FI80913B - FOERFARANDE FOER FRAMSTAELLNING AV CELLULOSAFIBER RESPEKTIVE AENDLOESA CELLULOSAFIBER SAMT ANORDNING FOER UTFOERANDE AV FOERFARANDET. - Google Patents

Description

8091 3

A method of making cellulosic fibers and fibers, respectively, and an apparatus for performing the method

The invention relates to a process for preparing cellulose fibers and strands, respectively, from a cellulose dimethylacetamide solution (dmac) and / or a 1-methyl-2-pyrrolidone-lithium chloride solution by wet spinning, the cellulose solution being pressed through spinning nozzles, the fibers formed being drawn and then spun. and an apparatus for wet spinning cellulose solutions to perform the method.

This type of process is disclosed in AT-A-372 412. When cellulose is dissolved in the disclosed system, no derivatization occurs, but in DMAC, for example, the following solvate complex is assumed to exist:

Cell - Ö [- H q ti® '' C1 φ \ ···; · -J4j'ch3 f NC “3 f 1

It has been found that the textile properties of fibers made from such solutions, especially when spinning solutions in aqueous spinning baths, are in no way satisfactory - compared to, for example, the properties of cellulose fibers obtained by a conventional viscose process.

However, the viscose process has the advantages of a mature process, namely relatively cheap starting chemicals and flexibility at the moment, i.e. the ability to produce a wide range of fiber grades for a variety of uses with small changes in ro-ration parameters, but also significant disadvantages that are becoming increasingly significant. In this way, the production of spinning solutions 2 80913 is multi-stage and batch-based, there are still problems in the recovery of chemicals and in terms of environmental protection.

For these reasons, research has for some time sought to develop economical and environmentally friendly alternative methods for the production of cellulosic fibers.

The object of the invention is therefore to eliminate the disadvantages associated with the method defined at the outset with regard to the fiber properties obtained and to provide a reliable method and a suitable wet spinning device for producing fibers with good tear strength and sufficient elongation.

Another important object of the invention is to be able to use aqueous spinning baths for coagulating and reconstituting cellulose.

The method according to the invention is characterized in that an increasing concentration of coagulant is applied to the spinning bath in the spinning bath and the fibers removed from the spinning bath are subjected to post-treatment in a lye bath after stretching.

The invention is based on the finding that the slower the fiber formation - i.e. the better the properties of the fibers. coagulation and reconstitution of the cellulose part occurs.

Suitable coagulants are, for example, organic solvents, such as lower alcohols, pyridine, acetonitrile, tetrahydrofuran or mixtures thereof, which may also contain water.

In a spinning bath, the reconstitution of the cellulose is achieved simultaneously with the coagulation, and even faster the more polar the coagulant is. Fibers spun from cellulose solutions according to the conventional wet spinning process using an aqueous spinning bath therefore have poorer textile values than, for example, fibers obtained with acetonitrile or alcohol baths, namely a reasonable tear strength and a very low tear strength. In addition, the fiber cable can be stretched after coagulation of the cellulose with water in a conventional manner by up to 10 *, while when using baths formed with organic solvents, the fiber cable can be stretched considerably more.

In addition, due to the relatively poor solubility of lithium chloride in organic solvents, a large amount of solvent is needed to wash the salt out of the fibers. In addition, complete circulation control of the spinning bath must be provided to recover the solvent.

According to the process of the invention, water is preferably used as the coagulant to obtain products with textile values at least as good as those of the fibers obtained according to AT publication 372 412 by spinning a solution of DMAC-LiCl cellulose in acetonitrile without arranging concentration gradients.

Textile fibers to be treated, for example, according to the 3-cylinder spinning method, must have a minimum elongation of 10%, in addition to which a tear strength of more than 25 cN / tex is desirable.

The use of water as a coagulant offers the additional advantage that the resulting spinning bath containing DMAC and / or 1-methyl-2-pyrrolidone and dissolved LiCl can be used directly again for the necessary activation of cellulose. Without prior activation, the cellulose only dissolves in lithium chloride-containing systems from temperatures of about 150 ° C, although severe degradation of the cellulose already occurs and thus the average degree of polymerization (DP) of the cellulose is drastically reduced. In addition, the solutions thus obtained are strongly discolored and are not suitable for further processing into shaped products. Various methods for activating cellulose are mentioned in AT patent publication 372 JJ12, namely: heating the cellulose in DMAC or 1-methyl-2-pyrrolidone under reflux, whereby the amide has a sufficiently high vapor pressure to penetrate the fiber capillaries. The addition of lithium chloride then takes place at temperatures where there is no significant decrease in DP, - activation with water, followed by displacement of the water with dimethylacetamide or 1-methyl-2-pyrrolidone, respectively (solvent exchange); this activation can also take place using steam, followed by a solvent exchange, - activation in a mixture of DMAC, water and LiCl, followed by fractional distillation, - impregnation of the cellulose with liquid ammonia and subsequent displacement of the ammonia with the amide.

The spinning solution is further treated by rectification (redistillation) to separate the water. LiCl can be obtained from the pool product by crystallization or a solution of LiCl in DMAC and / or 1-methyl-2-pyrrolidone can be used immediately again for spinning solution preparation.

* The spinning bath may contain a predetermined proportion of DMAC or 1-methyl-2-pyrrolidone as well as LiCl to provide fiber properties. If it were desired to achieve slower fiber formation in conventional spinning bath control by increasing the concentration of these components in the fiber bath, such an attempt would lapse that at high concentrations of amide and LiCl the effect of the coagulant is no longer sufficient and spinning deteriorates due to fiber rupture and the outlet member.

The maximum possible concentration of amide and LiCl in a spinning bath depends on the cellulose concentration of the spinning solution and the spinning bath temperature in conventional spinning bath control. Cooling of the spinning bath also results in a slowing down of the cellulose reconstitution and thus a maximum reduction in the amide concentration used in the spinning bath. For spinning solutions with a high cellulose concentration, a higher amide content can be set in the spinning bath because the cellulose precipitates more easily from solutions with cellulose concentrations of about 10% by weight. The maximum concentration of DMAC in the spinning bath for spinning an 8% by weight cellulose solution (7% by weight * LiCl, 85% by weight * DMAC) at a spinning bath temperature of 20 ° C is about 70% by weight.

Also, sequential coupling of spinning baths with decreasing amide concentration does not lead to the goal because the expanded gel fibers obtained from baths with high amide and LiCl content are, as shown, thick and rigid.

If, according to the invention, an increasing concentration of coagulant is provided in the passage of the fibers through the spinning bath, then the stretchability of the fibers after spinning in an aqueous spinning bath increases to more than 40 * compared to less than 10 * in conventional spinning bath control. Thus, above all, an improvement in the tear strength of the fibers in both the standard and wet conditions has been combined.

The fibers are stretched in an additional bath (air, hot water, amide / water mixture). However, the standardized elongation of the fibers obtained is only 5 and 7 *. However, without stretching in the additional bath and only by drawing in the spinning bath, higher stretches of> 10 * are possible, albeit at the expense of fiber strength. As already shown, elongation values below 10 * are too small for textile use. The improvement in elongation without a significant loss of standardized fiber strength is achieved by the post-treatment of the fibers in the lye bath according to the invention.

The increasing concentration of coagulant is very conveniently controlled by an open tube surrounding the spinning nozzles on the spinning bath side.

6 80913 Immediately after the spinning nozzles, the amide and LiCl released from the spinning solution result in a strong enrichment of the spinning bath inside the tube with these components, forming a concentration gradient along the length of the tube. The concentration of bath coagulant increases towards the open end of the tube and is almost equal to the concentration prevailing in the surrounding spinning bath. On the contrary, conventional spinning bath control attempts to remove the solvent components contained in the spinning solution as quickly as possible and thus achieve rapid fiber formation.

In the area immediately after the spinning nozzles, according to the invention, much higher amide concentrations can be set than 70 wt.% Without any deterioration in the spinning safety. In the areas thereafter and after leaving the open end of the tube in the surrounding spinning bath, the highly swollen gel fibers may first solidify continuously with increasing concentrations of coagulant, so that no adhesion to the removal members occurs.

In a similar spinning bath composition, the fiber strength is improved both under standardized conditions and also when wet with concentration gradients adjusted by 10 to 20% in accordance with the invention compared to conventional spinning bath control. When pure water is used as the coagulant, it is even possible to increase the standard tear strength by about 35.

The post-treatment of the stretched fibers is preferably carried out in an aqueous solution of alkali metal hydroxide or liquid ammonia.

Particularly preferred is post-treatment in a solution of 2 to 8% by weight of alkali metal hydroxide at temperatures of 10 to 100 ° C and a residence time of up to 20 minutes.

Treatments of cellulosic fibers and fabrics with concentrated alkali metal hydroxide solutions or organic bases - mostly under tension - are known as mercerization used to provide permanent refining effects such as gloss and improved dye absorption. In this case, however, sodium hydroxide is generally used in concentrations of 26 to 30% by weight of NaOH. For example, if viscose fibers are subjected to such a treatment, then their standardized strength and their wet strength are clearly reduced, their wet modulus is reduced; only the braid strength increases.

From the solvent systems DMAC and / or 1-methyl-2-pyrrolidone and LiCl in the post-treatment of spun fibers according to the invention, it has surprisingly been found that their elongation increases up to 100 essa with only very small strength losses. The higher the concentration of alkali metal hydroxide, the greater the weight loss of the fibers due to the dissolved low molecular weight cellulose fractions. The solubility of aqueous NaOH reaches a maximum of 12.5 by weight. In addition to this, aqueous liquors with a higher concentration also cause unnecessarily high fiber strength losses.

If potassium hydroxide is used instead of sodium hydroxide, the weight loss of the fibers can be kept even lower due to the lower dissolution force of potassium hydroxide.

It is also essential to wash the fibers well after post-treatment, because especially in a higher temperature aqueous alkali bath, DMA or 1-methyl-2-pyrrolidone still adhered to the fibers is cleaved and thus wasted for recovery.

After post-treatment, the fibers are pressed, washed, possibly cut, dried with a known device and dried.

The device according to the invention for wet spinning is characterized by a spinning chimney with spinning nozzles sinking into the spinning bath, in that a tube surrounded by spinning nozzles is placed in the spinning nozzle and is open only towards the spinning bath side.

8 80913

The flow of the concentration of the spinning solution components or coagulant, respectively, between the fibers through the interior of the tube can be altered by changing the length and / or cross-section of the tube and the composition of the circulating, controlled spinning bath. The longer the tube is formed and the smaller its cross section, the higher the amide and LiCl content of the spinning bath in the tube. In the area immediately after the spinning nozzles, this concentration is always the highest.

The cross-sectional shape of the pipe is arbitrary and is determined by the distribution and number of spinning nozzles in the spinneret. In most cases, pipes with a circular cross-section are used.

According to a preferred embodiment, the inner side of the tube placed in the spinning chimney has circumferential or annular parts, respectively, to form a plurality of successive chamber parts.

These parts do not in any way prevent free tension of the fibers through the spinning bath, but more effectively prevent the spinning bath section in the tube from mixing too quickly with the surrounding spinning bath through the free end of the tube, thus ensuring the formation and maintenance of a certain concentration gradient throughout the spinning process.

The spinning nozzles of the fibers with a flat cross-section - to form so-called strips - are formed in the form of slits according to another suitable embodiment.

The invention is explained in more detail below by means of the drawing and examples. Unless otherwise specified, all percentages are by weight.

Figure 1 schematically shows an embodiment of a wet spinning device according to the invention with a tube surrounding the spinning nozzles. Figure 2 shows an enlarged and 9,80913 sectional view of a tube with internal parts which is part of a device according to the invention.

According to Fig. 1, the spinning bath 1 has a spinning bath 2. The liquid containing the coagulant enters the spinning bath 1 through the perforated plate behind the spinning pipe 3 and exits the spinning bath 1 through the overflow pipe 5. Nozzle cups with spinning nozzles (not shown) are placed in the screw connection of the nozzles of the spinning barrel 3. A pipe 6 with an adjustable length, open on the spinning bath side, surrounding the spinning nozzles, is placed in the spinning chimney. The spinning solution arrives from the spinning stack 3 through the spinning nozzles first in the area surrounded by the spinning tub 2 tube 6, forming fibers 7 which are assembled as a fiber bundle and pulled out through a fiber guide 8 by a roll 9. From the roll 9 a fiber cable is fed

Of course, the pipes 6 must not prevent the fiber cable from being pulled.

By feeding DMAC and / or 1-methyl-2-pyrrolidone and LiCl through the spinning solution, the concentration of these solvent components in tube 6 is increased; a concentration-gradient is formed from the nozzles towards the open end 10 of the tube 6, because only there is a more thorough mixing with the main part of the spinning bath 2 in the bath.

The tube 6 according to Figure 2 is substantially cylindrical and has circumferential or annular parts 11 on its inner side. In addition to the length and diameter of the tube 6, the number and inner diameter of the inner parts 11 can also be varied in this structure. It has proved very appropriate that:. that the perforated inner parts 11 are continuously provided with an inner diameter decreasing towards the open end 10 of the pipe 6, so that in most cases the fiber rope running sharply conically towards the fiber guide 8 is surrounded as tightly as possible by the inner parts 11. The open end of the pipe 6 also has a smaller diameter than the pipe 6. The inner parts 11 form 10 8091 3 chamber parts in which the concentration of the coagulant increases from the spinning nozzle strip in the direction of the open tube end 10. The rapid equalization of the concentration in the inner part of the pipe 6 caused by the flow events is very much prevented by this divided structure.

Example 1

A solution of sulfite cellulose in LiCl and DMA was prepared according to the water / solvent exchange activation method. The composition of the solution in cellulose / DMAC / Lici parts by weight was 7/86/7. The cellulose had a DPcu of 440, the viscosity of the solution was determined with a Haake-Viscotester viscometer (VT 24, measuring system E 500, speed step 1) and was 300 Pa at 20 ° C. The spinning solution was filtered with a metal fiber non-woven filter candle (pore size 20 μm), heated in a thin-layer heat exchanger to 105 ° C and spun horizontally through a spinning chimney into a spinning bath. The spinning chimney was equipped with four gold / platinum nozzle cups with 1053 holes and a nozzle diameter of 0.06 mm. The spinning bath was fed behind the spinning barrel from a perforated plate at 15 liters / min. at 20 ° C. Various glass cylinders, nominal width 6 cm, with varying cylinder lengths as shown in connection with Figure 1 could be placed in the spinning chimney.

After reaching equilibrium, the concentration gradient formed in the tube was dependent on the composition of the spinning solution and the composition of the spinning controlled spinning bath.

The fiber cable could be pulled out of the spinning bath by the first roll, guided through the stretch bath by the second roll, and wound at the winding point. Water at 92 ° C was used as a stretch bath. The immersion intervals were 90 cm in the spinning bath and 70 cm in the stretching bath.

The cable wound on a spool was cut once, assembled with a tie wire, washed in the form of a rope and post-treated. Washing and finishing were also performed with strands under tension, but without stretching. Washing was performed at 65 ° C with water, then spiked, excess material removed by squeezing or centrifugation, and the strands dried.

The spinning conditions and the values of the fibers obtained in each case are shown in Table I.

12 8091 3

TABLE I

_ I

Spinning bath H2O H2O H2O 40% DMAC / 40% DMAC / 70% DMAC / composition 60% H2O 60% H2O 30% H2O

Pipe length / cm / - 20 30 - 20

Spinning solution,. j its outlet speed from the nozzles / m / min7 4.50 4.50 4.50 4.50 4.50 4.50 1. Roll / m / min7 6.2 5.6 5.4 5.5 5, 1 5.3

Veto 1.38 1.24 1.20 1.22 1.13 1.18 2. Tela / m / min7 6.4 6.4 6.4! 6.4 6.4 6.4

Maksim. _ j, · elongation -10% /% / 3.2 14.3 18.5 16.4 25.5 20.8

Total bet 1.42 1.42 1.42 | 1.42 1.42 1.42 'Titer / * dtex7 1.84 1.88 1.82 1.92 1.82 1.79 13 8091 3 TABLE I (continued)

Spinning H2O H2O H2O I 40% DMAC / 40% DMAC / 70% DMAC

composition 60% H2 ° 60 * H2 ° 30% H2O

FFK

/ CN / tex? 19.8 24.0 26.5 25.7 29.2 27.2

FDK

/% / 6.86.66.3 6.3 6.1 6.0 ffn ^ cN / tex7 7.9 13.0 13.6 12.6 16.3 14.4

FDN

[\] 10.8 12.0 11.6 I 11.9 9.9 11.2 FFr: fiber strength standardized FDr: fiber elongation standardized FFn: fiber strength when wet FDn: fiber elongation when wet

The fibers were post-treated in an alkali bath in various concentrations of aqueous alkali metal hydroxide and at different temperatures or in liquid ammonia at -33 ° C, respectively.

The treatment was carried out in the form of a rope, then washed with hot water, dried and dried.

The post-treatment conditions and the values of the fibers after the alkali treatment are shown in Table II. For comparison, the values of the untreated fibers are shown (spinning conditions see Table I, spinning bath composition 40% DMAC, 60Ϊ H 2 O).

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Table II shows that with suitable post-treatment in a lye bath for standardized fiber stretches too small for textile use, it is possible to improve from 5-7 t without a large strength loss to more than 12 t.

Example 2

The fibers prepared according to Example 1 were continuously treated with aqueous alkali metal hydroxide under tension, but without stretching.

The fiber optic cable was then washed, lubricated and dried.

The treatment conditions and the values obtained for fiber strength and elongation are shown in Table III. The values of the untreated fiber are again presented as a comparison (cf. Table II).

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Claims (8)

A process for preparing cellulose fibers from a solution of cellulose in dimethylacetamide (DMAC) and / or 1-methyl-2-pyrrolidone and lithium chloride by liquid spinning, wherein the cellulose solution is pressed through spin nozzles and the fibers thus formed are drawn through a folding bath and stretched thereon. characterized in that in the folding bath, an increasing concentration of the folding agent is arranged along the passage length of the fibers and the fibers drawn from the folding bath are subjected to a stretching treatment in a leaching bath. Method according to claim 1, characterized in that the increasing concentration of the precipitating agent is adjusted by means of a tube surrounding the spin nozzles and which is open on the side of the precipitating bath. Process according to claim 1 or 2, characterized in that water is used as a precipitating agent. Process according to any of claims 1-3, characterized in that the post-treatment is carried out in an aqueous solution of alkali metal hydroxide or in liquid ammonia. Process according to claim 4, characterized in that the post-treatment is carried out in a solution having a concentration of 2 to 8% by weight of alkali metal hydroxide at a temperature of 10 - 100 ° C and with a delay time of up to 20 minutes. Apparatus for fluid spinning of cellulose solutions for carrying out the process according to any of claims 1-3 with a spinneret (3) having a spinning nozzle (3) having a spinning nozzle (3) characterized in that a spout (3) is a tube (6). which surrounds the nozzles provided, which tube is only open on the side of the trap bath. 20 8091 3 Device according to claim 6, characterized in that the pipe (6) arranged at the spinning pipe (3) has peripheral and annular parts (11) on the inside, respectively, for forming a number of successive chamber parts. 8. Apparatus according to any one of claims 6 or 7 for forming fibers with a flattened cross-section, characterized in that the spinneret nozzles are slit-shaped.