DE3341277A1 - METHOD FOR PRODUCING INCREASED DENSITY OF POLYACRYLNITRILE FIBERS - Google Patents

Description

BAYER AKTIENGESELLSCHAFT 5090 Leverkusen, Bayerwerk

Central area,.

Patents, trademarks and licenses Jo / m-c · ·· '«. "3

Process for the production of polyacrylonitrile fibers of increased density

Acrylic fibers, ie fibers made from acrylonitrile homopolymers or acrylonitrile copolymers with at least% by weight of acrylonitrile units, usually have a density of 1.17 to 1.19 g / cm ³ .

It is known to increase the density of acrylic fibers ("stabilization") in order to be able to convert the acrylic fibers with increased density into carbon fibers. For example, it has been suggested (Indian Journal of Technology, Vol 13, June 1975, pages 277-280.), Polyacrylonitrile filaments a few minutes in diluted KMnO. solution to boil and then 2 to 8 hours at 150 - 220 ⁰ C to oxidize.

US Pat. No. 4,364,916 describes stabilizing polyacrylonitrile fibers by making the fibers subjecting them to hydroxylamine treatment, washing them, afterwards by a hot bath of an ammonium,

Le A 22 622

Calcium or magnesia per manganate solution. There follows a further washing step and then the actual stabilization by heating in an oxygen atmosphere at about 240 to 31o C. This Stabiliserung ⁰ 5 takes about 35 minutes.

A disadvantage of this process, in addition to the long stabilization time, is the multistage process. In addition comes that ammonium, calcium and magnesium permanganate solutions are difficult to access. When using 10 potassium permanganate a partial decomposition of the Fibers observed.

The object of the invention is therefore to provide a simple method by means of which a polyacrylonitrile fiber with a density of -1.220 g / cm ³ can be produced.

This object is achieved by adding hydroxylamine to the spinning solution, spinning the spinning solution dry, the spun threads are drawn and subjected to a thermal treatment.

The invention therefore relates to a process for the production of polyacrylonitrile threads with a density of 1.220 g / cm ³ from polymers with at least 85% by weight of acrylonitrile units by dry spinning a spinning solution, optionally washing, drawing and heating

the spun threads, characterized in that one

Le A 22 622

a) adding hydroxylamine to the spinning solution,

b) the stretching is carried out in a ratio of 1: 4 to 1:12 and

c) the stretched material for at least 100 seconds

to a contact heat of 150 to 300 ⁰ C, preferably 160 to 220 ⁰ C, exposed.

Treatment with oxidizing agents such as permanganate is not required.

The addition of hydroxylamine to polyacrylonitrile spinning solutions is known from DE-OS 27 24 952. The resulting

sponnenen threads are not subjected to the heat treatment according to the invention, its density does not reach the required minimum value of 1.220 g / cm ^3, and the hydroxyl amine additive does not take place, in order to increase the density, special, ₅ to make J to the yarns flammability.

The amount of hydroxylamine to be added according to the invention depends on the content of nitrile groups. Preferably, hydroxylamine is used in an amount from 0.1 to 3 mol%, based on nitrile groups, were added. Hydroxylamine can be added either directly or in the form of a hydroxylamine salt, with it in the second case is required, the hydroxylamine in the spinning solution by adding an amine, for example by addition of ethylenediamine, triethylamine, aniline, morpholine, pyridine, piperidine, dimethylpiperazine, diethylenetriamine or to release triethylenetetramun. After this

Le A 22 622

After adding the hydroxylamine, the spinning solution should be kept at a temperature between 50 and 150 ^° C. for at least 10 minutes before spinning. Suitable hydroxylamine salts are hydroxylamine hydrochloride and hydroxylamine sulfate.

The acrylonitrile polymers on which the acrylic fibers are based with at least 85% by weight of acrylonitrile units are known to the person skilled in the art. Acrylonitrile polymers are preferred with at least 98% by weight acrylic

10 nitrile units, in particular acrylonitrile homopolymers, used whose K values (Cellulosechemie J_3 (1932), 58) are between 60 and 120, preferably 80 and 110. The polymers are in the usual way, i.e. from about 25 to 35% by weight spinning solutions in di-

methylformamide, dimethylacetamide or N-methylpyrrolidone spun, drawn, washed and prepared.

The strengths of the filaments obtained are between 4 and 8 cN / dtex, the single filament denier is 0.5 to 20 dtex. The filaments are thermally treated on hot contact surfaces, preferably on godets, calenders or heating rails, under tensions of 0.1 to 0.2 cN / dtex and is after at the latest Completed 20 minutes. The contact heat treatment preferably lasts for 2 to 10 minutes.

The obtained by the process according to the invention

Filaments have strengths of 1.5 to 3.0 cN / dtex and are dark brown to black. You can go to filter,

Le A 22 622

Sealing and reinforcing materials processed or converted into carbon fibers using known methods will.

The density is determined according to the method of H. de Vries, H.G.Weijland, Research Journ. 28, No. 2 (1958), Pages 183-184.

Le A 22 622

example 1

In 37.5 kg of dimethylformamide were added 12.25 kg of an acrylic nitrilhomopolymerisates a K value of 90, 0.16 kg hydroxyl amine hydrochloride and 0.13 kg triethylenediamine (corresponding to 1 mol% based on nitrile) was added at room temperature and at 80 ⁰ C stirred for an hour. The spinning solution was dry spun at a tur shaft temperature of 160 ⁰ C and an air temperature of 28O ⁰ C. At a take-off speed of 200 m / min, the result was an individual spinning titre of 9.1 dtex. The spinning bath was stretched in water at 98 ° C 7-fold, washed prepared was added, under tension at 18O ⁰ C and dried on spools.

Filamante fiber data:

Titer 1.4 dtex

Tensile strength 4.8 cN / dtex elongation 13%
Shrinkage 3%
Density 1.180 g / cm ³ .

The filaments were then passed over 13 hot godets under a pretension of 0.1 cN / dtex. The temperature of the godets 1 to 4 was 180 ⁰ C, on the smooth 5-8200 ⁰ C and the godets 9-13220 ⁰ C. The result is shown in the table below.

Le A 22 622

>
to
to Experimental
No. Lingering text
(sec.) colour density
(g / cm ³ ) strength
(cN / dtex) Modulus of elasticity
(cN / tex) 622 1 30th yellow 1.180 4.8 900 2 40 light brown 1.184 4.6 900 3 60 dark
Brown 1, 188 4.3 850 3 120 black
Brown 1, 220 2.8 700 4th 240 black 1, 250 1.9 650 5 360 black 1,320 1.7 600

A comparative experiment carried out under the analogous above Conditions with a hydroxylamine-free polyacrylonitrile homopolymer fiber did not lead to any increase in density in the period investigated.

Example 2

A spinning solution was produced, spun and aftertreated analogously to Example 1. The addition of hydroxylamine hydrochloride however, and triethylenediamine were 0.48 kg and 0.39 kg, respectively, 3 mol% based on Nitrile groups.

Fiber data of the filaments:

Titer 1.4 dtex tear strength 4.5 cN / dtex elongation 14%
Shrinkage 2%

Density 1.180 g / cm ³

The filaments were passed over 13 hot godets under a pretension of 0.2 cN / dtex. The temperatures on the godets 1 to 4 was 170 ⁰ C, the godet 5 to 8 19O ⁰ C and the godets 9-13210 ⁰ C.

The result is shown in the table below.

Le A 22 622

ro Experimental
No. Lingering text
(sec.) colour density
(g / cm ³ ) strength
(cN / tex) Modulus of elasticity
(cN / tex) to
to 1 30th light brown 1.183 4.4 850 229 2 40 dark brown 1.186 4.2 830 3 60 dark brown 1.192 3.7 790 4th 120 black 1,280 2.3 710 5 240 black 1.330 1/5 580

-JIl-

The increased amount of hydroxylamine resulted in compared to Example 1 for a further acceleration of the increase in density.

Le A 22 622

Claims (4)

Patent claims 1. A process for the production of polyacrylonitrile threads with a density of 1.220 g / cm ³ from polymers with at least 85% by weight of acrylonitrile units by dry spinning a spinning solution, optionally washing, drawing and heating the spun threads, characterized in that one a) adding hydroxylamine to the spinning solution, b) the stretching is carried out in a ratio of 1: 4 to 1:12 and c) the stretched material is ^{exposed to contact heat of 150 to 300 °} C., preferably 160 to 220 ^° C., for at least 100 seconds. 2. The method according to claim 1, characterized in that the amount of hydroxylamine 0.1 to 3 mol%, based on nitrile groups. 3. The method according to claim 1, characterized in that the contact heat treatment 2 to 10 minutes and the filaments under thread tension 20 voltages of 0.1 to 0.2 cN / dtex can be maintained. 4. The method according to claim 1, characterized in that the spinning solution after the addition of the hydroxyl Le A 22 622 amine least 10 minutes, maintained at a temperature between 50 and 15O ⁰ C. Le A 22 622