Abstract:

Objective To benefit from the performance advantages of two-component composite staple yarns, a new spinning method for sheath-core staple yarns based on ring spinning machine was developed. The twist distribution in the sheath and core layers of sheath-core staple yarn is studied because it has a significant impact on the settings of spinning process parameters and the yarn properties.

Method The conventional front roller was replaced with the coaxial front roller with different diameters. Two fiber slivers were output with different speeds at the front roller nip. The slow fiber sliver was twisted around its axis, while the fast fiber sliver was spirally wrapped around the outside of the slow counterpart, thus forming a sheath-core structure. Based on the geometry of spinning triangle, the twist in sheath layer was calculated theoretically, and the twist in sheath and core layers of sheath-core yarn were measured by the filament simulated tracer method and image technology.

Results Through the fitting analysis of the twist in sheath and core layers, it is found that the twist in sheath layer is a quadratic function of the setting twist. Additionally, the twist in sheath layer is inversely proportional to the yarn diameter, which is consistent with theoretical analysis. Furthermore, the twist in core layer exhibits a linear relationship with the setting twist. The R² values for all fitted curves exceed 0.95, indicating that the fitting results are highly reliable. The breaking strength and elongation of sheath-core yarn are superior to those of ring-spun cotton yarn. At a twist of 550 twist/m, the breaking strength and elongation of sheath-core yarn with a sheath-core proportion of 65/35 are 68.0% and 85.5% higher than those of ring-spun cotton yarn, respectively. As the setting twist and core proportion increase, the breaking strength and elongation of sheath-core staple yarn increase. This is because as the setting twist increases, the twist in sheath and core layers increase, thereby enhancing the breaking strength and elongation of sheath-core staple yarn. Additionally, it is well known that polyester fibers have superior tensile properties compared to cotton fibers. Therefore, as the core proportion increases, the tensile properties of sheath-core staple yarn improve. The CVm of sheath-core staple yarn decreases as the core proportion increases. At a twist of 550 twist/m, the CVm decreases by 7.2% when the core proportion increases from 25% to 35%. This is because, as the core proportion increases, the width of sheath fiber bundle decreases, enhancing the control over the edge fibers and reducing the loss of edge fibers. The CVm decreases as the setting twist increases. When the sheath-core proportion is 65/35, the CVm decreases by 6.0% as the twist increases from 490 to 550 twist/m. The twist of sheath and core fiber bundles in the spinning triangle increase with setting twist increases. This enhances the cohesion of fibers, reduces the loss of fibers, and thus improves the evenness of sheath-core staple yarn. The harmful hairiness of sheath-core staple yarn decreases with increasing setting twist. When the sheath-core proportion is 65/35, the harmful hairiness decreases by 8.8% as the twist increases from 490 to 550 twist/m. This is because as the setting twist increases, more fibers are involved in the yarn, resulting in reduced hairiness.

Conclusion A method of one-step spinning sheath-core staple yarn based on ring spinning machine was developed. The spinning efficiency of this method is high, and the yarn spun by this method has good properties. In addition, the relationship between twist in sheath and core layer and setting twist was established by combining theoretical modeling with experiment. The results show that the twist in sheath layer has a quadratic function relationship with setting twist, and the twist in core layer is positively linearly correlated with setting twist. The breaking strength and breaking elongation of cotton/polyester sheath-core staple yarn are better than those of cotton ring yarn at the same linear density and twist.

Key words: staple sheath-core yarn, output with different speed, spinning technique, twist in sheath layer, twist in core layer, composite structure yarn