US2957748A

US2957748A - Production of fibers and threads having high dyestuff affinity from polyacrylonitrile

Info

Publication number: US2957748A
Application number: US756545A
Authority: US
Inventors: Lieseberg Friedrich
Original assignee: BASF SE
Current assignee: BASF SE
Priority date: 1957-08-28
Filing date: 1958-08-22
Publication date: 1960-10-25
Anticipated expiration: 1977-10-25
Also published as: DE1049530B; NL230811A; FR1202492A; BE570682A

Description

Oct. 25, 1960 F. LlEsEBERG 2,957,748

PRODUCTION OF FIBERS AND THREADS HAVING HIGH DYESTUFF AFFINITY FROM POLYACRYLONITRILE Filed Aug. 22. 1958 INVENTOR.

FRIEDRICH IESEBERG Bywbza wt FM ATTORNEYS PRODUCTION OF FIBERS AND THREADS HAV- ING HIGH DYESTUFF AFFINITY FROM POLY- ACRYLONITRILE Friedrich Lieseberg, Ludwigshafen (Rhine), Germany, assignor to Badische Anilin- & Soda-Fabrik Aktiengesellschaft, Ludwigshafen (Rhine), Germany This invention relates to the production of fibers and threads with high dyestuif affinity from polyacrylonitrile by the wet stretch spinning process.

The iuvention'relates especially to the production of fibers Vand threads with high dyestuff affinity from polyacrylonitrile by spinning solutions of polyacrylonitrile in dimethylformamide with the interposition of an air stretch into a precipitating bath of dimethylformamide and water andstretching the spun tow after passing through the precipitating bath under defined conditions in three baths of water yand dimethylformamide.

In the production of fibers or threads from polyacrylonitrile by the wet spinning process the tow of threads is usually led through the coagulation and stretching baths without interruption from the spinning jet to the final ready-stretched threads. Dimethylformamide is almost exclusively used as solvent in practice. The use of water as the coagulant yields threads which readily tear when stretched. Precipitation with the air of organic solvents, for example with glycerine or isopropanol, or with aqueous salt solutions, gives better threads. It is known that it is advantageous to spin into baths which contain mixturesof dimethylformamide and water as the precipitant. In this method, the stretching of the threads is usually effected in a hot inert gas atmosphere.

The Wet-spun threads almost always have a curved kidney-shapedV cross-section. In so far as they consist of pure polyacrylonitrile, they can only be dyed with difficulty. At least it is necessary to apply special dyeing methods, such as the cuprous ion method. In order to achieve deep full dyeings by the ordinary dyeing methods, it has hitherto been necessary to prepare copolymers with monomershaving affinity for dyestuffs.

The object of the present invention is the production of fibers and threads having high dyestuff affinity from pure polyacrylonitrile.

Ihe object of the invention is achieved by a wet spinning process according to which a solution of polyacrylonitrile in dimethylformamide is spun, with the interposition of an :air stretch, into a precipitating bath of dimethylformamide and water with a dimethylformamide content of 60 to 85%. After passing through the precipitating bath, the spun tow is then stretched in three successive baths of water and dimethylformamide of which the first lhas a dimethylformamide content of 2 to 20%, preferably 5 to 10%, the dimethylformamide concentration of the three stretching baths decreasing in the direction of the withdrawal of the thread in the ratio of approximately 1:0.5:0.01.

The ldrawing represents a diagrammatic illustration showing the formation of the fibers and their passage through the coagulating bath `and the stretching baths. The method of operation, for example, may be as follows: A 20% solution of pure polyacrylonitrile in dimethylformamide is supplied from a container which is under oxygen-free nitrogen, by means of a metering pump, to a jet having several hundred holes. The jet is Y2,957,748 Patented Oct. 25, 1960 ice built into a spinning aggregate which has become known under the name of Thiele spinning funnel. The spinning funnel is arranged with its outlet dipping into a bath of dimethylformamide and Water. Behind this precipitating bath there are arranged three stretching baths of aqueous dimethylformamide. The spun tow is led continuously through the 4-bath arrangement. When preparing fibers, the staple fibers fall into a hot water aftertreatment bath to which brightening agents may be added.

When the spinning solution leaves the jet, it rst passes through an air space between the jet and the surface of the precipitating liquid of 3 to 20 millimeters, the individual threads of the spinning solution being subjected to a certain pull in a manner analogous to that applied in dry-spinning. The precipitating liquid, which is led in circulation, embraces the threads and draws them through the spinning funnel into the precipitating bath arranged beneath the same. The dimethylformamide content of the precipitating liquid in this bath should preferably amount to 60 to 85%. The tow is prestretched in the spinning funnel. By the diffusion of the solvent into the bath liquid, there takes place, with simultaneous orientation of the thread molecules, by partial coagulation, a peripheral skin formation which is at first thin but which penetrates into the interior of the thread as the diffusion of the solvent into the aqueous precipitating liquid progresses, and a thread is formed which responds to the pull. The tow is stretched in the following three baths. The first stretching bath should have a dimethylformamide content of 2 to 20%, preferably 5 to 10%, and the dimethylformamide content of the three stretching baths should decrease in a ratio of approximately l:1/2:l/ 100. The stretching baths may have any temperature between room temperature and 100 C. The first stretching bath is preferably at room temperature and the other two at about 100 C.

Since the fresh water for maintaining the concentration stages is led only into the final, third stretching bath, the aqueous dimethylformamide solutions of the baths moves inY countercurrent to the movement of the tow. With a pH of the precipitating bath of about 5, the pH of the stretching baths should increase within a range of from 5 to 7. Brightening agents and also water-softening agents may be added to the stretching baths. It is usual to stretch to a ratio of 1:5. Higher stretching ratios, for example, 1:7 may also be provided. The residence times of the spun tow in the stretching baths should be in a definite gradation to each other in a similar way to the dimethylformamide concentration of the baths. It has proved to be suitable, with a residence time of l to 4 seconds in the first stretching bath, to arrange the gradation in theV approximate ratio 1:1/4: l/ 4. These are based on the withdrawal speeds of the tow from the baths. After stretching, the spun tow may be cut into staple bers. The fibers are with advantage subjected to a hot water treatment with or without the addition of a brightening agent. A Avery fine crimping is thereby obtained. The fibers thus prepared have a circular or almost circular cross-section as an obvious feature of difference from all hitherto known commercial types of fiber from pure polyacrylonitrile or acrylonitrile copolymers.

The high dyestuff afiinity of the threads of fibers prepared according to this invention is probably caused by a large number of submicroscopic cavities. This is indicated by the relatively great inner surface and the small mean pore diameter of the filaments. If the inner surface of the hitherto known types of polyacrylonitrile fibers is assumed to be about 8 square meters per gram, the inner surface of the fibers of the process according to this invention is about ten times as large, i.e. about square meters per gram. In a corresponding way, with a mean pore diameter of the known types of fiber of about 40 millimicrons, the mean pore diameter of the fibers prepared according to this invention amounts to only one quarter, namely about millimicrons.

The threads or bers can be dyed in full shades with basic dyestufs, for example Rhodamin B extra (Color Index, 2nd edition 1956, No. 45,170), both in a sulfuric acid bath with the addition of sodium sulfate or in an acetic acid bath with the addition of sodium acetate. It is even possible to achieve almost equally deep shades in cold dyestui liquors, a possibility which is not available with pure polyacrylonitrile bers wihch have been dry-spun and 4after-stretched wet or with acrylonitrile copolymers. Dyeing may be carried out in a similarly favorable way with dispersion dyestuffs. Cold dyeing gives somewhat paler shades of color. As compared with the commercial types of fibers from pure acrylonitrile and copolymers, however, even here a clearly better dyestut affinity can be recognized.

The following example will further illustrate this invention but the invention .is not restricted to this example.

Example A solution of polyacrylonitrile in dimethylformamide is supplied by means of a metering pump to a jet with 300 holes each hole having a diameter of 0.25 millimeter. The jet is built into a Thiele spinning funnel aggregate. Beneath the spinning funnel there is a precipitating bath in a channel. When the spinning funnel is in operation, the column of precipitating liquid is about 75 centimeters in height. The length of the bath is so dimensioned that the spun tow can travel in the bath a distance of 1 meter. At a conveying output of the spinning pump of 41 grams per minute and taking into consideration the total jet cross-section of the 300- hole jet, an exit speed of 2.8 meters per minute is achieved. The draw-off speed of the spun tow amounts to 18 meters per minute, making a stretch of 645% of the original length. The precipitating bath has a dimethylformamide concentration of 74.2%, a pH of 5.2 and a temperature of 16 C. The spun tow is led by means of drawing means through three successive stretching baths (bath length 450 centimeters). The bath temperature, dimethylformamide content, pH value and residence time of the tow in the baths m-ay be seen from the following table:

fibers obtained have an almost circular cross-section. Their dimethylformamide content amounts t0 0.06%.

4 Physical tests supplied the following data:

Swelling value, 47.60%

Moisture absorption in normal climate (20 C. at relative humidity 1.90%

Tensile strength, dry, 3.59 g./denier Tensile strength, wet 2.61 g./ denier Wet strength, therefore, is 72.7% of the dry strength.

Extension, dry, 28.6%

Extension, wet, 31.1%

Titer, 3.26 deniers.

The fibers may be dyed well in deep, full shades with the basic dyestuff Rhodamin B extra (ibid.) (1% concentration with reference to air-dried fibers) in a sulfuric acid bath with the addition of sodium sulfate at a fiber at bath ratio of 1:50 in 2 hours at 20 C. The shade of color deepens at a higher bath temperature.

What I claim is:

1. 1n the process for the production of fibers and threads from polyacrylonitrile by extruding a solution of polyacrylonitrile in dimethylformamide through a jet into air, passing the resulting filaments through a spinning funnel into a coagulating liquid comprising dimethylformamide and water and stretching said filaments in the presence of an aqueous liquid, the steps comprising withdrawing said filaments from said coagulating liquid, passing said filaments through a first stretching bath comprising 2 to 20 percent by weight of dimethylformamide and 98 to 80 percent by weight of water, and then passing said vfilaments through two additional stretching baths comprising dimethylformamide and water, the three stretching baths having (a) dimethylformamide contents which decrease in a ratio of approximately 1:1/z:1/ 100, (b) pH values which increase between the limits 5 to 7, and (c) a temperature which lies between 15 and 100 C.

2. ln the process for the production of fibers and threads from polyacrylonitrile wherein a solution of polyacrylonitrile in dimethylformamide is extruded through a jet into air, the resulting filaments are passed through a spinning funnel into a coagulating liquid comprising dimethylformamide and water and said filaments are stretched in the presence of an aqueous liquid, the steps comprising, withdrawing said filaments from said coagulating liquid, passing said filaments through a rst stretching bath comprising 2 to 20 percent by weight of dimethylformamide and 98 to 80 percent by weight of water with a residence time of 1 to 4 seconds, and then passing said filaments through two additional stretching baths comprising dimethylformamide and water, the three stretching baths having (a) dimethylformamide contents which decrease in a ratio of approximately 1:1/zz1/100, (b) pH values which increase between the limits 5 to 7, and (c) a temperature which lies between 15 and 100 C., the residence times of said filaments in the successive stretching baths corresponding approximately to the ratio lzlizl.

References Cited in the file of this patent UNITED STATES PATENTS 2,721,785 Zybert Oct. 25, 1955 2,723,900 Hooper Nov. 15, 1955 UNITED STATES PATENT OFFICE CERTIFICATION OF CORRECTION Patent No.. 2,957,748 October 25, 1960 Friedrich Lieseberg 1t is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent Should read as corrected below Column 1q line 311, for "air" read aid lcolumn 2, line 58, for "Avery" read very column 4, line 16, for "'at", first occurrence, read to Signed and sealed this 16th day of May 1961.

f SEA L) Attest:

ERNEST W. SWIDER l DAVID L. LADD Attesting Officer Commissioner of Patents

Claims

1. IN THE PROCESS FOR THE PRODUCTION OF FIBERS AND THREADS FROM POLYACRYLONITRILE BY EXTRUDING A SOLUTION OF POLYACRYLONITRILE IN DIMETHYLFORMAMIDE THROUGH A JET INTO AIR, PASSING THE RESULTING FILAMENTS THROUGH A SPINNING FUNNEL INTO A COAGULATING LIQUID COMPRISING DIMETHYLFORMAMIDE AND WATER AND STRETCHING SAID FILAMENTS IN THE PRESENCE OF A AQUEOUS LIQUID, THE STEPS COMPRISING WITHDRAWING SAID FILAMENTS FROM SAID COAGULATING LIQUID, PASSING SAID FILAMENTS THROUGH A FIRST STRETCHING BATH COMPRISING 2 TO 20 PERCENT BY WEIGHT OF DIMETHYLFORMAMIDE AND 98 TO 80 PERCENT BY WEIGHT OF WATER, AND THEN PASSING SAID FILAMENTS THROUGH TWO ADDITIONAL STRETCHING BATHS COMPRISING DIMETHYLFORMAMIDE AND WATER, THE THREE STRETCHING BATHS HAVING (A) DIMETHYLFORMAMIDE CONTENTS WHICH DECREASE IN A RATIO OF APPROXIMATELY 1:1/2:1/100, (B) PH VALUES WHICH INCREASE BETWEEN THE LIMITS 5 TO 7, AND (C) A TEMPERATURE WHICH LIES BETWEEN 15 TO 100*C.