Low temperature dyeing of nylon 6,6 by shift-in-pH method

Dyeing of nylon 6,6 has been commenced with different commercial acid dyes at an initial pH value of 11 to 8 using required amount of caustic soda and the pH is reduced as the dyeing proceeds by the gradual addition of sulphuric acid. This shift-in-pH method gives full exhaustion of acid dyes with Nylon 6,6 at 60°C in 40-45 min and also shows higher uptake of dyes in comparison to that of conventional method of dyeing at 95°C for I h in acidic pH (4.3). The degree of sulphonate groups in the dye structure is employed to describe the phenomenon of dyeing with acid dyes. There is practically no loss in tenacity of dyed nylon in comparison to that of the fibre dyed by the conventional method. The advantages with the modified method are saving in process time, energy and labour. The shift-in-pH method also reduces effluent pollution through the use of NaOH and H 2 SO 4 instead of acetic acid or phosphate buffer as in temperature -controlled process.