Indian Journal of Fibre & Texti le Research Vol. 3 1 , December 2006, pp. 565-572

Studies on enzymatic hair removal and softening of cotton hosiery yarns

Bhaarathi Dhurai a & V Natarajan

Department of Texti Ie Technology, Kumaraguru College of Technology, Coimbatore 64 1 006, [ ndia

Received 23 March 2005; revised received a/ld accepred 21 Ocrober 2005

Enzyme softening of ring-spun carded and combed, and rotor-spun yarns of 30s count ( 19.68 tex) has been carried out using B io-soft L+ enzyme with the aim of improving their knittabi l i ty through improvement in yarn hairiness and frictional properties. A central composite rotatable design, proposed by Box and Behnken, was used to conduct experiment for developing mathematical models for the yarn characteristics, such as hairiness, kinetic friction and compression properties, in terms of the variables, namely enzyme concentration, temperature and treatment t ime. Quasi-Newton numerical method was used to optimize the process variables of enzyme softening treatment and the responses with reduction in hairiness i ndex considered as the objective function. The studies show that the enzyme softening not only results in reduction of hairiness and improvement of frictional coefficients but also leads to improved compressional softness of yarns. Enzyme softening of ring-spun carded yarn resu l ts in high level of reduction in hairiness (28%) and kinetic friction (50%). The improvement in compressional softness is pronounced in rotor-spun yarn, whi le hairiness reduction is predominant in ring­spun yarns. Optimum values for process variables have been mathematical ly calculated from the experimental resu lts. Optimized conditions for enzyme soften ing are found to be 2.25-3% (owm) enzyme concentration, 50°C temperature and 50-60 min treatment t ime.

Keywords: Box & Behnken design, Cel lu lase enzyme, Cotton hosiery yarn, Compressional properties, Frictional softness, Quasi-Newton optimization method

IPC Code: [nl. CI.8 D06B3/00

1 Introduction Enzymatic treatments are being w idely used for

cotton fin ish ing to i mprove fabric softness, smoothness and fash ionable appearance. 1 -3 The possibil i ties for treating cellulosic materials, such as cotton, v iscose, Iyocel l and jute, with cellulase enzymes, have grown recently . The best known application of cellulase is in den im garment washing process, as an alternative to stone washing and in the modification of cotton fabric to i mprove the surface properti es 4-5 The presence of protruding fibres on the surface of cotton fabric g ives rise to a fuzzy appearance as well as reduction i n the l uster of fabrics. These protrudi ng fibres are easi ly removed by treatment with cellulase enzyme, which degrades cellulose by catalyzing the hydrolytic cleavage of 1 -4�-glucosidic l inkages of cellulose molecule 6- 1 2 A study on low stress mechan ical behaviour of enzyme­treated cotton and cotton/polyester yarns showed a significant weight loss and change 111 their compressional characteristics I 3

The present work i s aimed at studying the influence of enzymatic soften ing of cotton hosiery yarns on

" To whom al l the correspondence should be addressed. E-mai l : bhaarathi_dhurai @yahoo.com

their hairiness, kinetic friction and compressional characteristics. The optimization of process variables has also been done, where reduction in hairiness is considered as the objective function.

2 Materials and Methods

2,1 Materials

Ring carded, ring combed and rotor-spun yarns (hosiery) of l inear densi ty 1 9.68 tex were used for the optimization of enzyme treatment. The yarns were industrially scoured and bleached before subjecting to enzyme action. The enzyme used was B io-soft L+ which is an acid type cel lu lase enzyme (Biocon India Ltd . , Bangalore, I ndia) , obtained by fermentation of non-pathogenic modules of the aspergillous and trichoderma species.

2.2 Methods

2.2.1 Enzyme Treatment

Yarn samples were conditioned at 65% RH and 27°C for 24 h . The enzyme treatment was conducted i n hank form i n microprocessor controlled washing fastness tester, maintaining the pH at 5 and material: l iquor ratio at 1 : 1 0. The enzyme-treated samples were

566 INDIAN 1 . FIBRE TEXT. RES . . DECEMBER 2006

boi led at 80DC, washed, dried and conditioned again before testing.

The enzyme treatments were carried out according to a central composite design, proposed by Box and Benhken, with three independent variables (Table I ) . The actual values of the variables corresponding to the coded level s are shown in Table 2.

2.2.2 Test Methods

The hairi ness index value was determined on Premier yarn evenness tester with hairiness attachment, working on photoelectric principle. Kinetic friction value ()l) was measured in Lawson Hemphi l l yarn friction tester (ASTM : D3 1 08-95). Softness of yarns was evaluated by studying

. . 1 1 d h b .

compression properties ' an smoot ness y uS l l1g coefficient of friction (ki netic) and photomicrograph of yarn surface. Weight loss was determined by measuring the difference in weight of the condi tioned untreated and treated samples. Strength of yarns was determined on Tensomaxx 7000-Automatic single yarn strength tester. The compression properties, l ike

Table I - Box and Benhken design for three variables

Exp. No. Coneeillration Temperature Time % °C min

(X I ) (.1'2) (Xl )

I - I - I 0

2 - I 0

3 - I 0

4 0 5 - I 0 - I

6 I 0 - I 7 - I 0 I

8 I 0 9 0 - I - I

1 0 0 - I I I 0 - I

1 2 0 I I 1 3 0 0 0 1 4 0 0 0

1 5 0 0 0

Table 2 - Coded and actual values of variables

Variable Coded level - I 0

Enzyme cone. (XI ). % owm 2 3 Temperature (..1'2). °C 46 50 54

Time (Xl). min 40 50 60

l inearity of compression (LC), compression resi l iency (RC), compression energy (WC), and compression rate (EM C), were measured on Kawabata compression tester KES-FB3 . Photomicrographs of yarn surfaces of treated and untreated yarn samples were taken on Projectina Micro-Macro Projector at the magnification of x I OO.

2.2.3 StatiMical Allalysis

Quadratic polynomial equations were formulated for each yarn property in terms of independent variables, namely concentration (XI ), temperature (X2) and t ime (x)) , of enzyme treatment using statistical software package SYSTAT (version 5 .02). Generalized equation i s as follows:

Y = bo + I bi Xi + I bi iX;"- + I bij Xi Xj

where bo. bi . hi i . and bij are the coefficients of the regression equations; i, j , the integers wi th i > j : and Y, the response or dependent variable (yarn property) .

Contours were plotted for each response with 2 independent variables at a time, maintaining the th ird variable at constant level using software MATLAB (version 4.2 b) .

2.2.4 Optimization of Proce,�s Variables alld Respollses

Opti mization of process variables was done using a Quasi-Newton numerical method while reduction in hairiness index was treated as the objective function. 1 4

The other properties, l ike coeffic ient of friction reduction, strength loss, weight loss, compression energy, Ii neari ty of compression, compression res i l iency and compression rate, were treated as constrai nts.

The procedure followed for optimization i s as fol lows. To maximize the values of the parameters of surface and softness characteristics of softened ring and rotor yarns, the regression equations of surface and softness parameters were multiplied by - I and thei r minimum l imi t is added. To minimize the values of regression equations of control parameters of softened yarns, the max imum value of each control parameter is i ncluded in its respective regression equation.

The constrained scalar function of several variables at its in it ial estimate is mathematically calculated as shown below:

Min imize/ex) subject to G(x" X2, X3 . . . . XII) <0

DHURAI & NATARAJAN: ENZYMATIC HAIR REMOVAL AND SOFrENING OF COTTON HOSIERY YARNS 567

where x and G(x) represent the matrices of the objective and constrained function respectively, and j(x) i s a scalar function. The values of the constraints were fixed at <0. After running the m-fi le and retrieving the constraints, the optimum value of process variable and the value of responses at optimized condi tions for ring and rotor yarns were found out.

3 Results and Discussion The experimental results are summarized in

Tables 3-5 . Regression equations for individual characteristics of yarns are given i n Tables 6-8. Rotor yarn structure is characterized by a distinct core and sheath and consists of mere hooks and entangled fibres. Ring yarns are of less hooked and entangled fibres with very good orientation and compact

Table 3 - Surface characteristics of unsoftened and softened yarns

Exp. No.

Unsoftened yarn I 2 3 4 5 6 7 8 9 1 0 I I 1 2 1 3 1 4

1 5

Ring carded yarns Hair iness Kinetic

i ndex friction. f.l 7.28 5 .98 6.26 6.47 5 .98 6.06 6.0 1 5 .79 5 . 1 1 5 .79 6. 1 4 5 . 1 3 5 .33 5.24 5 .22

5 .97

0.32 0. 1 2 0. 1 1 0. 1 2 0. 1 4 0.22 0. 1 6 0. 1 9 0. 1 4 0.2 1 0.26 0.3 0. 1 2 0.25 0.28

0.24

Ring combed yarn Hairiness Kinetic

index friction, f.I 6.00 5 .70 5 .46 5.5 1 5.45 5.75 5.69 5 .60 5.47 5.55 5.45 5 . 1 4 5.75 5.69 5.66

5.65

0.26 0.20 0.20 0.20 0. 1 8 0.20 0.2 1 0.20 0.22 0.20 0.2 1 0.2 1 0.22 0.22 0.22

0.22

Rotor yarn Hairiness Kinetic

i ndex friction, �l 4.00 3 .80 3.5 1 3.93 3.5 1 3 .93 3.5 1 3 .5 1 3.75 3 .24 3.63 3.64 3.34 3.78 3.49

3.66

0.2400 0.2200 0.2 1 50 0.2240 0.2 1 1 5 0.2260 0.22 1 0 0.23 1 0 0.2260 0.2300 0.2280 0.2260 0.2250 0.2270 0.2260 0.2280

Table 4 - Softness characteristics of unsoftened and softened yarns

Exp. No. LC

Unsoftened 0.3 1 1 1 yarn

I 0.4304 . 2 0.4560 3 0.4400 4 0.40 1 3 5 0.4 1 03 6 0.4 1 1 2 7 0.3964 8 0.4075 9 0.4248 1 0 0.3288 I J 0.3384 1 2 0.4 1 63 1 3 0.40 1 0 1 4 0.4048 1 5 0.393 1

Ring carded yarn EMC RC

%

37 .00

44.22 38.82 40.60 46.96 39. 1 8 40. 1 7 42.97 45 . 1 2 44. 2 1 38.90 4 1 .6 1 46.76 42.20 42.68 42.26

%

20.49

26.00 28.88 27. 1 2 27.88 22.02 25.94 29.03 27.22 23.25 30.43 32.42 24.67 30. 1 0 28. 1 4 28.74

WC gf/4mm

0. 1 02

0. 1 2 1 2 0. 1 1 1 6 0. 1 203 0. 1 253 0. 1 053 0. 1 392 0. 1 076 0. 1 1 69 0. 1 1 90 0. 1080 0. 1 080 0. 1 1 1 7 0. 1 095 0. 1 1 28 0. 1 1 99

LC

0.254

0.35 1 0.358 0.36 1 0.377 0.356 0.357 0.36 1 . 0.378 0.348 0.357 0.36 1 0.370 0.359 0.365 0.367

Ring combed yarn EMC RC

%

36.00

4 1 .0 1 42. 1 4 42.57 44.03 48.25 42.75 46.93 4 1 . 1 1 38.78 43.32 4 1 .68 42.25 43 .53 39.20 40.3 1

%

26.26

3 1 .9 1 3 3 1 . 1 77 28. 1 20 32.477 27.690 30. 1 70 3 1 . 1 42 40.338 27.963 3 1 .063 29. 1 20 28.669 3 1 .827 30.900 3 1 .860

WC gfl4mm

0. 1 1 00

0. 1 3 1 2 0. 1 1 26 0. 1 223 0. 1 353 0. 1 253 0. 1 42 1 0. 1 276 0. 1 250 0. 1 2 1 0 0. 1 280 0. 1 270 0. 1 2 1 8 0. 1 300 0. 1 1 48 0. 1 1 80

LC

0.389

0.402 0.4 1 5 0.405 0.398 0.438 0.429 0.444 0.438 0.435 0.442 0.460 0.394 0.44 1 0.453 0.43 1

LC - Linearity of compression, EMC (%) - Compression rate, RC (%) - Compression res i l iency, and WC(gf/4mm) - Compression energy.

Rotor yarn EMC RC

%

37.00

52.04 45 .04 47.82 47.79 46. 1 6 49.22 44.00 47.4 1 43.53 45.60 45 . 1 8 47.25 44.59 45 . 1 6 46. 1 0

%

1 7.70

29.74 22.32 3 1 .07 24.88 33. 1 2 30.32 28.88 28.94 32. 1 8 3 1 .52 28.82 3 1 .44 32.96 29.93 32.62

WC g f/4mm

0. 1 27

0. 1 79 0. 1 47 0. 143 0. 1 56 0. 1 57 0. 1 63 0. 1 63 0. 1 5 1 0. 1 54 0. 1 47 0. 1 60 0. 1 35 0. 1 52 0. 1 64 0. 152

568 INDIAN J . FIBRE TEXT. RES. , DECEMBER 2006

Table 5 - Characteristics of control parameters of unsoftened and softened yarns

Exp.No. Ring carded :tarn Ring combed :tarn Rotor :tarn Weight Strength Weight Strength Weight Strength

g g/tex " g/tex " g/tex 0 b

Unsoftened 0.38 1 5 1 4.7 1 0.3766 1 7.545 0.3754 14.79 yarn

I 0.3578 1 3 .3699 0.36 1 2 1 7. 1 5 0.35 1 1 1 3 .76 2 0.3498 1 2.96 1 0 0.3597 1 6.67 0.3435 12.94 3 0.35 17 1 3 .4699 0.36 1 1 6.06 0.3454 1 2 .98 4 0.3566 13 .59 1 0 0.3578 1 4.65 0.3499 13 .74 5 0.3574 1 3 .9500 0.36 1 9 17.36 0.35 1 I 1 3 .76 6 0.353 1 3 .720 0.363 1 5 .70 0.3476 1 3.62 7 0.3524 1 3 .8 1 1 0.3636 16.56 0.3476 1 3 .60 8 0.35 1 7 13 .7597 0.3604 1 5 .34 0.3454 12.40 9 0.3536 1 3 .8303 0.3636 16. 1 0 0.3487 1 3 .83 1 0 0.3562 1 3 .9 1 I 0.3634 1 5 .89 0.3495 1 3 . 8 1 I I 0.3543 1 4.22 0.3602 15 .73 0.349 1 1 3 .87 1 2 0.3532 1 3 .649 0.361 I 1 5 .45 0.3484 1 3 .80 1 3 0.3536 1 3 .83 0.3598 1 5 . 1 8 0.3487 1 3 .83 1 4 0.3532 1 3 .95 0.3600 1 5 . 1 1 0.3484 1 3 .80 1 5 0.3562 1 3 .9 1 1 0.3602 1 5 .22 0.3495 1 3. 80

Table 6 - Regression equations for surface characteristics of ring and rotor yarns

Yarn Regression equation F-ratio P value R�

Ring carded Hairi ness i ndex reduction , % 6.2 1 7 0.0 1 0.629 Y=25 .868+4. 1 89 xr5.567 x,2-4.265x/ Kinetic friction reduction , % 1 6.397 0 0.868 Y= I 8 .559+5. 1 56x,+26.899x,2+ 1 5 .336 x/+ 1 5 .47x, X2

Ring combed Hairiness index reduction, % 4.356 0.03 0.543 Y=5.899+ 1 . 1 46 x,+ 1 .729x2- 1 .405x2x, K inetic friction reduction , % 8.452 0.008 0.585 Y= I I .769+5.404x, 2+4.654x/

Rotor Hairiness i ndex reduction , % 0. 1 47 0.993 0 Y=9.923+0.25x,+ I .438x2+0.3 1 3x,-0.206x,2-0.956X2

2 + 2.894x, 2 +0. 788x ,xrO. 938x ,x,-0.063x2x,

Kinetic friction reduction, % Y=9.2+ 1 .6 x,+2.298x,

2+ 1 .723 x2- 1 .898x}

structure. Ring combed yarn i s less hairy than ring carded yarn. The dist inct structure of r ing and rotor yarns shows different levels of enzyme action over them, which results i n the d ifferent levels of changes in characteristics of enzyme- softened yarns.

3.1 Surface Characteristics

Within the experimental conditions, a mIl11mUm value of hairiness i ndex of 5 . 1 1 (29.8 1 % reduction) and a max imum of 6.47 ( 1 1 . 1 3% reduction) have been obseved in ring carded yarns. The hairiness index in ring combed yarn after enzyme softening i s found to be a minimum o f 5 . 1 4 ( 1 4.33% reduction)

1 5 .072 0 0.858

and maximum of 5 .75 (4.2 1 % reduction). The corresponding values for softened rotor yarn are 3.24 ( 1 9.00% reduction) and 3 .93 ( 1 .8% reduction) respectively (Table 3). The experimental conditions at which the min imum and maximum hairiness occur vary in the three types of yarns.

The regression analysis (Table 6) shows that the surface characteristics are highly influenced by all the three processing variables i ndividually for ring carded yarn . It is also observed that the concentration and temperature have direct i nfluence, whereas there is marginal i nteractive i n fluence of treatment time along with the temperature on hairi ness i ndex reduction for

DHURAI & NATARAJAN: ENZYMATIC HAIR REMOVAL AND SOFTENING OF COTTON HOSIERY YARNS 569

ring combed yarn . I t i s noted that the variables have marginal influence on hairiness i ndex reduction i n rotor yarn.

It is also observed from Table 3 that at various experimental condi tions, the enzyme softening improves the coefficient of k inetic friction (J.!) of ring carded, ring combed and rotor yarns . Coefficient of kinetic friction varies between 0. 1 1 and 0.3 in ring carded yarn, between 0. 1 8 and 0.22 i n ring combed yarn, and between 0.2 1 5 and 0.23 1 in rotor yarn . A maximum reduction of 65.63%, 28% and 1 5 .4% and a minimum reduction of 1 6.62%, 1 2% and 7 .7% respectively have been observed in kinetic friction of ring carded, ring combed and rotor yarns respectively.

Table 6 shows that all the three processing variables influence the reduction percentage of k inetic friction of ring carded yarn in positive direction, whereas the concentration and temperature influence significantly the kinetic friction reduction of ring combed and rotor yarns .

3.2 Compressional Characteristics

It is observed from Table 4 that the enzyme softening improves all the compressional characteristics, namely l inearity of compression,

compression rate, compression resil iency and compression energy, to the varying level in ring carded, ring combed and rotor yarns. In ring carded yarn, the l inearity of compression varies from 0.3288 to 0.456 (an increase from 5 .7 1 % to 46.6%), compression rate from 38 .82% to 46.96% (an increase from 5% to 26.92%), compression res i li ency from 22.02% to 32.42% (an increase from 7 .5% to 58 .2%) and compression energy from 0. 1 053 gf/4mm to 0. 1 392 gf/4mm (an increase from 3.2% to 36.47%).

In ring combed yarn , the l inearity of compression varies from 0.348 to 0.378 (an i ncrease from 37% to 48 .45%), compression rate from 38.78% to 48.25 % (an increase from 7 .72% to 34%), compression resil iency from 27 .69% to 40.338% (an increase from 5 .4% to 53 .6 1 %), and compression energy from 0. 1 1 23 gf/4mm to 0. 1 42 1 gf/4mm (an increase from 2 .4% to 29 .2%).

The compression parameters of rotor yarn, such as l inearity of compression, varies from 0.394 to 0.460 (an increase from 1 .3% to 1 8 .3%), compression rate from 43.53% to 52.04% (an i ncrease from 1 7 .65% to 40.65%), compression res i liency from 22.32% to 33 . 1 3 % (an i ncrease from 26. 1 % to 87 . 1 %), and compression energy from 0. 1 35 gf/4mm to 0. 1 79 gf/4mm (an increase from 6.3% to 40.94%).

Table 7 - Regression equations for softness characteristics of r ing and rotor yarns

Yarn

Ring carded

Ring combed

Rotor

Regression equation

Linearity of compression (LC) Y=0.375+0.044x I2+O.048 X2X, Compression rate (EM C), % Y=42.5 1 + 1 .748 x,+2.94xIX2+2.6J9x2x, Compression resi l iency(RC), % Y=28.984 -2.848x2 -6.483X2X, Compression energy(WC), gf/4mm Y=0.099+0.02 Xl 2

Linearity of compression (LC) Y=0.363+0.005 xl+0.006X2+0.007x,-0.003 X22 + 0.004XIX, Compression rate(EMC), % Y=40.74+ 1 .569x2+2.874 xI

2- 1 .993x2X,

Compression res i l iency (RC), (%) Y=30.6 1 3+ 1 . 9 1 8xI Compression energy(WC), gf/4mm Y=0. 1 28+0.008 XIX2

Linearity of compression (LC) Y=0.44 1 - 0.009xTO.0 1 6 XI +0.0 1 2 x,2 -O.01 8x2x, Compression rate (EM C) , % Y=45.344+2.266xI2 + I . 743xIX2 Compression resiliency (RC), % Y=33.288-2.793 XI -3.8 1 2 xl 2 -3. 1 36 X22

Compression energy(WC), gf/4mm Y=0. 1 52- 0.007 x2+0.005 xI 2+O.O I I XIX2

F-ratio P value R2

1 0.734 0.002 0.641

0.292 0.002 0.7 1 7

1 0.474 0.002 0.636

9.837 0.008 0.43

1 7.069 0 0.965

3.488 0.054 0.488

3 0. 1 02 0. 1 92

3.74 0.076 0.222

1 0.8 0.01 0.857

5 .876 0.0 1 7 0.495

7.009 0.007 0.657

8.244 0.004 0.639

570 INDIAN 1 . FIBRE TEXT. RES., DECEMBER 2006

Table 8 - Regression equations for control parameters of ring and rotor yarns

Yarn Regression equation F-ratio P value R2

Weight loss, % 1 1 .76 1 0.00 ) 0.867 Ring carded Y=7.08+0.275 x,+0.275x,-O.85 XI X, -O.25x, x, + 0.25 X2X,

Strength loss, % 7.036 0.006 0.738 Y=5.53+2. ) 8X, 2 +) .55x2

2 - ) .59 X,2+ ) . ) 05 X2 x,

Weight loss, % 9.635 0.002 0.987 Ring combed Y=4.4+0.256xI+O. 1 42 xr0.488 x/+O.263xIX2

Strength loss, % 9.692 0.002 0.843 Y= 12 .675+2.693 XI + 1 .85 x2+ 1 .403 x,-4.636xI 2

Rotor Weight loss. % 4.399 0.O3? 0.423 Y=7.24+0.275 X I+O.4X2 Strength loss, % 1 4.868 0 0.892 Y=6.343+0.733xI+O.73 x,+2.67x, 2_2.92xIX2 + 0.925 X IX,

Process parameters are accounted for the change i n compressional characteristics to vary ing degree i n al l the three types of yarn studied. For ring carded and rotor yarns, the regression equations wi th high degree of accuracy and significant levels were obtained, whereas in case of ring combed yarn, the regression equations show poor significant levels and accuracy (Table 7) . The regression analysis shows that all three processing variables i nfluence the reduction of control parameters significantly (Table 8) .

3.3 Characteristics of Ring- and Rotor -spun Yarns

From the experimental results, i t is observed that there is a remarkable improvement in kinetic friction and hairiness i ndex of ring yarn (carded) as compared to ring (combed) and rotor-spun yarns. The k inetic friction i s reduced to the maximum level of 50% in ring-spun carded yarn .

Compression properties, such as l inearity of compression, compression energy and compression rate, i mprove in case of rotor-spun yarn than in case of ring-spun yarn . Therefore, it can be i nferred that as a result of enzymatic soften ing the rotor yarn gets improved in 'compressional softness' , whereas ring yarn gets i mproved i n 'frictional softness' . There is no significant difference i n the properties of weight loss and strength loss between ring- and rotor-spun yarns (Table 5) .

I t i s clearly observed from the photomicrographs (Figs 1 -3) of the untreated and enzyme-treated samples (at optimized conditions) that the untreated sample has more protruding fibres and fuzzy appearance than enzyme-treated samples. The enzyme- treated rotor-spun yarn has clearer surface than the corresponding ring yarns. As the hairs present in the ring yarn surface are more prominent,

--. -.,....---- ' . . �""'''' ''It .,

(b)

Fig. I - Photomicrographs of (a) unsoftened and (b) softened ring carded yarns

they get i nto int imate contact with enzyme, result ing i n their effective removal . Therefore, more reduction in kinetic friction of ring yarn has been observed especially i n carded yarn.

Contour plots having a system of concentric circles ( 'peak' response surface) w i th a minimum point

DHURAI & NATARAJAN: ENZYMATIC HAIR REMOVAL AND SOFrENING OF COTION HOSIERY YARNS 57 1

Fig. 2 - Photomicrographs of (a) unsoftened and (b) softened ring combed yarns

" , � ",,- "

(b)

Fig. 3 - Photomicrographs of (a) unsoftened and (b) softened rotor yarns

� 70 <: ED 0 'il " '" SJ

:: .() c 0 ',:3 D Jl .� D

� 10 1

� 9.S

§ 9 11 i 8.6

:: '" .5 7.5 � :: 7 :� 6.5

:z: ,

4S � 44 � :'! 42 <:

.� 40 <t e 38 0 u

36 1

. . . . . . .

. . . . .

. . . . . .

. . ' . . '

. .

�.

,

. " ' ;' . "

. . ..: . . .

. . . . .

.

. .

' , . . . . . . . ;

. ,��� . ... . . ' . ' . . : ...... : . . . , '

. , -1

.. . . . . .

Fig. 4 - Effect of concentration and temperature on (a) ki netic friction of softened ring carded yarn, (b) hairiness i ndex reduction of softened rotor yarn and (c) compression rate of softened ring combed yarn at 50 min treatment t ime

towards the low concentration have been observed for kinetic friction reduction i n ring carded, ring combed and rotor yarns and with the maximum points towards the centre of low concentrations are observed for the properties such as hairiness i ndex reduction of ring carded yarn, and l inearity of compression and compression res i l iency of rotor yarns (Fig. 4a). Contour plots with a system of concentric semi ell ipses ( , ri s ing ridges ' responses surface) are observed for the properties such as l inearity of compression and compression energy of ring carded yarn; hairiness index reduction and l inearity of

572 INDIAN J . FIBRE TEXT. RES . . DECEMBER 2006

Table 9 - Optimized values of processing variables and softened yarn characteristics

Yarn characteristic

Concentrat ion. % owm

Temperature, OC

Time, min

Kinetic friction reduction, %

Hairi ness reduction, %

Weight loss, %

Linearity of compression

Compression rate, %

Compression res i l iency, %

Compression energy. gf/4mm

"Yalues are in coded form.

R ing carded yarn

3 ( I ")

50 (0")

60 ( l " )

50 ( fl=0. 1 6)

28 (5.24 HI )

7 .5 0.4

44

26

0. 1 4

Ring combed

yarn

Rotor yarn

2.4 (0.8") 2 .25(0.75")

50 (0 ") 50 (0 ")

50 (0") 50 (0")

1 8 1 2 .4 (fl=0.2 1 ) (�l=0.2 1 )

9.5 8.5 (5 .43 H I ) (3.66 H I )

7.23 8 0.27 0.43 42 46

32 28

0.45 0. 1 55

compression of ring combed yarn; and hairiness index reduction, compression rate and weight loss of rotor yarn (Fig. 4b) . 'Rising ridges' response surface shows that the optimum point of yarn characteristics is lying away from the experimental set- up.

'Saddle' response surfaces are observed for the properties, such as compression rate, compression resi l iency and weight loss of ring carded yarn; compression rate, compression resi l iency, compression energy and weight loss of ring combed yarn; and compression energy and strength loss of rotor yarn (Fig. 4c).

3.4 Optimum Conditions for Enzymatic Softening

The optimized values for variables of enzyme softening and characteristics of softened yarns are given i n Table 9. It is observed that the higher concentration of cellulase enzyme and longer treatment time are required to get optimized softened yarn characteristics for ring carded yarn fol lowed by

ring combed and rotor yarns. But the treatment temperature remains same for al l the three yarns.

4 Conclusions 4.1 Enzyme softening of ring-spun carded yarn

shows high level of reduction in hairiness (28%) and kinetic friction (50%) .

4.2 High improvement in softness characteristics (compression characteristics) has been observed in case of softened rotor yarn (40.65 % in compression rate, 87. I % in compression resi l iency and 40.94% in compression energy) .

4.3 Opt imized conditions of process variables for enzyme softening are found as 2.25-3% (owm) for enzyme concentration, 50°C for temperature and 50-60 min for treatment time . .

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