DE2817409A1 - PROCESS FOR THE PRODUCTION OF FLAME RESISTANT AND AGAINST YELLOWING RESISTANT FEDES AND POLYACRYLNITRILE-BASED FIBERS OR FILMS - Google Patents

Description

a.

Lenzing man-made fiber

Corporation

in Lenzing (Upper Austria)

Austria

Process for the production of flame retardant and yellowing resistant threads resp. Polyacrylonitrile-based fibers or films

809848/0610

The invention relates to a method for the production of flame retardant and yellowing resistant Threads or fibers or films based on polyacrylonitrile.

A number of proposals for the production of flame-retardant fibers based on polyacrylonitrile are known. It is known to spin solutions of copolymers of chlorine- or bromine-containing vinyl compounds, optionally mixed with phosphorus-containing compounds or with finely divided antimony trioxide (Sb ₇ O ₃ ), a synergistic effect between the halogen in the copolymers and the antimony trioxide being assumed. It is also known to produce threads from the solution of a mixture of polyacrylonitrile and chlorine- or bromine-containing polymers, with antimony trioxide or phosphorus-containing compounds also being used as synergistic additives. The methods practiced up to now have the disadvantage that the solutions of the chlorine-containing copolymers in dimethylformamide (DMF) are extremely unstable in terms of temperature and oxidation. The solutions turn dark brown in a few hours at room temperature. As a result, the threads and fibers made therefrom have a strong yellow tinge. If antimony trioxide is used as an additive, difficulties arise in the fine distribution of this substance, because antimony trioxide is insoluble in the solvents in question, in particular dimethylformamide. If the antiomontrioxide is unevenly distributed, the strength and flexibility of the fibers produced are reduced. If phosphorus compounds are used instead of antimony trioxide, some of these are also sparingly soluble and by far not as effective as antimony trioxide.

The present invention aims to avoid the outlined disadvantages and difficulties and the task arises, threads or fibers or films based on polyacrylonitrile produce that have both reduced flammability and immunity to yellowing.

According to the invention, this object is achieved by that a solution of acrylonitrile-vinylidene dichloride copolymer

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and tetrabromophthalic anhydride is spun or precipitated. The invention is based on the knowledge that a synergistic Relation between the chlorine content of the vinylidene dichloride in the copolymer and the bromine content of the added tetrabromophthalic anhydride exists, which can be further improved by the addition of antimony trioxide, which is known per se.

The particular advantage of this process is that tetrabromophthalic anhydride is not only the flame retardant The effect of the chlorine is synergistically enhanced, but also, surprisingly, to a large extent, the brown discoloration of the solution of the copolymer in DMF. It is well known that copolymers of acrylonitrile and halogen-containing vinyl compounds In contrast to pure PAC, they yellow quickly in solution. This phenomenon is described in the literature by splitting off Hydrogen chloride explained. The unpredictable color stabilizing The effect of the tetrabromophthalic anhydride could clearly be attributed to the presence of an anhydride function in the molecule will. It can be shown that on the one hand bromine-free anhydrides such as maleic anhydride and phthalic anhydride and pyromellitic anhydride the oxidative-thermal discoloration of the solution, the latter anhydride showing the greatest effect. On the other hand, tetrabromophthalic anhydride loses its stabilizing effect almost completely when it is converted into a monoester with an alcohol. One special embodiment of the method according to the invention exists hence adding pyromellitic anhydride to the spinning solution in order to produce particularly white threads and fibers produce.

If exceptionally high flame retardancy is required, there is a preferred embodiment of the invention Process in that finely divided antimony trioxide is added to the spinning solution.

A preferred solvent is dimethylformamide, in which tetrabromophthalic anhydride is soluble.

The use of tetrabromophthalic anhydride for flame-proof impregnation is known from GB-PS 1 234 292 per se.

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281740S

ka-imfc, According to this earlier proposal, a fabric was made Pelyacaryl nitrile threads subsequently with a solution of Tris (~ hydroxyraethyl) phosphonium oxide, tetrakis ihydroxymethyl) pthiosphonium chloride and bromine-containing compounds such as Z; B. Tetrabromophthalic anhydride but also dibromopropanol and other compounds impregnated and dried * The chemicals mentioned by Tiler are only superficially applied to the fiber and not evenly distributed in the interior of the threads or fibers or films. In particular, there is no improvement in the whiteness of the fadeii expected ^

The invention is illustrated by the following examples assuredi

The values given in the examples for the flame-retardant effect of the polymers were determined as follows: A 3 % strength solution of the polymers in DMF was prepared. From this solution a 40 p. thick film ^ cast * After removing the solvent, the LOI value of this film was determined according to the AESTM standard D 2863. Limiting oxygen index ASTM.

The values for the anti-aging effect were determined as follows: A 5 % solution of the polymers in DMF was heated in ampoules at a temperature of 70 or 80 ° C. for one to four hours. After cooling, the contents of the ampoules were measured in a spectrophotometer at 400 nm against DMF. The information was given in% permeability (DMF = 100%). Measurement results are shown graphically in the figures.

The following abbreviations were used in the examples: PAC for polyacrylonitrile, ACN- for acrylonitrile, VDC for vinylidene dichloride, PHT 4 for tetrabromophthalic anhydride and DMF for dimethylformamide.

Example 1: A 30% solution of PAC in DMF was prepared. For this purpose, dried PAC powder was mixed with cold DMF and the mixture was stirred for 4 weeks Slowly heated to 80 ° C. for hours. The solution was then cooled to room temperature and using a with a elongated gap provided groove evenly on a glass plate

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poured out. After the DMF had evaporated, a film of 40/1 thickness. The film was peeled off from the glass plate Clamped into the framework of an LQI test apparatus. Afterward the LOI test was carried out according to ASTM regulation D-2863. An LOI value of 18% was measured.

Example 2: According to the procedure outlined in Example 1 a copolymer of ACN and VDC was dissolved in DMF. This copolymer was prepared and contained according to known methods so much VDC that the end product has a chlorine content of 30%. The determination of the LQI value resulted in a Weirt of 25%.

Example 3: The solution from Example ί was successively with 3, 6, 9 and 12% PHT 4 added and stirred until the added substance had completely dissolved. There were Obtained 4 solutions containing 2, 4, 6 and 8% bromine. The solutions were made according to the method described in Example 1 converted into films from which an LOI test was carried out In the above ranking, the following LOI values were obtained: 18.5% - 18.5% - 18.5% - 19.0%.

Example 4: The same amounts of PHT 4 were added to the solution from example 2 and treated further as in example 3 has been described. The LOI determinations on the finished films gave the following results:

2% bromine - 26%

4% bromine - 27.5%

6% bromine 2 9%.

It can be seen from the values that adding PHT to the copolymer increases the LOI value considerably, whereas the same addition shows no effect with pure PAC.

Example 5: The solution from Example 2 and the solutions from Example 4 were made with 0.5 and 1.5% antimony trioxide

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-T-

displaced .. In contrast to the PHT 4, Sb-O dissolved during the Did not stop stirring, but remained suspended in the mass.

Films were produced from the solutions, from which the LOI value was in turn determined. The results were in Fig. 1 laid down «You can see from the curves that the effect des Sb-O., to the level of the LOI value in the presence of PHT 4 is considerably larger than the pure, PHT 4-free Copolymers. "

The following 3 examples serve to illustrate the color stabilizing effect of PHT 4.

Example 6r A 5% strength solution of the copolymer was obtained with 30% chlorine produced in DMP, mixed with 2.5% PHT 4 and at Heated? 0 ° C for four hours- The same thing happened with a solution without additive of the solution measured.

From Figure 2 it can be seen that after four hours the permeability of the solution with additive is 43% higher than that of a solution with no additive.

Example 7: The same experiment was carried out at a temperature of SO C made. From Figure 3 it can be seen that the light transmission a solution with an additive is 30.5% higher than that of a solution without an additive.

Example 8: A 5% solution of a copolymer was obtained ACN and VDC made with a chlorine content of 20.5% in DMF; A certain amount of this solution was in each case with the following Add accessories:

0.5% maleic anhydride 2% phthalic anhydride 2% PHT 4

2% monobutyl tetrabromophthalate, 2% pyromellitic anhydride

These solutions were each held at 70 ° C. for four hours. The same thing happened with a solution without any

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Additions. After four hours, the solutions were measured for light transmission at 400 nm against a sample of pure DMF.

The following light transmittances - based on pure DMF - were found:

1.) without addition 27%

2.) with 0.5% maleic anhydride 48%

3.) with 2% phthalic anhydride 54%

4.) with 2% PHT 4 53%

5.) with 2% tetrabromophthalic acid

monobutyl ester 3 5%

6.) with 2% pyromellitic anhydride 70%.

It can be seen from the values that, in principle, substances with an anhydride function are solutions of copolymers from ACN and VDC in DMF stabilize against oxidative and thermal yellowing. As expected, the most effective is pyromellitic anhydride, because this compound contains two anhydride groups in the same molecule.

Example 9: A 23% strength solution of a copolymer was obtained ACN and VDC made with a chlorine content of 26% in DMF. The mixture was heated to 80 ° C. and stirred until a clear solution had emerged, turning brownish in the process. The viscous mass was heated to 80 C in a Pressure vessel transferred to the bottom outlet of which a spinneret with 30 holes had been attached. By means of a nitrogen overpressure from 3 atm the mass was pressed through the nozzle holes into a solution of 50% DMF in water at 25 ° C. The emerging Threads were pulled through the 1 m long bath by means of a pair of rollers at a speed of 7 m / min and then directly thereafter passed into a second bath, also 1 m long, which contained pure water at 90 ° C. This bath became the bundle of threads withdrawn and wound up at a speed of 30 m / min. The threads were then placed in a drying cabinet at 60.degree dried. They showed a slight yellow tinge. A flammability test has now been carried out on the material as follows: An approx. 20 cm long fuse was formed from the threads and hung vertically. The lower end of the fuse was with

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■ exposed to a 1 cm high flame for 3 seconds. This inflamed the fuse and burned about 2 seconds, whereupon the flame from. itself extinguished.

Example 10: 6% PHT 4 was added to the solution from Example 9 and stirred until the additive had completely dissolved. The slightly yellow colored mass was after the in Method described in Example 9 formed into threads. The strings were white. The flammability test went as follows: The fuse ignited when the fire was lit. However, the flame went out in a split second.

Example 11: The solution from Example 10 were additionally 0.5% antimony trioxide was added and this was then spun into threads according to the method described in Example 9. The subsequently The burning test carried out with the threads proceeded in such a way that when the fuse was flamed there was no longer any inflammation at all occurred. The fibers only charred in the flame to a black, brittle residue.

Example 12: The solution from Example 10 was additionally 2% Pyromellitic anhydride was added and this was then spun into threads by the method described in Example 9. After this The threads showed a pure white hue on drying.

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Claims (4)

-S- claims: 1. Process for the production of flame retardant and threads or fibers resistant to yellowing or Films based on polyacrylonitrile, characterized in that a solution of acrylonitrile-vinylidene dichloride copolymer and Tetrabromophthalic anhydride is spun or precipitated. 2. The method according to claim 1, characterized in that dimethylformamide is used as the solvent. 3. Procedure according to the. Claims 1 and 2, characterized in that finely divided antimony trioxide (Sb ₂ CU) is added to the solution before spinning. 4. Process according to claims 1 or 2, characterized in that pyromellitic anhydride or another acid anhydride is added to the solution prior to spinning. 809848/0610 ORIGINAL INSPECTED