Methods of forming ultra-fine fibers and non-woven webs
A nonwoven web product including ultra-fine fibers is formed utilizing a spunbond apparatus that forms multicomponent fibers by delivering first and second polymer components in a molten state from a spin pack to a spinneret, extruding multicomponent fibers including the first and second polymer components from the spinneret, attenuating the mulicomponent fibers in an aspirator, laying down the multicomponent fibers on an elongated forming surface disposed downstream from the aspirator to form a nonwoven web, and bonding portions of at least some of the fibers in the nonwoven web together to form a bonded, nonwoven web product. The multicomponent fibers can include separable segments such as islands-in-the-sea fibers, where certain separated segments become the ultra-fine fibers in the web product. In addition, carbon tubular fibers can be formed by extruding island-in-the-sea fibers including polyacrylonitrile or pitch sheath segments in the fibers, separating the segments of the fiber, and converting the polyacrylonitrile of pitch to carbon by a carbonization process.
1. A method of forming fibers, comprising:
delivering at least first and second polymer components in a molten state from a spin pack to a spinneret, wherein the first polymer component comprises at least one polymer that is at least partially dissolvable in a dissolving medium and the second polymer component comprises at least one of polyacrylonitrile and pitch; and
extruding fibers including the first and second polymer components from the spinneret, wherein at least some of the fibers include islands-in-the-sea fibers, each islands-in-the-sea fiber includes island segments disposed within a sea section, the sea sections of the islands-in-the-sea fibers comprise the first polymer component, and at least some of the island segments comprise sheath-core segments including a sheath section comprising the second polymer component surrounding a core section.
2. The method of claim 1 , wherein each of the sheath segments of the islands-in-the-sea fibers have a transverse cross-sectional dimension that is no greater than about 500 nanometers.
3. The method of claim 1 , wherein the core sections of the fibers comprise the first polymer component, and the method further comprises: separating the sea sections and core segments from the sheath segments of islands-in-the-sea fibers to form tubular fibers comprising the second polymer component.
4. The method of claim 1 , further comprising:
carbonizing at least the second polymer component in the tubular fibers to form carbon tubular fibers.
5. The method of claim 1 , further comprising:
separating the sea sections from the island segments of islands-in-the-sea fibers; and
carbonizing at least the second polymer component in the island segments.
6. A method of forming fibers, comprising:
extruding fibers including a plurality of different polymers from a spinneret, wherein at least some of the fibers include islands-in-the-sea fibers, each islands-in-the-sea fiber includes island segments disposed within a sea section, the sea sections of the islands-in-the-sea fibers comprise the first polymer component, and at least some of the island segments comprise sheath-core segments including a sheath section comprising the second polymer component surrounding a core section, wherein each of the sea section and the core segments comprises at least one polymer that is at least partially dissolvable in at least one dissolving medium; and
dissolving the sea sections and core segments from the sheath segments of islands-in-the-sea fibers to form tubular fibers.