A carbon-fiber-precursor acrylic fiber bundle which can smoothly pass through a flame-resistance impartation step and a carbonization step. The carbon-fiber-precursor acrylic fiber bundle has a high-density part as a portion thereof, wherein the high-density part satisfies the following requirements (A) and (B). Requirement A: The high-density part has a maximum fiber density ρ.sub.max of 1.33 g/cm.sup.3 or higher. Requirement B: The portion extending between an intermediate-density point and a maximum-density-region arrival point has an increase in fiber density of 1.3×10.sup.−2 g/cm.sup.3 or less per 10 mm of the fiber bundle length.

A carbon-fiber-precursor acrylic fiber bundle which can smoothly pass through a flame-resistance impartation step and a carbonization step. The carbon-fiber-precursor acrylic fiber bundle has a high-density part as a portion thereof, wherein the high-density part satisfies the following requirements (A) and (B). Requirement A: The high-density part has a maximum fiber density ρ.sub.max of 1.33 g/cm.sup.3 or higher. Requirement B: The portion extending between an intermediate-density point and a maximum-density-region arrival point has an increase in fiber density of 1.3×10.sup.−2 g/cm.sup.3 or less per 10 mm of the fiber bundle length.

The present invention provides: an acrylic fiber having a fineness of 0.5 to 3.5 dtex and having excellent gloss, pilling resistance, and texture; a method for producing said acrylic fiber; and a spun yarn and a knitted fabric containing said acrylic fiber. Provided is an acrylic fiber having a filament fineness of 0.5 to 3.5 dtex, wherein the product K of the value of knot strength (cN/dtex) and the value of knot elongation (%) is from 8 to 30 inclusive, and the number of recesses having a depth of 0.1 μm or greater is 10 or fewer.

The present invention provides: an acrylic fiber having a fineness of 0.5 to 3.5 dtex and having excellent gloss, pilling resistance, and texture; a method for producing said acrylic fiber; and a spun yarn and a knitted fabric containing said acrylic fiber. Provided is an acrylic fiber having a filament fineness of 0.5 to 3.5 dtex, wherein the product K of the value of knot strength (cN/dtex) and the value of knot elongation (%) is from 8 to 30 inclusive, and the number of recesses having a depth of 0.1 μm or greater is 10 or fewer.

In a method of making a carbon fiber, carbon nanotubes (CNT) are mixed into a solution including polyacrylonitrile (PAN) so as to form a CNT/PAN mixture. At least one PAN/CNT fiber is formed from the mixture. A first predetermined electrical current is applied to the PAN/CNT fiber until the PAN/CNT fiber is a stabilized PAN/CNT fiber. A heatable fabric that includes a plurality of fibers that each have an axis. Each of the plurality of fibers includes polyacrylonitrile and carbon nanotubes dispersed in the polyacrylonitrile in a predetermined weight percent thereof and aligned along the axes of the plurality of fibers. The plurality of fibers are woven into a fabric. A current source is configured to apply an electrical current through the plurality of fibers, thereby causing the fibers to generate heat.

A flame resistant polymer is obtained by reacting polyacrylonitrile with amine and nitro compounds, the polyacrylonitrile being polymerized by aqueous suspension polymerization using a redox initiator and containing an S component at an amount of 3,000 μg/g or less. A PAN-based polymer in which both yarn producing properties and flame resistance are improved can be realized.

A flame resistant polymer is obtained by reacting polyacrylonitrile with amine and nitro compounds, the polyacrylonitrile being polymerized by aqueous suspension polymerization using a redox initiator and containing an S component at an amount of 3,000 μg/g or less. A PAN-based polymer in which both yarn producing properties and flame resistance are improved can be realized.

A method for producing polyacrylonitrile (PAN) fiber, the method comprising: (i) mixing PAN with an ionic liquid in which the PAN is soluble to produce a PAN composite melt in which the PAN is dissolved in the ionic liquid; (ii) melt spinning the PAN composite melt to produce the PAN fiber; and (iii) washing the PAN fiber with a solvent in which the ionic liquid is soluble to substantially remove the ionic liquid from the PAN fiber. Also described herein is a method for producing carbon fiber from the PAN fiber as produced above, the method comprising oxidatively stabilizing the PAN fiber produced in step (iii), followed by carbonizing the stabilized PAN fiber to produce the carbon fiber. The initially produced PAN fiber, stabilized PAN fiber, resulting carbon fiber, and articles made thereof are also described.

The present disclosure relates to the production of polyacrylonitrile-based polymers with high conversion by a process comprising reacting acrylonitrile with at least one comonomer in the presence of a radical initiator in a liquid medium, wherein the radical initiator is present in an amount of from about 0.6 wt % to about 1.8 wt %, relative to the amount of acrylonitrile, and wherein no chain transfer agent is present. The polyacrylonitrile-based polymers produced may be used for producing carbon fiber, typically carbon fiber used in manufacturing composite materials.

A method of producing a precursor fiber for carbon fiber includes extruding a polyacrylonitrile copolymer solution from a spinneret into the air, immersing it in a coagulation bath liquid stored in a coagulation bath, redirecting traveling of the coagulating fiber bundle by a first guide immersed in the coagulation bath disposed below the spinneret, and pulling it out of the coagulation bath liquid into the air to prepare a coagulated fiber bundle, which is then subjected to at least a washing step in water, stretching step, oil agent applying step, and drying step, wherein the depth-directional coagulation bath immersion length, which means a distance between the starting point of the immersion of the spinning dope solution in the coagulation bath liquid and the first guide immersed in the coagulation bath where traveling of the coagulating fiber bundle is redirected, is 3 to 40 cm.