, a solution of cellulose in an amine oxide solvent is forced through a spinnerette 61 to form a multi-filament tow 62 which passes through a minimal air gap 63 (2-10 cm) into a regeneration means 65. The regeneration means 65 is in the form of a conical shaped bath which is constantly fed through inlet port 66 with fresh highly concentrated solution of 70% w/w amine oxide (N-methylmorpholine-N-oxide) in water. The bath 65 has an overflow port 68 at the upper end.

The filament tow 62 extends down through the bath to emerge through a lower exit port 69 at the lower apex of the conical bath 65. There will of course be some leakage of amine oxide solution from around the tow 62 so that there is a flow of amine oxide from upper regions of the bath out through the exit port 69. Thiε flow of solution is parallel with the direction of movement of the filament tow 62.

A typical residence time for the filament tow aε it passes through the bath 65 may be 200-300msecs, preferably 240 msecs. On emerging from the bath the tow 62 passes through an aqueous wash 67 which may be water, or a weak solution of amine oxide in water, which is jetted onto the tow 62 through a nozzle 60 as the tow is wound over a take- up roller 64. The wash from liquid flowing from the roller 64 can pass to a drain or into a reservoir in which the roller 64 is partially immersed.

Now with reference to Figure 8, the solution of cellulose in amine oxide is forced through an elongate spinnerette 71 to form a multi-filament tow band 72. The filaments "2 pass through a minimal air gap 73 and then pass into a cascade 75 of liquid comprising a highly concentrated solution of amine oxide in water. The liquid cascade 75 is provided by a pair of elongate jets 76, arranged one on each side of the tow band 72 and through which the solution is jetted onto the tow band. The liquid is held by the tow band and runs down the band which is also moving down towards a plate 70 with a slot gap 79 therein. The tow band 72 passes through the plate 70 and the high concentration solution is removed for recirculation. The tow band is then washed by a curtain 77 of water jetted onto one side of the tow band through an elongate jet 78. A portion 74 of the plate 70 is turned downwardly to provide a splash surface for the wash liquid so that water rebounds onto the reverse surface of the tow band 72.

The following Examples of producing filaments in accordance with the present invention will now be given by way of illustration only.

A series of filament tows was produced using apparatus illustrated in Figure 6 with a 15% w/w solution of cellulose in N-methylmorpholine-N-oxide solvent (as described above) being extruded through the spinnerette 51. The tows 52 were then fed through the air gap 53 into the trough 55, and various treatment liquids were fed into the trough 55 via the conduit 56.

Depending on the particular filament being produced, water was fed into the trough 55 at various positions along its length, thereby altering the residence time of the _filament m the upper zone of the trough 55. No water was introduced via the conduit 57 in those tests where the filament tow 52 was passed directly into water fed via the conduit 56.

Samples produced according to this method are numbered 1-9 in Table 1. Sample 10 was produced using the apparatus shown in Figure 7, and sample 11 was produced using the apparatus of Figure 8. The fiber samples produced were washed and dried and subjected to physical tests the results of which are presented in Table 2.

TABLE 1

Spinning conditions

% Amine Oxide w/w m water Residence Times (msec)

Sample

Regeneration Means Regeneration Means

Wash Wash

1 67 0 ∞ -

2 0 - CO -

3 67 20 1000 CO

4 70 - CO -

5 0 - CO -

6 0 - CO -

7 70 16 600 CO

8 70 15 270 CO

9 70 - CO -

10 70 15 240 CO

70 10 220 00

¹¹

In this table the symbol ∞ indicates a relatively long time, in excess of several minutes. TABLE 2

Properties of Dry Filaments

Sample dtex Fibrillation Tenacity Elasticity Modulus Total Index (CN/tex) at break % CN/tex crystall¬ inity of filaments

1 1.88 2 16 198 692

2 1.88 7 28 13 645

3 1.72 3 15 8 542

4 2.09 1 15 10 475

S ? .09 7 24 13 597

6 2.17 7 28 14 838 55%

7 2.52 1 14 11 514

8 2.35 1 30 12 909 55%

9 3.02 1 12.8 14 547 25%

10 1.49 0 30.5 14 1005

11 1.43 0 36.9 15.9 1054

Test 1 Crystallinity

The crystallinity of the filaments was measured by X- ray diffraction techniques, in particular equilateral wide angle X-ray scattering of oriented lyocell filaments and the crystallinity determined by integration under the equilateral scan for oriented samples according to the method illustrated in Figure 9, where the percentage crystallinity is given by the formula

% crystallinity C- + C₂ x 100

C_x + C₂ + A Test 2 Fibrillation

A sample of 100 filaments of 5mm length was shaken for

20 minutes in a 2 x 1 inch (5.08 x 2.54cm) stoppered glass tube containing 8mls of distilled water and 4gms of glass microspheres . The tube was shaken at 1800-1900 rpm clamped to the 15cm arm of a scientific shaker.

The fibrillation index is a subjective index in which the filaments are viewed on a glass slide under a microscope after removal from the tube, and are assigned a rating from 0-10 (0 representing fibrillation and 10 representing substantial fibrillation) according to their appearance after being abraded. For example a fiber made in accordance with sample 6, that is a highly crystalline lyocell filament, has a high tendency to fibrillate, as is illustrated in Figure 1 of the drawings, and has been assigned a Fibrillation index of 7.

A fiber made in accordance with sample 11 shows a substantially reduced tendency to fibrillate. This is shown in Figure 2 and has been assigned a fibrillation index of 1.

Test 3. NMR Spectroscopy

The test samples were subjected to cross polarisation/magnetic spinning conditions ¹³C solid state NMR spectroscopy with a 2 ms (millisecond) contact time and a 3 s (second) recovery delay. The spectral assignments uεed are described in Macromolecules 1982, 15, pages 686-687.

Test 4. Attenuated Total Reflection Infra Red Spectroscopy

Test samples were subjected to measurement by Attenuated total reflection infra-red spectroscopy using a germanium crystal. This provided surface specific absorbance information to a depth of = 100 nm.

It can be seen from the results in Table 2 that those samples with a tendency to fibrillate, i.e. Samples 2, 5 and 6, were regenerated in water, whereas those samples that were regenerated in 70% amine oxide solution, i.e. Samples 4 and 7 to 11, show little or no tendency to fibrillate. Samples 1 and 2, which were regenerated in 67% amine oxide solution, showed a slight increased tendency to fibrillate compared to Samples 4 and 7 to 11, but less than Samples 2,5 and 6.

Thus, it can be seen that the tendency to fibrillate can be controlled by the amine oxide concentration in the aqueous regeneration liquid.

Filaments made in accordance with Sample 8 and in accordance with Sample 6 were subjected to infra-red spectroscopy as per Test 4. The resultant Absorbance Spectra for the surfaces of the filaments are shown in Figure 4 with the lyocell according to the present invention (Sample 8) in the upper curve and lyocell with a high tendency to fibrillate (Sample 6) being shown in the lower curve. It can be seen that for Sample 6 there iε a more pronounced peak at about 3440cm^"1 than for Sample 8.

Filaments made in accordance with Sample 6 and Sample 4 were subjected to ¹³C NMR Spectroscopy. The resultant spectra are shown in Figure 5A for lyocell with a high tendency to fibrillate, and in Figure 5B for lyocell according to the present invention. The resonance peaks at

88 and 85 ppm correspond respectively with the C atom local crystalline resonance and the C, disordered resonance. It is apparent that Sample 4 in accordance with the present invention has a lower crystalline material content for the C₄ atom than Sample 6, which has a high fibrillation index.

The total crystallinity of a number of samples was measured in accordance with Test 1. Sample 6 had a total crystallinity of about 55%, which is also typical for a lyocell filament manufactured according to the method described in WO-A-94/28218, in which a solution of 15% w/w of cellulose in amine oxide (N-methylmorpholine-N-oxide) , as described above, is forced under pressure through a spinnerette to form a multi-filament tow, which passes through an air gap into a spin bath containing about 25% amine oxide w/w in water.

With reference to Figure 3, there iε illustrated a graph of % crystallinity against amine oxide concentration in water in the spin bath for lyocell made in accordance with WO-A-94/28218.

The upper curve is measured according to Test 1 and the lower curve iε measured by ¹³C NMR according to Test 2. It is apparent from both measuring techniques that for spin bath concentrations of between 0-50% amine oxide in water, the crystallinity of the fibers is substantially constant and that for concentrations of between 60-70% the crystallinity of the fibers falls dramatically.

Sample 9 has a total crystallinity, measured in accordance with Test 1 of about 25%. The Sample 9 filament was immersed for several minutes in a bath of 70% w/w amine oxide and had a uniformly low crystallinity throughout its εtructure . Sample 8 was immersed in the bath of 70% w/w amine oxide solution for 270 milliseconds and has a total crystallinity of about 55%.

Since

(i) both filaments of Samples 8 and 9 have improved fibrillation characteristics (i.e. a reduced tendency to fibrillate) over the filament of Sample 6;

(ii) the Infra-red absorbance shown in Figure 4 indicates that the surface of the filament of Sample 6 differs from the surface of the filament in Sample 8 ;

(iii) the NMR Spectra shown in Figure 5 for Samples 4 and 6 indicate a lower crystallinity at the C₄ atom resonance,- and

(iv) the indications shown m Figure 3 point to the formation of low crystallinity lyocell in a high amine oxide concentration spin bath,

then it is apparent that the low fibrillation filaments made m accordance with the present invention have a skin structure that differs from the core of said filaments, and that the filament structure has a skin with a lower crystallinity than the core

The skin/core structure of the filaments can be observed using, for example, transmission detection microscopy on a dyed or stained filament

Furthermore the wide angle X-ray detraction (WAXS) results showed that lower crystallinity lyocell has a less orientated structure than more crystalline lyocell. The

WAXS azimuthal half width (full width at half height) for lyocell is typically 22" and the orientation is substantially constant irrespective of amine oxide concentration m the regeneration bath until a concentration of about 60% is reached. Thereafter the half width increases up to about 35' at 70% amine oxide concentration

The average angle of crystallite chain disoπentation is about 12' at 60% amine oxide concentration and about 20^* at 70% amine oxide concentration Thus, whilst lyocell according to the present invention is far from isotropic, it is more disoriented that standard lyocell

Claims

1. In the manufacture of a cellulose body from a solution of cellulose, the crystal morphology of the body is controlled through the concentration of solvent in the regeneration solution.

2. A method of making lyocell filaments in which filament is spun from cellulose dissolved in an amine oxide solvent and is given a skin/core structure, by passing the filament through a regeneration bath containing an aqueous solution of amine oxide containing at least 60% by weight of an amine oxide, and thereafter washing the filament in an aqueous medium.

3. A method as claimed in claim 2 , wherein concentration of amine oxide in the regeneration bath does not exceed 72% by weight.

4. A method as claimed in claim 2 or claim 3, in which the filament is given a skin of lower crystallinity than the core of the filament.

5. A method as claimed in any one of claims 1 to 4, in which the body or filament passes through a washing process in which it is washed by an aqueous solution of amine oxide containing a maximum of 25% by weight of amine oxid .

6. A method as claimed in claim 5, in which the amine oxide content of the wash process solution does not exceed

20% w/w.

7. A method as claimed in any one of claims 2 to 6, wherein the residence time in the regeneration bath does not exceed 1 second.

8. A method as claimed in claim 7, wherein the residence time in the regeneration bath is from 220 to 600 milliseconds .

9. A lyocell filament made by a method aε claimed in any one of claims 2 to 8.

10. A lyocell filament having a skin with a different structure to the core.

11. A lyocell filament as claimed in claim 10 in which the core has a higher crystallinity than the skin.

12. A filament according to claim 11, wherein the cellulose of the filament skin is substantially non- crystalline, and preferably the crystallinity does not exceed 25% .

13. A filament according to claim 11 or claim 12, wherein the cellulose of the filament skin is lesε oriented than that of the filament core.

14. Fibers made from filaments, each of which filaments being according to any of claims 9 to 13.

15. Woven and non-woven textiles produced from filaments, each of which filaments being according to any of claims 11 to 15, or from fibers according to claim 14.

16. Apparatus for the production of a lyocell filament having a skin/core structure, the apparatus including filament regeneration means through which spun filament passes in operation, the filament regeneration means including means for providing a liquid flow of a high concentration amine oxide solution in water, the apparatus being arranged so that, in operation, the filament path through the regeneration means is substantially parallel with at least a portion of the liquid flow path.

17. Apparatus as claimed in claim 16, wherein the regeneration means comprises a substantially vertical funnel shaped bath with filaments and amine oxide solution entering the wide end of the bath and exiting the narrow end of the bath.

18. Apparatus aε claimed in claim 16, wherein the regenerated meanε comprises an elongate inclined trough with filament and amine oxide solution passing down the trough.

19. Apparatus as claimed in claim 16, where the regeneration meanε comprises a cascade of an aqueous solution of amine oxide which is jetted onto the filament of lyocell.

20. Apparatus as claimed in any one of claims 16 to 19, further including an aqueous wash system for washing the filaments to prevent further changes in the crystallinity.

21. Apparatus as claimed in claim 20, when dependent upon claim 17 or claim 19, wherein the aqueous wash system comprises a jet or curtain or spray of water which iε directed onto the filaments after they emerge from the regeneration means.

22. Apparatus as claimed in claim 20 when dependent upon claim 18, wherein the aqueous wash enters into the trough at a mid layer location.

23. Apparatus as claimed in claim 21, wherein the high concentration solution of amine oxide in water may be recycled to the regeneration means.