Application Cellulase enzymes were initially promoted with the promise of completely eliminating stone as the abrasive agent in achieving the stone wash look. Using cellulase as a substitute for the pumice stones prevents the damage to washing machines and the garments, eliminates the disposal of the used stones, improves the quality of the waste water and eliminates the need for labour intensive removal of stones from the finished garments. However, due to increased time and other considerations, the trend today is to use combinations of stone and cellulase to achieve the worn out look more quickly. Some highly abraded finishes cannot be achieved just by using cellulase alone. In such cases partial substitution of stones with the enzymes can achieve the desired look.

Process The activity of any enzyme depends primarily on the pH and temperature of the reaction system. Basically, cellulases can be divided in to four basic groups according to the pH required for optimum enzymatic activity. One group is called acid cellulase because the pH ranges from 4.5 to 5.0. There are Hybrid cellulases whose optimum pH is 4.5 to 7.0. The third group called the neutral cellulases is active from a pH 6.0 to 8.0 but is optimal at pH 6.2. The fourth group is commonly reffered as to alkaline cellulase enzymes because its optimum pH is 7.2 to 8.5. The performance of the acid cellulase enzymes is charecterized by its highly aggressive action on cotton. However, acid cellulases are associated with backstaining, which may be undesirable and excessive strength loss. The action of the hybrid, neutral and alkaline cellulase enzymes towards cellulase is less aggressive and requires longer time cycles. They do, however, produce less backstaining.

Process related to control parameters

Temperature Control Tight temperature control is required to obtain reproducible results. As a thumb rule every 10 degree C increase in temperature, enzyme activity doubless, but above a certain temperature the enzymes denatures and loses its activity completely. The temperature needed to denature a certain enzymes depends upon the lenght of time that the enzyme is being held at that temperature. For runs lesser than 30 minutes, the best suitable temperature for acid or neutral cellulases is 60 degree C but for runs longer than that,55 degree C would yeild desired result. The use of direct steam in enzyme bath to keep the tenperature constant should be avioded as live steam denatures the cellulases. If the machine has a large temperature drop, it is possible that a start temperature of 65 degrees C will give the optimal use of the cellulases.

pH control As previously mentioned, the activity or color removal from Denim by eaxh type of cellulases is the function of the pH. For the Hybrid cellulases maximum color removal occurs at pH of 5.5 but at both pH 4.5 and 6.5 this enzyme still has above 90% of it's original activity. Acid cellulases has the maximum activity or color removal at pH 4.5 to 5.0, but at pH 6.0 the activity or color removal is reduced to less than 40%. Neutral enzymes have an optimum pH at 6.2 but only 80% remains at pH 5.0 and 7.0. Since the pH profile for the Hybrid cellulase is much broader than that of acid and neutral cellulases, the hybrid cellulases provides greater reproducibility of the finished look. But because of its much narrower pH profile, acid and neutral cellulases require much tighter control of pH during stonewashing to achieve a higher level of reproducibility. The buffering of the cellulase bath is very important as alkalinity is often released from the garments, which deteriorates the activity of the cellulases. A 4.5 pH buffer can be used to ensure the pH of the acid cellulase abrasion bath remains within the range of optimum activity. A 6.0 pH buffer can be used to control the neutral cellulase enzyme baths at their optimum pH level. A 5.5 pH buffer can be used with hybrid enzyme whose optimum pH is 5.4 to 5.6.

Other Process related Factors

Clean Up Cycle: The clean up procedure depends on the desired look. A good alkaline scour is necessary to clean away the released indigo. Im many cases, a small amount of chlorine bleach or reducing agent is incorporated in the clean up process to help remove loose colour on the garments. Another reason for the alkaline wash after the cellulase treatment is to directivate the residual cellulase enzyme and prevent further strength loss of the fabric. If cleaner garments, labels or pockets are required, Detergents and selected polymers, should be added to the clean up baths.

Liquor to the good ratio: The amount of water needed depends on the goemetry of the machine but generally liquid:Good ratio of 5:1 to 10:1 gives optimum results in the washer. It is very important not to overload the machines as this will result in reduced agitation of the garments in the bath causing streaks.

Cycle time/Dose Rate: The amount of enzyme use and the cycle time should give the level of abrasion desired in a reasonable amount of time and at a reasonable expense. The time needed of tumbling to obtain the desired looks depends on many factors, such as liquor ratio, type of washing machine, and the fabric construction of the garment. The abrasion cycle time can be reduced by using higher dosage of the cellulases, but only to a limited extent because the mechanical effect becomes the rate-limiting factor. Too high dosage reduces the strength of the garment and increases backstaining. Generally , at a given concentration longer cycle times result in greater backstaining. Normally a significant amount of backstaining occurs in the first 30 minutes of the abrasion cycle. At the end of the 90 minutes, the bachstaining will double over the first 30 minutes. It is also important to note that a medium concerntration of enzymes for 60 minutes.

Experiences have shown that the greater uniformity will be achieved through the use of low or medium levels of enzymes. If uniformity becomes a problem, the enzymes level could be reduced by 15% and accordingly the time should be increased by 5 to 10 minutes, until the desired uniformity is achieved.

Auxallaries related factors

Buffers: The most commonly used buffers are acetate, citrate, phosphate and carbonate. All these buffers perform the job well but each has different pH optimum ac acetate has an optimum of 4.8, citrate of 5.4, phosphate of 4.5 and 6.8, and carbonate of 7.2. The buffers are used on the basis of optimmum pH of the enzymes.

Surfactants: Surfactants play an interesting role in the application of Cellulase enzymes. Firstly, they act to remove the excess sizes that remain in the garments secondly, surfactants wet out the garment surfaces and permit the spectrum products to access and penetrate the fabric surface down to individual fibres. Thirdly, surfactants suspends the indigo dyes into the wash liquor which acts as anti redepositing agent thus giving garments with low backstaining. Fourthly, surfactants work as an emulsifiying agent which removes any oil and grease that may be present on garment surface.

The best surfactants for the use long with the cellulases are nonionic ethyoxylated alcohols as they provide a good weting ability without affecting the activity of the cellulases itself. In garment processing with spectrum series a small amount of nonionic surfactant can provide the desired effects. The non-ionic to be used can be one which have a Hydrophillic balance of 11 or more. In otherwords the nonionics, which have more than 12 mols of ethylene oxide. A dosage of 0.05g/It. to a maximum of 0.25gm/It. is sufficient