Internal chemical modification of carbon fibers to yield a product of reduced electrical conductivity

An improved process for the internal chemical modification of a carbonaceous fibrous material containing at least 90 percent carbon by weight comprising:

• (a) contacting said fibrous material for about 5 to 120 minutes with a mixture consisting essentially of nitric acid and sulfuric acid at a temperature of about 60.degree. to 95.degree. C. wherein the mole ratio of nitric acid to sulfuric acid within said mixture ranges between about 8 to 1 and 1 to 8 and the concentration of water in admixture with said acids ranges from 0 to 30 mole percent based upon the total mole concentration of said acids and said water, and
• (b) removing excess acids adhering to the resulting carbonaceous fibrous material to yield a fibrous product containing about 3 to 30 percent bound oxygen by weight which exhibits a substantially reduced electrical conductivity by at least 40 percent when compared to that of the carbonaceous fibrous material prior to said contact and a single filament tenacity of at least 200,000 psi.

An improved process for the internal chemical modification of a carbonaceous fibrous material containing at least 90 percent carbon by weight which is derived from an acrylic fibrous material comprising:

• (a) contacting said fibrous material for about 10 to 30 minutes with a mixture consisting essentially of nitric acid and sulfuric acid at a temperature of about 70.degree. to 85.degree. C. wherein the mole ratio of nitric acid to sulfuric acid within the admixture ranges between about 8 to 1 and 1 to 8 and the concentration of water in admixture with said acids ranges from 0 to 30 mole percent based upon the total mole concentration of said acids and said water, and
• (b) removing excess acids adhering to the resulting carbonaceous fibrous material to yield a fibrous product containing about 3 to 30 percent bound oxygen by weight which exhibits a substantially reduced electrical conductivity by at least 40 percent when compared to that of the carbonaceous fibrous material prior to said contact and a single filament tenacity of at least 200,000 psi.