Indian Journal of Fibre & Textile Research Vol . 28, June 2003, pp. 1 63- 1 69

Effect of add-on finish and process variables on properties of air-jet spun polyester yarns

G K Tyagi", Amarjot Singh, Anil Gupta & A Goyal

The Technological Institute of Textile & Sciences, Bhiwani 1 27 02 1 , I ndia

and

K R Salhotra Department of Textile Technology, Indian Institute of Technology, New Delh i I I O 0 1 6, India

Received 1 January 2002; accepted 14 March 2002

The effects of add-on finish and some other process variables on mechanical and mass irregularity characteristics of air-jet spun polyester yarns have been studied using the Box-Behnken design. It is observed that the add-on finish plays a dominant role in influencing the yarn properties. The correlations between spinning parameters and mechanical properties are found to be highly significant. On the other hand, the yarn irregularity exhibits poor correlation with the process variables. Imperfection indices show a general ascending relationship with add-on finish and other process variables studied.

Keywords: Add-on finish, Air-jet Spinning, Fibre-to-fibre friction, Flexural rigidity, Murata jet spinner, Polyester yarn, Wrapper fibre

1 Introduction All important yam characteristics are known to de­

pend on yarn structure and air-jet spinning is no excep­tion to it. The air-jet spun yarn is a fasciated type of yam consisting of a core of parallel fibres held together by wrappers. The wrapper fibres which provide neces­sary transverse forces for inter-fibre cohesion play a major role in determining the yam characteristics. The incidence of wrapper fibres depends, to a considerable extent, on the characteristics of fibres and the spinning parameters used. These fibre characteristics include fineness, length, strength and breaking extension. An­other important variable influencing yam properties is the level of finish. It determines the yarn structure and hence the yam properties. A high static fibre-to-fibre friction is helpful I . Also, for improved yam uniformity, good drafting at a high speed is essential . The effects of various fibre and machine parameters on yam structure and the consequent changes in yam properties have been thoroughly studied2-7 . There are occasional refer­ences for the fibre tenacity and fibre friction interac­tions8.9, but no study regarding the role of add-on finish in influencing yam quality in air-jet spinning has been reported so far. The present work was, therefore, aimed

" To whom all the correspondence should be addressed. Phone: 24256 1 ; Fax: 009 1 -0 1 664-243728; E-mai l : titsintr@nde.vsnl .nel . in

at studying the influence of four process variables, viz. level of add-on finish, first nozzle pressure, main draft and spinning speed, on the properties of polyester MJS yarns using the Box-Behnken design.

2 Materials and Methods 2.1 Preparation of Yarn Samples

Polyester staple fibres of 44 mm length, 1 .55 dtex fineness and 26.39 cN/tex tenacity (stelometer gauge, 1/8 inch) were hand opened and separated into three lots of 1 0 kg each. Fibre finish LV 40 was dissolved in water and sprayed as uniformly as possible on two lots of polyester. Two different add-on spin finish levels (0.08% and 0. 1 6% owf) were used. The conversion to drawn sliver was carried out by using a MMC carding machine and a Lakshmi Rieter' s draw frame DOI2S. Three drawing passages were given and the linear den­sity of finisher sliver was adjusted to 3 . 1 ktex for al l the samples. The slivers were then spun into 1 4 tex yarns on air-jet spinner (802MJS) operating under normal mi ll conditions. As per the Box-Behnken design, the experi­mental combinations of the four variables were chosen and MJS yam samples produced. The actual levels of four variables corresponding to the coded levels (Table 1 ) are given in Table 2. The other process parameters, namely second nozzle pressure, feed ratio, and distance between the first nozzle and the nip of front roller,

1 64 INDIAN J. FIBRE TEXT. RES . , JUNE 2003

Table I - Experimental plan for selected variables

Experimental Variables combination Add-on spin First nozzle Main Spinning

No. finish pressure draft speed (X, ) (X2) (X3) (X4)

S, - 1 - 1 0 0 S2 + 1 - 1 0 0

S1 - 1 + 1 0 0

S4 + 1 + 1 0 0

S5 - 1 0 - 1 0

S6 + 1 0 - I 0

S7 - 1 0 + 1 0 S8 + 1 0 + 1 0 S9 - 1 0 0 -I SIO + 1 0 0 - 1

S " - 1 0 0 + 1 S '2 +1 0 0 + 1

S I 3 0 - I - I 0 S '4 0 + 1 - 1 0 S '5 0 - I + 1 0 S 'h 0 + 1 + 1 0 S I7 0 - 1 0 - I

SI X 0 +1 0 - I

S ,<j 0 - 1 0 + 1 S20 0 + 1 0 + 1 S2 ' 0 0 - I - I

S22 0 0 + 1 - I S2J 0 0 - 1 + 1 S24 0 0 + 1 + 1

S25.3 ' 0 0 0 0

Table 2 - Variables and their levels used in experimental plan

Variables - 1

Spin finish (X,), % 0

First nozzle pressure (X2), kg/cm2

2

Main draft (X3) 30

Spinning speed (X4), mlmin 1 60

Coded levels 0 + 1

0.08 0. 1 6 2.5 3

35 40

1 80 200

27

26

25

24 ��� 23

22

21

were kept constant and taken as 3 .5 kg/cm2, 0.98 and 39.5mm respectively.

2.2 Tests

The yarns were tested for tenacity and breaking extension on the Instron (model 44 1 1 ) . Fifty tests were made for each sample at a crosshead speed of 5 rnImin. The flexural rigidity was tested on ring yarn stiffness tester using the ring loop method 1 0 .

Yarn hairiness was measured by Zweigle hairiness meter (model G565). The yarn unevenness and imperfections were determined on the Uster evenness tester; for each sample, 1 500m of yarn was scanned at a speed of 1 00 m/min. Flat abrasion resistance of al l the yarns was determined by Taber abrasion tester. The coefficients of fibre-to-fibre and fibre-to-metal friction were measured on an Instron tensi le tester using the attachment developed by Sengupta et al i i .

3 Results and Discussion

The test results were analyzed using SYST AT 10. The response surface equations for each property were obtained.

3.1 Tensile Properties

To produce a strong yarn, it is important to maximize the number of wrapper fibres to ensure a high transverse force necessary for the inter-fibre friction. Careful scrutiny of the response surface equation (Table 3) and spatial diagrams (Fig. 1 ) reveals that the first nozzle pressure is a major contributor to yarn tenacity. The tenacity increases considerably with the increase in first nozzle pressure due to the expected increase in the incidence and extent of wrapper fibres. The use of add-on finish

Fig. l-Effect of add-on finish and process variables on tenacity

TYAGI el al: A IR-JET SPUN POLYESTER YARNS 1 65

Yarn property

Table 3-Response surface equations"

Response surface equation Correlation F-ratio Standard coefficient error

Tenacity, g/tex 23.685+ 1 .224XI+ 1 .265X2+O.86X)+0.886X4+O.622XI2-

0.30 I X2 2 -0.588X4 2+0.605X2XJ

0.9 1 6 29.97 0.5 1 5

Breaking extension, % 1 1 .35 1 +0.53X 1+0.588X2+O.338X)+0.7 16X4-O.873XI2-

0.49 I X/-0.28 I X42

0.833 24.80 0.356

Abrasion resistance, cycles 1 625+ 1 66.25XI+ 75.25X2+64. 1 67X)+43.333X4+48.79XI2-

37 .46X2 2 - 1 8 .085X4 2

0.967 96.50 27.326

Flexural rigidity x 10-3, g.cm2

Hairiness/200m

Unevenness, U%

5.53 1 +0.20 I XI +0.265X2+O.222X3+O. 1 72X4+O.098X IX 2

646.538-54.5XI+ 79.833X2+95X3+2 1 1 .5X4+50.846XI2-

62.654X4 2 +54.25X2X3

14 .265+0.458XI+0.387X2+0.577X4+0.736XI2+0.553X2

2+0.6

7X/

0.864

0.887

0.587

3 1 .63 0. 1 2 1

25.82 67.393

5.68 0.689

Thick places/km 24 1 .766+55 .75XI+38.833X2+4 1 .50X3+36.4 1 7 X4+ 77 .965X12

+34.84X/+36.7 1 5X42-22.75XIX4+ 1 6.25X2X3

0.958 53 . 1 3 1 7 .699

Thin places/km 1 29.7 1 2+ 12 .667XI+ 1 3 .833X2+36.75X3+21 .9 17X4-1 9.8 1 5X/+8.8 I X4

2 0.866 25.80 1 3 .89 1

Neps/km 60.632+9.667XI+ 1 1 .4 1 7X2+9.667X3+6.4 1 7X4-6.298X/ 0.850 28.4 1 5 .866

"Only significant terms considered ( 99% level of confidence )

offers considerable advantage in air-jet spinning in respect of tensile properties. As can be seen from Fig. 1 , a lower tenacity is observed in the yarns spun without adding any fibre finish. The tenacity considerably i ncreases as the add-on finish level i s increased from 0% to 0. 16%. The increase in yarn tenacity can be attributed to the increase in fibre-to­fibre friction with the addition of fibre finish (Table 4), which generates greater frictional force among the core fibres. The first nozzle pressure also plays a prominent role in influencing the tenacity of MJS yarns. The yarn tenacity markedly increases as the first nozzle pressure increases from 2 kg/cm2 to 3 kg/cm2• The tenacity increases substantially on increasing the spinning speed. Fig. 1 also shows that the tenacity increases as the main draft increases from 30 to 35 after which it levels off. This increase can be attributed to the improved fibre orientation of core fibres with higher main draft.

Fig. 2 shows the interaction effect of different process variables along with the add-on finish on breaking extension. It is observed that the yarn breaking extension increases as the level of add-on spin finish increases from 0% to 0.08% and then drops sl ightly at 0. 1 6% add-on finish. The initial increase in yarn breaking extension can be ascribed to the increase in inter-fibre cohesion with add-on finish, which restricts the sl ippage of fibres in the yarn during tensile loading. At higher first nozzle pressure, the breaking extension is higher than that at lower

Table 4 - Effect of spin finish on frictional coefficients of polyester fibre

Level of spin finish, %

Nil 0.08 0 . 1 6

Coefficient o f fibre friction Fibre-fibre Fibre-metal

().lrr) ().lrm)

0.385 0.401 0.428

0. 1 98 0.220 0.234

first nozzle pressure, i rrespective of the level of add­on finish. The increase in spinning speed also produces a similar effect. Such behaviour of yarn breaking extension could be attributed to the above­mentioned factors in respect of tenacity. Fig. 2 also shows that there is a maximum level of breaking extension at intermediate level of main draft, both at lower and higher levels of add-on finish. At higher levels of add-on finish, less wrapper fibres are expected to be formed due to the increased inter-fibre frictional hindrance, which would reduce the yarn breaking extension.

3.2 Abrasion Resistance

Fig. 3 depicts the variation in abrasion resistance with the change in process variables in air-jet spinning of polyester fibres yarns. It can be observed that the higher the add-on finish, the higher is the abrasion resistance. As the level of add-on finish increases, the fibre-to-fibre friction increases which reinforces the sheath, resulting in higher abrasion resistance. This has been observed in an earlier

1 66 INDIAN J. FIBRE TEXT. RES., JUNE 2003

c­o � 12 Ol c:: o Qj 1 1 Ol c:: :;;: :Jl 10 Iii

Fig. 2-Effect of add-on fi n ish and process variables on breaking extension

VI Q) <3 >-'-'. 1800 OJ u c:: .!'l 1700 VI 'iii � 1 600 c:: o .� 1500 .0 «

1 900 1 900

1 800 1 800

1 700 1 700

1 600 1 600

1 500 1 500

Fig. 3--Effect of add-on finish and process variables on abrasion resistance

stud/ 2 that an increase in spinning speed promotes inter-fibre cohesion and thus improves the abrasion resistance. Higher main draft also markedly improves the abrasion resisfance. The increase in first nozzle pressure too increases the abrasion resistance.

3.3 Flexural Rigidity

The F-ratio, coefficient of correlation and response surface equation for flexural rigidity are given in Table 3. The correlation coefficient of 0.864 indicates good correlation between the process variables and flexural rigidity. The response surfaces (Fig. 4) show that the first nozzle pressure has the highest influence on flex­ural rigidity, fol lowed by main draft, add-on finish and spinning speed. Flexural rigidity increases considerably on increasing the level of add-on finish. As mentioned earl ier, the inter-fibre friction which restricts the free­dom of movement of core fibres increases with the in­crease in level of add-on finish, resulting in higher

flexural rigidity. The higher first nozzle pressure, in general , produces more rigid yarns. The increase in spinning speed and main draft increases the flexural rigidity due to the higher incidence of wrapper fibres and wrapped- in length, which limit the freedom of movement of the core fibres.

3.4 Hairiness

Fig. 5 shows that the add-on finish has l ittle effect on hairiness. Spinning speed appears to have the highest influence on hairiness, the later increases with the increase in spinning speed. The least number of hairs is achieved at the lowest spinning speed of 160 mlmin and the hairs tend to markedly increase as the spinning speed is further increased to 200 mlmin due to the increase in intensity of air- flow in the vicin ity of the front roller. Yarn hairiness increases sl ightly with the increase in main draft. The increase in first nozzle pressure also shows a slight increase in hairiness.

TYAGl et al: A IR-JET SPUN POLYESTER YARNS 1 67

3.5 Mass Irregularity and Imperfections

The low value of correlation coefficient (Table 3 ) indicates somewhat poor correlation between yarn irregularity and process parameters. The three­dimensional diagrams of the response surfaces are given in Fig. 6. On the other hand, the other indicators

M , ;? 5.6 )( � 5.6 '5 :g> 5.4

� ::J 5.2 )( Q> u::

6.0

5.6

5.6

5.4

5.2

of mass irregularity show better correlations with process variables. Fig. 7 shows that the number of thick places decreases slightly as the level of add-on finish increases from 0% to 0.08% and then increases considerably at 0. 16% add-on finish. The number of thick places increases rapidly with the increase in

Fig. 4--Effect of add-on fi nish and process variables on flexural rigidity

1100

E 900 o o � 700 .� 500 :x:

300

18 <!. ::::l 1 7 <Ii � 16 c: c: � 15 Q> c: ::::l 14

1 100 1 100 900 900 700 700 500 500 300 300

Fig. 5--Effect of add-on finish and process variables on hairiness

18 1 8 17 17 -16 16 15 1 5 14

14

Fig. &--Effect of add-on finish and process variables on unevenness

1 68 INDIAN J. FIBRE TEXT. RES., JUNE 2003

E 450 450 -'" '" Q) � 350 350 Ci. -'" u :c f- 250 250

Fig. 7-EfTcct of add-on fi n ish and process variables on thick places

230

E 1 84 -'" 230

V> 1 84 Q) 1 38 u '" a. 92 c :c f- 46

1 38rw� 92

46

Fig. 8--Effect of add-on finish and process variables 011 thin places

80 80 80

70 70. 70 E -'" 60 60 60 V> a. 50 Q) 50 50 Z

40· 40 40

Fig. 9--Effect of add-on finish and process variables on neps

spinning speed beyond 1 80 m/min. The increase in first nozzle pressure from 2 kg/cm" to 3 kg/cm2 results in a linear increase in the number of thick places. On the other hand, the number of thick places, introduced by higher level of add-on finish, increases much faster with the increase in main draft beyond 35 .

Fig. 8 shows that unl ike thick places, thin places do not show much increase with the increase in add-on finish. At higher main draft, the thin places are higher. The increase in first nozzle pressure does not result in any consistent increase in thin places.

TYAGI et al: AIR-JET SPUN POLYESTER YARNS 1 69

Neps show a consistent increase with the increase in level of add-on finish (Fig. 9) . Regarding the effect of other factors studied, there is a consistent increase in the nep level.

4 Conclusions 4.1 The use of add-on finish offers significant advan­tage in respect of tensile properties of air-jet yarns. Add-on finish, main draft, spinning speed and first nozzle pressure are the most important factors influ­encing tenacity, abrasion resistance and flexural rigid­ity. Each of these increases with the increase in the levels of influencing factors. 4.2 The breaking extension shows an ascending rela­tionship with the increase in spinning speed, main draft and first nozzle pressure. On the other hand, the breaking extension increases initially when the level of add-on finish increases and it decreases thereafter. 4.3 Yarn hairiness increases with the increase in spinning speed. First nozzle pressure, main draft and add-on finish have only a slight effect on hairiness. 4.4 There is a poor correlation between U% and process variables. Minimum number of thick places are observed at 0.08% (owf) add-on spin finish. However, the thick places increase when the spin­ning speed, main draft and first nozzle pressure in­crease. Thin places show a marginal increase with the increase in level of add-on finish, spinning speed and first nozzle pressure. The increase in main draft

results in an increase in number of thin places. The nep level increases with the increase in level of add­on finish, spinning speed, main draft and first nozzle pressure.

Acknowledgement

The authors are thankful to Dr. A Mukhopadhyay, Department of Textile Technology, The Technologi­cal Institute of Textile & Sciences, Bhiwani, for his help in the statistical analysis of the yarn samples.

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