The device (1) comprises a first roller (3) rotatable about a first rotation axis (3A) and a second roller (5) rotatable about a second rotation axis (5A), parallel to the first rotation axis (3A). The two are in mutual contact and define between them a yarn passage (7) and at least of them is motorized. The device further comprises 5 guide members (9) defining a feed path of at least a yarn (F; F1, F2, F3, F4), associated with the yarn passage (7) between the first roller (3) and the second roller (5). The guide members (9; 13) are movable with respect to the rollers (3, 5) in a direction substantially parallel to the first rotation axis (3A) and to the second rotation axis (5A), so as to take the yarn path temporarily outside the mutual contact 10 area between the rollers.

Provided is a strand extending in the longitudinal direction, wherein the strand includes filaments of one type having a gradient-length effect through spiral rotational twists and an irregular fine texture through self-thermal shrinking. The filaments of the strand have natural coiling characteristics that are very similar to those of natural hair of black people, and these characteristics are caused by the facts that the filaments have 3-dimensional waveforms occurred due to many fine and irregular windings or projections and that the waveforms exhibit fractal structure features and a fine kinky texture.

Provided is a strand extending in the longitudinal direction, wherein the strand includes filaments of one type having a gradient-length effect through spiral rotational twists and an irregular fine texture through self-thermal shrinking. The filaments of the strand have natural coiling characteristics that are very similar to those of natural hair of black people, and these characteristics are caused by the facts that the filaments have 3-dimensional waveforms occurred due to many fine and irregular windings or projections and that the waveforms exhibit fractal structure features and a fine kinky texture.

Provided is a strand extending in the longitudinal direction, wherein the strand includes filaments of one type having a gradient-length effect through spiral rotational twists and an irregular fine texture through self-thermal shrinking. The filaments of the strand have natural coiling characteristics that are very similar to those of natural hair of black people, and these characteristics are caused by the facts that the filaments have 3-dimensional waveforms occurred due to many fine and irregular windings or projections and that the waveforms exhibit fractal structure features and a fine kinky texture.

Provided is a strand extending in the longitudinal direction, wherein the strand includes filaments of one type having a gradient-length effect through spiral rotational twists and an irregular fine texture through self-thermal shrinking. The filaments of the strand have natural coiling characteristics that are very similar to those of natural hair of black people, and these characteristics are caused by the facts that the filaments have 3-dimensional waveforms occurred due to many fine and irregular windings or projections and that the waveforms exhibit fractal structure features and a fine kinky texture.

A partially separated fiber bundle includes separation-processed sections, each divided into a plurality of bundles of at least three bundles, and not-separation-processed sections, that are alternately formed along the lengthwise direction of a fiber bundle that comprises a plurality of single fibers. The partially separated fiber bundle is characterized in that, at any width-direction cross-section taken along the lengthwise direction thereof, a rate of single fibers contained in a region at which adjacent divided fiber bundles are joined by a not-separation-processed part is 67% or less relative to the total single fibers in the width-direction cross-section.

A partially separated fiber bundle includes separation-processed sections, each divided into a plurality of bundles of at least three bundles, and not-separation-processed sections, that are alternately formed along the lengthwise direction of a fiber bundle that comprises a plurality of single fibers. The partially separated fiber bundle is characterized in that, at any width-direction cross-section taken along the lengthwise direction thereof, a rate of single fibers contained in a region at which adjacent divided fiber bundles are joined by a not-separation-processed part is 67% or less relative to the total single fibers in the width-direction cross-section.

A method for making a fiber reinforcement with variations in transverse cross section is disclosed. The method includes forming a fiber comprising polymeric material and exposing the fiber to a heat treatment, such that at least a portion of the polymeric material at or near said surface of said fiber is at or above the melting point temperature and substantially all of the polymeric material at or near the core is below the melting point temperature. The method further includes cooling the fiber to a temperature below the melting point temperature.

A method for making a fiber reinforcement with variations in transverse cross section is disclosed. The method includes forming a fiber comprising polymeric material and exposing the fiber to a heat treatment, such that at least a portion of the polymeric material at or near said surface of said fiber is at or above the melting point temperature and substantially all of the polymeric material at or near the core is below the melting point temperature. The method further includes cooling the fiber to a temperature below the melting point temperature.

A partially separated fiber bundle includes separation-processed sections, each divided into a plurality of bundles of at least three bundles, and not-separation-processed sections, that are alternately formed along the lengthwise direction of a fiber bundle that comprises a plurality of single fibers. The partially separated fiber bundle is characterized in that, at any width-direction cross-section taken along the lengthwise direction thereof, a rate of single fibers contained in a region at which adjacent divided fiber bundles are joined by a not-separation-processed part is 67% or less relative to the total single fibers in the width-direction cross-section.