the effect of blend ratios of unrelaxed and relaxed acrylic fibres on physical properties of...

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The effect of blend ratios of unrelaxed and relaxedacrylic fibres on physical properties of high-bulkworsted yarnsS. Shaikhzadeh Najar , S. M. Etrati , M. H. Seyed-Esfahani & H. Hadia Department of Textile Engineering, Amirkabir University of Technology, Tehran, Iranb Department of Textile Engineering, Amirkabir University of Technology, Tehran, Iranc Department of Textile Engineering, Amirkabir University of Technology, Tehran, Irand Department of Textile Engineering, Amirkabir University of Technology, Tehran, IranPublished online: 08 Jul 2010.

To cite this article: S. Shaikhzadeh Najar , S. M. Etrati , M. H. Seyed-Esfahani & H. Hadi (2005) The effect of blend ratiosof unrelaxed and relaxed acrylic fibres on physical properties of high-bulk worsted yarns, The Journal of The TextileInstitute, 96:5, 311-318, DOI: 10.1533/joti.2005.0015

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The effect of blend ratios of unrelaxed andrelaxed acrylic fibres on physical properties ofhigh-bulk worsted yarns

doi:10.1533/joti.2005.0015

S. Shaikhzadeh Najar, S. M. Etrati, M. H. Seyed-Esfahaniand H. HadiDepartment of Textile Engineering, Amirkabir University of Technology, Tehran, Iran

Abstract: High-bulk acrylic yarns which contract and increase in bulk during the heat relaxation processare produced by blending two types of fibres with different shrinking power in the spinning process. Inthis paper, high-bulk acrylic yarns (steamed and dyed) with different shrinkable fibre blending ratioswere produced. Experimental results show that by increasing the shrinkable fibre blending ratio up to40%, the specific volume and shrinkage of both dyed and high-bulk acrylic yarns are steadily increasedwhile their tensile strengths are decreased. Further increasing the shrinkable fibre blending ratio causesthe specific volume and tensile strength properties to decreased and increased respectively. However,the yarn shrinkage does not change significantly. It is also found that both dyed and high-bulk acrylicyarns have the highest elongation at 20% shrinkable fibre blending ratio. In general, the specific volumeand tensile strength of high-bulk acrylic yarns are more than those of dyed acrylic yarns but theirshrinkage and elongation values are similar.

Key words: High-bulk yarn, acrylic fibre, shrinkable and non-shrinkable fibres, blend ratio, physicalproperties, heat relaxation process, worsted spinning.

INTRODUCTION

There is a great tendency towards increasing yarn volume,which in turn affects handling, covering power and ther-mal insulating properties of yarn and end-products (Piller1973). In recent years, due to the low cost of ‘acrylonitrile’,acrylic fibre gained the capability of high-bulk yarns simi-lar to wool yarn character (Ishtiaque and Behera 1983) forknitwear products (Wynne 1997).

Some man-made fibres, and, in particular, the variousacrylics, have special thermo-mechanical properties whichenable temporary strains to be heat-set into the individualfibres (Hamilton 1961, Wray 1969). These strains may bereleased when the yarn is relaxed (Hamilton 1961, Wray1969). High-bulk acrylic yarns which contract and increasein bulk on relaxation are produced by blending standardand high-shrinkage fibre in spinning (Hamilton 1961, Piller1973, Wray 1969, Wynne 1997). The resulting yarn is then

Corresponding Author:Dr S Shaikhzadeh NajarDepartment of Textile EngineeringAmirkabir University of Technology, Tehran, IranTel: 009821 64542613; Fax: 009821 6400245Email: [email protected]

given a heat relaxation treatment (steam or hot water) toshrink or relax the high-shrinkage fibres from strain. Fibreswithin the yarn are held together by inter-fibre friction,so the pre-relaxed fibres must buckle outwards when theunrelaxed fibres shrink, creating bulkiness and a warm, softfeel to the yarn (Hamilton 1961, Piller 1973, Wray 1969,Wynne 1997).

The bulking mechanism in high-bulk yarns thus de-pends not only on the contractile properties of the high-shrinkage fibres themselves, but also on the interactionof the two components within the actual yarn (Hamilton1961, Wray 1969). The yarn’s internal structure factorsincluding fibre blend proportions, yarn twist, and possiblyany preferential radial distribution of the two componentsrelative to the yarn axis are therefore of major importance(Hamilton 1961, Piller 1973, Wray 1969). It has been re-ported that within a certain value of unrelaxed acrylic fibresblended with relaxed fibres, the best compromise betweenthe yarn bulk, shrinkage, strength and elongation can be ob-tained (Bhattacharya 1980, Edwards and Sneyd 1958, Hadi2000, Hamilton 1961, Heckert 1957, Ishtiaque and Behera1983, Lulay 1995, Malaguzzi and Sala 1971, Naik et al.1980, Oxtoby 1987, Piller 1973, Wray 1969, Wynne 1997).However, there is little published work to investigate andcompare the high-bulk acrylic (continuous bulking system)

C© The Textile Institute 0174 311 JOTI 2005 Vol. 96 No. 5 pp. 311–318

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S. Shaikhzadeh Najar, S. M. Etrati, M. H. Seyed-Esfahani and H. Hadi

Table 1 Raw material specifications

Material Fineness (den) Strength Elongation (%) Length (mm)(cN/tex)

Filament 3.22(8.97)∗ 27.64(8)∗ 43.43(7.64)∗ –Shrinkable fiber 2.55(10.05)∗ 32.97(14.28)∗ 13.84(16.29)∗ 108.7(40.06)∗Non-shrinkable fibre 3.16(9.22)∗ 23.32(11.63)∗ 31.68(11.63)∗ 86.5(33.18)∗

∗The CV% values are indicated in brackets.

Table 2 Spinning preparation process

Machine Linear density Draft Twist Doubling Delivery lineartype of sliver (Ktex) (T.P.M) density (Ktex)

Gill box blender27.57 (Unrelaxed)28.35 (Relaxed) 18.3 20 30.61

Gill-box I 30.61 9.8 8 25.2Gill-box II 25.2 8.5 8 23.5Gill-box III 23.5 12 8 7.8∗2 = 15.6Speed frame 7.8 10 14.2 1 0.77

yarn’s physical properties produced in the worsted spin-ning system with those of grey (single and two-fold) andsteam-dyed yarns, as the shrinkable fibre blending ratio ischanged. Therefore, the aim of this paper is to investigatethe effect of shrinkable fibre blending ratio on bulk, shrink-age, tensile strength and elongation of high-bulk (steamedand dyed) and grey acrylic worsted yarns.

EXPERIMENTAL METHODS

Spinning processing

In this research, acrylic tow (AKSA) with linear density of120 Ktex and nominal fibre fineness of 3 den was used.Having utilized a tow-to-top stretch-breaking machine(SEYDEL), two different shrinkable and non-shrinkableacrylic fibre tops with linear densities of 27.57 and28.35 Ktex were respectively produced. Table 1 showsthe raw material specifications. The shrinkable and non-shrinkable acrylic tops were then blended with shrink-able fibre blending ratios of 0/100, 20/80, 40/60, 50/50,60/40, 80/20 and 0/100 on a blender gilling machine. Asshown in Table 2, the produced blended slivers passedthrough standard worsted spinning preparation machines(Hadi 2000) and thus seven samples of acrylic rovingswith linear density of 0.77 Ktex (1.3 Nm) were produced.Finally, seven samples of two-fold worsted acrylic yarnswere produced using standard worsted ring spinning andtwo-for-one twister machines (Hadi 2000). The yarn countand twist level for these seven blended acrylic worstedyarns were constant at the measure of 30/2 Nm and210 T.P.M respectively.

Bulking and dyeing processing

The bulking process was carried out using Superba con-tinuous bulking system (Hadi 2000, Oxtoby 1987). Thesteaming temperature was at a measure of 94◦C.

In order to dye the bulked acrylic yarns, hank prepa-ration was carried out and then the high-bulk yarns weredyed with Cathionic dye. The common hank dyeing pro-cedure was used (Hadi 2000, Wray 1969).

Yarn experimental investigation

The physical properties of produced yarns (single, twisted,steamed and dyed yarns) including the yarn count, twist,tensile strength and breaking elongation, percentage ofshrinkage, and specific volume were investigated. The sam-ple size was calculated according to the following formula(Hadi 2000):

K =(

t∗C VA

)2

(1)

where K is number of test, t is probability factor (1.96%for 95% probability), CV is coefficient of variation and A isallowance error (2.5–7%). Table 3 shows the sample sizesfor yarn experimental investigations.

The yarn count and twist of produced yarns weremeasured using standard test methods (Booth 1968,Saville 2000) (Tables 4 and 5). The percentage of yarnshrinkage was calculated (Table 6) by measuring greyand shrunk yarn count relationship, as indicated in the

Table 3 Sample size for yarn experimentalinvestigations

Test type Sample size (K)

Yarn count 10Yarn twist 10Tensile strength 50Elongation 50Specific volume 4∗

∗ For grey yarn K = 3.

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Effect of blend ratios on physical properties of high-bulk worsted yarns

Table 4 Yarn count results (Nm)

Shrinkable fibre blend ratio 0 20 40 50 60 80 100

Single yarn X 29.30 29.90 29.20 29.71 29.97 29.59 30.14CV% 2.85 3.0 2.86 2.29 3.21 2.59 1.03

Twisted yarn X 14.97 15.07 15.06 14.95 15.07 14.85 15.05CV% 1.95 1.78 2.3 2.23 1.95 3.72 1.85

Bulked yarn X 15.0 12.73 11.95 11.87 11.82 11.73 11.85CV% 2.71 2.16 2.28 1.56 2.84 1.12 1.92

Bulked (dyed) yarn X 14.78 12.79 11.97 12 11.71 11.71 11.77CV% 1.72 2.29 2.26 1.82 1.28 2.56 0.66

following equation:

Shrinkage (%) = Nm0 − Nm

Nm0∗ 100 (2)

where Nm0 is grey yarn count (metric yarn count) and Nmis bulked (shrunk) yarn count (metric yarn count). Yarn-specific volume or yarn bulk was measured using WRONZYarn Bulkometer (Hadi 2000, Shirley Development Ltd.,Saville 2000). A typical picture of this apparatus is shownin Fig. 1. For the purpose of this test, yarn bulk is de-fined as the volume occupied by 1 g of yarn at a givenpressure, measured in cm3/g (Shirley Development Ltd.,Saville 2000). To measure the bulk, a neatly aligned hankof yarn containing a known number of turns is placed ina channel 10 cm long ×5 cm wide (50 cm2 area), anda load of 500 g is then placed on the sample to com-press the yarn. When the load comes to rest (in 60 sectime), the height of the load above the base is measured.The bulk of the yarn under the pressure of 10 g/cm2

is then calculated from the volume of the yarn and its

mass. The size of hank used in the test depends on thelinear density of the yarn and can be calculated from theformula:

Number of turns = 90000Yarn Count in Tex

(3)

The experimental results of yarn-specific volume areshown in Table 7. The yarn tensile properties were mea-sured using Uster Dynamat Tensile tester II. The yarntest length and pre-tension were 50 cm and 0.5 g/texrespectively. The rate of loading was adjusted to give atime to break the specimen of 20 sec (Hadi 2000, Booth1968). The experimental results of yarn tensile propertiesare shown in Table 8.

All experiments were performed under the conditionsof 22 ± 2◦C and 45 ± 2% r.h.. The experimental results ofyarn physical properties were statistically analysed usingANOVA and Multiple Range Test methods (Hadi 2000).

Table 5 Yarn twist results (T.P.M)


Single yarn X 366 361.9 373.4 376.1 368 367.5 369.1CV% 3.11 4.77 3.99 6.53 3.04 4.59 5.11

Twisted yarn X 208.2 210.2 216 213 212.4 217.4 213.8

CV% 4.14 3.79 3.18 3.63 2.97 2.94 4.53Bulked yarn X 212.2 229.2 258.8 255.4 259.4 267.4 254.2

CV% 5.54 4.57 4.08 2.86 4.74 5.01 5.01

Bulked(dyed) yarn X 204 229.4 250.2 252.6 254.2 264.8 256.8CV% 6.75 5.9 3.8 4.92 4.09 4.48 5.69

Table 6 Yarn shrinkage results (%)


Bulked yarn X −0.17 15.51 20.63 20.59 21.50 20.90 21.30CV% −1935.54 15.31 11.51 7.16 12.10 17.66 6.66

Bulked(dyed) yarn X 1.25 15.18 20.48 19.69 22.27 21.01 21.79CV% 204.82 11.91 13.89 12.21 7.13 21.65 7.37

313C© The Textile Institute doi:10.1533/joti.2005.0015 JOTI 2005 Vol. 96 No. 5

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Figure 1 A typical picture of WRONZ Yarn Bulkometer (Shirley Development Ltd.).

RESULTS AND DISCUSSIONS

The effect of shrinkable fibre blending ratio onyarn shrinkage

The effect of shrinkable fibre blending ratio on yarn shrink-age is shown in Fig. 2. It is shown that by increasing theshrinkable fibre ratio up to 40%, the steamed and dyedyarns’ shrinkage increases and then reaches a steady con-dition. This result is in agreement with those obtainedby others (Bhattacharya 1980, Edwards and Sneyd 1958,Hamilton 1961 and Wray 1969). It may be assumed thatwithin the range of 40–100% shrinkable fibre ratios, theinternal structure of yarns does not allow the shrinkageprocess to be carried out completely. Statistical analysisresults indicate that within the range of 40–100% shrink-able fibre blend ratio, both yarn shrinkage and yarn twistremain significantly unchanged (Hadi 2000).

The effect of shrinkable fibre blending ratio onyarn-specific volume

The effect of shrinkable fibre blending ratio on specificvolume of twisted, bulked and dyed yarns is shown inFig. 3. It is demonstrated that by increasing the shrink-able fibre blending ratio up to 20%, the specific volume of

twisted yarn is not changed and then is decreased by in-creasing the shrinkable fibre ratio. It is reasonable to statethat the lower yarn-specific volume is due to lack of fibrecrimp in finer fibre (Brown 1969). On the other hand, in-creasing the shrinkable fibre ratio up to 40% causes thespecific volume of both bulked and dyed yarns to be dra-matically increased. Increasing the yarn twist level withinthe range of 0– 40% shrinkable fibre blend ratio (Table 5)illustrates that the yarn’s internal structure has changed.Edwards and Sneyd (Edwards and Sneyd 1958), Lulay(Lulay 1995) and Oxtoby (Oxtoby 1987) also quote a blendof about 40% unrelaxed fibre results in maximum yarnbulk. Further increasing the shrinkable fibre blending ra-tio results in a decrease in yarn-specific volume to a certainvalue similar to that of the normal acrylic (100% non-shrinkable fibre) yarn. The yarn-specific volume reductionis because the percentage of relaxed fibre component isdecreased. The lower dyed yarn-specific volume in com-parison with the steamed yarn is presumably related to thetension effects in hank preparation and hank dyeing pro-cesses (Piller 1973) and/or lower strength of dyed yarn. Itis reasonable to state that after the hank dyeing process,the tension applied to the wet yarn due to the weight ofabsorbed water by yarn hank (before drying process) wouldpresumably diminish yarn bulk.

Table 7 Yarn-specific volume results (cm3/g)


Twisted yarn X 9.63 9.59 9.53 9.49 8.88 8.72 8.43CV% 1.5 0.55 2.23 2.5 1.48 1.99 1.05

Bulked yarn X 8.76 12.75 13.5 13.09 11.88 10.72 8.59CV% 2.75 3.28 1.69 1.97 2.79 2.17 2.41

Bulked(dyed) yarn X 7.64 9.47 10.49 10.25 9.95 9.24 7.91CV% 1.59 0.92 0.66 3 2.92 3.2 4.62


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Tab

le8

Yar

nte

nsil

est

reng

th(T

(g/t

ex))

and

elon

gati

on(E

(%))

resu

lts

Shri

nkab

lefib

re0

2040

5060

8010

0bl

end

ratio

TE

TE

TE

TE

TE

TE

TE

Sing

leya

rn∗

X11

.55

14.3

910

.910

.55

11.6

19.

5612

.56

10.0

714

.55

9.94

15.1

710

.28

16.0

210

.95

CV

%11

.45

13.8

89.

9615

.41

10.9

912

.43

9.65

12.6

8.75

13.0

88.

39.

46.

596.

68

Tw

iste

dya

rn∗∗

X12

.86

17.6

911

.62

11.7

412

.61

10.6

914

.11

11.6

614

.87

1115

.33

10.8

17.9

211

.6C

V%

7.06

7.62

5.37

8.88

9.8

10.2

77.

196.

147.

016.

248.

497.

176.

77.

37

Bul

ked

yarn

∗∗∗

X12

.67

20.0

28.

4625

.92

7.1

23.7

66.

7721

.21

8.08

19.8

29.

9920

.83

12.2

421

.55

CV

%8.

918.

367.

8911

.49

7.42

6.29

6.84

5.26

9.93

7.7

7.33

8.49

9.87

9.39

Bul

ked

(dye

d)ya

rn∗∗

∗X

9.86

16.8

78.

0426

.16

6.34

24.4

66.

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.24

6.45

18.3

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.82

11.4

721

.15

CV

%11

.27

11.2

110

.37

11.7

57.

659.

038.

5212

.54

8.23

8.37

8.39

10.3

97.

447.

03

∗ A60

0g

wei

ghtw

asus

ed.

∗∗A

1500

gw

eigh

twas

used

for

blen

dra

tios

of0,

50,6

0,80

and

100

and

inot

her

case

sa

1000

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twas

used

.∗∗

∗ A15

00g

wei

ghtw

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end

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twas

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.


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24

024

810121416182022

6S

hrin

kage

(%

)

0 10 20 30 40 50 60 70 80 90 100

Shrinkable fiber (%)

Bulked yarnDyed yarnPoly. (Bulked yarn)Poly. (Dyed yarn)

Figure 2 The effect of shrinkable fibre blending ratio on yarn shrinkage.

The effect of shrinkable fibre blending ratio onyarn tensile strength

The effect of shrinkable fibre ratio on tensile strength ofsingle, twisted, bulked and dyed yarns is shown in Fig. 4.

It is evident that the single and twisted yarns’ strengthare higher than those of bulked and dyed yarns. Increas-ing the shrinkable fibre ratio up to 45% causes both thebulked and dyed yarns’ strength to be steadily decreased.

14

7

8

9

10

11

12

13

Spe

cific

vol

ume

(cm

3/g)

0 10 20 30 40 50 60 70 80 90 100

Shrinkable fiber (%)

Poly. (Twisted yarn)Poly. (Dyed yarn)Poly. (Bulked yarn)

Twisted yarnBulked yarnDyed yarn

Figure 3 The effect of shrinkable fibre blending ratio on yarn-specific volume.

0 10 20 30 40 50 60 70 80 90 100

Shrinkage fibers (%)

18

17

16

15

14

13

12

11

10

9

8

7

6

Str

engt

h (g

/tex)

Poly. (Twisted yarn)Poly. (Single yarn)

Poly. (Dyed yarn)Poly. (Bulked yarn)

Single yarnTwisted yarn

Dyed yarnBulked yarn

Figure 4 The effect of shrinkable fibre blending ratio on yarn tensile strength.


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0 10 20 30 40 50 60 70 80 90 100

Shrinkable fibers (%)

8

10

12

14

16

18

20

22

24

26

28

Elo

ngat

ion

(%)

Poly. (Twisted yarn)Poly. (Single yarn)

Poly. (Dyed yarn)Poly. (Bulked yarn)

Single yarnTwisted yarn

Dyed yarnBulked yarn

Figure 5 The effect of shrinkable fibre blending ratio on yarn elongation.

The reduction of yarn strength is because during the steam-ing process, the shrinkable fibre migrates towards the yarncentre and hence only about 45% of the fibres supportthe tensile forces; the remaining 55% of the fibres (non-shrinkable) are buckled and appear on the yarn surfaceand therefore initially remain relatively untensioned (Ox-toby 1987). The result is that one group of fibre tendsto be extended and broken before the other group isable to contribute completely to withstand the load andconsequently the high-bulk yarn strength is decreased(Oxtoby 1987). Moreover, further increasing shrinkablefibre ratio increases the yarn strength since the unrelaxedfibres are still in the drawn state and have greater molecularorientation and strength (Wray 1969). It is also demon-strated that the high-bulk yarn strength is more than thatof the dyed yarn. This is a common phenomenon in textilefibre or yarn dyeing processing in which the fibre or yarntensile strength decreases as dye stuff penetrates into thefibre or yarn (Nunn 1979).

The effect of shrinkable fibre blending ratio onyarn elongation

Figure 5 shows the effect of shrinkable fibre ratio on sin-gle, twisted, bulked and dyed yarn elongation. It is shownthat increasing the shrinkable fibre ratio up to 40% causesthe single and twisted yarns elongation to be decreased.Further increasing unrelaxed fibre blend ratio resulted inpartially increasing the yarn elongation. However, the situ-ation for both bulked and dyed yarns is different. Increasingthe shrinkable fibre blending ratio up to 20% causes theyarn elongation to dramatically increase. It seems likelythat the shrinkable fibre crimp is higher, which in turnresults in a higher yarn elongation. Moreover, for similarreasons (Oxtoby 1987) as described before, and due to theincreasing of fibre slippage or reduction of fibre-to-fibrefriction, further increasing the shrinkable fibre ratio up to60% decreases the yarn elongation. Thus, the variations

trend and magnitude of bulked and dyed yarn elongationwith shrinkable fibre ratio seem similar.

CONCLUSION

The aim of this paper was to investigate the effect of blendratios of unrelaxed and relaxed acrylic fibres on physi-cal properties of high-bulk yarns. Acrylic high-bulk yarns(steamed and dyed) with different shrinkable fibre blendingratios were produced. The physical properties of producedyarns (single, twisted, steamed and dyed yarns) includingthe percentage of shrinkage, specific volume, strength andelongation were investigated.

It is found that by increasing the shrinkable fibre blend-ing ratio up to 40%, the specific volume and shrinkageof both dyed and high-bulk acrylic yarns are steadilyincreased while their tensile strengths are decreased. Fur-ther increasing the shrinkable fibre blending ratio causesthe specific volume and tensile strength properties to bedecreased and increased respectively. Meanwhile, statisti-cal analysis indicated that further increasing the shrinkablefibre ratio has no significant effect on yarn shrinkage. It isalso found that both dyed and high-bulk acrylic yarns havethe highest elongation at 20% shrinkable fibre blendingratio. In general, the specific volume and tensile strengthof high-bulk acrylic yarns are more than those of dyedacrylic yarns but their shrinkage and elongation valuesare similar. It is suggested that maximum yarn (dyed andsteamed) bulk; shrinkage and minimum yarn strength areobtained at about 40% shrinkable fibre blending ratio.

ACKNOWLEDGMENT

The authors wish to express their gratitude to the managerof Nakhiran Textile Co., and in particular to Mr. Maniee,for providing experimental facilities for this research.


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the effect of blend ratios of unrelaxed and relaxed acrylic fibres on physical properties of...

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