According to statistics, for every 1kg of waste textiles recycled, 3.6kg of carbon dioxide emissions can be reduced, 6000L of water can be saved, and 0.3kg of fertilizers and 0.2kg of pesticides can be reduced. The "14th Five-Year Plan for the Development of the Textile Industry" points out that the development of high-value utilization technology of waste textiles is one of the key technologies for the development of the "14th Five-Year Plan". The author believes that the key lies in the high-value utilization, it is understood that after decades of development, the country has formed a number of industrial clusters of recycled cotton recycling, treatment and reuse, especially in Wenzhou, Zhejiang Province, the most concentrated, products are mostly used in low-end clothing, textile accessories and cleaning or insulation industry, such as jeans, uppers, bags, mops, carpets, greenhouse insulation quilts and various geotextiles, etc., have made full use of various waste textile raw materials. However, at present, it is still mainly rotor spinning and various non-woven processing, and the added value is low, mainly due to the deterioration of fiber quality after the reprocessing of waste textiles, and the reuse value is low.
As the spinning method with the most mature technology and the widest product coverage, although the market share is constantly squeezed by new spinning methods such as rotor spinning and air-jet vortex spinning, it has always occupied a dominant position in the market due to its unique yarn forming principle (the most adequate transfer of fiber inside and outside) and the wide adaptability of products, and the product positioning has been at a high level. It is understood that there have been several head recycled cotton processing enterprises in China, which have cooperated with large foreign clothing brands (such as Zara, H&M, Uniqlo, etc.) to provide high value-added recycled cotton ring spinning products, and the relevant information is rarely reported. In order to study the characteristics and application potential of recycled cotton ring spinning yarn, this paper verified the effectiveness of the fiber blending theory based on the blended raw materials of recycled cotton and raw cotton, and tested and compared the differences in yarn preparation and yarn performance of ring spinning and rotor spinning methods, which provided a basis for the subsequent development of recycled cotton ring spinning yarn.
1. Experiment
1.1 Raw material performance
Due to the short fiber length of recycled cotton, it is impossible to produce ring spinning yarn alone, and Ne20 woven yarn is produced by blending with raw cotton, of which recycled cotton is a batch of customized processing samples, raw cotton is Xinjiang secondary cotton, the blending ratio is 50/50, and the main quality indicators of raw materials are shown in Table 1.
Table 1 AFIS test results of recycled cotton and raw cotton fibers
1.2 Test equipment and testing instruments
The spinning machines used in this article are all from Rieter setting machines.
Testing instruments: Uster AFIS PRO2 single fiber tester, Uster UT5 strip dry uniformity tester, UTJ4 and UTR4 yarn strength tester, etc.
1.3 Test process
50% recycled cotton + 50% raw cotton → B34 blending machine, A79 cotton cleaning machine→ A21 condenser→ C70 carding machine→ SB-D22S draw frame→ RSB-D50 draw frame
Ring spinning route: CMT1801 roving frame → G38 ring spinning frame
Rotor spinning route: R37 rotor spinning machine
2. Comparison of mixing theory analysis and yarn drafting preparation
2.1 Verification of fiber blending theory
In the case of recycled cotton and raw cotton blending, theoretically, the comprehensive properties of the blended raw materials can be obtained according to the following formula:
Average value of blended fiber performance index:
（1）
The discrete coefficient of this index in blended fibers:
（2）
Among them, Ki is the mixed weight ratio of each component, Xi is the average value of each component's fiber index, and Ci is the discrete coefficient of a component.
Taking fiber length as an example, the fiber length frequency difference analysis was introduced by using the fiber length root number distribution measured by AFIS, and the weighted reconstruction of section length and distribution frequency was used to more intuitively reflect the fiber changes of different length segments. According to the above formula, the length data of recycled cotton and raw cotton were weighted and calculated, and the results obtained were analyzed for frequency difference with the AFIS measured results of the final green strips, and the results obtained are shown in Figure 1.
As can be seen from Figure 1, compared with the actual results of AFIS, there is no significant difference in the calculation results of the fiber length after blending (no obvious inflection point), and the difference is about 4.8% (considering that the raw material blending method is used for recycled cotton and raw cotton, the carding process will produce different cotton drop ratios for these two groups of fibers with obvious differences, which is likely to lead to the above differences). It can be seen that the AFIS fiber length index of pure cotton variety blending can be accurately predicted by using the weighting calculation of fiber blending theory.
2.2 Comparison of ring spinning and rotor spinning into yarn drafting preparation
In order to verify the influence of ring-spinning roller roller drafting and rotor spinning on the final yarn quality by comparing the differences of yarn formation with the same cooked strips.
The fiber whisker samples output at the front jaws after drafting of the G38 spinning frame and the fiber ring samples condensed in the R37 spinning cup were collected to prepare AFIS samples for testing, and the fiber frequency difference analysis was used to calculate, and the results obtained are shown in Figure 2.
It can be seen from Figure 2 that compared with the R37 fiber ring, the curve of the G38 fiber whisker shows an overall shift to the left, and there are two obvious inflection points, indicating that compared with the carding roller drafting, the fiber is more obviously damaged after roller drafting, and only the long fiber above 33mm has a slight advantage, and the difference between the two is about 7.3%. This once again verifies that although the teeth of the rotor spinning carding roller directly act on the single fiber itself, the ring spinning roller rubber roller brings greater fiber internal injury to the drawn whisker, resulting in a drastic shortening of the fiber length in the whisker, which also provides an idea for the subsequent improvement of the ring spinning process.
3. Comparison of the performance of ring spindle yarn and rotor yarn
3.1 Comparison of appearance results such as yarn lines, dry yarn defects, etc
The results of capacitive strip CVm, photoelectric strip CV FS and low-sensitivity yarn defects for ring-spindled yarn and rotor spinning yarn are shown in Figure 3, and the high-sensitivity yarn defects and hairiness index are shown in Figure 4.
As can be seen from Figures 3 and 4, ring spinning yarn is far worse than rotor spinning yarn in terms of capacitive strip dryness uniformity or coefficient of variation of fine structure on the yarn surface, as well as yarn defects and hairiness. This is mainly due to the rotor spinning using carding rollers to re-open the fiber, and then combine into a thin layer of fiber in the spinning cup condensation groove until it reaches the required thickness of the yarn (this is the unique post-merger effect of rotor spinning), so that the yarn obtains a high uniformity, and is always better than ring spinning yarn, and ring spinning is very sensitive to fiber length, and the content of short and short fibers in the recycled cotton blended with raw materials is very high, coupled with a large amount of dust, impurities, etc. can not be self-discharged, which leads to the result of poor quality indicators.
As can be seen from Figure 5, the dust and impurities on the surface of the ring spinning body are much higher than those on the rotor spinning body. Different from ring spinning, rotor spinning uses the gripping and binding effect of the spinning cup condensation groove on the fiber ring, and realizes twisting through the rotation of the yarn body around itself, which will play a certain restraining and cleaning effect on the surface of the yarn section, coupled with the friction and false twisting effect on the surface of the yarn body such as the twisting head and the fixed twister, so that the surface of the rotor spinning body has less hairiness and the yarn is more smooth. In traditional ring spinning, only the velvet roller on the front roller can remove the slightest linter or impurities, coupled with the open drafting and twisting winding method, so that there are a large number of neps or impurities on the surface of the yarn body.
Based on the above-mentioned comparative test results of strip drying, yarn defects, hairiness, impurities, etc., it can be preliminarily judged that the final appearance of ring spinning yarn should be far worse than that of rotor spinning yarn, but the actual blackboard effect (see Figure 6) In addition to surface impurities, neps and other indicators, the overall style consistency of ring spinning yarn is better than that of rotor spinning yarn, which has a huge contrast with the above test data, mainly because the rotor spinning yarn presents a dense similar "long and short thick sections" on the blackboard effect, which is related to the unique wrap-around structure of the rotor spinning yarn.
Although Uster has introduced an additional photoelectric sensor/OM sensor since the USTER® TESTER 5, in addition to the capacitive sensor (which is not sensitive to the yarn structure), it is possible to test the yarn tightness and other related indicators, which are measured by irradiating the yarn at an angle of 90 degrees in 2 different directions, and create a fine structure coefficient of variation CV FS This parameter, however, has not effectively integrated the capacitive and photoelectric unevenness curves, so as to achieve dual judgment and prediction of the final fabric appearance quality in the two dimensions of quality and vision. In contrast, Changling Textile Machinery instead re-excavated and studied the characteristics and application methods of the DR value and its curve, and put forward several indicators and graphics that use the offset rate to predict the appearance quality of the fabric, but unfortunately there is no opportunity to make a visual comparison, but I believe that the industry's exploration of predicting the final fabric appearance quality through yarn indicators will not stop.
3.2 Comparison of internal performance results such as yarn elongation and compactness
The breaking strength and elongation of ring spinning yarn and rotor spinning yarn are shown in Figure 7, and the physical density and diameter index are shown in Figure 8.
It can be seen from Fig. 7 and Fig. 8 that compared with rotor spinning yarn, whether it is the breaking strength of the yarn, or the physical density and diameter of the yarn, the ring spinning yarn is more compact, although the twist set by the ring spinning is 50T/m lower than that of the rotor spinning, and the breaking strength of the rotor spinning has reached the limit (through the optimization of process parameters, the optimization of special equipment and other measures have been unable to further improve).
On the one hand, this is due to the "forced twisting" method of ring spinning (the steel traveler restricts the fiber whisker to rotate around itself), and compared with the "soft twisting" method of rotor spinning (relying on the spinning cup condensation groove to hold the fiber ring under the action of centrifugal force to realize the rotation of the yarn body), the twisting efficiency of ring spinning is higher. The unique wrapping structure of rotor spinning makes the fiber participation support low when the yarn is stretched and broken, and the ring spinning realizes the most adequate fiber internal and external transfer in the front jaw twisting triangle, which makes the fiber participation support very high when the yarn is stretched and broken, so that the final ring spinning can still achieve good breaking strength in the case of serious fiber damage after drafting.
IV. Conclusion
The comparative test of recycled cotton, raw cotton blended ring spinning and rotor spinning verified the effectiveness of the fiber blending model and the differences in the performance and appearance style of the two yarns (including yarn unevenness, yarn defects, hairiness, surface dust impurities, tensile properties, compactness, etc.).
(1) Taking the fiber length of AFIS as the research object, the fiber length index calculated according to the fiber blending theory can be well matched with the measured results of AFIS, which indicates that for pure cotton varieties, the weighted calculation of fiber blending theory can accurately predict the blending results.
(2) Using frequency difference analysis, it was found that the drafting of ring spinning had a relatively more serious damage to the fiber.
(3) The ring spinning yarn is far worse than the rotor spinning yarn in terms of strip dryness, yarn defects, hairiness, impurities and other indicators, but the actual blackboard effect is better than that of the rotor spinning yarn, indicating that the existing testing methods cannot predict the appearance quality of the fabric.
(4) Compared with rotor spinning yarn, ring spinning yarn has higher breaking strength and tighter yarn structure.
Considering that the application of recycled cotton rotor spinning yarn has long been mature, and compared with recycled cotton ring spinning yarn has its own unique advantages, if the surface impurities and neps of ring spinning yarn are improved through technical research, the follow-up application prospects will be very broad.
Source: Yan Rui Ion (China) Textile Instrument Co., Ltd
Editor: China Yarn Network New Media Team
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