Pitting inhibition in fiber dyeing solutions by two oxyanions

Pitting inhibition efficiency of SO₄⁻ and NO₃⁻ on AISI 316L stainless steel in contact with Cl⁻-containing fiber dyeing solutions together with the influence of the anions on absorption behavior of the solutions were investigated. The purpose of the study is to experimentally determine an optimized dyeing solution efficient on both – inhibition of the steel’s pitting and exhaustion of the dyes dissolved.

Methods such as electrochemical cyclic polarization, UV-visible range spectrophotometry and scanning electron microscopy have been used to assess the performance of two inhibitors on both pitting inhibition of the steel and dissolving ability over the reactive dyes. To find out a promising dyeing solution mixture in both aspects, Cl content of the original dyeing solution was replaced gradually with the inhibiting anions, where the total anionic content was kept constant to unchange the dye exhaustion potential of the solution. Then, those solutions came out with diverse pitting inhibition, and dye absorption levels were compared together for reducing/avoiding the pitting issues of the reactive dyeing vessels of the industry.

Rather high absorption levels detected by visible range spectrophotometry on the solutions showing sound inhibition levels indicated possibility of unaltered reactive dyeing qualities with an enhanced vessel lifetime as the inhibitive anions replace Cl⁻. Nitrate performed better than sulfate both on inhibition and absorption in the dyeing solutions. Also, 316L vessels became open to an extra anodic protection in inhibitor added solutions.

The findings are valid for a certain group of reactive dyes and dyeing solutions held at 70°C. However, the testing methods are available to almost any dyeing solution and dyeing temperature.

The work presents a combined testing of pitting inhibition and absorption behavior of dyeing solutions involving Cl⁻ that has not been reported so far. It shows that solution recipes least harmful to the steel vessels can be outlined for various reactive or other types of dye groups.