Cationization of cotton is emerging as an effective tool to solve the environmental problem associated with dyeing of cotton with anionic dyes between normal or existing method of reactive dyeing of cotton with the use of cationizing agents like "X" chemical and "DICHLORO ETHANE" "along with "METHYLAMINE" to dye cotton without alkali and salt i.e. "FREE SALT DYEING". The effect of cationization on colour strength and colour fastness of various reactive dyes was found and cationization show lighter increase in light shades and lesser increase in dark shade than normal cotton dyeing. The impact on the environmental pollution and the dyed fabric quality were ascertained and compared with existing dyeing system and the cationization gives very less environmental pollution. The cationized cotton show similar kind of fabric quality as like normal dyeing of cotton. Cationization of cotton was found to be cheaper than the normal dyeing process.
The fibre reactive dyes are known as the best for cotton for its wide range of application and better fastness properties. However, all the reactive dyeing systems require huge amount of electrolyte and alkali to exhaust and fix the dye respectively.
These electrolytes are neither exhausted nor destroyed and hence remain in the dye bath after dyeing. All the above, only 60-65% dye utilization is attainable even with the use of salt in the normal dyeing systems.
When alkalinity is introduced in the bath in order to facilitate the formation of covalent bond between the fibre and the functional groups of the reactive dye, the abundance of hydroxyl ions causes significant hydrolysis of reactive dyes. Those hydrolyzed dyes are called "Dead" dyes as they have no affinity towards cotton and hence remains in the dye bath, deposition of the same on the fibre significantly lower the fastness properties, that calls on severe wash-offs.
Reactive dyeing thus pollutes the environment by discharging highly colored reactive dye bath and higher electrolyte concentration.
The author is an Asst. Professor with Dept. of Textile Chemistry of MLV Textile & Engg. College in Bhilwara, Rajasthan.
Originally Published in Textile Review, January-2012