Method for the preparation of carbon fiber from polyolefin fiber precursor, and carbon fibers made thereby

1. A method for the preparation of carbon fiber from polyolefin fiber precursor, the method comprising partially sulfonating said polyolefin fiber precursor to produce a partially sulfonated polyolefin fiber, and subjecting said partially sulfonated polyolefin fiber to carbonization conditions to produce said carbon fiber, wherein partial sulfonation of said polyolefin precursor fiber produces a surface-sulfonated polyolefin fiber by sulfonating a surface layer of said polyolefin fiber precursor while leaving a core portion of said polyolefin fiber precursor unsulfonated, wherein subsequent carbonization volatilizes the unsulfonated core portion and carbonizes the surface-sulfonated portion to produce a hollow carbon fiber.

2. The method of claim 1 , wherein said surface-sulfonated polyolefin fiber is produced by subjecting said polyolefin fiber precursor to a sulfonation treatment step for a period of time less than the time needed to sulfonate the polyolefin fiber precursor through its core.

3. The method of claim 1 , wherein said surface-sulfonated polyolefin fiber is subjected, in the absence of an external sulfonating source and in an oxygen-containing environment, to a desulfonation temperature at which gaseous sulfur oxide species are released from the sulfonated surface portion to migrate toward the core of said surface-sulfonated polyolefin fiber, wherein said desulfonation temperature is at least 50° C. and below a carbonization temperature.

4. The method of claim 3 , wherein said surface-sulfonated polyolefin fiber is subjected to said desulfonation temperature for a period of time less than the time required for the entire polyolefin fiber to be sulfonated through the core, wherein subsequent carbonization volatilizes the unsulfonated core portion and carbonizes the surface-sulfonated portion to produce a hollow carbon fiber.

5. The method of claim 3 , wherein said surface-sulfonated polyolefin fiber is subjected to said desulfonation temperature for a period of time that causes the entire polyolefin fiber to be sulfonated through the core, wherein subsequent carbonization produces a solid carbon fiber.

6. The method of claim 3 , wherein said desulfonation temperature is at least 50° C. and up to 300° C., and said surface-sulfonated polyolefin fiber is subjected to said desulfonation temperature for a time up to 1 hour.

7. The method of claim 3 , wherein said desulfonation temperature is at least 70° C. and up to 160° C., and said surface-sulfonated polyolefin fiber is subjected to said desulfonation temperature for a time less than 1 hour.

8. The method of claim 3 , wherein the method employs a desulfonation pressure of at least 0.1 atm and up to 2 atm, and said surface-sulfonated polyolefin fiber is subjected to said desulfonation temperature for a time less than 1 hour.

9. A method for the preparation of carbon fiber from polyolefin fiber precursor, the method comprising partially sulfonating said polyolefin fiber precursor to produce a partially sulfonated polyolefin fiber, and subjecting said partially sulfonated polyolefin fiber to carbonization conditions to produce said carbon fiber, wherein partial sulfonation of said polyolefin fiber precursor is accomplished by melt mixing polyolefin precursor resin with a sulfonated material to produce a melt-mixed composite, spinning the melt-mixed composite to produce a melt-mixed composite fiber, followed by subjecting the melt-mixed composite fiber to a desulfonation temperature of at least 50° C. and below a carbonization temperature under a nominal applied stress along the fiber length to avoid fiber shrinkage.

10. The method of claim 9 , wherein said sulfonated material is an organic sulfonated compound or material.

11. The method of claim 10 , wherein said organic sulfonated compound or material is selected from sulfonated graphene, sulfonated diene rubber, sulfonated polyolefin, sulfonated polystyrene, polyvinyl sulfate, and sulfonated lignin.

12. The method of claim 9 , wherein said sulfonated material is a non-metallic inorganic sulfate.

13. The method of claim 12 , wherein said inorganic nonmetallic sulfate is selected from ammonium sulfate or ammonium bisulfate.

14. The method of claim 12 , wherein said desulfonation temperature is at least 50° C. and up to 300° C., and said melt-mixed composite fiber is subjected to said desulfonation temperature for a time up to 1 hour.

15. The method of claim 9 , wherein said desulfonation temperature is at least 70° C. and up to 160° C., and said melt-mixed composite fiber is subjected to said desulfonation temperature for a time less than 1 hour.

16. A method for producing a hollow carbon fiber, the method comprising subjecting a multi-component polymer fiber composite to a carbonization step, wherein said multi-component polymer fiber composite is comprised of a sulfonated outer layer and an unsulfonated core, wherein said unsulfonated core is volatilized during carbonization to form a hollow core, and said sulfonated outer layer is carbonized to form a carbon outer layer, wherein at least the sulfonated outer layer is comprised of a polyolefin.

17. The method of claim 16 , wherein said unsulfonated core has a complex shape, wherein said unsulfonated core is volatilized during carbonization to form a carbon fiber having a complex-shaped hollow core.

18. A method for producing a hollow carbon fiber, the method comprising subjecting a multi-component polymer fiber composite comprised of a non-fugitive polymer outer layer and a fugitive core to a fugitive removal step to produce a hollow polymer fiber, and subjecting said hollow polymer fiber to a sulfonation step followed by a carbonization step to convert said hollow polymer fiber to said hollow carbon fiber, wherein at least the non-fugitive polymer outer layer is comprised of a polyolefin.

19. The method of claim 18 , wherein said fugitive core has a complex shape to produce a hollow carbon fiber having a complex-shaped hollow core.

20. The method of claim 18 , wherein said fugitive removal step comprises dissolving the fugitive core in a solvent.

21. A method for producing a carbon fiber possessing a circular- or complex-shaped outer surface, the method comprising subjecting a multi-component polymer fiber composite to a carbonization step, wherein said multi-component polymer fiber composite is comprised of a sulfonated core having a circular or complex shape and an unsulfonated outer layer, wherein said unsulfonated outer layer is volatilized during carbonization, and said sulfonated core is carbonized to form a carbon fiber having a circular- or complex-shaped outer surface, wherein at least the sulfonated core is comprised of a polyolefin.

22. The method of claim 21 , wherein said sulfonated core is surface-sulfonated with an inner core portion of the sulfonated core being unsulfonated, wherein the surface-sulfonated core, when carbonized, volatilizes the unsulfonated inner core portion and carbonizes the surface-sulfonated portion of the core to produce a hollow carbon fiber having a circular- or complex-shaped outer surface.

23. A method for producing a carbon fiber possessing a circular- or complex-shaped outer surface, the method comprising subjecting a multi-component polymer fiber composite comprised of a non-fugitive polymer core having a circular or complex shape and a fugitive outer layer to a fugitive removal step to produce a polymer fiber having a circular- or complex-shaped outer surface, and subjecting said polymer fiber having a circular- or complex-shaped outer surface to a sulfonation step followed by a carbonization step to convert said polymer fiber possessing a circular- or complex-shaped outer surface to a carbon fiber possessing a circular- or complex-shaped outer surface, wherein at least the non-fugitive polymer core is comprised of a polyolefin.

24. The method of claim 23 , wherein said sulfonation step is conducted such that said non-fugitive polymer core is surface-sulfonated with an inner core portion of the non-fugitive polymer core being unsulfonated, wherein subsequent carbonization volatilizes the unsulfonated inner core portion and carbonizes the surface-sulfonated portion of the core to produce a hollow carbon fiber having a circular- or complex-shaped outer surface.

25. The method of claim 23 , wherein said fugitive removal step comprises dissolving the fugitive outer layer in a solvent.