Bio-polishing of Knit Goods and Influence of Bio-polishing Enzymes on Physical Properties of Cotton Knit Goods

Introduction:
Apart from polishing the fabrics, the treatment offers a number of other benefits in physical properties such as improvement in pill resistance, cooler fill, brighter luminosity of colors and softness. At the same time, the treatment results in certain adverse effects like loss in weight and strength. All the above effects are influenced by a number of factors like, composition of the acid cellulase, history of pretreatments given to the fabrics and process parameters used at the time of treatment.

Various developments have taken place in the eco-friendly processing of textiles involving enzymes. Among the various enzymes, cellulase is extensively used on cellulosic material. There are two types of cellulase, namely, acid cellulase and neutral cellulase. Acid cellulase used in biopolishing, which is very popular finishing treatment given to cellulosic fabric. Apart from polishing the fabrics, the treatment offers a number of other benefits in physical properties such as improvement in pill resistance, cooler fill, brighter luminosity of colors and softness. At the same time, the treatment results in certain adverse effects like loss in weight and strength. All the above effects are influenced by a number of factors like, composition of the acid cellulase, history of pretreatments given to the fabrics and process parameters used at the time of treatment. Moreover, the treatment has influence on post treatments given to the fabrics.

In the textile industry, especially in the apparel sector, cotton is widely used because of its superior properties and it still holds the name as king of fibres. Cotton blended fabrics faces a major problem i.e. pilling. Pilling is defined as the tendency of fibres to loose from a surface and form balled or matted particles that remain attached to the surface of the fabric. For the consumer, it affects fabric aesthetics and comfort. For the manufacturer, fabric pilling is a headache that affects the appearance and wear-ability of finished apparels. Pilling is a complex phenomenon comprised of multiple stages that progressively accelerate the rate of fibre removal from the yarn structure, thus shortening the life span of garments and other textile properties.

Pilling is particularly problematic for knitted fabrics. At the same time, knitted fabrics have several advantages over woven fabrics, such as higher production rates, lower production costs and softer fabric structures. Still, the pilling problem that results from the slack fabric structure remains a significant objection. Essentially there are a number of methods to reduce pilling in commercial use. One approach is to apply surface active agents, like a polymeric coating that binds fibers to the fabric surface. These are often friction reducing lubricants, such as acrylic copolymers. Shearing and singeing are common methods used to produce a clean, smooth surface on fabrics. Singeing, in particular has the real potential to scorch the fabric surface. The down side of surface active agents includes a reduction in hydrophilicity and the gradual loss of the agent after a few washes, which eventually makes fabrics harsh and fuzzy.

Enzymatic removal of fuzz is carried out under milder conditions and is absolutely safe, efficient and permanent. Cellulase enzymes give fabrics a clear, even surface appearance. They reduce the tendency to pill and improve softness, especially when compared to traditional softeners. Moreover, they accomplish this without polluting the environment. As a result, cellulases are increasingly being applied to textile finishing. They are widely used to remove fibrils and fuzz fibres from cotton fabrics.

Requirement Profile of Cotton Knitting Yarn:
A knitting yarn (100% cotton) for high-production circular weft knitting should exhibit the quality characteristics as indicated in the following Table .

In contrast to weaving yarns, the yarn strength of knitting yarns is secondary, as the loading placed on the yarn during knitting is lower than that with a high-production weaving machine. However, the yarn must exhibit enough elongation and elasticity.

There must be no weak places or thick places that can result in stop holes in the knitted material, or even broken needles. Particularly important is the ability of the yarn to pass easily through the various guide elements of the machine (low friction value). The moisture content of the yarn should be evenly distributed. In most cases, a constant and high hairiness value with a low twist is required in order to achieve a soft fabric handle. However, this hairiness value must remain constant and be without periodic variations, and also be of a level suitable for the type of end product.

For single jersey materials the yarn evenness and count variations are important parameters. The short, medium and long-term count variations lead to cloudy or stripy fabrics as soon as a certain mass variation level is overstepped. In addition, neps & vegetable matter and high dust content refer to the types of foreign matter that is particularly disturbing. These lead to wear of the needles, holes in the knitted material and, in many cases, to dyeing problems.

Requirement profile of cotton knitting yarn:


Count variation CVt, cut length 100m**
< 1.8 %
Count variation CVt, cut length 10m**
<2.5%
Breaking tenacity [Fmax!tex]
> 10 cN/tex
Elongation at breaking force [Efmax]
>5%
Yarn twist(am value)
Ring-spun yarn 94-110 (3.1-3.6 am value) /
Rotor-spun yarn up to 25 % higher than ring-spun yarn

Paraffin waxing/surface friction value
0.15μ
Yarn irregularity**
< 25 % value of Uster® Statistics
Hairiness H***
[e.g. > 50% value of the Uster® Statistics]
Hairiness variation between bobbin H****CVb
<7%
Seldom-occurring thin and thick place faults (CLASSIMAT values)
< A3/ B3/ C2/ D2 or Dl or more sensitive (Cleaning limit)
Remaining yarn faults (CLASSIMAT values)
A3 + B3 + C2 + D2 =< 5/100,000 m

* A low breaking force value must be compensated by a higher elongation at breaking force value ** Highest requirements with single jersey

*** Higher, but constant hairiness as a result of the cloth appearance and handle. The minimum hairiness value must be set based on agreements between the partners

**** Variation between packages. Higher values can lead to 'rings' with single-colored fabrics

Enzymes for Biopolishing:
Cellulases are derived from both fungal and bacterial sources. They find extensive application on cellulosic materials and about 1 0% of the finishing of these materials is estimated to be performed by these enzymes to achieve various effects. They also find application in food, pharma and paper industries.

Cellulases used in bio-finishing of cellulosic fabrics are derived from more than ten different fungal species which vary in their component composition, application pH and special effects produced. Cellulases derived from the fungus, Trichoderma reesei is widely used in textile finishing since it gives higher yield in industrial production. In addition to cellulases originating from the above fungus, those originating from Humicola insolens can also degrade cotton cellulose efficiently and they find extensive application in biostoning of denim fabric.

Cellulases are high molecular colloidal protein bio-catalyst in metabolite form. Industrial cellulases represent complex of a number of cellulases, cellobiase and related enzymes of completely non uniform composition in a molecular weight range of 10,000 to 4 million.

Enzymes or cellulases have a protein like structure with primary, secondary, tertiary and quaternary structures and that are susceptible to degradation due to temperature, ionizing radiation, light, acids, alkali, and biological effect factors. Cellulases are capable of breaking the 1,4-B-glucoside bond of cellulose randomly. When cotton fabric is treated with a cellulase solution under optimum condition: Cellulase hydrolyse cellulose by reaching to the 1, 4-B-glucoside bond of the cellulose molecule.

As a result of which the fabric surface becomes smooth with the loss of surface fibres and the hand becomes soft. There is also loss in strength proportional to the amount of weight reduction.

There are mainly three types of cellulases:
1) Acid stable (more effective in pH range of 4.5 - 5)
2) Neutral stable (effective at pH 7)
3) Alkaline stable (not used widely)

Action of Cellulases:
Enzymes are large molecular complex and can’t penetrate interior of the fabric. Hence enzyme action takes place preferentially on the surface. Where cleavage of cellulose chain occurs, Microfibrils, which are loose fibres break off under the influence of bio-catalytic degradation and results in better mechanism or modify the surface of the fabric.

Enzymes contain activity centre in three dimensional structure form namely fissures, holes, pockets, cavities, hollows.

These enzymes first of all form an enzyme substance complex on the surface of the cellulose.

Bio-reaction then takes place in the above mentioned substrate mentioned enzyme substrate complex.

Finally, the complex disintegrates with the release of the reaction products and the original enzymes, which are once again available.

The mechanism of cellulase action on cellulose as shown by Fig.2 is as follows: (i) the endoglucanases degrades cellulose by selectively cleaving through the amorphous sites and breaking long polymer chains into shorter chains, (ii) cellobiohydrolases degrades cellulose sequentially from the ends of glucose chains, thus producing cellobiose as the major product and it plays a mediator role in degrading cellulose, and (iii) B-glucosidases complete the hydrolysis reaction by converting cellobiose into glucose. 
 

Figure 2: Mechanism of cellulases action on cellulose
Enzyme Inactivation:
To prevent any damage of the fabric after the finishing operation it is very essential that the reaction be terminated at the end of treatment by enzyme inactivation. If the enzyme is not inactivated entirely then at the end of the reaction fibres get damaged and even extreme cases total destruction of the material may result. The enzyme inactivation is therefore of great importance from the technical point of view.

There are two distinct process of termination of enzyme:
1) Hot treatment at 80 0C for 20 minutes.
2) By raising the pH to 11-12.

Chemistry of Enzyme Finishing :
More than with other chemical reactions, the enzyme catalysed hydrolysis of cellulose is strongly influenced by factors such as pH, temperature, time and agitation. The optimal pH for a particular cellulase depends upon its origin. Trichoderma-based products (sometimes called ‘acid cellulases’) work best at pH 4.5 - 6, whereas cellulases from Humicola (often called ‘neutral cellulases’) are more effective at pH 6 - 6.5. The reaction temperature is also critical since at low temperatures, the reaction rate is slower than desired, but very high temperature can deactivate the enzyme by providing enough energy to alter its molecular alignments and thereby destroy its catalystic ability.

Since enzymes are true catalysts and are not consumed during the chemical reaction, the hydrolysis reaction will continue until either the reaction conditions change or the cellulose is physically removed from the reaction mixture. Mechanical agitation is important in order for the hydrolysis reaction to proceed efficiently. Recent work has demonstrated that the kinetics of the reaction is controlled by mass transfer effects. The absorption-desorption mechanism of enzyme action depends on agitation to remove hydrolysis by-products and expose new fibre areas to attack.



Because the enzyme’s catalytic action is not reduced during the reaction, effective methods of ending the hydrolysis must be employed to prevent excessive fibre loss. Since the molecule’s physical alignments are crucial to its catalytic ability, procedures that alter the cellulase molecule’s internal structure can be used to deactivate the catalysis and halt the hydrolysis. High temperatures (> 70 0C or 160 0F for at least 20 min or short drying at 120 0C or 248 0F), high pH (>10) and high electrolyte content as well as enzyme poisons can serve to terminate the reaction by distorting the enzyme’s molecular shape.

Recent developments in enzyme manufacturing have led to commercial products that contain a preponderance of one cellulase component. These ‘Mono-component’ enzymes are produced from modified Humicola strains and are primarily endo-glucanases active at pH 7 - 7.5 and are referred to as ‘Alkaline cellulases’.

Processing of Bio-polishing of Garment:
  1. Fill the machine with water
  2. Add nonionic wetting agents (0.2 to 0.3 gpl)
  3. Adjust pH 4.5 to 5.5 with acetic acid
  4. Add 2 gpl lubricant (non-ionic)
  5. Load the garment in the machine and run the machine for 30 minutes at 45 - 50 0C
  6. Remove one garment from the machine and compare with the unwashed garment to see the effect of bio-polishing
  7. If bio-polishing is satisfactory, raise the temperature gradually to 85 0C and maintain the temperature for 10 minutes to deactivate the enzyme
  8. Drain the liquor
  9. Cold rinse for 5 - 10 minutes followed by hydro extraction and tumble dry
Advantages of Using Enzymes for Bio-polishing are:
  1. Hairiness, fluffs and pills are removed.
  2. Material sticking (the burr effect) is prevented.
  3. Improved handle.
  4. Achievement of surface smoothness and a clear structural appearance.
  5. Improved lustre.
  6. Material texture relaxation.
  7. Increased flexibility and therefore a soft handle even with over end-products and mercerized fabric.
  8. Improved sewability.
  9. Fast to washing, low pilling tendency, no napping in use, or during care operation.
  10. Stone wash effect without pumice stone and dyestuff destroying chemicals.
  11. Poor quality, uneven, napped, knoppy material surface (ie) typical second quality goods are converted into elegant, lustrous, soft, top quality with a fine, high quality surface appearance.
Disadvantages of this Finishing Technique:
  1. Loss in weight
  2. Loss in strength
Cellulases have been used on a large scale for years in medicine analysis, food chemistry and other industries.

Trouble-shooting for Bio-finishing :

As mechanical agitations important to effect the bio-finishing, only selected processes and machines can be used, for example tubular fabric preferably cut to open width and treated in open width washers. In the rope form the loosened fibre particles are filtered out by the fabric and cannot easily be removed. The pad-batch process, jig or package dyeing machines are not effective in bio-finishing.

Not all cellulase enzymes give identical results, even with similar fabrics in similar equipment. Cellulases derived from Trichoderma typically are the most aggressive in their action, whereas mono-component endo-glucanases often require the most mechanical action to achieve the desired effects. Slow deactivation of the cellulases during transport and storage can adversely affect the reproducibility of the resulting effects. If cotton is not washed carefully before bio-finishing, secondary fibre compounds as residual biocides can deactivate the cellulases. The same is true for natural or synthetic tannic acids, and resist or fastness improving agents for wool or nylon in cellulose fibre blends.

Deactivation of cellulases after the desired effects have been achieved is very important. If the enzyme is not completely removed from the fabric, or is not effectively deactivated, the hydrolysis reaction will continue, although at a slower rate. As very large molecules, cellulases cannot diffuse into the crystalline parts of the cellulose fibres. They react on the fibre surface, so fibre damage takes time. But eventually enough hydrolysis will have taken place to weaken the affected fabrics or garment, leading to customer complaints and returns.

Undesirable deactivation may be caused by high temperature and time, for example, caused by transport and storage and also by enzyme poisons such as certain surfactants (especially cationic ones), formaldehyde-containing products or heavy metal ions. An activation effect on cellulases was reported by Nicolai and co-workers. Alkaline pretreatment, low concentrations of selected non-ionic surfactants, polycarboxylic acids and polyvinyl pyrrolidone can enhance the bio-finishing of celluloses.

The use of pH buffers during the hydrolysis reaction is strongly recommended, especially when abrading denim fabrics.

Cellulase enzymes have very narrow pH ranges of effectiveness and denim fabrics can have significant quantities of residual alkali from the indigo dyeing process. Buffers are required to maintain the appropriate reaction conditions for maximum enzyme effectiveness. Because the effect of processing auxiliaries on cellulase catalysis is difficult to predict, it is important to evaluate any changes in processing formulas carefully by conducting small scale trials before making significant changes in production procedures.

Removal of protruding fibres from garment surface using cellulase enzymes is called bio-polishing. These enzymes are proteins and capable of hydrolysing cellulose (cotton). In bio-polishing they act upon the short fibres protruding from fabric surface and make the fibres weak which are easily removed during washing. This process imparts soft and smooth feel and reduces fuzz or pilling tendency. This process is applicable to garment made of cotton and its blends.

Two kinds of cellulases are commercially available, acid cellulases, which have activity in acidic medium in pH range of 4.5 - 5.5 and neutral cellulases, which have activity in pH range of 5.5 - 8.0. Both these types are active in the range of 45 0C to 60 0C.

Materials & Methodology:
  • Material used : Knitted Fabric (100% cotton)
  • Type : Single Jersy
  • Type : 32
  • Grey width : 36”
  • CPI : 42
  • WPL : 46
  • GSM : 140
Details of Chemicals:
  1. Hydrogen Peroxide (50%)
  2. Sodium Hydroxide
  3. Cidascour LTJ (Solvent)
  4. Sodium Carbonate
  5. Lissapol D (Wetting agent)
  6. Hydrose (Reducing agent)
  7. Sodium hexametaphosphate (Sequestering agent)
  8. Sodium silicate (Stabiliser)
  9. Urea (Hygroscopic agent)
  10. Sodium Chloride
  11. Acetic acid (Buffer)
Dyes Used:
  1. Reactive Navy Blue HER
  2. Reactive Red HE4R
  3. Drimarene Orange KGL
Enzyme Used:
Cellusoft-SO, which has an activity of 750 EGU/gm. It is an acid stable cellulase, produced by submerged fermentation of a trichoderma microorganism.

Pretreatment:
A. Scouring:
Recipe :
  • Sodium Hydroxide : 2.5%
  • Sodium Carbonate : 1%
  • Cidascour LTJ : 0.5%
  • Wetting Agent : 0.5%
  • Sodium hexametaphosphate : 0.2%
  • Temperature at boil : 80 0C
  • Time : 4 - 5 hours
  • pH : 9 - 10
  • M : L : 1 : 20
B. Bleaching:
Recipe :
  • Hydrogen Peroxide (50%) : 0.5 - 1%
  • Sodium Silicate : 1%
  • Sodium hexametaphosphate : 0.2%
  • Temperature : 85 0C
  • Time : 2 hours
  • pH : 10 - 10.5
  • M : L : 1 : 20
Process Sequence:


C. One bath scouring and Peroxide bleaching:
Recipe :
  • Sodium Hydroxide : 2.5%
  • Lissapol D : 0.5%
  • Hydrogen Peroxide : 2 - 3%
  • Sodium Silicate : 1.5%
  • Sodium hexametaphosphate : 0.2%
  • Temperature : 80 0C
  • Time : 2 - 3 hours
  • pH : 10 - 10.5
  • M : L : 1 : 20
Process Sequence:



Dyeing:
Recipe :
  • Dye : Light shade (0.5%), Medium shade (1.5%) & Dark shade (3%)
  • Salt : 60gpl
  • Soda ash : 15gpl
  • Temperature: 80 - 85 0C
  • Time : 2 hours
  • M : L : 1 : 15
  • pH : 8.5 - 9.5
After Treatment:


Process Sequence: a. Dyeing followed by bio-polishing:



Process Variables :
  1. Concentration
  2. Temperature
  3. pH
  4. Time
  5. M : L Ratio
  6. Mechanical Agitation
To achieve optimum bio-polishing, the process variables have been varied as mentioned below.
  1. Concentration of enzyme: 0.5%, 1%, 2%, 2.5%, 3% & 4%.
  2. Temperature: 40 0C, 45 0C, 50 0C, 55 0C & 60 0C.
  3. pH: 3 - 4, 4 - 5 & 5 - 6.
  4. M: L: 1:5, 1:10, 1:15 & 1:20.
  5. Mechanical Agitation: Vigorous Stirring, Medium Stirring & Without Stirring.
Testing & Analysis:
The following tests have been carried out to assess the properties of bio-polished cotton knitted fabric.
  1. Wash fastness (ISO-3),
  2. Abrasion resistance,
  3. Weight loss,
  4. Pilling,
  5. K/S value using C.C.M.
Results & Discussion:
Factors affecting bio-polishing:
Bio-polishing is affected by many factors. Major ones are enzyme, type of fabric and process variables.

The predominant process variables which control the bio-polishing are temperature, pH, duration of treatment, and material to liquor ratio, enzyme concentration and mechanical agitation.

To find the effect of above mentioned factors the authors carried out the bio-polishing by following ways.
  1. Keeping M:L ratio, pH and temperature constant and varying the concentration of enzyme.
  2. Keeping temperature and pH constant and varying the material to liquor ratio.
  3. Keeping M:L ratio constant and varying the temperature.
  4. Keeping temp and M:L Ratio constant and varying the pH of solution.
  5. Keeping all these parameters constant and varying the duration of treatment.
Effect of Concentration:
Concentration of enzyme is a major factor, which affects the performance of the bio-polishing of the knitted fabric.
There are different types of enzymes available in the market. Each enzyme has an optimum concentration, pH and temperature range.
In this study, the authors used CELLUSOFT-SO, which is an acid stable cellulase. By varying the concentration of cellulase and keeping the other parameters, such as pH, temperature, time and material to liquor ratio constant, the authors observed that the best bio-polishing can be obtained at the following conditions:
  • M:L Ratio : 1 : 10
  • Temperature : 55 0C
  • Time : 50 minutes.
  • pH : 4 -5
To observe the effects of conc. of Enzyme on bio-polishing, the authors treated knitted fabric with various concentrations of Cellusoft-SO viz, 0.5%, 1%, 1.5%, 2%, 2.5%, 3% and 3.5%. Results obtained are depicted in Table 1.
 

From this Table, it can be concluded that as the concentration of cellulase increases from 0.5% to 2.0%, weight loss increases significantly. Optimum percentage weight loss is obtained at 3% concentration. Increase in concentration of enzyme causes an increase in strength loss. Fabric thickness is reduced with increase in concentration of enzyme. Hence 3% concentration of enzyme is the optimum dose.

Effects of Temperature:
Tmperature affects the performance of cellulase. Each enzyme has an optimum temperature range where enzyme activity is maximum. Hence it is essential to determine the optimal temperature. Increase in temperature decreases the enzyme activity rapidly and the enzyme action comes to almost zero and the enzymes are permanently deactivated at 70 0C. Low temperature shows reduction in reaction speed but does not deactivate the enzyme. It is therefore possible to use a lower temperature by a longer cycle. The activity of Cellusoft-SO at 40 0C is only 50%. It is also observed that every 10 0C rise in temperature doubles the activity of enzyme, as long as it is not deactivated.

To observe the effects of temperature on bio-polishing, the authors treated knitted fabric with the following recipe. Results obtained are depicted in Table 2.

Recipe:
  • M:L Ratio : 1 : 10
  • Concentration : 3%
  • Time : 50 minutes.
  • pH : 4 - 5


The optimum result is obtained at 55 0C temperature.

Effects of pH:
pH is also a critical factor affecting the efficiency of bio-polishing. A particular type of cellulase is most effective and can be operated at a certain specific pH range. To observe the effects of pH on bio-polishing, the authors treated knitted fabric with 3% Cellusoft-SO at various pH viz, 3 - 4, 4 - 5, 5 - 6, 6 - 7 & 7 - 8. Results obtained are depicted in Table 4.

The authors observed that the activity of enzyme is maximum at pH 5 - 5.5. But optimum bio-polishing effect is obtained at pH 4-5.

Effects of M:L Ratio:
M:L Ratio has a substantial effect on bio-polishing. As the liquor ratio increases the bath conc of cellulase decreases, and the fabric weight loss decreases. The dilution affects substantially enzymatic activity.

To observe the effects of M : L ratio on bio-polishing, the authors treated knitted fabric with 3% Cellusoft-SO at various M : L ratios, viz, 1:5, 1:10, 1:15 & 1:20.

Recipe:
  • Temperature : 55 0C
  • Concentration : 3%
  • Time : 50 minutes
  • pH : 4 – 5
Results obtained are depicted in Table 4. From this table, it is found that as the liquor ratio increases the pilling rating of treatment sample decreases. At the low M:L Ratio, the fabric show very low pilling and at higher M:L Ratio, pilling tendency of fabric is more. Thus, pilling rating goes on increasing with increases in liquor ratio.

The best result is obtained at 1 : 10 M:L Ratio.

Effects of Duration:
To observe the effects of duration of enzyme treatment on bio-polishing, the authors treated knitted fabric with 3% Cellusoft-SO for various durations viz, 30 minutes, 40 minutes, 50 minutes & 60 minutes.

Recipe:
  • Temperature : 55 0C
  • Concentration : 3%
  • M:L Ratio : 1 : 10
  • pH : 4 - 5
The best result is obtained at 50 minutes treatment time.

Effects of Enzyme Treatment on Dyeing Property:
To observe the effects of enzyme treatment on dyeing property, bio-polishing of cotton knitted fabric has been carried out before dyeing as well as after dyeing.

Recipe for Enzyme Treatment:
  • M:L Ratio : 1:10
  • Temperature : 55 0C
  • Time : 50 minutes
  • pH : 4 - 5
  • Concentration : 3%
One bath Bio-polishing and Dyeing :
Enzymatic cellulose degradation is also possible during reactive dyeing. Here the dyeing process as well as bio-polishing will be affected. Number of washes, time, cost and energy can be saved by this one bath method. However, it should be noted that there is some reduction in colour yield of reactive dyeing. This is because reactive dyeing is carried out in acidic pH during bio-polishing. But precaution is taken during addition of soda-ash as reactive dyes require alkaline condition for its fixation. The fabric is made neutral before adding soda-ash. It is found that neutral stable enzymes are more suitable in this type of one bath treatment.

Recipe:
Conventional Method One Bath Method
  • Concentration of Enzyme : 3%
  • M : L Ratio : 1:10
  • Temp. : 55 0C
  • Time : 50 minutes Time : 2.5 3 hours.
  • pH : 4 – 5
Changes in physical properties due to biopolishing enzymes:

Pilling:
After the biopolishing of the knitted fabrics it was observed that the pilling resistance ratings of the fabric samples knitted from combed yarn and from open-end yarns were similar to each other, and there was no significant difference between them. The pilling resistance of open-end yarns-based knitted fabrics and combed ringspun yarn-based knitted fabrics were better than the carded ring-spun yarn-based knitted fabrics. When the number of turns of the Martindale Instrument was increased up to 5000t/m, both ring and open-end yarns demonstrated higher pilling values.

Strength:
The biopolishing process partly hydrolyses the cotton, which has a negative effect on fabric strength level. Fabrics from combed yarns gave the best strength level. Fabrics from combed yarns gave the best strength values for untreated and enzymatic treated in three different stages, rather than fabrics from carded and open-end yarns. The fabric sample strength loss caused by enzymatic treatment after pre-treatment or dyeing processes is nearly the same in all type of fabrics, approximately around 11 %. In fabric samples enzyme treated twice after pre-treatment together with the dyeing processes, loss in strength is about 25% in average, and the fabric samples from combed yarn exhibit a noticeably higher loss of strength.

Fabric Weight:
After the biopolishing process, 1-5% loss in fabric weight is occurred. Weight loss of enzymatic treated fabric samples after pre-treatment was slightly higher than for those which were enzymatic-treated after dyeing. The reason for this is the high number of process phases, the high amount of mechanical forces and the long process period, which cause the removal of the fuzzes from the yarn surface. When the weight loss is compared according to the yarn spinning system, the fabric from carded yarn had the highest value while the open-end yarn had the lowest. The amount of weight loss that occurs after the double enzymatic treatment was significantly higher.

Colour Change:
K/S of enzyme treated carded yarn fabrics appeared higher i.e. darker after enzyme processing, however, K/S value remains unchanged significantly with reference to weight loss for vat dyed fabrics and fabrics dyed after cellulase treatment with direct and reactive dyes. In the case of fabrics pretreated with cellu lases and then dyed, the decrease in the K/S values after laundering less compared to untreated fabrics, especially after 20-30 wash cycles.

Dimensional Stability:
Hydrolysis of cellulose molecules in different regions of the cotton fibres alters the dimensional stability of the fabrics, which is further influenced by single jersey, interlock and woven structures. EG-rich cellulase treatment of fabrics show lower shrinkage compared to CBH-rich and total crude cellulase. While control sample results about 3% shrinkage, the enzyme treatments result the shrinkage in the range of 0.5% to 1.0%. Dimensional stability further increases with number of washes with EG-rich enzymes compared to total cellulases EG and after 10 washes, the EG-rich enzyme treated fabrics show about 80% less shrinkage, independent of concentrations.

Water Absorbency:
Water absorbency and water retention properties of fabrics, after biopolishing are modified with reference to the control fabrics, further controlled by fabric construction parameters and extent of hydrolysis. The cellulase treated fabrics showed higher energy dissipation under wet conditions (heats of sorption), implying that they might offer slightly superior thermal comfort performance under hot and humid conditions. Water retention capacity of cotton and cotton/linen increases by 24-28% due to splitting of micro fibrils and surface peeling effects. As the enzyme hydrolysis removes accessible amorphous portions in different reasons during hydrolysis, the adsorption of moisture decreases with treatment time. Wettability of the fabrics after biopolishing reduces from 4.52 seconds to 0.78 seconds for medium weight and from 20.1 to 12.9 seconds for heavy weight fabric, which further decreases in the case of combined enzyme and softener treatment.

Conclusion:
  1. The best result is obtained at 3% concentration of enzyme.
  2. 1:10 M:L ratio gives the best result.
  3. At pH range of 4 - 5, enzyme shows maximum activity.
  4. At 55 0C temperature, enzyme activity is maximum.
  5. Mechanical agitation supports enzyme activity.
  6. Depth of shade increases when enzyme treatment is given before dyeing and the depth decreases when enzyme treatment is given after dyeing.
  7. Pilling tendency decreases with application of enzyme.
  8. One bath application saves energy, time & cost. But the bio-polishing effect is not as good as the two bath method.
  9. Wash fastness of the enzyme treated sample before dyeing is very poor.
  10. Wash fastness of the enzyme treated sample after dyeing is good.
  11. Wash fastness of one bath enzyme treated sample is moderate.
  12. Biopolishing of cotton fabrics with cellulase enzyme results in both beneficial and adverse effects. By suitably optimizing the process conditions, the strength loss during the process can be aimed to a required level, without compromising other handle properties.
References:
  1. The Indian Textile Journal published on October , 2010.
  2. Hobberg T and Thumm S: Finishing of Lyocell – Part 3, Melliand International, 1999, 5(1), 83-85.
  3. Stohr R: Enzyme- Biokatalysatoren in der Textilveredlung, Melliand Textilberichte, 1995, 76(11), 1010-1013.
  4. Enzyme Nomenclature, Amsterdam-London-New York, Elsevier, 1973.
  5. Influence of Biopolishing Enzymes on Physical Properties of Cotton Knit Goods By: Chinta S. K., Landage S. M. & Ketan Verma published on www.fibre2fashion.com on October, 2012. 
Published by:
S. M. Hossen Uzzal
B.Sc. in Textile Technology
Monno Fabrics Ltd. Manikgonj

0 comments:

Comment here

Textile Learner is the largest Textile Blog over the net. It is an ultimate reference for textile students. It describes textile articles in comprehensive. It also supplies news on latest textile technology, educational institute news of the world.