EP0178293B1 - Process for the production of cellulose threads and fibres, and device for carrying out the process - Google Patents

Description

The invention relates to a process for the production of cellulose threads or fibers from a solution of cellulose in dimethylacetamide (DMA) and / or 1-methyl-2-pyrrolidinone and lithium chloride by wet spinning, the cellulose solution being pressed through spinnerets and the threads formed thereby a felling belt is drawn and then stretched, and a device for wet spinning cellulose solutions to carry out the process.

A method of this kind is described in AT-B - 372.412. When cellulose is dissolved in the specified system, there is no derivatization, but for example in DMA the presence of the following solvate complex is assumed:

It has been found that the textile properties of threads or fibers produced from such solutions - in particular when spinning the solutions in aqueous precipitation baths - are in no way satisfactory compared to the properties of cellulosic threads obtained, for example, by the conventional viscose process.

The viscous process has the advantage of a sophisticated process, namely currently relatively cheap starting chemicals and flexibility, i.e. the possibility of producing a wide range of fiber qualities for various applications with small changes in the process parameters, but also serious disadvantages, which are becoming increasingly difficult. The manufacture of the spinning solutions is multi-stage and complex, and there are also problems with chemical recovery and environmental protection.

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

The invention therefore has as its object to eliminate the disadvantages associated with the initially defined method with regard to the fiber properties that can be achieved and to create an operationally reliable method and a suitable wet spinning device, with which threads or fibers of good tensile strength and at the same time sufficient stretch can be produced.

Another important object of the invention is to be able to use aqueous precipitation baths for the coagulation and reconstitution of the cellulose.

The process according to the invention is characterized in that a concentration of precipitant increasing along the passage of the threads is provided in the precipitation bath and the threads drawn off from the precipitation bath are subjected to an aftertreatment in an alkaline alkali bath after they have been drawn.

The invention is based on the knowledge that the slower the thread formation - the better the properties of the threads or fibers - i.e. the coagulation and reconstitution of the cellulose - takes place.

Examples of suitable precipitants are organic solvents, such as lower alcohols, pyridine, acetonitrile, tetrahydrofuran or mixtures thereof, which may also contain water.

The coagulation causes the cellulose to be reconstituted simultaneously with the coagulation, etc. the faster, the more polar the precipitant is. Threads spun from the cellulose solution by the usual wet spinning process using an aqueous precipitation bath therefore have poorer textile data than e.g. threads obtained with acetonitrile or alcohol baths, namely moderate tensile strength cond., very low elongation at break and poor wet strength. In addition, after coagulation of the cellulose with water, the fiber cable can be stretched by a maximum of 10% in a conventional manner, while the fiber cable can be stretched much more when using baths with organic solvents.

As a result of the relatively poor solvency of the organic solvents for lithium chloride, however, the solvent requirement for washing out the salt from the threads is very high. In addition, complete recycling of the precipitation or spinning bath must be provided to recover the solvents.

In the process according to the invention, water is preferably used as the precipitant, resulting in products with textile data which are at least as good as those of fibers which, according to AT-B - 372.412, are obtained by spinning a CMA-LICI cellulose solution in acetonitrile without provision a concentration gradient were obtained.

Textile fibers that are to be processed using the 3-cylinder spinning process, for example, must have a minimum elongation of 10%, and a tensile strength above 25 cN / tex is desirable.

The use of water as Fäilmitell offers the additional advantage that the precipitating bath obtained, containing DMA and / or 1-methyl-2-pyrrolidinone and LiCI, can be used again directly for the necessary activation of the cellulose. Without prior activation, cellulose only dissolves in the lithium chloride-containing systems at temperatures above about 150 ° C, although there is already a strong breakdown of the cellulose and the average degree of polymerization (DP) of the cellulose is drastically reduced accordingly. In addition, the solutions obtained in this way are strongly discolored and unsuitable for further processing into shaped products. Various methods of activating the cellulose are listed in AT-B - 372.412, including:

Heating cellulose in DMA or 1-methyl-2-pyrrolidinone under reflux, the amide having a sufficiently high vapor pressure to penetrate the fiber capillaries. The lithium chloride is then added at temperatures at which there is no noticeable DP reduction,

Activation with water, whereupon the water is displaced by dimethylacetamide or 1-methyl-2-pyrrolidinone (solvent exchange); this activation can also be carried out using steam, whereupon solvent exchange also takes place,

Activation in a mixture of DMA, water and LiCI, followed by removal of the water by fractional distillation,

Impregnation of the cellulose with liquid ammonia and subsequent displacement of the ammonia by the amide.

The precipitation bath is worked up by rectification, the water being removed. LiCI can be obtained from the bottom product by crystallization or the solution of LiCI in DMA and / or 1-methyl, -2-pyrrolidinone can be used again immediately to prepare the spinning solution.

To influence the fiber properties, the precipitation bath can already contain a certain proportion of DMA or 1-methyl-2-pyrrolidinone and LiCI. If one wanted to force a slower thread formation by increasing the content of the precipitation bath of these components in the usual precipitation bath management, such an attempt fails because the concentration of amide and LiCl is too low and the effect of the precipitation agent is no longer sufficient and the spinning pattern deteriorates Fiber tears and sticking of the fiber cable to the take-off element occurs.

The maximum possible concentration of amide and LiCI in the precipitation bath depends on the cellulose concentration in the spinning solution and the temperature of the precipitation bath. A cooling of the precipitation bath also leads to a delay in the reconstitution of the cellulose and thus to a reduction in the maximum applicable amide concentration in the precipitation bath. With spinning solutions with a high cellulose concentration, a higher amide content can be set in the spinning bath, since the cellulose is more easily precipitated from solutions with cellulose contents of approx. 10% by mass. The maximum DMA concentration in the precipitation bath for spinning an 8 mass cellulose solution (7 mass% LiCl, 85 mass% DMA) at 20 ° C precipitation bath temperature is approx. 70 mass%.

A series connection of precipitation baths with a decreasing concentration of amide is also not expedient because of the well-formed consistency of the swollen gel threads, as they occur in baths with high amide and LiCI contents.

If, according to the invention, an increasing concentration of precipitant is provided along the passage of the threads through the precipitation bath, the stretchability of the threads after spinning into an aqueous precipitation bath increases to more than 40% compared to less than 10% with conventional precipitation bath guidance. Above all, this is associated with an improvement in the tensile strength of the threads, both in the conditioned and in the wet state.

The threads are drawn in a second bath (air, hot water, amide / water mixture). The stretch cond. However, the threads obtained are only 5 and 7%. Without stretching in the secondary bath and only by warping in the precipitation bath, higher strains> 10% are possible, but at the expense of fiber strength. As already explained, elongation values below 10% are too low for textile applications. An increase in elongation without significant loss in fiber strength cond. is achieved by the aftertreatment of the threads according to the invention in an alkali bath.

The increasing concentration of precipitant is particularly expediently set by a tube which surrounds the spinnerets and is open on the precipitation bath side.

Immediately after leaving the spinnerets, the amide and LiCl released from the spinning solution lead to a strong enrichment of the precipitation bath portion within the tube with these components, a concentration gradient being formed over the tube length. The concentration of the precipitant in the bath increases towards the open end of the pipe and is almost the same as the concentration in the surrounding precipitating bath. In contrast, in the conventional spinning bath management, the aim is to remove the solution components contained in the spinning solution as quickly as possible and, accordingly, to cause rapid thread formation.

In the area immediately after the spinnerets, the amide concentration according to the invention can be set to be much higher than 70% by mass, without any loss of spin resistance being found. In the subsequent zones and after they emerge through the open tube end into the surrounding precipitation bath, the gel threads, which initially swell up, can become increasingly larger Solidify concentrations of precipitant continuously so that there is no sticking to the trigger elements.

With the same precipitation bath composition, the fiber strength is both cond. as well as wet by the concentration gradient set according to the invention increased by 10 to 20% compared to the usual spinning bath guidance. If pure water is used as the precipitation bath, even an increase in the tensile strength is conditional. possible by approx. 35%.

The post-treatment of the drawn threads is advantageously carried out in an aqueous solution of alkali metal hydroxide or in liquid ammonia.

The aftertreatment is particularly preferably carried out in a solution having a concentration of 2 to 8% by mass of alkali metal hydroxide at temperatures between 10 and 100 ° C. and a residence time of up to 20 minutes.

Treatment of cellulosic threads and fabrics with concentrated solutions of alkali metal hydroxide or with organic bases - usually under tension - are known as mercerization to produce permanent finishing effects, white gloss and increased dye absorption. However, sodium hydroxide solution is generally used in concentrations of 26 to 30% by mass of NaOH. If, for example, viscose threads are subjected to such a treatment, their strength condenses. and their wet strength drops significantly, their wet modulus is reduced; only the loop strength increases.

In the aftertreatment according to the invention of threads spun in the solvent system DMA and / or 1-methyl-2-pyrrolidinone and LiCl, it has surprisingly been found that their elongation increases by up to 100% with only a slight loss in strength. The higher the concentration of alkali metal hydroxide, the greater the weight loss of the threads as a result of detached low-molecular cellulose fractions. The dissolving power of aqueous NaOH reaches a maximum at 12.5%. In addition, highly concentrated aqueous alkalis also cause large losses in the strength of the fibers.

If potassium hydroxide solution is used instead of sodium hydroxide solution, the weight loss of the threads can be kept even smaller due to the lower dissolving power of the potassium hydroxide solution.

Good waxing of the threads before the aftertreatment is also essential, since DMA or 1-methyl-2-pyrrolidinone still adhering to the threads is cleaved, in particular in a water bath with a higher temperature, and is therefore lost for recovery.

Following the aftertreatment, the threads are squeezed, washed, optionally cut, finished with known equipment and dried.

The device according to the invention for wet spinning with a spinning whistle which is inserted into a precipitation bath and has spinning nozzles is characterized in that a tube surrounding the spinning nozzles is attached to the spinning whistle and is only oven-side towards the precipitation bath side.

The course of the concentration of the spinning solution components or the precipitant along the passage of the threads inside the tube can be changed by varying the length and / or the cross-section of the tube and the composition of the feed bath which is fed in a circle. The longer the pipe is designed and the smaller its cross-section, the higher the amount of amide and LiCI in the precipitation bath in the pipe. This content is always highest in the area immediately after the spinnerets.

The cross-sectional shape of the tube is arbitrary and is determined by the distribution and number of spinnerets on the spinning pipe. In most cases, tubes with a circular cross-section are used.

According to an advantageous embodiment, the tube attached to the spinning pipe has peripheral or ring-shaped internals on the inside to form a number of chamber sections lying one behind the other.

These internals in no way hinder the free passage of the threads through the precipitation bath, but more effectively prevent the precipitation bath part located inside the tube from mixing too quickly through the open end of the tube with the surrounding precipitation bath and thus ensure the formation and maintenance of a certain concentration gradient during of the entire spinning process.

To form threads with a flattened cross-section - so-called ribbons - the spinnerets are designed in a shield-like manner according to a further expedient embodiment.

The invention is explained in more detail below with reference to the drawing and the examples. Unless otherwise defined, all percentages are mass%.

Fig. 1 shows schematically an embodiment of a device according to the invention for wet spinning with a tube surrounding the spinnerets. In Fig. 2 is a pipe equipped with internals, which is part of a device according to the invention, enlarged and shown in section.

According to FIG. 1, the precipitating bath 2 is located in a spinning tub 1. The liquid containing the precipitant enters the spinning tub 1 behind the spinning whistle 3 through a perforated plate 4 and leaves the spinning tub 1 through the overflow 5 Nozzle caps, not shown, are used with spinnerets. A tube 6 of variable length which surrounds the spinning nozzles and is open on the precipitation bath side is attached to the whistle. The spinning solution gelled from the whistle 3 through the spinnerets first into the zone of the precipitation bath 2 surrounded by tube 6, threads 7 being formed which lead to a thread cable can be withdrawn from the godet 9 via a thread guide 8. The thread cable is fed from the godet 9 to a gas or liquid bath, not shown, where the stretching takes place.

The withdrawal of the thread cable must of course not be hindered by the tube 6.

With the entry of DMA and / or 1-methyl-2-pyrrolidinone and LiCI through the spinning solution, the concentration of these solution components in the tube 6 is increased, a concentration gradient is formed from the nozzles to the open end 10 of the tube 6, since only there a more thorough mixing with the main part of the precipitation bath 2 located in the tub takes place.

The tube 6 according to FIG. 2 is essentially cylindrical and has peripheral or annular internals 11 on its inside. In addition to the length and the diameter of the tube 6, the number and the inner diameter of the internals 11 can also be varied in this embodiment. It has proven to be particularly expedient to provide the perforated diaphragm-like internals 11 with an inner diameter which decreases continuously toward the open end 10 of the tube 6, so that the thread cable, which usually runs in a steeply conical shape to the yarn guide 8, is surrounded as closely as possible by the internals 11. The open end 10 of the tube 6 also has a smaller diameter than the cylindrical main part of the tube 6 in accordance with the course of the thread cable. Chamber sections are formed by the internals 11 in which the concentration of precipitant increases from the spinnerets in the direction of the open tube end 10 . A rapid concentration equalization in the interior of the tube 6 through flow processes is largely prevented by this section formation.

example 1

A solution of sulfite pulp in LiCI and DMA was made by the water / solvent exchange activation method. The composition of the solution in parts by weight of cellulose / DMA / LiCI was 7/86/7. The DP _{cuen of} the cellulose was 440, the viscosity of the solution was determined with a Haake Viscotester viscometer (VT 24, measuring system E 500, speed level 1), it was 300 Pa.s at 20 ° C. The spinning solution was filtered through a metal fleece filter candle (20 µm pore size), heated to 105 ° C. in a thin-layer heater and spun horizontally into a precipitation bath using a spinning pipe. The spinning pipe was equipped with four gold / platinum nozzle cones with a 1053 hole and 0.06 mm nozzle diameter. The precipitation bath was fed in behind the spinning pipe from a perforated plate in an amount of 15 l / min at a temperature of 20 ° C. Various glass cylinders, nominal width 6 cm, with variable cylinder lengths according to the type described in connection with FIG. 1 could be attached to the whistle.

The concentration gradient formed in the tube after reaching equilibrium was dependent on the composition of the spinning solution and on the composition of the precipitation bath circulated.

The thread cable was withdrawn from the precipitation bath by means of a first godet, passed through a drawing bath with a second godet and wound up on a winding unit. Water at 92 ° C. was used as the drawing bath. The diving distances were 90 cm in the precipitation bath and 70 cm in the stretching bath.

The cable wound on the spool was cut through once with a twine, washed in rope form and aftertreated. The waxing and aftertreatment was also carried out on filaments under tension, but without drawing. The waxes were carried out at 65.degree. C. with water, then they were aged, the excess equipment was removed by squeezing or centrifuging, and the filaments were dried.

Spinning conditions and data for the fibers obtained in each case are summarized in Table I.

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

The treatment was carried out in strand form, after which it was washed with hot water, softened and dried.

Post-treatment conditions and fiber data after the lye treatment are summarized in Table II. For comparison, the data of an untreated fiber (spinning conditions see Table I, precipitation bath composition 40% DMA, 60% H ₂ 0) are given.

Table II shows that by means of a suitable aftertreatment in the alkali bath, the fiber elongations which are too low for textile applications are conditional. can be increased from 5 to 7% to over 12% without a great loss of strength.

Example 2

Fibers produced according to Example 1 were continuously aftertreated with aqueous alkali metal hydroxide under tension, but without drawing.

The fiber cable was then washed, stranded and dried.

Treatment conditions and the fiber strength and elongation values obtained are summarized in Table III. For comparison, the data of an untreated fiber (see Table 111) are entered.

Claims (8)

1. A process for the production of cellulose threads or fibres from a solution of cellulose in dimethylacetamide (DMA) and/or 1-methyl-2-pyrrolidinone and lithium chloride by wet spinning, in which the cellulose solution is forced through spinning jets and the threads which are thereby formed are pulled through a precipitation bath and then stretched, characterized in that an increasing concentration of precipitating agent is established in the precipitation bath along the region where the threads are pulled through and the threads are drawn out of the precipitation bath are subjected to a secondary treatment in an alkaline steeping bath at the end of their stretching treatment.

2. A process according to Claim 1, characterized in that the increasing concentration of precipitating agent is established by means of a tube which surrounds the spinning jets and is open on the precipitation bath side.

3. A process according to one or both of Claims 1 and 2, characterized in that water is added as the precipitating agent.

4. A process according to one or more of Claims 1 to 3, characterized in that the secondary treatment is performed in an aqueous solution of alkali metal hydroxide or in liquid ammonia.

5. A process according to Claim 4, characterized in that the secondary treatment is carried out in a solution having a concentration of 2 to 8% by weight of alkali metal hydroxide at temperatures between 10 and 100°C and with a residence time of up to 20 minutes.

6. A device of wet spinning cellulose solutions for performing the process according to one or more of Claims 1 to 3, comprising a spinning pipe (3) comprising spinning jets which is immersed in a precipitation bath (2), characterized in that a tube (6) which surround the spinning jets is placed in the spinning pipe (3), which tube is only open on the precipitation bath side.

7. A device according to Claim 6, characterized in that the tube (6) which is placed on the spinning pipe (3) comprises on its inner side peripheral or circular built-in baffles (11) in order to form a number of chamber sections located behind one another.

8. A device according to one or both of Claims 6 or 7 for the production of threads with a flattened cross-section, characterized in that the spinning jets have a slit-shaped structure.

Images