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In this experiment, enzymatic treatment of denim apparels with acid, neutral and mixture of acid and neutral cellulases was performed in the washing machine under the concentrations of 0.5, 1.0, 2.0, 3.0 and 3.5% (owg).

Figure 2.7. The view of fluorescence microscope.

Table 2.3. Analyses used for denim sample

Analysis Method used Ref.

Tensile strength Grab test ASTM D 5034

Stiffness Bending length BS 3356

Color change Gray scale AATCC Evaluation 1

Weight Dry weight, conditioning ASTM D 3776

Water absorption Static immersion test BS 3449 Microscopy SEM

Microscopy FM

The cellulase enzyme hydrolyse cellulose and allowing changes on color and fiber polymer chain which affects on the fabric properties. The effect of cellulase enzymes with various concentrations of 0.5-3.5% on the properties of denim apparels in terms of tensile strength, stiffness, color fading, weight and water absorption was determined and is shown in Tables 3.1-3.4. From these Tables 3.1-3.4, it can clearly be understood the washing effects from the each others.

Tensile strength is the measure of the breaking force of the fabric which affects fabric mechanical property. The tensile strength evolution after enzyme washing with various concentrations can be seen in Table 3.1.

On washing at various concentrations of cellulase enzymes the tensile strength decreased due to the cellulose hydrolysis by enzymes. As a result, the warp and weft both yarns in the fabric are affected by enzyme and the weft yarns are more affected in its strength than warp due to the undyed weft yarns are more hydrolysed by enzyme.

It can be seen from Table 3.1 that, at low concentration (0.5%) of enzyme, 6.5%, 5.6% and 5.0% strength losses were observed in warp direction when the apparels were treated with acid, neutral and mixed enzymes; and 22.7%, 19.5% and 18.5% strength losses, respectively were observed with higher enzyme concentrations (upto 3.5%). Whereas, 11.0%, 8.8% and 8.0% strength loss and 33.0%, 30.8, and 28.6% strength losses were observed in weft respectively. The decrease in tensile strength at 0.5 to 3.5% was higher with acid cellulase than neutral cellulose due to the different amino acid compositions of acid and neutral celluloses. Campos et al. [62] reported that differences in amino acid residues of acid and neutral cellulases seem to be the main reason for their hydrolysis behavior to cellulose. Hydrolysis of cellulose would certainly affect fabric tensile strength. Cavaco-Paulo et al. [42] investigated that during dyeing the insoluble indigo is known to form agglomerates in aqueous solutions and these indigo molecules bind on warp yarn surface. As a result, in denim washing, firstly indigo agglomerates are fractioned into smaller particle with cellulases, and then hydrolyse the cotton yarn/cellulose. On the other hand, cellulases directly hydrolyse the undyed weft yarns. This seems to be the main reason for high strength loss in undyed weft than colored warp. Buchert and Heikinheimo [37] and Kleman-Leyer et al. [63] have previously been obtained similar results for tensile strength with undyed cotton cellulose.

Table 3.1. Effect of enzyme washing with different concentrations of cellulase on the tensile strength of denim apparel in warp and weft directions

Cellulase conc. (%)

Loss in tensile strength in warp direction, (%)

Loss in tensile strength in weft direction, (%) Acid enzyme Neutral enzyme Mixed enzyme Acid enzyme Neutral enzyme Mixed enzyme 0.0 0 0 0 0 0 0 0.5 6.5 5.6 5.0 11.0 8.8 8.0 1.0 10.5 8.9 8.5 13.9 11.7 11.0 2.0 16.6 13.4 12.6 22.0 21.3 19.1 3.0 22.7 17.0 16.6 28.6 27.2 26.4 3.5 22.7 19.5 18.5 33.0 30.8 28.6

Table 3.2. Effect of enzyme washing with different concentrations of cellulase on the fabric weight and color shade of denim apparel in warp and weft directions

Cellulase conc. (%)

Fabric weight loss, (%) Color shade loss, (%) Acid enzyme Neutral enzyme Mixed enzyme Acid enzyme Neutral enzyme Mixed enzyme 0.0 0 0 0 0 0 0 0.5 1.6 1.4 1.1 10 10 10 1.0 2.9 2.4 2.5 20 10 20 2.0 3.4 3.3 3.2 30 20 30 3.0 4.2 3.7 3.4 40 30 30 3.5 4.5 4.2 3.7 40 30 40

Table 3.3. Effect of enzyme washing with different concentrations of cellulase on the stiffness of denim apparel in warp and weft directions

Cellulase conc. (%)

Stiffness loss in warp direction,(%) Stiffness loss in weft direction, (%) Acid enzyme Neutral enzyme Mixed enzyme Acid enzyme Neutral enzyme Mixed enzyme 0.0 0 0 0 0 0 0 0.5 28.9 22.2 22.2 6.2 6.2 6.2 1.0 31.1 28.9 28.9 9.3 9.3 6.2 2.0 44.0 43.1 43.1 15.6 12.5 12.5 3.0 44.7 43.3 43.1 18.7 15.6 12.5 3.5 44.9 44.0 43.1 18.7 15.6 12.5

Table 3.4. Effect of enzyme washing with different concentrations of cellulase on the water absorption of denim apparel

Cellulase conc. (%) Water absorption, (%)

Acid enzyme Neutral enzyme Mixed enzyme

0.0 0 0 0 0.5 15.1 17.5 16.7 1.0 19.1 20.6 20.6 2.0 23.0 21.4 23.8 3.0 23.8 23.0 25.4 3.5 23.8 23.0 25.4 It is seen from Table 3.2 that, treatment of denim garments under investigation with acid, neutral and mixed cellulase decreased the weight loss and this decrease is little bit higher at higher enzyme concentrations up to 3.5%. The main reason of weight losses is the hydrolysis behavior to cellulose by enzymes. With higher enzyme concentration the rate of hydrolysis increased and weight loss is increased. During washing, acid and neutral both cellulases are hydrolysed cotton. First, it attacked on projecting fibers (micro-fibrils) on surface, then attacked on yarn portion, hydrolyzed them slowly and penetrated inside the fabric.

As a result, fibers are hydrolysed and broken down quicker with the friction of rotating cylinder of the washing machine. Hydrolysis of cellulose would certainly affect fabric weight losses in washing process. Table 3.2 shows that acid cellulase caused up to 4.5% weight loss, neutral cellulase up to 4.2% loss and mixed cellulase up to 3.7% loss at the concentrations of 3.5%.. It is observed that the weight loss decreased more in acid enzyme than neutral enzyme, and weight loss is less when denim apparel washed with mixed enzymes.

Again, denim hydrolysis was measured by monitoring the color shade change. It can be seen from the Table 3.2 that the color shade decreased with higher concentrations from 0.5% to 3.0%. The color shade is not decreased more, with the increasing of concentration from 3.0 to 3.5%. In enzyme washing, the part of the primary wall of indigo-dyed denim apparel is always in contact with cellulase. At the contact point, the surface dyes are partly detached from the main fiber chain and indigo dye bonds are broken from the yarn surface. As a result, the treated denim apparel becomes duller and color is faded. In addition, mechanical friction inside washing machine accelerate cellulose hydrolyses and destroy color.

Grieve et al. (2006) has previously been obtained similar result for color fading of denim apparels. The results disclose that increasing the cellulase concentration from 0.5 to 3.0% has effect on color fading and from 3.0 to 3.5% has no effect on color shade change, because most indigo agglomerates are fractioned into smaller particle at 3.0% cellulase concentration, and with increased concentration up to 3.5% cellulases, remaining indigo agglomerates are not fractioned into smaller particle, as a result color will not fade further. It can be seen from the Table that acid cellulase caused 10 - 40% color loss, neutral cellulase 10 - 30% loss and mixed cellulase caused 10 - 40% loss. It is observed that the decrease in color shade at 3.5% was higher with acid cellulase than neutral cellulose. This means that indigo color fading also depends on the nature of cellulase enzymes with increasing cellulose concentrations.

It can be seen from the Table 3.3 that the stiffness of denim apparels decreased after they were exposed to acid, neutral, and mixed enzymes at concentrations of 0.5 - 3.5%. After treatments, the starch of warp yarns are removed first, then it hydrolyzed cellulose similar to color fading mechanism by cellulases discussed earlier. As a result, bending length was less and stiffness decreased in comparison to untreated denim for all the three cases. The decrease in stiffness at concentrations of 0.5 to 3.5% was higher with acid cellulase than neutral cellulase. Cavaco-Paulo et al. [42] investigated that acid cellulases have a higher affinity for indigo than neutral cellulases. Thus, more hydrolyses occurred by acid cellulase and stiffness decreased. It can be seen from the Table that acid cellulase caused 28.9-44.9%, neutral cellulase 22.2-44.0% and mixed cellulase caused 22.2-43.1% stiffness loss in warp direction and 6.2-18.7%, 6.2-15.6%, 6.2-12.5% respectively in weft direction. Water absorption is the measure of the level of water in the denim apparel which affects fabric properties. Table 3.4 shows the changes in water absorption with the increasing of concentration of cellulases from 0.5-3.5% in denim washing, due to the loosening of surface fibers by enzymatic treatment. The loosening of surface fibers would certainly affect fabric water absorption. From the Table it can be seen that, the water absorption increased 15.1-23.8% at 0.5-3.0% concentration with acid cellulase, 17.5-23.0% with neutral enzyme, and 16.7-25.4% with mixed cellulase, and does not cause any further increase of water absorption when the concentration increased from 3.0 to 3.5%. With increased water absorption, the denim apparel shows increased water vapor permeability that means comfortness or softness increased. Therefore, there is a strong relationship between water absorption and fabric comfortness and softness; which affects the properties of denim apparels.