Melt spinnable copolymers from polyacrylonitrile, method for producing fibers or fiber precursors by means of melt spinning, and fibers produced accordingly

Abstract

The invention relates to a method for the production of thermally stabilised melt-spun fibres in which polyacrilonitrile (PAN) fibres or PAN fibre precursors produced by melt-spinning are treated in an aqueous alkaline solution, comprising in addition a solvent for PAN. Likewise, the invention relates to fibres which are producible according to this method.

Claims

1. A melt-spinnable copolymer of polyacrylonitrile (PAN), which is produced by copolymerisation of 99.9 to 80% by mol of acrylonitrile with at least one comonomer selected from a) 0.1 to less than 5% by mol of at least one alkoxyalkylacrylate of the general formula I, ##STR00009## with
R=C.sub.nH.sub.2n+1 and n=1−18 and m=1−8, b) 0 to 10% by mol of at least one alkylacrylate of the general formula II ##STR00010## with
R=C.sub.nH.sub.2n+1 and n=1−18, c) 0 to 10% by mol of at least one vinyl ester of the general formula III ##STR00011## with
R=C.sub.nH.sub.2n+1 and n=1−18, and d) 0 to 10% by mol of at least one vinyl ether of the general formula IV ##STR00012## with
R=C.sub.nH.sub.2n+1 and n=1−18, the sum of the comonomers a) to d) being at most 20% by mol and the copolymer having an average-weight molar mass (Mw) in the range of 10,000 to 150,000 g/mol.

2. The copolymer according to claim 1, which is spinnable in a temperature range of 160 to 240° C. with an addition of at least one external plasticizer.

3. The copolymer according to claim 1, which has a melt viscosity which is constant or decreases with increasing temperature up to 240° C.

4. The copolymer according to claim 2, wherein the at least one external plasticizer is selected from the group consisting of water, acetonitrile, nitroalkanes, alkyl alcohols, ionic liquids, glycols, dimethyl sulphoxide, dimethylformamide, dimethylacetamide, N-methylpyrrolidone, ethylene carbonate, propylene carbonate, aqueous sodium rhodanide solution, and mixtures thereof.

5. The copolymer according to claim 1, wherein the copolymerisation is effected by a precipitation polymerisation in an aqueous medium, an emulsion polymerisation in an aqueous medium, and/or a polymerisation in a solvent.

6. The copolymer according to claim 5, wherein the solvent is selected from the group consisting of dimethylsulphoxide, dimethylformamide, dimethylacetamide, N-methylpyrrolidone, ethylene carbonate, propylene carbonate, aqueous sodium rhodanide solution, and mixtures thereof.

7. The copolymer according to claim 1, wherein comonomer a) is present in an amount of 3.0 to 4.9% by mol.

8. The copolymer according to claim 1, wherein comonomer in b) is present in an amount of 1 to 5% by mol.

9. The copolymer according to claim 1, wherein comonomer in c) is present in an amount of 1 to 5% by mol.

10. The copolymer according to claim 1, wherein comonomer in d) is present in an amount of 1 to 5% by mol.

11. The copolymer according to claim 1, wherein the copolymer has an average-weight molar mass (Mw) in the range of 15,000 to 100,000 g/mol.

12. A method for the production of fibres or fibre precursors by melt-spinning, in which i) a copolymerisation of 99.9 to 80% by mol of acrylonitrile with at least one comonomer selected from a) 0.1 to less than 5% by mol of at least one alkoxyalkylacrylate of the general formula I, ##STR00013## with
R=C.sub.nH.sub.2n+1 and n=1−18, b) 0 to 10% by mol of at least one alkylacrylate of the general formula II ##STR00014## with
R=C.sub.nH.sub.2n+1 and n=1−18, c) 0 to 10% by mol of at least one vinyl ester of the general formula III ##STR00015## with
R=C.sub.nH.sub.2n+1 and n=1−18, and d) 0 to 10% by mol of at least one vinyl ether of the general formula IV ##STR00016## with
R=C.sub.nH.sub.2n+1 and n=1−18, the sum of the comonomers a) to d) being at most 20% by mol, is implemented in the presence of at least one initiator, and ii) the copolymer is spun with a melt-spinning unit comprising an extruder, a melt pump, and at least one nozzle suitable for spinning, to form mono- or multifilaments.

13. The method according to claim 12, wherein, immediately before or during the extrusion in ii), at least one external plasticizer is added, wherein the at least one external plasticizer is selected from the group consisting of water, acetonitrile, nitroalkanes, alkyl alcohols, ionic liquids, glycols, dimethyl sulphoxide, dimethylformamide, dimethylacetamide, N-methylpyrrolidone, ethylene carbonate, propylene carbonate, aqueous sodium rhodanide solution, and mixtures thereof.

14. The method according to claim 12, wherein the fibres are carbon fibres, and the method further includes: iii) stabilizing the filaments by a temperature treatment at a temperature of 200 to 350° C. and iv) carbonizing the filaments at a temperature of 800 to 1,200° C.

15. The method according to claim 14, wherein the stabilizing of the filaments is effected at a temperature of 220 to 320° C.

16. The method according to claim 12, wherein the initiator is selected from the group consisting of azo compounds, peroxides, hydroperoxides, alkylperoxides, peroxodicarbonates, peroxy esters, dialkylperoxides, persulphates, perphosphates, redox initiators, and mixtures hereof.

17. A fibre produced by spinning the copolymer according to claim 1.

18. The fibre according to claim 17, which is a carbon fibre.

Description

EXAMPLE

(1) A PAN copolymer with an end solid content of 20% and with the following characteristics was produced in an emulsion polymerisation: composition: 4.4% by mol of methoxyethlyacrylate, 3.1% by mol of methylacrylate, 0.5% by mol of itaconic acid.

(2) The polymer dispersion was precipitated in 0.1% aluminium sulphate solution, the precipitated polymer was washed extensively with water and ethanol and dried in a vacuum at 50° C.

(3) The relative viscosity of a 1% DMSO solution at 30° C. is at 1.8.

(4) The polymer powder was mixed in a mixer with acetonitrile and water, the total mixture comprised 14% by weight of acetonitrile and 14% by weight of water. Subsequently, the polymer was able to be melt-spun using a 40-hole nozzle at a nozzle temperature of 190° C., the melt-spinning unit used being equipped with a pressure chamber located subsequent to the spinning nozzle in accordance with U.S. Pat. No. 5,168,004. The fibres had a single filament titre of 5 dtex, a round cross-section and a compact, cavity-free inner structure.