The Influence of Various Spinning Methods on Yarn Properties

1. Physical Properties of Short Fibers

Different short fiber spinning processes have varying effects on the physical properties and appearance of yarns, and even on the characteristics of the final product.

(1) Different spinning methods affect yarn structure. The structure of short fiber yarn differs from that of filament yarn, primarily in the arrangement of fibers both externally and internally. External structure includes the yarn's appearance and surface texture, such as fiber arrangement on the yarn surface, yarn hairiness, coefficient of friction, yarn properties, abrasion resistance, and other surface characteristics.

(2) The internal structure of yarn mainly involves the arrangement of fibers across the entire cross-section of the yarn and its longitudinal direction, including fiber orientation, elongation, displacement, and twist. Internal structure includes yarn strength, fiber blending degree, bending strength, compressibility, and resilience (with a tendency to knot).

2. Spinning Process

To understand the influence of spinning processes on yarn structure, 3dtex, 38 mm viscose short fibers were used in trial spinning trials within five different spinning process systems.

A. Traditional ring spinning process; B. Compact ring spinning process; C. Twin-nozzle (MTS) pseudo-wrap spinning process; D. Vortex spinning (MVS) spinning; E. Rotor spinning.

(1) The external structure of the yarns mentioned above can be seen using a scanning electron microscope. Microelectronic photographs were used to examine five processes: rotor spinning, air-jet spinning, vortex spinning, conventional ring spinning, and compact ring spinning. The external fiber orientation of the yarns produced by these five processes can be observed in the photographs. Compact ring spinning exhibits the best orientation, with more fibers forming the yarn structure, almost all fibers being integrated into the yarn body. This improves upon short-fiber yarns, clearly showing the twist structure. Furthermore, one end of the fiber is twisted into the yarn body along its length.

(2) In traditional ring spinning, under the same twist conditions, the surface of the yarn is disordered, with many fiber ends not twisted into the yarn body, and individual fibers protruding outside the yarn body. This may be due to the ring/tracer or yarn guide.

(3) Vortex spinning, similar to ring spinning, features well-arranged fibers within the yarn body. At a spinning speed of 350 rpm, the wrapped fibers form a fine spiral. The twist is essentially the same as ring-spun yarn, with the actual twist closely matching the calculated twist. The ratio of wrapped fibers to untwisted core fibers is very high, almost completely covering the core fibers. Therefore, the appearance of vortex yarn is basically similar to ring-spun yarn, with the external wrapped fibers forming a true twist together with the untwisted core.

(4) Double-nozzle false-twist yarn, fundamentally different from vortex yarn, has only 6%-8% wrapped fibers in double-nozzle air-jet yarn, with approximately 90% of the fibers being extended and untwisted. It is clearly visible that the wrapping tightness of the wrapped fibers around the core is greater than that of vortex yarn.

(5) Rotor spinning: Regardless of whether the rotor yarn belongs to the true twist category, the fibers on the rotor yarn are disordered, and the fibers in the middle of the yarn show no clear spiral shape in the Z and S directions; the fibers are straight. It is clear that the wrapped yarn is not tangled, which is an advantage of rotor yarn and the basis of its characteristics.

3. Hairiness

The fly and hairiness formed during spinning is a very troublesome problem. Hairiness has many negative effects in downstream processing. The hand feel and final product properties of textiles are affected by hairiness. The Zweigle hairiness tester is used to classify 1mm-2mm hairiness and separate harmful hairiness larger than 3mm. If the hairiness of ring-spun yarn is 100%, then the 1mm-2mm hairiness of compact ring-spun yarn, vortex yarn, and rotor yarn is less than that of ring-spun yarn. Double-nozzle false-twist wrapped yarn has poorer wrapping and more hairiness. The SO-Called detector can be used to measure the fly caused by friction during subsequent processing. The friction force is measured using a rubber ring. Compact yarns offer better abrasion resistance than non-traditional yarns. Rotor-spun yarns have less hairiness, especially noticeable in viscose fibers. While the fibers on the yarn don't break, many hairs are trapped within the yarn body by the wrapped fibers, resulting in less hairiness in rotor-spun yarns.

4. Yarn Volume

Yarn volume is an important indicator of yarn coverage. At the same twist, compact ring-spun yarns have lower coverage than conventional ring-spun yarns. To maintain the same strength, compact ring-spun yarns can have their twist reduced to increase yarn volume, achieving coverage equivalent to conventional ring-spun yarns. Twist can be reduced by 5%–10%. The Denkenolorf yarn structure tester provides measured yarn volume for a yarn length of 0.3 mm. Yarn volume testing included dual-nozzle MJS air-jet spinning of the same yarn count. Because air-jet spinning is wrapped and false-twisted, it has a larger volume for the same yarn count than ring-spun yarn. Microelectronic scanning radiography images show that a small number of wrapped fibers are on the yarn core, and their short lengths make many parts of the yarn essentially untwisted.

The abrasion resistance and stress load of the warp yarns were tested using the So-Called simulation index, allowing for simultaneous testing of the required 15 yarns. Ideally, tightly spun ring yarn exhibits superior fiber arrangement compared to ordinary ring-spun yarn. Non-traditional spinning technologies all have shortcomings. This new type of spinning requires processing when making warp yarns. In air-jet spinning, compared to true-twisted yarn, the yarn has fewer fibers and exhibits some straightening and entanglement. Therefore, the yarn's mechanical and physical properties vary, especially during winding, which is a key difference between non-traditional spinning and ring-spun yarn.

5. Internal Structure of Yarn

The formation of fibers within the yarn is related to its external structure. The arrangement of the yarn core and the extension of fibers along the yarn length can be obtained during drafting using electronic scanning radiography. The parallelism of fibers visible in the yarn cross-section affects yarn strength, and the characteristics of yarn strength are related to the clamping length during testing.

Reducing the possibility of weak points and strength loops: Normal yarn strength is tested on a tensile testing machine with a clamping length of 520 mm, although 100 mm and 18 mm clamping lengths are also possible. A shorter clamping length increases yarn breaking strength because it reduces the probability of weak points and strength loops, thus decreasing the chance of breakage. If the fiber distribution and orientation are good, a shorter test clamping length significantly increases yarn breaking strength, especially noticeable in ring-spun and tightly ring-spun yarns. Rotor-spun yarns have lower breaking strength; even if the breaking length is shorter than the fiber length, the fiber hooks prevent an increase in breaking strength due to fiber bending. In summary, the more yarn fibers are clamped, the better the longitudinal orientation of the fibers, and the higher the yarn breaking strength. Electron imaging shows that rotor yarn has a wound structure; even with a clamping length less than 5 mm, 100% of the fibers are clamped and break. With a clamping length of 0 mm, the fiber breakage length is shorter than the fiber length, and poor core fiber orientation results in low breaking strength.

Air-jet yarn has strength between ring-spun, compact, and rotor yarns. It is mainly air-jet yarn, with a more parallel core than rotor yarn and fewer wrapped fibers, resulting in slightly higher strength than rotor yarn.

6. Characteristics of Yarn Deformation Affected by Yarn Formation

For example, yarn bending strength is a characteristic affected during yarn formation, but testing yarn bending strength is difficult. A new method for testing yarn bending strength has now been developed. Experiments show that if the bending strength of compact yarn is 100%, then rotor-spun and vortex-spun yarns are 200%, and double-nozzle air-jet yarns are 300%. These numerical relationships can be compared with ring-spun yarns in some non-traditional spinning processes on woven and knitted fabrics. Fabrics made from non-traditional spinning processes have a rougher and stiffer hand feel than those made from ordinary ring-spun yarns. There is also a slight difference in bending strength between ordinary ring-spun yarns and compact yarns.

Another issue arises: when the yarn deforms, it flattens and deforms under compression on the warp and weft cross-sections. Yarn thickening point testing shows that the number of thickening points decreases as the yarn compression force increases.

The rotor yarn structure causes a fiber distribution pattern. At the fiber-wrapped areas, the hand feel is stiffer, and the yarn has less deformation force than at unwrapped areas. Knitted and woven fabrics produced from rotor yarns often have a less uniform and coarser appearance than those made from ring-spun yarns.

For comparison, the yarn thick places were tested under a pressure of 100cN, indicating that the yarn has an optimal twist structure. In MTS dual-nozzle air-jet yarn with the same deformation, approximately 95% of the fibers are parallel and untwisted, making it more prone to deformation. Based on this test, rotor-spun yarn feels stiffer. Yarn deformation can be detected on the loom or in the appearance of the knitted fabric by the yarn's tightness.

7. Yarn Resilience

Yarn resilience is crucial for textile processing, such as preventing skewing in knitted fabrics. Resilience is measured by testing the yarn's knot force. The resilience differs between tightly wound ring-spun yarns, ordinary ring-spun yarns, and non-traditional yarns. Rotor-spun yarns, whether twisted or untwisted, have lower knot forces.

Air-jet-spun yarn has lower resilience, mainly due to the higher proportion of parallel untwisted fibers. Truly twisted yarns have greater resilience than non-traditional yarns, therefore resulting in less fabric skewing when further processed into knitted fabrics.

Yarn structure is one of the most important characteristics of yarn. Yarn appearance is related to yarn properties, and the internal fiber arrangement of the yarn has a significant impact on these properties, especially on further processing and the properties of the final product. Poor yarn structure greatly affects subsequent processing, while good yarn structure provides excellent functionality and wide applicability. Textiles made from tightly spun yarns have the most ideal appearance and structure in terms of adaptability.