METHOD FOR THE THERMAL STABILISATION OF FIBRES AND SAID TYPE OF STABILISED FIBRES

Abstract

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

Claims

1-15. (canceled)

16. A method of thermally stabilising melt spun acrylic fibres in which an acrylic fibre produced by melt spinning or a fibre precursor, which involves pre-stabilising the acrylic fibre produced by melt spinning or the fibre precursor with a mixture comprising a solvent for polyacrylonitrile and an aqueous alkaline solution.

17. The method according to claim 16, wherein the mixture comprises from 0.1 to 60% by volume of the solvent and from 40 to 99.9% by volume of the aqueous alkaline solution.

18. The method according to claim 16, wherein the solvent is selected from the group consisting of dimethylsulphoxide, dimethylformamide, dimethylacetamide, N-methylpyrrolidone, ethylene carbonate, propylene carbonate, aqueous sodium rhodanide solutions, and mixtures thereof.

19. The method according to claim 16, wherein the pre-stabilisation is effected in a modification bath comprising the mixture at a temperature of 20 to 80° C., within a dwell time of 5 s to 2 min.

20. The method according to claim 16, wherein the aqueous alkaline solution comprises from 3 to 15 mol/l of at least one alkaline earth- or alkali salt.

21. The method according to claim 16, wherein the proportions of solvent and aqueous alkaline solution in the mixture are adjusted as a function of the titre.

22. The method according to claim 16, wherein an oxidative stabilisation and carbonisation under inert gas, at temperatures of 800 to 1,700° C. follows the pre-stabilisation.

23. The method according to claim 22, wherein the oxidative stabilisation is effected at a temperature of 200 to 350° C. in an oxygen- or air-containing atmosphere.

24. The method according to claim 16, wherein the fibre precursor is produced by a method in which i. a copolymerisation of 95 to 80% by mol of acrylonitrile with at least one comonomer selected from a) 5 to 20% by mol of at least one alkoxyalkyl acrylate of the general formula I ##STR00004##  with  R=C.sub.nH.sub.2n+1 and n=1-8 and m=1-8, b) 0 to 10% by mol of at least one alkylacrylate of the general formula II ##STR00005##  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 ##STR00006##  with  R=C.sub.nH.sub.2n+1 and n=1-18, is implemented in the presence of at least one initiator and ii. the copolymer is spun with an extruder with at least one nozzle at the extruder outlet to form mono- or multifilaments.

25. The method according to claim 24, wherein the copolymer has a melt viscosity which is constant or decreases with increasing temperature up to 240° C.

26. The method according to claim 24, wherein 8 to 12% by mol of the comonomer in a) and/or 1 to 5% by mol of the comonomer in b) and/or 1 to 5% by mol of the comonomer in c) are present.

27. The method according to claim 24, wherein the copolymerisation is effected by precipitation polymerisation, emulsion polymerisation and/or polymerisation in a solvent.

28. The method according to claim 27, 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.

29. A melt spun fibre stabilised thermally according to the method of claim 16.

30. The melt spun fibre according to claim 29, which is further processed to form a carbon fibre by an oxidative stabilisation and carbonisation under inert gas, at a temperature of 800 to 1,700° C.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0036] The subject according to the invention is intended to be explained in more detail with reference to the subsequent examples and Figures, without wishing to restrict said subject to the specific embodiments shown here.

[0037] FIG. 1 shows, with reference to a schematic diagram, the temperature dependency of the storage modulus of standard non-meltable acrylic fibres and meltable acrylic precursors before the treatment according to the invention.

[0038] FIG. 2 shows, with reference to a diagram, the temperature dependency of the storage modulus of an untreated fibre

[0039] FIG. 3 shows an IR spectrum of an untreated fibre

[0040] FIG. 4 shows, with reference to a diagram, the temperature dependency of the storage modulus of a fibre treated according to the invention

[0041] FIG. 5 shows an IR spectrum of a fibre treated according to the invention

[0042] FIG. 6 shows a photo of an untreated (at the top) and a multifilament (at the bottom), treated according to the invention, made of 42 fibres which were both subjected to an oxidative stabilisation at 230° C. Melting of the untreated filament can be clearly recognised, the treated filament melts and does not bond.

[0043] The effect of the treatment is described with the following tests:

1. Bonding of the Fibres:

[0044] Approx. 500 mg fibre short section is placed between aluminium foil and incubated in the drying cabinet with loading by a weight of approx. 100 g at various temperatures respectively for 10 min. It is recorded from what temperature the result is bonding of the aluminium foil by the fibres. This temperature corresponds to a softening- or melting temperature.

2. Melting Table Microscopy:

[0045] The thermal behaviour of the fibres is observed under the melting table microscope. It is recorded whether melting of the fibres can be detected.

3. Solubility of the Fibres:

[0046] Approx. 500 mg fibre short section is stored in 10 ml MDSO and it is noted after what time the fibres dissolve. Crosslinkings are detected with this test method.

4. Dynamic-Mechanical Analysis (DMA):

[0047] The storage modulus of a fibre of 10 cm length is determined as a function of the temperature. FIGS. 2 and 4 describe the basic course of the curves. Non-modified PAN (not meltable) shows a loss of the storage modulus with the temperature up to approx. 140° C., thereafter a constant residual storage modulus is maintained which ensures the mechanical stability of the fibre. Meltable PAN, which was not treated, shows a loss of the storage modulus up to approx. 80° C., at this temperature the modulus has decreased to 0. Above 80° C., the fibre is so soft that it is no longer mechanically loadable and tears (see FIG. 1).

EXAMPLES

Comparative Example

Untreated Melt Spun Fibre

[0048] An untreated melt spun fibre made of a PAN copolymer with 10% methoxyethylacrylate and a molar mass of 15,000 g/mol, individual fibre titre 0.82 tex, was examined.

[0049] It was thereby shown during the bonding test that the fibres bond from 80° C. On the melting table microscope, complete melting at 185° C. could be observed. During the solubility test, the fibres were completely dissolved within 2 min. During the DMA, the modulus decreases, up to 100° C., to 0 (see FIG. 2).

[0050] From the IR spectrum (FIG. 3), an ester grouping at 1,730 cm.sup.−1 can be clearly detected, just as a nitrile group at 2,240 cm.sup.−1. Further characteristic bands are not present.

Example

Melt Spun Fibre Treated According to the Invention

[0051] A melt spun fibre treated according to the invention, made of a copolymer with 10% methoxyethylacrylate and a molar mass of 15,000 g/mol, individual fibre titre 0.82 tex, was examined. The fibre described in the comparative example was, for this purpose, placed in a modification bath of the composition 50% DMSO and 50% 4.5 M aqueous KOH for 60 s at 70° C. The fibre discolours to reddish brown. Subsequently, it is washed neutrally and dried in a vacuum at 50° C.

[0052] During the bonding test, it was shown that the fibres do not bond up to a temperature of 230° C. On the melting table microscope, no melting of the fibres could be observed up to 250° C., merely the colour of the fibres changed from reddish via reddish brown to black. The result of the solubility test is that the fibres are maintained entirely after 24 h. During the DMA, the modulus decreases to 250° C., but still has a value greater than 0 even at this temperature (see FIG. 4).

[0053] From the IR spectrum (FIG. 5), it results, in comparison to the IR spectrum in FIG. 3, that the intensity of the band of the ester grouping at 1,730 cm.sup.−1 has decreased significantly, whilst the intensity of the band of the nitrile group is constant at 2,240 cm.sup.−1. Furthermore, a band which can be ascribed to the formation of the PAN conductor structure occurs at 1,570 cm.sup.−1.