Carbon fibers having an internal cavity

Abstract

A reinforcing fiber is provided comprising a carbon fiber having a length and outer and inner surfaces defining a wall. The wall has a first cross section which defines an outer diameter and an inner diameter and a wall thickness. The wall thickness of the cylindrical carbon fiber tube is greater than or equal to 2 um.

What is claimed is:  
     
         1 . A reinforcing fiber comprising:
 a carbon fiber having a length and outer and inner surfaces defining a wall having a first cross section defining an outer diameter and an inner diameter and a wall thickness, the wall thickness being greater than or equal to 2 um.   
     
     
         2 . The reinforcing fiber of  claim 1 , wherein the specific tensile strength of the carbon fiber is greater than 5×10 4  meters. 
     
     
         3 . The reinforcing fibers of  claim 1 , wherein the wall is a cylindrical wall. 
     
     
         4 . The reinforcing fiber of  claim 1 , further comprising a second cross section taken at a second position along the length and having a cross sectional area substantially equal to that of the first cross section. 
     
     
         5 . The reinforcing fiber of  claim 1 , further comprising a second cross section taken at a second position along the length and having a cross sectional area that varies by less than 50% as that of the area of the first cross section. 
     
     
         6 . The reinforcing fiber of  claim 1 , wherein the outer diameter is greater than 7 um. 
     
     
         7 . The reinforcing fiber of  claim 1 , wherein the inner diameter is greater than 4 um. 
     
     
         8 . The reinforcing fibers of  claim 1 , wherein the carbon fiber further comprises first and second open ends. 
     
     
         9 . The reinforcing fiber of  claim 1 , wherein the carbon fiber further comprises a second cross section taken at a second position along the length, wherein the inner or outer diameters of the cross section vary by less than 5 um. 
     
     
         10 . A reinforcing fiber comprising:
 a carbon fiber having a length and outer and inner surfaces defining a tube and a first cross section defining an outer diameter and an inner diameter wherein the outer diameter and the inner diameter varying along the length.   
     
     
         11 . The reinforcing fiber of  claim 10  wherein the outer diameter and the inner diameter increase linearly along the length. 
     
     
         12 . The reinforcing fiber of  claim 10  wherein the outer diameter and the inner diameter increase and decrease repeatedly along the length. 
     
     
         13 . A method comprising:
 forming a polymer precursor from a polymer material, the polymer precursor having a length and outer and inner surfaces defining a cylindrical tube having a first cross section defining an outer and inner diameter and a wall thickness, the wall thickness being greater than or equal to 2 um.   
     
     
         14 . The method of  claim 13  wherein the polymer material is in sheet form. 
     
     
         15 . The method of  claim 13 , wherein the polymer material is a polymer material that flows;
 heating a first film and a second film to become formable;   pressing the first film and the second film together onto plates having half round channel having pins through a center of the half round channel; and   pulling the first film and the second film in a longitudinal direction across the half round channels with gas flowing through the pins to form a hollow filaments.   
     
     
         16 . The method of  claim 13 , wherein the polymer material is a first and second precursor film;
 pumping liquid precursors through a bushing in a longitudinal direction, the bushing having a gaseous delivery tube; and   flowing gases through the delivery tube to form a hollow filament.   
     
     
         17 . The method of  claim 13 , wherein the polymer material is a first and second precursor film;
 feeding the first film and the second film against a curved tool plate;   pulling the first film and the second film across the curved tool plate in a longitudinal direction to form two partial tubes;   mating the first film to the second film with the two tubes adjacent and longitudinally aligned;   pressing the two tubes to form a series of tubes; and   splitting the tubes into an individual hollow filaments.   
     
     
         18 . The method of  claim 17 , further comprising winding the hollow filaments on spools. 
     
     
         19 . The method of  claim 17 , wherein the feeding of the first film and the second film is more than 15 degrees from an initial direction. 
     
     
         20 . The method of  claim 17 , further comprising winding the hollow filaments on spools.