Study on the processing of stretch-broken ramie yarns in a cotton spinning system

Abstract

In this study, conventional long ramie fiber was stretch-broken into short fibers with lengths of 30 mm, 35 mm, 40 mm, 45 mm, and 50 mm. Then, these stretch-broken fibers were processed in a cotton spinning system. The results show that, compared to long ramie fibers processed in a conventional ramie spinning system, the stretch-broken fibers, with reasonable fiber length and high length uniformity, can be processed in a cotton spinning system with high efficiency and generally have better resultant yarn quality. For all of the stretch-broken yarns, the yarn processed from fiber with 40 mm length shows the best comprehensive performance.

Keywords

ramie fiber stretch-broken fiber cotton spinning system fiber length yarn quality

Research has been dedicated in recent years to developing renewable products in order to face the worldwide challenges of energy security, environmental protection, and economic growth. The use of natural fibers has generally offered a renewable resource.¹ As one of the important natural fibers, ramie is a member of the bast family, grown mainly in temperate and tropical areas. It is well known as “China grass” in the world, due to its dominant production in China.^2–4 Ramie fibers are obtained from the bast of the plant stem after decorticating, washing, and degumming.^3,5 They have the characteristics of high tensile strength, outstanding thermal conductivity, good moisture absorption, and excellent antibacterial function, and a fabric made of ramie fibers has a lot of favorable properties, such as good permeability, cooling and crisp feel, antimicrobial property, and so on.^5–8

Stretch-breaking was originally developed to convert continuous filament to staple fiber and was first used in manmade fiber processing.^9–13 The continuous filament is fed into the stretch-breaking machine composed of several pairs of rollers, by which the continuous filament is stretch-broken into the tops with the desired fiber length. Ramie fibers can also be stretch-broken in this way, because the average fiber length of ramie is too long and the variation of fiber length is too huge, which seriously impedes the process and the resultant yarn quality, especially the appearance and hairiness of conventional ramie yarn.^14–17 Therefore, conventional ramie processing frames can only run with low efficiency.¹⁶ After being stretch-broken, the average length of ramie fibers can be shortened to 30–50 mm and with low variation in fiber length. Therefore, these fibers can be processed in a cotton spinning system with a higher production rate, and yarn quality can also be improved.^15,16

In previous studies on ramie stretch-breaking,^14,18,19 raw degummed ramie fibers, with no further processing such as opening and carding, were directly stretch-broken and the results were not very satisfactory. Because many fibers in raw degummed ramie stick to each other, even after being stretch-broken, there were still many fiber stick bundles remaining;¹⁴ these fiber stick bundles would impede the downstream processing and yarn quality. In this study, combed slivers of ramie, instead of the raw degummed ramie, were stretch-broken in a conventional spinning process. Because fibers in combed slivers were separated and straightened completely after processing by opening, carding, and combing, they were more suitable for stretch-breaking. The resultant slivers, with fibers stretch-broken to cotton-type lengths, were processed in a cotton spinning system. Then, the quality of these yarns was tested and compared with that of conventional ramie yarn.

Experimental details

Materials

The combed ramie slivers of the conventional spinning process used in this study were obtained from Hunan Jingzhu Ramie Textile Co, Ltd, China. The physical and mechanical properties of ramie fibers in combed slivers are shown in Table 1. For fiber mechanical property tests, 30 repeats were done to obtain the average and variation of each parameter, such as tenacity, breaking elongation, and work rupture.

Table 1.

Properties of fibers in combed slivers.

Property	Weighted average length (mm)	Variation in length (CV %)	Fineness (dtex)	Tenacity (cN/dtex)	Variation in tenacity (CV %)	Breaking elongation (%)	Variation in breaking elongation (CV %)	Work rupture (cN/dtex)	Variation in work rupture (CV %)
Mean values	97.84	54.43	5.35	6.36	14.87	6.53	15.32	0.11	22.21

Stretch-breaking

A schematic diagram of the stretch-breaking machine used in this study is shown in Figure 1. Combed ramie slivers were fed into the machine, and five sets of rollers gripped the sliver with the presses P₁–P₅, respectively. The speed of rollers increased gradually, and long fibers in slivers were stretch-broken gradually in zones IV, III, II, and I, respectively. Then, the long fibers in input slivers were stretch-broken into short fibers in output slivers, which are better for downstream processing.

Figure 1.

Schematic diagram of stretch-breaking machine.

According to the previous research, the main stretch-breaking gauge (L₁) was the most important factor affecting the length parameters of stretch-broken fibers, and the content of short fibers would be minimized when the pre-stretch-breaking gauges (L₂, L₃, and L₄) were the same or integral multiples of the main stretch-breaking gauge (L₁).^15,18 Therefore, the main parameters of stretch-breaking employed in this study were set as shown in Table 2.

Table 2.

Stretch-breaking parameters.

Program	Stretch-breaking gauge (mm)				Stretch-breaking ratio^a				Press (P₁–P₅) (MPa)	Output speed (m/min)
Program	L₁	L₂	L₃	L₄	E₁	E₂	E₃	E₄	Press (P₁–P₅) (MPa)	Output speed (m/min)
1#	30	60	120	240	2.9	2.8	2.6	2.5	0.6	45
2#	35	70	140	210
3#	40	80	160	240
4#	45	90	180	225
5#	50	100	200	250

Stretch-breaking ratio means the ratio of roller speed in each stretch-break zone.

Fiber length tests

According to ASTM D519 (standard test method for length of fiber in wool top), a Y131 wool fiber comb sorter was used to test the length of ramie fiber. The fibers were grouped by length, and each group of fibers was weighed. Then the diagram of fiber length distribution (by weight) could be obtained, and length characteristic could be calculated from the length distribution. The test was repeated twice to obtain the mean length characteristic and distribution of ramie fibers by weight.

Fiber tensile property tests

Fiber tensile properties were tested using an XQ-2 fiber strength instrument: the pre-tension is 0.3 cN/dtex, the clamping distance is 20 mm, and the descending speed of the bottom clamp was 20 mm/min. The test environment temperature was 20 ± 2℃ and relative humidity was 65 ± 3%; the samples were conditioned in this environment for 24 h before test.

Yarn production

To compare with the conventional ramie yarn (the most popular is pure ramie yarn with a linear density of 27.8 tex), all the stretch-broken slivers were processed and spun to pure ramie yarn with a linear density of 27.8 tex. The same combed slivers were used both for the stretch-broken yarns and conventional ramie yarn.

The stretch-broken slivers were processed in a cotton spinning system as follows: combed slivers → stretch-breaking (GYFA313; stretch-broken slivers, with average fiber lengths of around 30 mm, 35 mm, 40 mm, 45 mm, and 50 mm, respectively) → drawing (two passages; FA303) → roving (FA454) → ring spinning (FA506), while the spinning procedure of conventional ramie yarn was: combed slivers → preparation (CZ304) → recombing (B311) → gilling (four passages; CZ304) → roving (FZ456) → ring spinning (FZ502).

All stretch-broken yarn samples were produced with the same drawing, roving, and spinning parameters, namely the same doubling, twist multiplier, and spindle speed, etc. Because of the large difference of fiber length, the stretch-broken yarn and conventional yarn had different optimum twist multipliers, so the twist multiplier employed in stretch-broken yarn and conventional yarn was different. The drawing, roving, and spinning parameters of stretch-broken yarn are compared to those of conventional ramie yarn in Table 3.

Table 3.

Parameters in yarn forming processing.

Processing	Stretch-broken yarn	Conventional ramie yarn^a
Drawing
Total draft	8.2	6.2
Doubling	8	6
Output speed (m/min)	250	60
Roving
Total draft	6.1	6.1
Twist multiplier (a_t/a_e)	105/1.10	67/0.70
Speed of spindle (r/min)	700	350
Ring spinning
Nip gauge (mm)	0	2
Total draft	23.85	23.83
Break-draft	1.3	1.15
Twist multiplier (a_t/a_e)	390/4.08	315/3.29
Speed of spindle (r/min)	12000	6500

Gilling instead of drawing was used for conventional ramie yarn in drawing processing.

The yarns made from stretch-broken fibers are defined as Y-S(30 mm), Y-S(35 mm), Y-S(40 mm), Y-S(45 mm), and Y-S(50 mm), respectively, while the conventional ramie yarn is defined as Y-C in this study.

Yarn tests

Yarn tensile properties were tested using an Uster Tensorapid: the distance between the jaws was 500 mm and the speed was 500 mm/min according to ASTM D2256 (standard test method for tensile properties of yarns by single-strand method). Yarn irregularity property was tested using an Uster Tester 3: the measurement length was 1000 m and the speed was 100 m/min according to ASTM D1425 (standard test method for evenness of textile strands using capacitance testing equipment). Yarn hairiness was measured using a Uster Zweigle HL400: the measurement length was 100 m and the speed was 200 m/min according to ASTM D5647 (standard guide for measuring hairiness of yarns by photo-electric apparatus). The test environment temperature was 20 ± 2℃ and relative humidity was 65 ± 3%; the samples were conditioned in this environment for 24 h before test.

Statistical analysis

T-testing was used for statistical analysis the test results.

Results and discussion

Fiber length distribution

Fiber length test results are shown in Table 4 and Figure 2. Test results show that the distribution of fiber length in the original combed slivers (Figure 2(a)) is wide, and the length irregularity is high, up to 54.43% (Table 4), which means the uniformity in fiber length is very poor. In addition, the contents of short fiber (<50 mm) and overlong fibers (>150 mm) in the combed slivers are high, up to 19.58% and 5.21% (Table 4), respectively. So this increases the difficulty in drafting and consequently causes higher additional irregularity in the end yarn. Therefore, the quality of yarn produced by conventional processing, especially in terms of yarn irregularity and hairiness, is poor.

Table 4.

Length characteristics of fibers in combed and stretch-broken slivers.

Properties	Mean values
	Combed slivers	Stretch-broken slivers
	Combed slivers	30 mm	35 mm	40 mm	45 mm	50 mm
Average length by weight (mm)	97.84	31.08	36.05	40.23	45.96	49.42
Variation in length (CV %)	54.43	27.61	30.63	29.53	36.66	35.90
Content of short fiber (<12.7 mm) (wt %)	0.29	2.18	1.73	1.68	2.30	1.89
Content of short fiber (<50 mm) (wt %)	19.58	97.84	89.53	82.48	63.12	50.51
Content of long fiber (>50 mm) (wt %)	80.84	2.16	10.47	17.52	36.88	49.49
Content of long fiber (>60 mm) (wt%)	67.93	0.15	1.45	3.82	18.67	22.98
Content of long fiber (>70 mm) (wt %)	56.12	0.01	0.43	1.92	9.55	10.45
Content of overlong fiber (>150 mm) (wt %)	5.21	0	0	0	0	0

Figure 2.

Fiber length distributions of (a) fibers in combed slivers and stretch-broken fibers with average lengths of (b) 30 mm, (c) 35 mm, (d) 40 mm, (e) 45 mm, and (f) 50 mm.

As shown in Table 4, the length of stretch-broken fibers mostly depends upon the main stretch-broken gauge (L₁), and the average length of stretch-broken fibers is close to the main stretch-broken gauge (L₁), which is in agreement with the earlier studies of Zhong and Ji et al.^15,18 Also, the fiber length distribution in stretch-broken slivers becomes much narrower (Figure 2(b) and (f)) compared with that of the original combed slivers (Figure 2(a)). Correspondingly, the irregularity of fiber length becomes small and short fiber content (<12.7 mm) is much lower in stretch-broken slivers, as shown in Table 4, which are beneficial for the control of fiber movement during drafting processing in drawing, roving, and ring spinning.^17,21

Fiber tensile properties before and after stretch-breaking

As shown in Table 5, fiber tenacity, elongation, and work rupture all decrease after stretch-breaking. This is because fiber structure has been damaged and the internal stress of fiber decreases, which will be a disadvantageous factor for downstream processing.

Table 5.

Tensile properties of fibers before and after stretch-breaking.

	Tenacity (cN/dtex)	Variation in tenacity (CV %)	Breaking elongation (%)	Variation in breaking elongation (CV %)	Work rupture (cN/dtex)	Variation in work rupture (CV %)
Before (combed sliver)	6.36	14.87	6.53	15.32	0.11	22.21
After (stretch-broken sliver)
30 mm	5.83	21.53	5.69	21.23	0.08	24.59
35 mm	5.87	23.45	5.74	19.84	0.08	27.37
40 mm	5.90	22.72	5.81	20.02	0.09	26.78
45 mm	5.94	20.51	5.92	22.47	0.10	24.16
50 mm	6.01	21.76	6.04	21.52	0.10	25.38

Yarn tensile properties

Test results for yarn tensile properties are shown in Table 6 (each result is the mean of 30 tested values). The t-test was used to analyze the difference between each stretch-broken yarn and conventional yarn. The confidence level was set as 0.05 (namely α = 0.05), and the analysis results are shown in Table 7. It can be seen that Y-C appears to have significant higher tenacity in comparison with Y-S(30 mm) and Y-S(35 mm), and closer tenacity in comparison with Y-S(40 mm) and Y-S(45 mm), whereas the tenacity of Y-S(50 mm) is significant higher than that of Y-C. This might be explained by the earlier studies of Yu and colleagues.^16,17 Yarn tenacity increases greatly as the length of fiber increases when the fiber is short, but when the fiber increases to a certain length, yarn tenacity does not increase notably with the increase of fiber length. On the other hand, the twist multiplier of Y-S is higher than that of Y-C, which also leads to the higher tenacity of Y-S(40 mm), Y-S(45 mm), and Y-S(50 mm).

Table 6.

Tensile property of yarns.

	Tenacity (cN/dtex)	Variation in tenacity (CV %)	Breaking elongation (%)	Variation in breaking elongation (CV %)	Work rupture (cN/dtex)	Variation in work rupture (CV %)
Y-C	21.59	11.37	3.96	9.88	45.78	22.80
Y-S(30 mm)	18.54	4.78	3.11	6.54	39.30	9.84
Y-S(35 mm)	19.84	5.36	3.15	6.87	40.38	10.44
Y-S(40 mm)	21.30	5.09	3.25	7.17	47.24	12.99
Y-S(45 mm)	22.50	7.19	3.21	6.29	49.67	9.88
Y-S(50 mm)	23.60	5.90	3.24	5.56	47.04	11.37

Table 7.

Significance test (t-test) for the difference of yarn tensile properties.

Inspection item	Sample 1	Sample 2	t_0.05(58)	Statistics	Significance	remark
Tenacity	Y-C	Y-S(30 mm)	2.002	6.40095	Significant	Y-S(30 mm) smaller than Y-C
		Y-S(35 mm)		3.58293	Significant	Y-S(35 mm) smaller than Y-C
		Y-S(40 mm)		0.59190	Non-significant	Y-S(40 mm) close to Y-C
		Y-S(45 mm)		1.69538	Non-significant	Y-S(45 mm) close to Y-C
		Y-S(50 mm)		3.90095	Significant	Y-S(50 mm) larger than Y-C
Breaking elongation		Y-S(30 mm)		10.55802	Significant	Y-S(30 mm) smaller than Y-C
		Y-S(35 mm)		9.92277	Significant	Y-S(35 mm) smaller than Y-C
		Y-S(40 mm)		8.53964	Significant	Y-S(40 mm) smaller than Y-C
		Y-S(45 mm)		9.33035	Significant	Y-S(45 mm) smaller than Y-C
		Y-S(50 mm)		9.15566	Significant	Y-S(50 mm) smaller than Y-C
Work rupture		Y-S(30 mm)		3.18856	Significant	Y-S(30 mm) smaller than Y-C
		Y-S(35 mm)		2.62743	Significant	Y-S(35 mm) smaller than Y-C
		Y-S(40 mm)		0.66045	Non-significant	Y-S(40 mm) close to Y-C
		Y-S(45 mm)		1.84728	Non-significant	Y-S(45 mm) close to Y-C
		Y-S(50 mm)		0.58843	Non-significant	Y-S(50 mm) close to Y-C

In terms of breaking elongation, Y-C yarn shows significant higher breaking elongation than that of stretch-broken yarns, because of the decrease on breaking elongation of stretch-broken fibers. Lower elongation of stretch-broken yarns may restrict the performance in downstream processing such as weaving, and fabric quality such as the handle of fabric.

For work rupture, Y-S(40 mm), Y-S(45 mm), and Y-S(50 mm) appear to have the closer work rupture with Y-C. Generally, this means that the stretch-broken yarns also can offer sufficient work rupture for end use.

Generally, considering yarn tenacity and work rupture, Y-S(40 mm), Y-S(45 mm), and Y-S(50 mm) are closer to Y-C, which means they have good ability to resist broken damage in downstream processing.

Yarn irregularity and yarn imperfections

Yarn irregularity test results are shown in Figure 3 (each result is calculated from five repeats). T-test results (α = 0.1) show that Y-S(30 mm) and Y-S(40 mm) have close irregularities that are lower than others, while Y-C has the highest. The trend of yarn irregularity values is similar to the trend of fiber length irregularity in slivers, so this might be explained by that the smaller the fiber length irregularity, the better control of fibers movement during drafting, and correspondingly the lower the yarn irregularity, which is also in agreement with the results of earlier papers.^16,17 Smaller fiber length irregularity is helpful for fibers evenly arranged in sliver or yarn.

Figure 3.

Irregularity of yarns.

Test results of thin places, thick places, and neps are shown in Figure 4. In terms of thin and thick places, Y-S(30 mm) has the best value in all kinds of yarns, and Y-S(40 mm) has a value close to Y-S(30 mm), whereas Y-C has the worst value, which is also caused by high content of short fibers and super long fibers that are harmful to the fiber movement control during drafting.

Figure 4.

Imperfection (thin places, thick places, and neps) of yarns.

Results concerning irregularity, thin places, and thick places reveal that the irregularity in fiber length has an important impact on the irregularity, thin places, and thick places of resultant yarns.

For neps in yarn, the nep content of Y-C is much higher than that of Y-S. This is because the average fiber length of Y-C is high, up to 97.84 mm. Compared to the short fiber, the longer fiber is regarded as more easy to entangle together to form neps during processing.²¹ Also, Y-S(40 mm) has the lowest nep content in all kinds of stretch-broken yarns.

Yarn hairiness

Test results of hairiness of yarns are shown in Figure 5 (each result is calculated from five repeats). T-test results for (α = 0.1) show that Y-S(40 mm) yarn has the lowest hairiness, while Y-C yarn has the highest. The variation trend of hairiness is similar to the variation trend of short fiber content (length: < 12.7 mm for Y-S, while length: < 50 mm for Y-C) content in slivers. The higher the short fiber content, the more the yarn hairiness. The reason is that higher short fiber content means more fiber ends, which are difficult to control in the twist triangle of ring spinning. Therefore, the probability of fiber ends protruding from the yarn body increased, hence increasing the hairiness of the yarn. In addition, a higher twist multiplier also has a positive effect on the reduction of hairiness of stretch-broken yarns.

Figure 5.

Hairiness of yarns.

Spinning efficiency

For the procedures from combed slivers to end yarn, the conventional ramie yarn was processed in a conventional ramie spinning system, while the stretch-broken ramie yarns were all processed in a cotton spinning system. The spinning process of stretch-broken ramie yarns does not have the processes of preparation and recombing, and only two passages of drawing are required (four passages of gilling are required for conventional ramie yarn). Therefore, the spinning process of stretch-broken ramie yarns is much shorter than that of conventional ramie yarn. In addition, the output speed of drawing (gilling) frame, the spindle speed of roving, and ring spinning frame in cotton spinning system are all much higher than those in conventional ramie spinning system, shown in Table 3, which means that cotton spinning system has much higher production rate than a conventional ramie spinning system. As shown in Table 8, yarn breakage rate during ring spinning in a cotton spinning system is also much less than that of a conventional ramie spinning system.

Table 8.

Yarn breakage rate during ring spinning.

	Average of three observed values
	Y-C	Y-S(30 mm)	Y-S(35 mm)	Y-S(40 mm)	Y-S(45 mm)	Y-S(50 mm)
Yarn breakage (number/(1000 spindles hour))	86	56	42	45	52	49

As can be seen from all test results, the positive results for all yarn properties are listed in Table 9. It can be seen that for all stretch-broken yarns, Y-S(40 mm) is the best in terms of irregularity, imperfections, and hairiness. Besides, Y-S(40 mm) has similar tensile properties to Y-C, and also has lower irregularity, less imperfections, and lower hairiness than Y-C. In addition, stretch-broken yarns can be processed in a cotton spinning system with high processing efficiency.

Table 9.

Yarn properties and their positive results.

Sample	Fiber tenacity	Yarn tenacity	Yarn irregularity	Yarn imperfections	Yarn hairiness	Spinning efficiency
Y-C	√	√
Y-S(30 mm)			√	√
Y-S(35 mm)						√
Y-S(40 mm)		√	√	√	√	√
Y-S(45 mm)	√	√
Y-S(50 mm)	√	√

Conclusion

The conventional combed ramie sliver with long fiber (around 100 mm) can be stretch-broken into slivers with short fiber lengths of 30–50 mm, which can be processed in a cotton spinning system. Compared with conventional fibers, the length variation and short fiber content of stretch-broken fibers decreases greatly, which is significantly helpful for downstream processing. The stretch-broken ramie yarns have generally better quality compared with that of conventional ramie yarn, especially in terms of yarn irregularity, imperfections, and hairiness. For all of the yarns made from stretch-broken ramie fibers, the yarn made from 40 mm length fibers shows comprehensively better quality in tensile and hairiness properties. For stretch-broken ramie fibers, a shortened yarn forming processing time with high efficiency is expected.

Footnotes

Declaration of conflicting interests

The authors declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Funding

The authors disclosed receipt of the following financial support for the research, authorship, and/or publication of this article: This work was supported by the National Nature Science Foundation of China (grant number 51173023), the Earmarked Fund for China Agriculture Research System for Bast and Leaf Fiber Crops (grant number CARS-19), and China Academy of Agricultural Science and Technology Innovation Project (grant number ASTIP-IBFC07).

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