Method of making fiber with gradient properties

A method of making a continuous-filament finished fiber having improved resistance to microfracture formation at a fiber-matrix interface, the method comprising:

• forming an inner-volume portion mixture comprising:
• a first solvent;
• a plurality of nanostructures selected from the group consisting of nanotubes, carbon nanotubes, halloysite nanotubes, and boron nitride nanotubes;
• and
• a first polymer selected from the group consisting of polyacrylonitrile (PAN), pitch, polyphenylene sulfide (PPS), viscose, cellulose, polyvinylidene chloride (PVDC), polyvinyl alcohol (PVA), and combinations thereof;
• forming an outer-volume portion mixture comprising:
• a second solvent;
• and
• a second polymer selected from the group consisting of polyacrylonitrile (PAN), pitch, polyphenylene sulfide (PPS), viscose, cellulose, polyvinylidene chloride (PVDC), polyvinyl alcohol (PVA), and combinations thereof;
• forming a precursor fiber by spinning the inner-volume portion mixture and the outer-volume portion mixture;
• heating the precursor fiber to oxidize the precursor fiber and to change a molecular-bond structure of the precursor fiber;
• and
• obtaining the continuous-filament finished fiber comprising:
• an inner-volume portion having a first outer diameter, and having the plurality of nanostructures, and the first polymer, the plurality of nanostructures substantially aligned along a longitudinal axis of the continuous-filament finished fiber and polymer chains of the first polymer oriented in a direction parallel to the longitudinal axis of the continuous-filament finished fiber;
• and
• an outer-volume portion having a second outer diameter, and having the second polymer,
• wherein the inner-volume portion of the continuous-filament finished fiber has a greater tensile modulus and/or tensile strength than the outer-volume portion of the continuous-filament finished fiber, resulting in the continuous-filament finished fiber having improved resistance to microstructure formation at the fiber-matrix interface.

A method of making a continuous-filament finished carbon fiber, the method comprising:

• forming an inner-volume portion mixture comprising:
• a first solvent;
• a plurality of carbon nanotubes;
• and
• a first polymer selected from the group consisting of polyacrylonitrile (PAN), pitch, polyphenylene sulfide (PPS), viscose, cellulose, polyvinylidene chloride (PVDC), and polyvinyl alcohol (PVA);
• forming an outer-volume portion mixture comprising:
• a second solvent;
• and
• a second polymer selected from the group consisting of polyacrylonitrile (PAN), pitch, polyphenylene sulfide (PPS), viscose, cellulose, polyvinylidene chloride (PVDC), and polyvinyl alcohol (PVA);
• forming a precursor fiber by spinning the inner-volume portion mixture and the outer-volume portion mixture;
• heating the precursor fiber to oxidize the precursor fiber and to change a molecular-bond structure of the precursor fiber;
• and
• obtaining the continuous-filament finished carbon fiber comprising:
• an inner-volume portion having a first outer diameter, and having the plurality of carbon nanotubes and the first polymer, the plurality of carbon nanotubes substantially aligned along a longitudinal axis of the continuous-filament finished carbon fiber and polymer chains of the first polymer oriented in a direction parallel to the longitudinal axis of the continuous-filament finished carbon fiber;
• and
• an outer-volume portion having a second outer diameter, and having the second polymer,
• wherein the inner-volume portion of the continuous-filament finished carbon fiber has a greater tensile modulus and/or tensile strength than the outer-volume portion of the continuous-filament finished carbon fiber, and further wherein the first polymer of the continuous-filament finished carbon fiber and the second polymer of the continuous-filament finished carbon fiber are the same.