Controlled chemical stabilization of polyvinyl precursor fiber, and high strength carbon fiber produced therefrom

1. A method for the preparation of carbon fiber from a sulfonated polyvinyl precursor fiber having sulfonic acid groups thereon, the method comprising:

(i) immersing the sulfonated polyvinyl precursor fiber into a liquid solution comprised of an ionic liquid solvent and a solute species capable of engaging in an elimination-addition equilibrium with said sulfonic acid groups, wherein said ionic liquid solvent has a boiling point of at least 350° C.;

(ii) heating said liquid solution, after said sulfonated polyvinyl precursor fiber has been immersed therein, to a first temperature of at least 25° C. at which said sulfonated polyvinyl precursor fiber engages in an elimination-addition equilibrium between said sulfonic acid groups and said liquid solution while the sulfonated polyvinyl precursor fiber is maintained at an applied tension of at least 0.1 MPa;

(iii) gradually raising said first temperature to a final temperature of at least 300° C. at an average temperature ramp rate of up to 50° C. per minute, wherein said final temperature is at least 20° C. above the first temperature and up to the boiling point of the liquid solution for sufficient time to convert said sulfonated polyvinyl precursor fiber to a pre-carbonized fiber; and

(iv) subjecting the pre-carbonized fiber produced according to step (iii) to a high temperature carbonization process to produce said carbon fiber, wherein said high temperature carbonization process is conducted at a temperature of at least 500° C.

2. The method of claim 1 , wherein said sulfonated polyvinyl precursor is sulfonated polyolefin precursor.

3. The method of claim 1 , wherein said first temperature at which said polyvinyl precursor fiber engages in said elimination-addition equilibrium is at least 50° C.

4. The method of claim 1 , wherein said first temperature at which said polyvinyl precursor fiber engages in said elimination-addition equilibrium is at least 120° C.

5. The method of claim 1 , wherein said first temperature at which said polyvinyl precursor fiber engages in said elimination-addition equilibrium is at least 150° C.

6. The method of claim 1 , wherein said applied tension is at least 1 MPa.

7. The method of claim 1 , wherein said applied tension is at least 2 MPa.

8. The method of claim 1 , wherein said applied tension is at least 5 MPa.

9. The method of claim 1 , wherein said first temperature is raised to said final temperature at an average temperature ramp rate of up to 20° C. per minute.

10. The method of claim 1 , wherein said first temperature is raised to said final temperature at an average temperature ramp rate of up to 10° C. per minute.

11. The method of claim 1 , wherein said first temperature is raised to said final temperature at an average temperature ramp rate of up to 5° C. per minute.

12. The method of claim 1 , wherein said final temperature is at least 40° C. above said first temperature and up to the boiling point of the liquid solution.

13. The method of claim 1 , wherein said final temperature is at least 70° C. above said first temperature and up to the boiling point of the liquid solution.

14. The method of claim 1 , wherein said pre-carbonized fiber is infusible and incombustible.

15. The method of claim 1 , wherein said liquid solution includes at least one free-radical scavenger.

16. The method of claim 15 , wherein said free-radical scavenger is selected from hindered phenols, thioesters, phosphites, and aromatic amines.

17. The method of claim 1 , wherein steps (i) to (iii) are conducted as a continuous process on a continuously fed precursor fiber.

18. The method of claim 1 , wherein steps (i) to (iii) are conducted as a batch process on batch-fed precursor fiber.

19. The method of claim 1 , wherein said sulfonated polyvinyl precursor fiber having sulfonic acid groups thereon is produced from non-functionalized precursor fiber in a separate step before step (i), or is produced from non-functionalized precursor fiber during step (i) or during steps (i) and (ii).

20. The method of claim 1 , wherein said high temperature carbonization process is conducted at a temperature of at least 1000° C.

21. The method of claim 1 , wherein said high temperature carbonization process is conducted at a temperature of at least 2000° C.

22. The method of claim 1 , wherein said high temperature carbonization process is conducted at a temperature of at least 2500° C.

23. The method of claim 1 , wherein said carbon fiber has a tensile strength of at least 200 ksi.

24. The method of claim 1 , wherein said carbon fiber has a modulus of at least 20 Msi.

25. The method of claim 1 , wherein said carbon fiber has an ultimate elongation of at least 0.5%.

26. The method of claim 1 , wherein said carbon fiber has an ultimate elongation of at least 0.8%.

27. The method of claim 1 , wherein said carbon fiber has a surface area of at least 1000 m 2 /g.

28. The method of claim 1 , wherein said carbon fiber is processed in spoolable filament web or mat form.

29. The method of claim 1 , wherein, directly prior to step (i), the sulfonated polyvinyl precursor fiber is produced by treating an unsulfonated precursor fiber in oleum.

30. The method of claim 1 , wherein said final temperature is at least 350° C.

31. The method of claim 1 , wherein said ionic liquid solvent has a boiling point of at least 400° C.

32. The method of claim 31 , wherein said final temperature is at least 400° C.

33. The method of claim 1 , wherein said solute is a salt of a strong mineral acid.

34. The method of claim 33 , wherein said salt is ammonium sulfate.