GB2307203A - Production of cellulose fibres having reduced tendency to fibrillation - Google Patents

Abstract

Process for the production of cellulose fibres having a reduced tendency to fibrillation, in which a solution of cellulose in a tertiary amine-oxide is spun into fibres and the freshly spun fibres are contacted with a textile agent comprising at least two reactive groups, and are heat-treated, characterized in that the heat treatment is carried out by means irradiation with electromagnetic waves.

Description

PROCESS FOR THE PRODUCTION OF CELLULOSE FIBRES HAVING A REDUCED TENDENCY TO FIBRILLATION The invention is concerned with a process for the production of cellulose fibres having a reduced tendency to fibrillation.

This application is divided out of British Patent Application No. 9424722.8 which discloses a process for the production of cellulose fibres having a reduced tendency to fibrillation, in which a solution of cellulose in a tertiary amine-oxide is spun into fibres and the freshly spun fibres are contacted with a textile agent, which carries at least two reactive groups, and are washed with an aqueous buffer, provided that as a textile agent glyoxal is not used.

As an alternative to the viscose process, in recent years there has been described a number of processes in which cellulose, without forming a derivative, is dissolved in an organic ; solvent, a combination of an organic solvent and an inorganic salt, or in aqueous saline solutions. Cellulose fibres made from such solutions have received by BISFA (The International Bureau for the Standardisation of man made Fibres) the generic name Lyocell. As Lyocell, BISFA defines a cellulose fibre obtained by a spinning process from an organic solvent. By "organic solvent, BISFA understands a mixture of an organic chemical and water. "Solvent-spinning" ist considered to mean dissolving and spinning without the forming of a derivative.

So far, however, only one process for the production of a cellulose fibre of the Lyocell type has achieved industrialscale realization. In this process, a tertiary amine-oxide, particularly N-methylmorpholine-N-oxide (NMMO), is used as a solvent. Such a process is described for instance in US-A 4,246,221 and provides fibres which present a high tensile strength, a high wet-modulus and a high loop strength.

However, the usefulness of plane fibre assemblies, for example fabrics, made from the above fibres, is significantly restricted by the pronounced tendency of such fibres to fibrillate when wet. Fibrillation means the breaking up of the wet fibre in longitudinal direction at mechanical stress in a wet condition, so that the fibre gets hairy, furry. A fabric made from these fibres and dyed significantly looses colour intensity as it is washed several times. Additionally, light stripes are formed at the abrasion and crease edges. The reason may be that the fibres consist of fibrils which are arranged in the longitudinal direction of the fibre axis and that the crosslinking between these is reduced.

WO 92/14871 describes a process for the production of a fibre having a reduced tendency to fibrillation. The reduced tendency to fibrillation is attained by providing all the baths with which the freshly spun fibre is contacted before the first drying with a maximum pH of 8,5.

WO 92/07124 also describes a process for the production of a fibre having a reduced tendency to fibrillation, according to which the freshly spun, i.e. not yet dried, fibre is treated with a cationic polymer. As such a polymer, a polymer with imidazole and azetidine groups is mentioned. Additionally, there may be carried out a treatment with an emulsifiable polymer, such as polyethylene or polyvinylacetate, or a crosslinking with glyoxal.

In a lecture given by S. Mortimer at the CELLUCON conference in 1993 in Lund, Sweden, it was mentioned that the tendency to fibrillation rises as drawing is increased.

It is the objective of the invention to provide a process which can be carried out in an easy way, allowing the production of cellulose fibres of the Lyocell type having a reduced tendency to fibrillation.

The process according to the invention for the production of cellulose fibres having a reduced tendency to fibrillation consists in that the freshly spun, not yet dried fibres are contacted with a textile agent, which carries at least two reactive groups, and are washed with an aqueous buffer, provided glyoxal is not used as textile agent.

As textile agents, especially dyes having two reactive groups have shown good results. According to the invention, however, textile agents which are colourless, i.e. do not absorb visible light, may also be used.

According to the invention, the use of textile agents which carry one or two vinylsulfone groups as reactive groups is preferred.

A convenient embodiment of the process according to the invention is characterized in that the freshly spun fibres are contacted with the textile agent in an aqueous alkaline medium.

It was shown that the tendency to fibrillation is especially reduced when an alkali carbonate and an alkali hydroxide is chosen as the alkaline medium.

Another preferred embodiment of the process according to the invention consists in that the fibres contacted with the textile agent are heat-treated. The heat treatment drastically reduces the impregnation time.

EP-A - 0 538 977, published on April 28, 1993, describes heat treatment of cellulose fibres impregnated with a dye. It was shown, however, that heating of the fibres impregnated with the textile agent by means of hot air may reduce the impregnation time, but that this carries the risk of the fibres not being heated uniformly. Thus for example, the fibres on the outside of a fibre bundle to be dried may already be partly dried, while the fibres inside the bundle have not yet reached the required temperature. This has a negative effect on the quality of the fibres produced.

It has been found that this drawback occurring in a simple heat treatment can be overcome by irradiating the fibres with electromagnetic waves, particularly microwaves. When irradiated with microwaves, on the one hand the fibres are heated uniformly and on the other hand premature drying of the fibres can be avoided, since irradiation with electromagnetic waves provides the possibility to weld the fibre bundle for example into a plastic wrapping and expose it in a welded condition to the electromagnetic field.

The above advantages are also given when the fibres, for example lying as plane fibre assembly on a conveyor, are moved through a narrow channel, in which they are exposed to electromagnetic waves. This channel can be designed in a way that only little air space above the fibres is left, thereby preventing a partial drying of the outer fibres of the bundle.

Simultaneously, this way of fixation of the textile agent also offers the possibility of a large-scale production easy to put into practice.

Thus, the invention further refers to a process for the production of cellulose fibres having a reduced tendency to fibrillation, in which a solution of cellulose in a tertiary amine-oxide is spun into fibres, and the freshly spun fibres are contacted with a textile agent which carries at least two reactive groups and are heat-treated, characterized in that the heat treatment is carried out by irradiation with electromagnetic waves.

Also according to this embodiment of the process according to the invention, the use of a textile agent which carries vinylsulfone groups as the reactive groups, is preferred, preferably being a dye. However, textile agents which are colourless, i.e. do not absorb visible light, can also be used.

Another preferred embodiment of the process according to the invention consists in carrying out the heat treatment by means of microwaves.

The invention will be explained in more detail by the following examples. All references to % are to be understood as weight %.

Production of the cellulose fibres According to the process described in EP-A - 0 356 419, a solution of cellulose in NMMO was prepared and extruded through a spinneret. The filaments thereby obtained were conducted through an air gap into an aqueous precipitation bath, in which the cellulose coagulated. The fibres obtained in the precipitation bath were washed, presenting a titer of 1,7 dtex.

The washed fibres were used for the examples hereinafter described and represent those fibres which in the present description and in the present claims are referred to as fibres freshly spun, not yet dried.

1) Treatment with textile agents without subsequent heat treatment A) General procedure 1 g of each of the fibres produced according to the above process were impregnated in 190 ml of an aqueous solution (bath), which contained a textile agent comprising two reactive groups and Na2SO4, at 40 C for 30 minutes. Then NaOH (3%), Na2CO3 (4%) or a mixture of NaOH, Na2CO3 (4% Na2CO3 and 0,2 g/l NaOH) were added for the fixation of the textile agent. After another 60 minutes at 40"C the fibres were washed several times, in order to remove the textile agent not fixed to the fibre.Then the washed fibres were treated for 30 minutes with an aqueous buffer, then again washed with water (for 15 minutes) and dried at 60"C. Afterwards the fibres were examined to determine their tendency to fibrillation and to determine other fibre parameters.

Evaluation of fibrillation The abrasion of the fibres among each other in washing processes and finishing processes in wet condition was simulated by the following test: 8 fibres with a length of 20 mm each were put into a 20 ml sample bottle with 4 ml of water and shaken during 9 hours in a laboratory mechanical shaker of the RO-10 type of the company Gerhardt, Bonn (Germany), at stage 12. Afterwards the fibrillation behaviour of the fibres was evaluated by microscope, by means of counting the number of fibrils per 0,276 mm fibre length.

Further fibre parameters The fibre tensile strength and fibre elongation at break were tested following the BISFA rule on "Internationally agreed methods for testing viscose, modal, cupro, lyocell, acetat and triacetat staple fibres and tows", edition 1993.

B) Examples According to the above process, fibres were treated with the dye Remazol Black B and Remazol Red RB as textile agent (made by Hoechst AG). The dye Remazol Black B carries two vinylsulfone groups and the dye Remazol Red B carries one vinylsulfone group and one monochlorotriazine group.

The bath contained 3% Remazol Black B and 0,5% Remazol Red RB respectively. The pH of the bath was 4,6 in each example. The used aqueous buffer was an aqueous solution which contained 3% acetic acid and 7% sodium acetate. The pH value of this solution was 4,6. After the treatment with the buffer, the fibres were washed with water for 15 minutes and afterwards examined. Table la indicates the fixing agent used in each case, the fibrillation (number of fibrils), the titer (dtex), the fibre strength (cN/tex) and the fibre elongation at break (%). Examples 1, 2 and 3 were carried out with the dye Remazol Black B and Example 4 with the dye Remazol Red RB.

Table ib shows the results of comparative tests carried out without dye.

Table la (Textile Agent)

Ex. Fixing agent Fibrils Titer Tensile Strength Elongation 1 NaOH 22 1,82 28,81 11,14 2 Na CO 2 2,07 26,39 | 10,67 3 NaOH+Na CO 0 2,34 24,94 10,04 4 NaOH+Na2CO3 5 2,34 30,00 11,74 Table ib (Comparative Examples)

Ex. Fixing agent Fibrils Titer Tensile Strength Elongation 5 NaOH > 60 1,80 33,76 12,71 6 Na CO 60 1,56 33,78 12,15 7 NaOH+NaxCOX > 60 1,72 30,18 12,14 8 NaOH+NavCO3 > 60 1,72 32,00 12,70 A comparison of the results of Tables la and 1b shows that the textile agent, in the present case the dyes Remazol Black B and Remazol Red RB, drastically reduces the tendency to fibrillation and that the combination of NaOH+Na2CO3, which is used for the fixation of the textile agent, also drastically further reduces the tendency to fibrillation.

It was shown that the above results are obtained also when using other textile agents which comprise two reactive groups.

Thus, Remazol Black B and Remazol Red RB may represent other textile agents which also carry at least two reactive groups.

2) Treatment with textile agents and subsequent heat treatment 1 g of each of the fibres produced according to the above process was impregnated in 190 ml of a bath (containing 0,2% Remazol Black B, 2% Na2CO3, 0,2% NaOH, pH = 11,5) three times for 30 seconds each, the fibres being squeezed off after each impregnation. Afterwards, each sample was heat-treated twice for 40 seconds in each case in a circulating-air oven at 1800C.

Subsequently, each heat-treated sample was treated for 30 minutes with the above mentioned acetate buffer (pH = 4,6), washed with water for 15 minutes, dried at 609C and examined.

The results are shown in Table 2, Example 10 representing a Control Sample (for Example 10, Example 9 was repeated without using a textile agent).

Table 2

Ex. Fibrils Titer Tensile Strength Elongation 9 24 1,56 1 33,78 12,15 10 > 57 1,80 1 33,76 12,71 From table 2 it can be seen that a heat treatment of the fibres impregnated with the textile agent drastically reduces the impregnation time, as well as the tendency to fibrillation is reduced.

With the dye Remazol Red RB, similarly good results could be attained.

3. Treatment with textile agents and subsequent irradiation with microwaves 10 g of the fibres produced according to the above process were impregnated in a 900 ml bath (10% Remazol Black B, 10% Na2SO4, 8% Na2CO3; the pH was adjusted with NaOH to 11,5) for 9 minutes. Afterwards, the fibres were squeezed off and divided into 2 parts of equal amount (Examples 12, 13). Example 11 was a Control Sample, indicating the properties of the fibres not treated with a textile agent. For Examples 12 and 13, the fibres were squeezed off after impregnation with the bath, and they either were heated to 180it for 180 seconds (Example 12) or irradiated with 90 watt microwaves for 50 seconds (Example 13). Afterwards, the fibres were treated for 30 minutes in the above acetate buffer at a pH of 4,6, washed with water for 15 minutes and dried at 60C. The results of the tests are shown in Table 3.

Table 3

Ex. Heating Fibrils Titer Tensile Strength Elongation 11 --- 56 1,83 31,98 11,52 12 180 sec.;1800C 11 1,91 23,70 9,77 13 50 sec.; 90 W 7 1,92 31,23 | 11,34 From Table 3 it can be seen that the irradiation with microwaves further reduces the heating time, the tendency to fibrillation being still further reduced. Similarly good results in terms of a reduced tendency to fibrillation were obtained, when instead of Remazol Black B other textile agents with at least two reactive groups were used. Particularly it was shown that the positive effect upon the tendency to fibrillation is similarly pronounced as with glyoxal.

Furthermore it was shown that the above positive effect brought about by irradiation with microwaves can also be observed with glyoxal and other dialdehydes, as can be deduced from the following example.

2 g of fibres produced according to the process described in section 1 were impregnated twice for 3 minutes each with 140 ml of a bath, containing 2% glyoxal and 0,66% crosslinking catalyst (for example Condensol FB, a mixture of ZnC12 and MgCl2, made by BASF). Afterwards, the fibres were squeezed off and divided into 2 parts (Examples 15, 16). Example 14 was a Control Sample, for Example 15 the fibres were treated for 10 minutes in a circulating-air oven at 100etc, and for Example 16 the fibres were subjected to a power of 500 watt by means of a microwave. The fibrillation results are indicated in the following Table 4.

The above methode was repeated, using glutardialdehyde (3,4%) instead of glyoxal. The fibrillation results of the obtained fibres are also reflected in Table 4 (Examples 17, 18 and 19 correspond to Examples 14, 15 and 16 respectively).

Table 4

Example Textile agent Treatment Fibrils 14 ---- ---- 35,5 15 Glyoxal 10 min.; 1000C 24,0 16 Glyoxal 60 sec.; 500w 8,5 17 ---- ---- 35,5 18 Glutardialdehyde 10 min.; 1000C 10,5 19 Glutardialdehyde 60 sec.; 500 w 21,0

Claims (12)

1. CLAIMS 1. A process for the production of cellulose fibres having a reduced tendency to fibrillation, in which a solution of cellulose in a tertiary amine-oxide is spun into fibres and the freshly spun fibres are contacted with a textile agent, which carries at least two reactive groups, and heat-treated, characterized in that the heat treatment is carried out by irradiation with electromagnetic waves.
2. 2. A process according to claim 1, characterized in that as a textile agent a dye or a colourless substance is used.
3. 3. A process according to claim 1 or 2, characterized in that a textile agent is used which carries at least one vinylsulfone group as reactive group.
4. 4. A process according to one of the claims 1 to 3, characterized in that the freshly spun fibres are contacted with the textile agent in an alkaline medium.
5. 5. A process according to claim 4, characterized in that the alkaline medium is formed by an alkali carbonate and an alkali hydroxide.
6. 6. A process according to one or more of the claims 1 to 5, characterized in that the heat treatment is carried out by means of microwaves.
7. 7. A process for the production of cellulose fibres having a reduced tendency to fibrillation, in which a solution of cellulose in a tertiary amine-oxide is spun into fibres and the freshly spun fibres are contacted with a textile agent, which carries at least two reactive groups, and are washed with an aqueous buffer, provided that as a textile agent glyoxal is not used.
8. 8. A process according to claim 7, characterized in that as a textile agent a dye or a colourless substance is used.
9. 9. A process according to claim 7 or 8, characterized in that a textile agent is used which carries at least one vinylsulfone group as reactive group.
10. 10. A process according to one of the claims 7 to 9, characterized in that the freshly spun fibres are contacted with the textile agent in an aqueous alkaline medium.
11. 11. A process according to claim 10, characterized in that an alkali carbonate and an alkali hydroxide is chosen as the alkaline medium.
12. 12. A process according to one or more of the claims 7 to 11, characterized in that the fibres contacted with the textile agent are heat-treated.