EP0048846A2 - Fibres and filaments from acryl polymers that contain carboxyl groups, their use and process for their preparation - Google Patents

Abstract

The invention relates to threads and fibers made from acrylonitrile polymers which contain 10 to 30% by weight of copolymer building blocks with carboxyl groups, to their use and to processes for their preparation. In the dry state, the threads and fibers have tensile strengths of more than 10 cN / tex and knot strengths of more than 6 cN / tex and can be processed further on customary machines and are suitable for the production of shaped structures with high water retention capacity. The polymer raw materials required for spinning are produced by saponification of acrylonitrile polymers in a heterogeneous phase with aqueous dilute acids.

Description

The invention relates to threads and fibers whose thread-forming substance contains, in addition to acrylonitrile units and other units copolymerizable with acrylonitrile, in particular acrylic and / or methacrylic acid residues and optionally acrylamide units, processes for their production and their use for the production of shaped structures which are distinguished by a high water retention capacity.

The carboxyl group content of the threads and fibers according to the invention should be 10-30, preferably 15-26% by weight. The fibers and threads according to the invention can be obtained from corresponding polymer raw materials by the spinning processes customary for polyacrylonitrile and are distinguished by good textile-technological properties - particularly with regard to the tear and knot strengths - which enable problem-free further processing, e.g. allow for textile fabrics. Textile technological properties of a fiber or a thread can be described as good if they reach the level of the wool.

Threads and fibers made of acrylic polymers that contain smaller amounts of carboxyl groups are known. For example, DE-OS 24 34 232 describes a process for the production of acrylic fibers with improved microscopicity, in which raw materials containing carboxyl groups are spun into fibers and stretched, the fiber-forming ones The substance is then crosslinked and the carboxyl groups are converted into the corresponding salt form in an aqueous alkaline medium. In the examples, polymers with up to 12% acrylic acid (corresponding to 7.5% carboxyl groups) or 15% methacrylic acid (corresponding to 7.8% carboxyl groups). Because of the crosslinking reactions carried out, such threads can only absorb a small amount of water.

DE-OS 23 37 507, DE-OS 23 35 696, DE-OS 23 35 697 and DE-OS 23 36 036 describe processes for the preparation of acrylonitrile-acrylamide copolymers by saponification of acrylonitrile copolymers in a homogeneous phase concentrated acids. It is important to dissolve the acrylonitrile polymers to be saponified as quickly as possible and hydrolysis in a homogeneous system in order to improve the quality of the products produced. It was found that any heterogeneity has an adverse effect on the quality of the products produced. The hydrolysis of the acrylonitrile groups takes place in these prior always with concentrated acids, in which the training ^g vernachläßi of carboxyl bar is small. The effect of concentrated acids on acrylonitrile polymers is also described in "Fiber Research and Textile Technology" 11 (1960), pages 362 and 363.

Fibers made from mixtures of polyacrylonitrile and homogeneously saponified polyacrylonitrile are described in "fiber research and textile technology" 14 (1963), pages 265-270. In the case of mixtures with a carboxyl group content of 8.5%, attention is already drawn to the strong tendency of the spinning solutions prepared from these mixtures to gel, which makes the spinning process noticeably more difficult.

There was therefore still the task of producing threads and fibers from acrylic polymers with a high carboxyl group content, which can be further processed into textile or wadding-like structures.

Surprisingly, it has now been found that saponified polyacrylonitriles with a carboxyl group content of up to 30% by weight can be spun in the heterogeneous phase using dilute acids by the spinning processes customary for polyacrylonitrile. The threads and fibers obtained can be easily crimped, carded and further processed into wadding, yarns and textile fabrics. Mixed processing with other fibers is also possible without difficulty. The sizes important for further processing such as tear and knot strength correspond to or exceed the values known from wool. In the dry state, they have tensile strengths of more than 10 cN / tex and knot strengths of more than 6 cN / tex, preferably even 8 and more cN / tex.

The threads and fibers according to the invention are particularly suitable for processing in admixture with other fibers for the production of yarns for clothing textiles with increased wearing comfort because of the swellability which can be adjusted via the carboxyl group content and the associated high water retention capacity. In particular in the pure processing of the threads and fibers according to the invention, absorbent wadding, nonwovens, tampons, fabrics, knitted fabrics and the like can be produced, which are distinguished by their water retention capacity. If such threads or fibers or shaped structures of such products according to the invention are treated with gaseous or anhydrous bases, the carboxyl groups can be converted into the salt form. Such methods, which are the subject of a parallel application, can increase the swelling capacity of the threads and fibers many times over without the threads becoming sticky or embrittled.

When in contact with alkaline aqueous media, the threads and fibers according to the invention and those derived therefrom put up structures very strongly. These properties make it possible, for example, to produce filter fabrics that let acidic aqueous media pass through but block alkaline media. The threads and fibers according to the invention and the structures produced therefrom are also outstandingly suitable as ion exchangers with very high exchange capacities.

The invention is also based on a method for producing such threads and fibers, the fiber raw material being produced by saponification of an acrylonitrile polymer or copolymer with aqueous dilute acids in a heterogeneous phase. The desired degree of saponification can e.g. with constant reaction conditions via the concentration of the acid used. In contrast to the homogeneous saponification reactions of polyacrylonitriles with higher acid concentrations, only carboxyl groups are preferably formed in the heterogeneous saponification with dilute aqueous acids. The non-uniformity of the polymers, particularly with regard to the sequence distributions, is likely to be considerably greater with heterogeneously saponified products than with homogeneously saponified polyacrylonitriles. However, the presumed greater non-uniformity of the saponification products may be the reason for their better processability into threads and fibers.

In addition to nitric and phosphoric acid, the saponification of the nitrile groups can preferably be carried out with the aid of dilute sulfuric acid, which should have a concentration of 40-50, preferably 45-49,% by weight. The polymers are introduced into the acid introduced and stirred for a few hours. In order to keep the reaction times short, it is advisable to work at boiling temperatures. Response times of 2.5 hours are usually sufficient. The polymer is then filtered off, washed and dried. It it has been found that the use of dilute acids to carry out the saponification reaction is also important for another reason. Suitable saponification products can only be obtained if the saponification reaction is carried out in a heterogeneous phase. A number of acids, however, act in higher concentrations as solvents or swelling agents for the polymer to be saponified. Such concentrations should therefore be avoided. The maximum acid concentration that is still suitable is the one at which the polymer particles introduced into the hydrous acid do not yet stick together. A slight swelling, however, is generally tolerable.

Homopolymers and copolymers of acrylonitrile are suitable as polymer raw materials for the saponification. The following may be considered: acrylamide, acrylic acid and their esters, vinyl esters and ethers such as vinyl acetate, vinyl stearate, vinyl butyl ether, vinyl haloacetate, such as vinyl bromoacetic acid, vinyl dichloroacetate, trichloroacetic acid vinyl ester, styrene, maleimide, vinyl halides and vinyl compounds such as vinyl chloride sulfates, such as vinyl chloride sulfates, such as vinyl compounds, such as vinyl compounds, such as vinyl chloride unsaturated vinyl chloride groups, such as vinyl compounds, such as vinyl compounds, such as vinyl compounds, such as vinyl compounds, such as vinyl compounds, such as vinyl compounds, such as vinyl compounds such as vinyl chloride, vinyl compounds, and sulfonyl chloride groups.

It is particularly cost-effective if it is possible to use the fiber raw material, which is produced on a large scale for the spinning of conventional acrylic fibers, for the saponification. The comomomers used can, as is known from acrylamide, have an advantageous effect on the saponification rate.

To produce spinning solutions, the saponified, dried polymer is dissolved in the solvents customary for polyacrylonitrile and spun by known methods using the dry or wet spinning process. The threads drawn from the nozzle can be stretched wet before, after or during washing. After this They are dried, and shrinkage can be allowed during drying. In general, the drying is followed by a further stretching process in the dry-hot state. To reduce the shrinkage, you can then shrink. In the manufacture of fibers, the cable strips produced are then usually crimped and cut to the desired length. If necessary or desired, the threads or fibers according to the invention can also be subjected to pressure damping.

In order to suppress possible slight swelling of the threads in the spinning process in the case of highly saponified polymers, instead of water, organic solvents which are miscible with the polymer solvent, such as, for example, can also be used in the precipitation, drawing and washing baths. Alcohols or ketones can be used.

The invention will be further explained below with the aid of examples. Unless stated otherwise, percentages and parts refer to amounts by weight.

example 1

700 g of a polymer composed of 93.7% by weight of acrylonitrile, 5.8% of methyl acrylate and 0.5% of sodium methallyl sulfonate, with a relative viscosity of 1.92, measured in 0.5% solution in dimethylformamide, were in 2800 g 48.2% by weight sulfuric acid (density 1.378 g / ml at 20 ° C.) boiled under reflux for 2.5 hours. After cooling, the polymer was washed free of sulfate and dried.

To determine the carboxyl group content, about 150 mg of the polymer were dissolved in 25 ml of dimethyl sulfoxide (DMSO), mixed with 60 ml of water and titrated potentiometrically with 0.1N sodium hydroxide solution. The factor of the sodium hydroxide solution was determined with oxalic acid, dissolved in 60 ml of water and mixed with 25 ml of DMSO. The titration gave a carboxyl group content of 25.5% by weight (based on -COOH) for the polymer described above, this corresponds to a content of acrylic acid of 40.7% by weight in the polymer.

600 g of the polymer saponified in this way were dissolved in 1900 g of dimethylformamide (DMF) to form a 24% spinning solution, the solution was then filtered and, at a delivery rate of 17.1 ml / min, through a 300-hole nozzle, hole diameter 0.06 mm , pressed into a precipitation bath with 24.5% DMF and 75% water and 0.5% acetic acid at a temperature of 35 ° C. After an immersion length of 50 cm, the thread was drawn off the nozzle at 6.9 m / min, stretched to 20.3 m / min in a bath with 40% DMF and 60% water at 55 ° C., in a further bath, The water held at 35 ° C, stretched to 23.3 m / min, washed in water at 50 ° C and stretched again to 26.1 m / min. After passing through an ethanolic Aviva bath, the thread was pre-dried on a duo at a temperature of 120 ° C. and allowed on another with a shrinkage of 1.3 m / min Duo dried at a temperature of 165 ° C. The thread was stretched to 35.0 m / min between the two duos. The thread was drawn off from the second duo at 48.5 m / min and shrunk back to 47.0 m / min in a hot air duct at 155 ° C.

After crimping and cutting, the fibers could be processed into a worsted. A cotton was also made by carding several times. The material could be further processed without interference into these shaped structures using conventional textile machines.

The textile technological properties of the threads thus produced are described below together with the results of Examples 2 to 6.

Examples 2 to 6

The polymer according to Example 1 was saponified as described in the previous example. However, the sulfuric acid concentrations were varied. The following polymers could be obtained.

The saponified polymers of Examples 2 to 4 were dissolved in 24% strength spinning solutions in DMF and pressed at a delivery rate of 15 ml / min through a 300-hole nozzle into a precipitation bath according to Example 1. The threads were drawn off the nozzle at 5.0 m / min and in a bath with 40% DIIF and 60% water at 60 ° C to 20.3 m / min and in a subsequent water bath at 60 ° C to 48.5 m / min. After washing and passing through an aqueous finish bath, the threads were predried in a duo at 150 ° C. and then dried in a second duo at 175 ° C., drawn off with a third duo and wound up after passing through a hot air duct at 155 ° C. The individual speeds of the duos are given in the following table.

The polymer from Experiment No. 5 could not be spun under the given conditions. The thread was swollen too much, it often tore due to its own weight and was strongly glued after drying.

The polymer from experiment No. 6 was spun as described in Examples 2 to 4, but the two draw baths were heated to 75 ° C. instead of 60.

Of the yarns of Examples 1 to 6 of the titer, the tear strength, the water retention capacity in deionized water and the _F lüssigkeitsrückhalte- assets in 0.1 N sodium hydroxide solution were measured. The knot strengths were determined on single filaments.

In order to determine the water or liquid retention capacity, about 500 mg of the cut up was used in each case Weighing the threads into a round cup made of polytetrafluoroethylene, the open bottom of which was provided with a fine-meshed network of V4a fabric. The inside diameter of the cup was 1.8 cm, the height, calculated from the net, was 3.9 cm. The beakers were placed with their contents in deionized water or in an aqueous 0.1N sodium hydroxide solution for one hour, 1 g / 1 of a wetting agent being added to each of the liquids. The sodium salt of diisobutylnaphthalenesulfonic acid has proven itself as a wetting agent. At the beginning of the liquid treatment, the samples are evacuated for 5 minutes to remove adhering air bubbles. After the treatment time, during which the samples were possibly swung back and forth in the liquid, the actual centrifugation is carried out using a laboratory centrifuge from Heraeus Christ GmbH, type UJO. The containers and samples are centrifuged at 4000 rpm for 30 minutes each. The distance between the cup nets and the axis of the centrifuge was 8.5 cm. The centrifuged fiber samples were then weighed out and then dried in a drying cabinet at 120 ° C. to constant weight. The weight difference between the moist and dried sample, divided by the dry weight, is given below in% as water retention or liquid retention.

Example 7

• Titer: 3,2 dtex
• Reißfestigkeit: 21 cN/tex
• Reißdehnung: 30 %
• Knotenfestigkeit: 10 cN/tex
• Wasserrückhaltevermögen: 29 %
• Flüssigkeitsrückhaltevermögen in 0,1-n NaOH: 788 %

The polymer from Example 3 was dissolved at 80 ° C. to form a 29% spinning solution and, with a delivery rate of 36 ml / min, pressed through a 50-hole nozzle, hole diameter 0.15 mm in a dry spinning shaft. Inert gas heated to 320 ° C. was blown in in the direction of the thread, the shaft wall was heated to 200 ° C. The threads were withdrawn from the spinning shaft at 220 m / min, two of these threads were fanned and washed with water under gentle tension at 50 ° C. On two duos _/ which were heated to 140 and 190 ° C, the threads were dried with slight stretching and pulled off by the second duo with a stretching of 1: 2.1. The total draw was 1: 3.0. Finally, the thread was shrunk by 15% in a hot air duct at 180 ° C. The individual filaments obtained in this way had the following properties:

• Titer: 3.2 dtex
• Tear resistance: 21 cN / tex
• Elongation at break: 30%
• Knot strength: 10 cN / tex
• Water retention: 29%
• Liquid retention capacity in 0.1-n NaOH: 788%

The fibers according to Examples 2, 3, 4 and 7 could also be further processed in the crimped state into wadding layers and worsted yarns.

Claims (6)

1. Threads and fibers, the thread-forming substance of which consists of an acrylic polymer which, in addition to acrylonitrile units and other units which can be copolymerized with acrylonitrile, contains 10-30% by weight of carboxyl groups, and which, in the dry state, have tensile strengths of more than 10 cN / tex and knot strengths of more than 6 cN / tex and which can be easily processed into wadding, yarns and fabrics using the usual textile technology processes. 2. Threads and fibers according to claim 1, characterized in that their liquid retention capacity in 0.1 normal aqueous sodium hydroxide solution is greater than 500%. 3. Use of the threads and fibers according to claims 1 and 2, for the production of shaped structures with high water retention. 4. A process for the production of threads and fibers according to claims 1 and 2 by spinning a polymer raw material according to the spinning process customary for acrylic threads and fibers, characterized in that the polymer raw material by saponification of an acrylonitrile polymer which, in addition to acrylonitrile, also copolymerisable from others with acrylonitrile Monomers can be built up, has been prepared in the heterogeneous phase with aqueous dilute acids, the acid concentration not yet leading to a sticking of the individual particles of the acrylonitrile polymer. 5. The method according to claim 4, characterized in that a terpolymer of acrylonitrile, methyl acrylate and with methallyl sulfonate is used as the acrylonitrile polymer. 6. Process according to claims 4 and 5, characterized in that for the saponification of a sulfuric acid with 40-50 preferably 45-49% by weight is used.