Method for producing carbon fibers from cellulose fibers treated with sulfonic acid salts

Abstract

The invention relates to a process for producing carbon fibers from cellulosic fibers, characterized in that cellulosic fibers, which contain a sulfonic acid salt of formula (I), wherein R.sup.1 represents a hydrocarbon group and K.sup.+ represents a cation, are converted into carbon fibers.

Claims

1. A process for the production of carbon fibers from cellulosic fibers, characterized in that cellulosic fibers, which contain a sulfonic acid salt comprised of ammonium tosylate are converted into carbon fibers.

2. The process according to claim 1, characterized in that the sulfonic acid salt has a solubility in water of at least 10 parts by weight per 100 parts by weight of water at (20° C., 1 bar).

3. The process according to claim 2, characterized in that it is a process in which a) cellulosic fibers are produced, b) said cellulosic fibers are brought into contact with the sulphonic acid salt in the form of ammonium tosylate and then c) the cellulosic fibers which contain the sulfonic acid salt are converted into carbon fibers.

4. The process according to claim 1, characterized in that the cellulosic fiber contains the sulphonic acid salt in an amount such that the content of sulfur is from 0.1 to 3 wt %, based on the total weight of the dried cellulosic fiber.

5. The process according to claim 4, characterized in that it is a process in which a) cellulosic fibers are produced, b) said cellulosic fibers are brought into contact with the sulphonic acid salt in the form of ammonium tosylate and then c) the cellulosic fibers which contain the sulfonic acid salt are converted into carbon fibers.

6. The process according to claim 1, characterized in that it is a process in which a) cellulosic fibers are produced, b) said cellulosic fibers are brought into contact with the sulphonic acid salt in the form of ammonium tosylate and then c) the cellulosic fibers which contain the sulfonic acid salt are converted into carbon fibers.

7. The process according to claim 6, characterized in that the cellulosic fibers are obtained in process step a) by spinning the cellulosic fibers from a spinning solution and then washing said cellulosic fibers with water.

8. The process according to claim 7, characterized in that until carrying out process step b), no process measures are carried out for drying the cellulosic fibers.

9. The process claim 6, characterized in that, in process step b), cellulosic fibers which have a water content of more than 20 parts by weight of water per 100 parts by weight of cellulosic fiber are brought into contact with a solution of the sulphonic acid salt.

10. The process according to claim 9, characterized in that until carrying out process step b), no process measures are carried out for drying the cellulosic fibers.

11. The process according to claim 9, characterized in that the cellulosic fibers contain more than 50 parts by weight of water per 100 parts by weight of cellulose.

12. The process according to claim 11, characterized in that until carrying out process step b), no process measures are carried out for drying the cellulosic fibers.

13. The process according to claim 6, characterized in that until carrying out process step b), no process measures are carried out for drying the cellulosic fibers.

Description

EXAMPLES

(1) Cellulosic Fiber

(2) A synthetic, tear-resistant cellulosic fiber used for the production of car tires is used as the cellulosic fiber in the example and the comparative examples. Such cellulosic fibers are known as tire cord fibers. The cellulosic fiber used was made from cellulose dissolved in an ionic liquid. The cellulosic fiber was obtained by coagulation of the cellulose from the spinning bath and not dried since its production. It had a water content greater than 70 parts by weight of water per 100 parts by weight of cellulose, hence the term “never-dried tire cord fiber”.

(3) The finishing and drying of the cellulosic fiber takes place in a continuous process on godets. Godets are rollers that allow the continuous flow of fiber along the system. There are 4 of these godets used. Between the first and the second godet, the fiber is loaded with the additives via an immersion bath. Between the third and fourth godet there is a hot air duct, in which drying takes place. At the end, a tension controlled winder winds up the finished and dried fiber material.

(4) The carbonization of the obtained dried cellulosic fiber was carried out in Example 1 and Comparative Example 1 also in a continuous process; in Comparative Examples 2 and 3, it was carried out batchwise

Example 1

(5) The never-dried tire cord fiber was wound in 2 turns around godet 1 (room temperature, 6.5 m/min) and pulled through a 0.3 molar aqueous solution of ammonium tosylate and wound in 6 turns around godet 2 (room temperature, 6.5 m/min) and then in 7 turns around godet 3 (80° C., 6.5 m/min). The fiber was wound through a heating duct (120° C., length: 1.5 m) on godet 4 (room temperature, 6.5 m/min) and then onto a bobbin.

(6) The sulfur content of the dried fiber was 1 wt %.

(7) The cellulosic fiber thus produced was continuously derivatized and stabilized under inert gas. The residence times were 13.8 min at 200° C., 27.7 min at 210° C. and 13.8 min at 240° C. Accordingly, the total residence time in the stabilization was 55.2 min. The thread tension was 0.34 cN/tex.

(8) The obtained stabilized fiber was then carbonized continuously under inert gas. For this purpose, the fiber was subjected to tensile stress. The thread tension was 2.6 cN/tex. The residence times were 1.58 min at 310 and 510° C., 4.74 min at 750° C., 1.58 min at 971° C. and 4.74 min at 1400° C. for a total of 12.65 min.

Comparative Example 1

(9) Comparative Example 1 was carried out in exactly the same way as Example 1, except for the following.

(10) The never-dried tire cord fiber was not pulled through a 0.3 molar solution of ammonium tosylate, but through a 1 molar solution of ammonium hydrogen phosphate.

(11) The phosphorus content of the dried fiber was 1 wt %.

(12) Accordingly, the total residence time in the stabilization was 55.2 min. The thread tension was 0.38 cN/tex.

(13) The thread tension in the carbonization was 1.1 cN/tex. As the thread tension was increased, the fiber ripped apart.

Comparative Example 2

(14) Comparative Example 2 was carried out in exactly the same way as Example 1, except for the following.

(15) The never-dried tire cord fiber was not pulled through a 0.3 molar solution of ammonium tosylate, but through a 0.3 molar solution of p-toluenesulfonic acid.

(16) The sulfur content of the dried fiber was 1 wt %.

(17) The cellulosic fiber thus produced was very fragile and brittle. It could not be further processed in a continuous process as it does not withstand any tensile load. The cellulosic fiber was therefore derivatized, stabilized and carbonized in a batch process. The following temperature program was used:

(18) Room temperature (about 21° C.) to 160° C. with a heating rate of 1 Kelvin/min; then at 160° C. for 30 minutes, then from 160° C. to 400° C. at a heating rate of 10 K/min; and finally from 400° C. to 1400° C. with a heating rate of 3.3 Kelvin/min.

Comparative Example 3

(19) Comparative Example 3 was carried out in the same way as Comparative Example 2, except that the never-dried tire cord fiber was not treated with any additive, neither ammonium tosylate nor toluenesulfonic acid, prior to its drying.

(20) For drying the never-dried tire cord fiber was wound in 7 turns around godet 1 (80° C., 6.5 m/min) and through a heating duct (120° C., length:) on godet 2 (room temperature, 6.5 m/min) and then on a bobbin.

(21) Thereafter, the cellulosic fiber was derivatized, stabilized and carbonized in a batch process according to Comparative Example 2.

(22) TABLE-US-00001 TABLE 1 Data of the obtained carbon fibers Comp. Comp. Comp. Carbon fiber from Example 1 Example 1 Example 2 Example 3 Additive Ammonium Ammonium p-toluene- — tosylate dihydrogen- sulfonic phoshate acid DP(EWN).sup.1 after 580 620 65 630 finishing and drying Carbonization continuously continuously batchwise batchwise Carbonization yield 30 30 29  15 (wt %) Carbon content >97 92 >99 >99 (wt %) Textile mechanical properties.sup.2 Tensile strength 1.6 1.0 1.0 n.d..sup.3 [GPa] Elongation at break 2.0 2.5 2.0 n.d..sup.3 [%] Modulus of 80 43 39 n.d..sup.3 elasticity [GPa] .sup.1DP(EWN): average degree of polymerization, by viscometry (alkaline iron tartrate complex solution) .sup.2Average values from 20 single filament measurements .sup.3n.d.: not determinable, the fibers are too fragile.

(23) The textile-mechanical properties of the fiber were determined by a tensile test using the instrument “Favimat” from Textechno.

(24) The carbonization yield indicates how much carbon of the cellulose in the cellulosic fiber has been converted to carbon of the carbon fiber.

(25) The carbon content indicates the wt % of carbon in the carbon fiber.