Original article

Comparative study of fiber trapping byfilaments in conventional and diagonalsirofil systems

Zhigang Xia1,2, Qinsheng Guo3, Wenxiang Ye1, Jun Chen1,Shengli Feng4 and Cailing Ding5,6

Abstract

In this study, geometrical and theoretical analyses were conducted comparatively for fiber trappings by filaments in the

left diagonal, conventional and right diagonal sirofil with right strand and left filament arrangement (denoted as LDS-RS-

LF, CS-RS-LF and RDS-RS-LF, respectively)and left diagonal, conventional and right diagonal sirofil with right filament and

left strand arrangement (LDS-RF-LS, CS-RF-LS and RDS-RF-LS, respectively). White filaments and blue rovings were

used to produce conventional and diagonal sirofil yarns to validate the analysis. Online and offline fiber trapping capacity

comparisons indicated that CS-RS-LF and CS-RF-LS had higher capacities of trapping fibers than LDS-RS-LF and RDS-RF-

LS, respectively, and lower capacities than RDS-RS-LF and LDS-RF-LS, respectively. Yarn appearance and tensile proper-

ties results revealed that diagonal sirofils with improved fiber trappings increased yarn hairiness and tensile properties,

while the ones with deteriorated fiber trappings decreased yarn hairiness and tensile properties. Sirofil yarn unevenness

CVm decreased as the fiber trapping enhanced by RDS-RS-LF and LDS-RF-LS and increased as the fiber trapping

weakened by LDS-RS -LF and RDS-RF-LS. This corresponded well to our theoretical hypotheses on fiber trappings

by filaments in conventional and diagonal sirofil systems.

Keywords

diagonal sirofil, spinning, fiber trapping, hairiness, yarn property

With the demands for high-quality fabrics with exquis-ite styles, various yarns with different property/functions are needed with special styles. Twisted fila-ment yarns are strong, smooth and uniform; however,ring staple yarns are hairy and irregular.1 Thus com-posite yarns, made by combining filaments with staplefibers, are desired to have an improved evenness, ten-acity and appearance.2 These yarns can be producedby sirofil and core-fil spinnings. Sirofil spinningstrengthens the produced yarn by ply-twisting thespaced filaments and staple strand together on a ringframe; therefore, the torsional filaments show a helicalconfiguration on the sirofil surface.3 Different fromthe sirofil, core-fil spinning improves the spun yarnstrength by hiding filaments in the staple strandinner core,4 producing core–sheath structured yarnswith the appearance of traditional staple yarns.5

Feeding the filaments between double rovings hasbeen regarded as an effective way to secure the

consistent complete coverage of staple sheath oncore filaments.6,7 Otherwise, the poor coverage of thestaple sheath encourages periodic exposures of corefilaments on the yarn surface, causing barber-pole

1College of Textile Science and Engineering, Wuhan Textile University,

China2State Key Laboratory Base of New Materials and Advanced Processing

Technology, Wuhan Textile University, China3Yuci Branch, Jingwei Textile Machinery Company Limited, China4Xiangyang Jihua 3542 Textile Company Limited, China5College of Textiles, Donghua University, China6National Engineering Research Center for Spinning Technology, Ruyi

Group, China

Corresponding authors:

Zhigang Xia, Wuhan Textile University, No.1 Sunshine Avenue, Jiangxia

District, Wuhan 430200, China.

Email: zhigang_xia1983@hotmail.com

Cailing Ding, Donghua University, No.2999 Peoples’ Northern Road,

Songjiang District, Shanghai 201620, China.

Email: rydcl@126.com

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problems for core-fil spun yarns.8,9 In specialty, the con-ventional sirofil and core-fil methods often suffer fiberloss problems during twisting of the staple strand, caus-ing the composite yarn quality deterioration.10

To overcome the fiber loss problems, fiber trappingcapacities should be enhanced by applying novel com-posite spinning methods. Twisting three core-fil com-posite strands together (also called TSMM) can partlyreduce staple fiber loss and solve the barber-pole prob-lems (i.e., the slippage between core filaments andsheath staple strands).11 Inevitably, the TSMM compo-nents increase triply to cause inconvenient operationand management during spinning. Unlike the conven-tional core-fil spinning, cluster-spinning employs elec-trostatic charging12 and a mechanical slotted roller13 tospread the multi-filaments when feeding them into thefront nip. Then potential loosened staple fibers aretrapped into a high-qualified composite yarn by clustermulti-filaments.14 However, electrostatic charging isnot safe for practical textile production. Similar toTSMM, roller-slotted cluster-spinning also fails in suc-cessful industrial applications due to its complex oper-ation.15 On the basis of siro-core and sirofil spinning,embeddable and locatable composite spinning (ELS) isdeveloped to solve the fiber loss problem by twistingtwo core-fil or sirofil composite strands together.16

Although ELS has been successfully applied to producesuper high-count worsted yarns due to its high fibertrapping efficiency, it has not been widely used forcommon composite yarn production because of twicethe increase in components and inconvenient oper-ation. Therefore, a simple and convenient way toimprove fiber trapping still remains to be found andstudied for the conventional sirofil and core-filspinnings.

In this study, the conventional sirofil spinning tri-angle was changed by a simple diagonal offset (patentCN201610010718.8) to solve the existed fiber lossproblems in conventional sirofil and core-fil systemsand the existing inconvenience problems in ELS sys-tems. The key mechanisms of filaments trappingstaple fibers were theoretically studied for differentdiagonal sirofil spinning triangles. The influence offiber trapping on yarn properties was also modeledand analyzed in theory. To validate the theoreticalanalysis, blue cotton roving and white filamentswere used to conduct conventional, left diagonaland right diagonal sirofil spinnings. Online trappingefficiencies in different spinning triangle zones werecomparatively examined. Thereafter, correspondingsirofil composite yarn properties were comparativelyinvestigated, including surface hairiness, unevennessand tensile properties.

Theoretical considerations of the fibertrapping by filaments in different sirofilsystems

Geometrical analysis of fiber trappings in differentsirofil systems

Single ring yarn properties will change obviously whenchanging spinning triangles by diagonally offsetting thespinning strand.17,18 How to influence sirofil yarn prop-erties by diagonally offsetting the spinning strand stillneeds deep and extensive investigation. To unlock themysterious mechanism of the fiber trapping by filamentsextensively, six sirofil geometrical models were estab-lished: a left diagonal sirofil with right strand and leftfilament arrangement (LDS-RS-LF) (Figure 1(a)), aconventional sirofil with right strand and left filamentarrangement (CS-RS-LF) (Figure 1(b)), a right diagonalsirofil with right strand and left filament arrangement(RDS-RS-LF) (Figure 1(c)), a left diagonal sirofil withright filament and left strand arrangement (LDS-RF-LS) (Figure 1(d)), a conventional sirofil with rightfilament and left strand arrangement (CS-RF-LS)(Figure 1(e)) and a right diagonal sirofil with right fila-ment and left strand arrangement (RDS-RF-LS)(Figure 1(f)).

For spinning with two spaced components, eachcomponent has the pre-twists before convergent twist-ing17; furthermore, the pre-twists can be trapped intothe convergent twisted inner structure.18 Filaments arestrong and continuous. In the spinning systems illu-strated in Figures 1(c) and (d), twisting filaments geo-metrically move below the pre-twisting staple strand,standing a good chance of contacting and trapping theloosened fibers into the composite yarn body.Moreover, the pre-twisting staple strand also has agood fiber trapping, as its peripheral fibers are nearto the convergence twisting point. On the contrary,when the pre-twisting staple strand moves below thetwisting filaments, loosened fibers from the staplestrand cannot be trapped by the twisting filaments ingeometry (Figures 1(a) and (f)). Even worse, the largediagonal stretched deformation of the below-movingpre-twisting staple strand leads to a serious departureof the convergence twisting point and pre-twistingstaple stem from the out-most peripheral staplefibers, aggravating the loosened fiber amount andhair-trapping of the pre-twist staple strand (Figures1(a) and 1(f)). In compromise, the pre-twisting staplestand and filaments show a symmetric moving path totheir convergence of forming composite yarn, with amedium controlling of fiber loss and hair formation.The change of the spinning triangle shape and fiber

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mass loss will cause variations of the resultant yarnstructure and properties, which is theoretically ana-lyzed below.

Theoretical analysis of fiber trappings in differentsirofil systems

In addition to the geometrical mechanism, the spinningtension and twist distributions are also key factorsinfluencing fiber trapping for different sirofil systems.Similar to previous mechanical analysis,15,19

Equations (1) and (2) can be derived

Ff ¼sin �

sin �þ �ð Þ � Fc ð1Þ

Fs ¼sin �

sin �þ �ð Þ � Fc ð2Þ

where Ff, Fs and Fc represent tensions of thefilaments, staple strand and composite strand, respect-ively; � represents the angle of the filament andthe composite strand axis line; and � represents theangle of the staple strand and composite strandaxis line.

After examination of different conventional anddiagonal sirofil systems, illustrated in Figures 2(a)–(c),the following in-equations and equations can be easilyobtained

�1 4�1 ð3Þ

�2 ¼ �2 ð4Þ

�3 5�3 ð5Þ

�1 þ �2 ¼ �3 þ �3 5�2 þ �2 ð6Þ

where Fc1, Fc2 and Fc3 represent composite strand ten-sions in the Figures 2(a)–(c) sirofil systems, respectively;�1, �2 and �3 represent the angle of the filament andcomposite strand axis line in the Figures 2(a)–(c) sirofilsystems, respectively; and �1, �2 and �3 represent theangles of the staple strand and composite strand axisline in the Figures 2(a)–(c) sirofil systems, respectively.

Then we can easily get obtain the followingequations

Ff1 ¼sin �1

sin �1 þ �1ð Þ� Fc1 5Fs1 ¼

sin�1sin �1 þ �1ð Þ

� Fc1 ð7Þ

Figure 1. Geometrical illustration of fiber trappings by filaments in different sirofil systems: (a) LDS-RS-LF; (b) CS-RS-LF; (c) RDS-

RS-LF; (d) LDS-RF-LS; (e) CS-RF-LS; (f) RDS-RF-LS.

Xia et al. 3

Ff2 ¼sin�2

sin �2 þ �2ð Þ� Fc2 ¼ Fs2 ¼

sin �2sin �2 þ �2ð Þ

� Fc2 ð8Þ

Ff3 ¼sin �3

sin �3 þ �3ð Þ� Fc3 4Fs3 ¼

sin�3sin �3 þ �3ð Þ

� Fc3 ð9Þ

According to previous studies, each spinning strandtorque is proportional to the tension on it,20 and thetwist is proportional to torque.21 Then we can obtainthe following equations

Tf1 5Ts1 ð10Þ

Tf2 ¼ Ts2 ð11Þ

Tf3 4Ts3 ð12Þ

Equation (10) shows that the high-tensioned staplestrand has more twists than the low-tensioned filamentsfor the sirofil yarn formation zone in Figure 2(a).Considering the left diagonal asymmetrical yarn forma-tion zone shape, the spinning filaments are apt to wraponto the spinning staple strand, fastening staple strandsurface hairs to form a smooth composite strand.Consequently, the resultant composite yarn surfacehas scarce hairiness and a dense array of filament heli-ces for the sirofil system in Figure 2(a). In contrast, the

resultant composite yarn in Figure 2(c) has excessivehairiness and a sparse array of filament helices becauseof the low-tensioned staple strand wrapping onto thehigh-tensioned filaments, according to Equation (12)and the sirofil shape in Figure 2(c). Equations (8) and(11) show that the staple strand has the same spinningtension and twists with the filaments for the sirofilsystem in Figure 2(b). Considering the symmetricalyarn formation zone shape, the same tensioned fila-ments and staple strand are twisted with each other ina similar symmetrical helical deformation. Therefore,the resultant composite yarn surface has medium hairi-ness and filament helices for the sirofil system inFigure 2(b) when compared with that in Figures 2(a)and (c).

Figures 2(c) and (d) are symmetrical; it can beinferred that the loose staple strand wraps thehigh-tensioned compact filaments, causing excessivehairiness and scarce filament helices on the resultantcomposite yarn surface for the sirofil system in Figure2(d). Figures 2(b) and (e) are symmetrical; the sametensioned filaments and staple strand are twisted witheach other to form a composite yarn with equivalentfilament and staple strand spirals, contributing to themedium hairiness and filament helices of the resultantcomposite yarn for the sirofil system in Figure 2(e).Figures 2(a) and (f) are symmetrical; therefore, theloose filaments wrap the spinning staple strand to

Figure 2. Theoretical illustration of fiber trapping by filaments in different sirofil systems: (a) LDS-RS-LF; (b) CS-RS-LF; (c) RDS-RS-

LF; (d) LDS-RF-LS; (e) CS-RF-LS; (f) RDS-RF-LS.

4 Textile Research Journal 0(00)

trap hairs, resulting in scarce hairiness and dense fila-ment helices on the resultant composite yarn surface forthe sirofil system in Figure 2(f).

The diagonal offset slightly enlarges the yarn wrap-ping arc on the pigtail guider to cause an increasedtwist up-flow blockage. Under this situation we canget Fc1¼Fc3¼Fc4¼Fc6

geometrical analysis, the sirofil systems of Figures 2(a)and (f) endure severe fiber loss due to their similar lowcapacities of trapping staple fibers; therefore, spun yarnsshould embrace decreased staple fiber numbers to createhairs for the sirofil systems of Figures 2(a) and (f).Theoretical analysis indicates that low-tensioned fila-ments are apt to wrap onto the high-tensioned staplestrand, consequently nesting the staple strand hairs intothe resultant yarn (Figures 4(a) and (f)). Therefore, thecomposite yarn spun by sirofil systems in Figures 2(a) and(f) will be endowed with low hairiness.

In contrast to the above, the sirofil systems inFigures 2(c) and (d) will produce composite yarnswith high hairiness; this is because the high-tensionedfilaments are wrapped by the staple strand without fiberloss, facilitating the staple strand fiber ends protrudingout to form hairs. Obviously, the conventional sirofilsystems in Figures 2(b) and (e) can produce yarns withnormal medium hairiness to compromise the left andright diagonal sirofil systems.

Experiments were conducted to verify thesehypotheses.

Experimental details

Blue dyed cotton rovings and white nylon multi-fila-ments were employed to produce right diagonal(Figures 5(a) and (f)), left diagonal (Figures 5(c) and(d)) and conventional (Figures 5(b) and (e)) sirofil spunyarns, respectively, with the constant roving-filamentsspacing at 4mm. In the standard spinning workshopof the Jingwei Textile Machinery Company, all sirofil

yarns were produced on an FA506 ring frame with thesame spinning settings: opening of the pressure barspacer 2.0mm; draft ratio 48.10; yarn twisting density988.47 twists per meters; spindle speed 11024 rpm; frontroller speed 142 rpm; ring type PG 1/2 3854; and travelertype UDR 3/0. Images of all sirofil triangle zones werecaptured by an iPhone 5 camera during spinning.

Composite yarns spun by conventional and diagonalsirofil systems were stored for at least 24 h under astandard atmospheric condition (20� 2% relativehumidity (RH) and 65� 2�C). Then they were testedin terms of yarn count, hairiness, unevenness CVmand tensile properties under the standard condition.An AUY120 electrical balance was employed to weighall yarn for counts per 100m after measuring by YG086Lea’s length tester; the tested length of each yarn was500m, and the results were averaged. After observing allyarn appearances on a PM4000 polarizing microscope(transmission and reflection) in the same magnification(objective �4; eyepiece �10), hairiness was tested on aYG173A hairiness meter by referring to the FZ/T01086-2000 CN textile industry standard23; the testspeed was 30m/min, the test segment length was 10mand 10 successive segments were tested for each yarn.An USTER 4-S unevenness tester was used for yarnunevenness tests according to the CN GB/T 3292.1-2008 capacitance unevenness standard24; the testingspeed and length were 400m/min and 400m, respect-ively, for each sample. A YG068C type automaticsingle yarn tensile tester was used to test the yarn tensileproperties; each sample was tested 20 times with a testspeed of 500mm/min and a gauge length of 500mm.

Figure 4. Appearance model comparison of yarns produced from different sirofil systems: (a) LDS-RS-LF; (b) CS-RS-LF; (c) RDS-RS-

LF; (d) LDS-RF-LS; (e) CS-RF-LS; (f) RDS-RF-LS.

6 Textile Research Journal 0(00)

Results and discussion

Online comparison of the fiber trapping capacity fordifferent sirofil systems

Flute pipe air suction10 and gravity facilitate the onlinefiber loss from the spinning staple strand, especially forthe fibers with high flexural rigidity.25 The online fiber

loss phenomenon shown in Figure 6 can be used toperform a qualitative analysis of fiber trappingcapacities.

Figures 6(a) and (f) exhibited serious fiber lossduring sirofil spinning, revealing the low fiber trappingabilities for LDS-RS-LF and RDS-RF-LS. CS-RS-LFand CS-RF-LS still suffer fiber loss (Figures 6(b) and(e)) due to their medium fiber trapping capacity

Figure 5. Practical online pictures for different sirofil systems: (a) LDS-RS-LF; (b) CS-RS-LF; (c) RDS-RS-LF; (d) LDS-RF-LS;

(e) CS-RF-LS; (f) RDS-RF-LS.

Figure 6. Online fiber trapping images for different sirofil systems: (a) LDS-RS-LF; (b) CS-RS-LF; (c) RDS-RS-LF; (d) LDS-RF-LS;

(e) CS-RF-LS; (f) RDS-RF-LS.

Xia et al. 7

mentioned above. In fact, the RF-LS sirofil systemseems to have a lower fiber loss than the correspondingRS-LF one. This may be due to the strand componentin the left-hand side of the spinning triangle usuallygetting more twists than that in the other side duringthe Z twisting.26,27 As expected, online fiber loss iseliminated for RDS-RS-LF (Figure 6(c)) and LDS-RF-LS (Figure 6(d)) due to their excellent fiber trap-ping capacities.

Offline comparison of the fiber trapping capacityfor different sirofil systems

The weight loss of the resultant spun yarn occurs due toimperfect fiber trapping during spinning.28 Therefore,weight comparisons of the offline resultant spun yarn(Figure 7) can be employed for a quantitative analysisof the fiber trapping capacities.10

The sirofil spun yarn weight results (Figure 7)revealed that LDS-RS-LF and RDS-RF-LS producedyarns of the lowest weight compared with other sirofilsystems, which corresponds well with their onlinesevere fiber loss phenomenon. The very high error ofthe yarn mass average revealed serious irregular fiberloss during the formation of LDS-RS-LF yarn.Specifically, the weight of yarn spun of LDS-RS-LFwas lower than that of RDS-RF-LS, which may bedue to the right diagonal offset endowing increasedtwisting of the filaments29 to trap staple fibers. Theweight of yarns of RDS-RS-LF and LDS-RF-LSwere relatively much higher than that of other sirofilsystems (Figure 7), validating the excellent fiber

trapping capacities of the RDS-RS-LF and LDS-RF-LS systems.

Appearance comparisons of yarns spun bydifferent sirofil systems

Figure 8 shows that the LDS-RS-LF and RDS-RF-LSyarns have fewer surface hairs and more filamentexposures than other sirofil yarns. The first reasonmight be the filaments wrapping on the staple spinningstrand to trap hairs. Secondly, severe staple fiber loss(Figure 6) caused a decreased fiber amount protrudingout of the yarn surface.

Different from LDS-RS-LF and RDS-RF-LS, thestaple strand and filaments were twisted coaxiallywith each other to reduce fiber loss in the CS-RS-LFand CS-RF-LS systems, causing increased hairs byenlarging the staple strand distributions on the yarnsurface. Obviously, the RDS-RS-LF yarn stems werewrapped by blue staple strands to form excessivehairs (Figure 8(c)), well in consonance with the theor-etical prediction (Figure 4). However, RDS-RF-LSyarn failed to exhibit an identical surface wrapping ofstaple fibers with the LDS-RF-LS one (Figure 8). Thismay be due to the left arranged staple strand have amore compact twisting structure in RDS-RF-LS thanthe right arranged one in LDS-RF-LS (Figure 6).

To compare the surface hair amount exactly, differ-ent sirofil yarn hairiness results are listed in Table 1.Apparently, RDS-RS-LF yarn had more hairs thanother yarns due to its surface staple fiber wrappingwithout loss. For the RS-LF arrangement, spun yarnhairs were reduced as the diagonal direction of compos-ite yarn changed from the right to the left. In contrast,spun yarn hairs were increased as the diagonal directionof composite yarn changed from the right to the left forthe RF-LS arrangement. This was consistent with thetheoretical analysis. In particular, the RDS-RS-LFyarn had much more favorite (hair length within3mm) and harmful30 (hair length exceeding 3mm)hairs than the LDS-RF-LS yarn; similarly, the CS-RS-LF yarn had many more hairs than the CS-RF-LS yarn and the LDS-RS-LF yarn had many hairsthan the RDS-RF-LS yarn. This exactly validatedthat the RF-LS arrangement could produce compositeyarns with higher qualities than the RS-LF arrange-ment for a similar function of trapping staple fibersby filaments.

The hairiness H value is the ratio of the total testedhairiness length to the tested yarn length.31 Accordingto a previous study, the hairinessH value can be used toexamine the fiber wrapping tightness.32 The hairiness Hvalue of RDS-RS-LF yarn was much higher than thatof LDS-RF-LS yarn (Figure 9), revealing the increasedtight staple fiber wrapping on the LDS-RF-LS yarn

Figure 7. Resultant sirofil spun yarn weight comparisons: (a)

LDS-RS-LF spun yarn; (b) CS-RS-LF spun yarn; (c) RDS-RS-LF

spun yarn; (d) LDS-RF-LS spun yarn; (e) CS-RF-LS spun yarn; (f)

RDS-RF-LS spun yarn.

8 Textile Research Journal 0(00)

surface. According to above, Z twists are apt to trans-port onto the left-hand component of the sirofil spin-ning triangle; on the basis of this mechanism, lowtwisted filaments of RDS-RF-LS will be wrapped onthe tight twisted staple strand (opposite to the situationof LDS-RS-LF) in a relative large wrapping area to gettight trappings of staple hairs. Therefore, the RDS-RF-LS yarn hairiness H value was much lower thanthat of LDS-RS-LF yarn (Figure 9). Similarly, theCS-RF-LS yarn hairiness H value was much lowerthan that of CS-RS-LF yarn (Figure 9) under thesame mechanism.

Irregularity comparisons of yarns spun by differentsirofil systems

Table 2 shows that the LDS-RS-LF yarn had extrahigher irregularity compared with other sirofil yarns.This might be caused by severe irregular and occasionaltotal loss of staple fibers during the production of LDS-RS-LF yarns. For the same RS-LF setting, the spunyarn unevenness CVm value was decreased (i.e.,19.63> 7.44> 6.72 in Table 2) as the capacity of trap-ping staple fibers increased (Figures 6 and 7). Yarnsspun by sirofil systems with the same RF-LS setting

Table 1. Hair number comparison of yarns produced by different sirofil methods

1 mm 2 mm 3 mm 4 mm 5 mm 7 mm 10 mm 12 mm

(a) LDS-RS-LF 1224.60

[56.62]

301.10

[19.34]

67.00

[10.76]

24.20

[5.53]

8.70

[3.13]

1.40

[0.97]

0.00

[0.42]

0.20

[0.63]

(b) CS-RS-LF 1575.50

[61.00]

386.60

[24.61]

81.80

[13.81]

27.60

[7.57]

7.80

[2.97]

1.20

[1.03]

0.30

[0.48]

0.00

[0.00]

(c) RDS-RS-LF 1795.00

[92.95]

478.60

[28.15]

108.40

[12.89]

35.90

[6.10]

14.70

[4.81]

2.70

[2.50]

0.60

[0.84]

0.20

[0.42]

(d) LDS-RF-LS 1480.40

[74.20]

363.70

[31.52]

81.30

[11.32]

24.00

[4.00]

7.90

[3.60]

0.80

[1.23]

0.10

[0.32]

0.00

[0.00]

(e) CS-RF-LS 1286.30

[85.45]

287.70

[37.31]

60.90

[15.14]

19.60

[7.88]

6.30

[4.27]

0.50

[0.71]

0.00

[0.00]

0.00

[0.00]

(f) RDS-RF-LS 1063.90

[114.29]

202.70

[31.57]

33.40

[4.30]

9.40

[2.32]

3.30

[1.42]

0.40

[0.70]

0.00

[0.00]

0.10

[0.32]

Figure 8. Surface appearance comparisons of different sirofil yarns: (a) LDS-RS-LF spun yarn; (b) CS-RS-LF spun yarn; (c) RDS-RS-LF

spun yarn; (d) LDS-RF-LS spun yarn; (e) CS-RF-LS spun yarn; (f) RDS-RF-LS spun yarn.

Xia et al. 9

had an increasing order of CVm values (i.e.,6.37< 6.89< 7.34 in Table 2), as the capacity of trap-ping staple fibers decreased (Figures 6 and 7). Under asimilar fiber trapping situation, the irregularities ofLDS-RF-LS, CS-RF-LS and RDS-RF-LS yarns werelower than that of RDS-RS-LF, CS-RF-LS and LDS-RS-LF yarns, respectively. This might be because thecontrol of the left-hand staple fiber strand wasimproved to suppress unexpected drawing of thestaple spinning strand33 during Z twisting in RF-LSsirofil systems.

On one hand, grave mass concentration would occurduring surface staple fiber ends wrapping unevenlyonto the yarn stem, increasing resultant yarn imperfec-tions.34 On the other hand, irregular fiber loss wouldincur increased yarn irregularity and imperfections; theincreased fiber loss corresponded to a reduced staplefiber wrapping onto sirofil yarn according to our afore-mentioned theoretical analysis. For sirofil with the RS-LF setting, sirofil yarn imperfections (including thin,thick places and neps) decreased as the fiber loss

decreased (Figures 6 and 7). This indicated that thefiber loss dominated the changes of yarn imperfectionsfor RS-LF sirofil systems. For RF-LS sirofil systems,the yarn imperfections increased firstly then slightlydecreased as the fiber loss decreased. This mightresult from the combination of the fiber loss and con-centrated staple hair-wrappings influencing the yarnimperfection variations for RF-LS sirofil systems.

Tensile property comparisons of yarns spun bydifferent sirofil systems

Table 3 shows that the yarn tenacity of CS-RS-LF washigher than that of LDS-RS-LF, while it was lowerthan that of RDS-RS-LF. The first key contributingfactor might be the increased fiber loss of LDS-RS-LF to decrease the fiber utilization for resisting the ten-sile drawing force, and the fiber loss elimination ofLDS-RS-LF to increase the fiber utilization for yarntensile drawing. Secondly, the configuration of fila-ments in the LDS-RS-LF yarn structure was compara-tively modeled to have a greater wrapping curve(Figure 4(a)), incurring the larger shear force to destroyfilaments during yarn tensile drawing; in contrast, fila-ments were regarded as having straightness in the RDS-RS-LF yarn inner structure, and therefore difficult tobe broken during the tensile drawing of yarn.

Table 2. Irregularity parameters of yarns produced by different sirofil methods

CVm

%

Thin place

–50%/km

Thick places

+50%/km

Neps +140%

/km

Neps +200%

/km

(a) LDS-RS-LF 19.63 20 125 250 165

(b) CS-RS-LF 7.44 0 10 60 20

(c) RDS-RS-LF 6.72 0 15 45 10

(d) LDS-RF-LS 6.37 0 15 50 20

(e) CS-RF-LS 6.89 0 20 115 35

(f) RDS-RF-LS 7.34 0 5 50 20

Figure 9. Hairiness H value comparison for different yarns:

(a) LDS-RS-LF yarn; (b) CS-RS-LF yarn; (c) RDS-RS-LF yarn; (d)

LDS-RF-LS yarn; (e) CS-RF-LS yarn; (f) RDS-RF-LS yarn.

Table 3. Tensile property information of yarns produced by

different sirofil methods

Tenacity

cN/tex

Elongation

ratio %

Breaking

work cN.cm

(a) LDS-RS-LF 55.28� 3.53 43.43� 3.77 8312.50� 800.28(b) CS-RS-LF 60.37� 2.71 44.89� 3.33 9220.08� 920.88(c) RDS-RS-LF 62.25� 1.46 46.69� 1.25 9936.37� 440.78(d) LDS-RF-LS 63.69� 0.78 47.03� 1.72 10,279.08� 237.83(e) CS-RF-LS 61.78� 1.58 46.26� 1.25 9814.24� 445.41(f) RDS-RF-LS 59.67� 4.16 43.78� 2.34 9101.43� 991.72

10 Textile Research Journal 0(00)

On the same principle, the yarn tenacity of CS-RF-LS was lower than that of LDS-RF-LS, while it washigher than that of RDS-RF-LS (Table 3). Accordingto above-mentioned analysis, the staple spinning strandin RF-LS sirofil systems had a tighter twisted structurethan that in RS-LF sirofil systems; therefore, RF-LSsirofil yarns were slightly stronger than the correspond-ing RS-LF sirofil yarns (i.e., 59.67> 55.28; 61.78>60.37; 63.69> 62.25). The yarn breaking elongationand work listed in Table 3 had similar regularitieswith yarn tenacity results.

Conclusions

In this study, the fiber trappings by filaments for con-ventional and diagonal sirofil were geometrically andtheoretically analyzed. Geometrical analysis revealedthat RDS-RS-LF and LDS-RF-LS improved thefiber trapping capacities of CS-RS-LF and CS-RF-LS, respectively, to eliminate fiber loss by movingfilaments below the staple strand and shortening thedistance from the strand periphery to the twisting con-vergence. In a contrary geometry, LDS-RS-LF andRDS-RF-LS deteriorated fiber trapping capacities tocause severe fiber loss. The theoretical analysisrevealed that RDS-RS-LF and LDS-RF-LS encour-aged staple fibers wrapping onto filaments, increasingthe hairs of yarn spun by corresponding CS-RS-LFand CS-RF-LS, respectively. In contrast, LDS-RS-LF and RDS-RF-LS facilitated filaments wrappingonto the staple strand to get more smooth yarnsthan the corresponding conventional sirofils. Theresults of theoretical model analysis indicated thatthe low fiber trapping capacity would cause severefiber loss to lighten the yarn count and deteriorateyarn irregularity; the staple fibers wrapping on high-tensioned filaments facilitated yarn hair formation,while the filaments wrapping on the compact twistedstrand prohibited hairiness formation.

For validating the geometrical and theoretical ana-lysis, different conventional and diagonal sirofil yarnswere produced using blue cotton roving and whitefilaments. The experimental results confirmed thatCS-RS-LF and CS-RF-LS had a higher capacity offiber trapping than LDS-RS-LF and RDS-RF-LS,respectively, and a lower capacity than RDS-RS-LFand LDS-RF-LS, respectively. Therefore, yarns spunby LDS-RS-LF and RDS-RF-LS had an attenuatedcount, reduced hairiness, deteriorated unevenness andenhanced tenacity after a comparison with that spun byCS-RS-LF and CS-RF-LS, respectively. Yarns spun byRDS-RS-LF and LDS-RF-LS had a coarsened count,increased hairiness, improved unevenness and deterio-rated tenacity after a comparison with that spun by CS-RS-LF and CS-RF-LS, respectively.

Declaration of conflicting interests

The authors declared no potential conflicts of interest with

respect to the research, authorship and/or publication of thisarticle.

Funding

The authors disclosed receipt of the following financial sup-port for the research, authorship, and/or publication of thisarticle: This work was supported by the National Natural

Science Foundation of China (grant no. 51403161), theNational Science Fund for Distinguished Young Scholars(grant no. 51325306) and the Department of Science &

Technology of Hubei Province (grant no. 2014CFB755).

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