An optimized sol-gel process for dyeing cotton fabrics with organic dyes

An optimized sol-gel process was developed to dye cotton fabric with organic dyes. Several model dyes were synthesized and characterized, and then used to prepare the corresponding sol-gel solutions on basis of the n-propyltriethoxysilane (nPTES) precursor. These solutions were applied to the fabric via the pad-dry-cure method. The affinity of the dyes toward the fabric was evaluated by measuring their uptake from the dye bath, which was found to vary between 3% and 16% depending on the molecular structure of the dye. Furthermore, four dyeing parameters were studied with respect to their effect on (i) the exhaustion of the dye bath using UV-visible spectroscopy, and (ii) on the obtained nuance of the textile employing colorimetric (Datacolor) and diffuse-reflectance spectroscopy. The process parameters are dyeing temperature, dye concentration, impregnation time, and the number of dyeing cycles. Our results showed the transfer of dye from bath to textile depends only weakly on temperature, and below 40°C the transfer reaches an optimum. Also, the dye transfer is rapid, where already after 1 minute, the color strength on the textile is close to the plateau value. However, residual dye uptake from the bath continues for up to 2 hours. Further intensification of the textile coloration requires the deposition of additional sol-gel layers or an increase in the dye bath concentration. On basis of these results, the optimal conditions of dyeing by this process were proposed.