Application of different concentrations of the natural dye potassium norbixinate (annatto) in polyamide 6.6 fabrics.

Polyamide fabrics were dyed with concentrations ranging from 4% to 0.25% (o.w.f.) of the natural dye, potassium norbixinate (annatto). The exhaustion, chromatic coordinates, colouristic intensity (K/S), and fastness to washing and rubbing were evaluated. The natural dye was characterised, and its maximum absorption peaks were identified at 452 nm and 482 nm through UV-vis scanning. Its main chemical groups were identified by FTIR-ATR. All dyeings exhibited high exhaustion percentage, with a maximum of 98.4% for 1% dye concentration. The dyed samples displayed visually appealing orange hues, with a maximum K/S value of 6.9. Most of the fastness test results were rated between 5 and 4/5, remaining within the standards established by most textile industries. Potassium norbixinate exhibited a similar tinctorial behaviour to synthetic acid dyes for polyamide, suggesting ionic chemical reaction interaction between dye and polyamide, highlighting the potential use in the textile industry.