Eco-friendly practices on textile treatments are necessary so that our environment can be prevented from being polluted. There are the various amount of environment-friendly treatments like eco-friendly pre-treatments, eco-friendly dyeing, and eco-friendly finishing. Here we only focus on eco-friendly pre-treatments.
Alternate Eco-Friendly Pre-Treatments
For a textile material to be finally converted into a finished garment it has to undergo numerous amount of processes. Dyeing and finishing are very essential as they impart aesthetic appearance onto the fabric. But dyeing can’t be straight away done over the grey fabric. The fabric has to be prepared first then taken to dyeing process. The preparatory consists of processes like designing, scouring, bleaching and mercerization. All the preparatory process is done with water medium thereby the water is been polluted completely. So by following eco-friendly methods to accomplish these process helps us to reduce effluents.
Conventional desizing process either is done as acid desizing or oxidative desizing. This process helps in removing the size paste present on the fabric. But this may degrade the fabric and also has other problems that residual peroxide may remain, High pH due to caustic and high TDS.
Enzymatic desizing is where we use enzymes to do our desired desizing process. Most commonly used enzymes are amylase. There are two types of amylase α – Amylase and β-Amylase. α-Amylase hydrolyzes randomly and act on 1:4 bond of starch backbone whereas β-Amylase release maltoic units from chain ends of the starch polymer. α-Amylase is basically used for desizing. It is obtained from pancreas or malt extract. α-Amylase has two acidic amino acids such as aspartic acid and glutamic acid. It has also got basic amino residue e.g. Histidine. Hence the action of enzyme evolves both acidic/Basic hydrolysis of starch. α-Amylase can be activated by Ca+2 ions and hence perform well in hard water.
The desizing enzymes are available in various forms which can act right from room temperature (longer period) in batch form to high temperature for continuous desizing. Enzymatic desizing carried out with pad-batch method, first pad the fabric with 50gpl enzyme pH 6-7then batch for 20-24 hours at room temperature and finally carry out washing in Jigger. It can also be carried in exhaust method in jigger method by having enzyme concentration – 5%, Wetting agent – 1%, pH 6-7% and carry out desizing at temperature 600C for 1 hour followed by washing.
Scouring is the process where we remove oil and waxes present in the outer layer of the cotton so that the absorbency property can be enhanced. The conventional method is done by Alkali scouring where 3-4% caustic soda is used at high temperature (90-950C) for long duration (2-3hours). It damages the fibre, the requirement of water is more.
Enzymes used for bio-scouring are pectinase for pectins removal, process for removal of proteins, lipase for removal of oils & Fats or waxes. The combination of 2 or 3 enzymes may be used to get the synergistic effect. Enzymatic scouring can be carried out with the exhaust as well as continuous method. In exhaust method enzymes – 1%, wetting agent – 0.5%, temperature – 50-60C and the process is carried in jigger machine for 1 hour. Continuous Method is carried by first padding with 10-15 gpl enzyme solution + wetting agent followed by steaming at 1000C for 2-3 minutes. An advantage of bio-scouring is that it requires less energy and time and also less weight loss with good absorbency.
Enzymatic degumming of silk
Silk consist of two fibroin filaments held together by connecting layer of sericin. Fibroin = 75% wt and Sericin = 25% wt in raw silk and both are proteins. Degumming is the removal of sericin layer prior to dyeing/printing or finishing to get bright/lustrous fabric.
Conventional Process of degumming alkaline soaping at pH 10-11 at 90-95C for 1 hours.
Enzymatic degumming is carried out with proteolytic enzymes. Degumming is carried out at 60C at pH 8 for 1 hour. Degumming is carried out at yarn stage if yarn dyeing is to be done. If it is fabric dyeing then sericin in filament yarn work as size in weaving and then degumming is done at fabric stage. The degumming waste liquor is rich in sericin content and is being used as raw material for the production of sericin powder in the cosmetic industry as the moisturizer in hair care products.
Enzymatic peroxide bleaching
Bleaching of cellulosic material with enzymes not possible. The enzyme can only be used for quicker decomposition of residual H2O2 on fabric. After H2O2bleaching, if residual peroxide is not removed and dyeing is done in the same bath, it will result in the reduction in colour yield (drop in depth of shade). Hence the fabric needs to be washed several times before dyeing, resulting in high water consumption. Hence enzymes are used to decompose residual H2O2.
The enzyme used is catalase. The procedure for H2O2 bath clean up first drain the bleaching liquor then fill with fresh water and adjust pH for dyeing. Add 1gpl catalase enzyme and check H2O2% in the bath after 10 min and then start dyeing in same liquor. The rinsing is not required, when the enzyme is used as all H2O2 has broken down and the residual enzyme has no effect on dyestuff. The various advantages of the use of catalase are that no need of heating and no rinsing of peroxide bath.
Thus various methods of eco-friendly pre-treatments were discussed above which have very minimal effect on the environment. Even though these methodologies are eco-friendly the only drawback is that these methodologies are costly.