Study of the dyeing properties of saffron and ultrafiltrated saffron powders,as colourants for natural and synthetic fibres

There is a noticeable growing interest in the use of natural dyes in contemporary textile dyeing, motivated by the requirements imposed, in favour of environmental prosperity. The use of natural dyes reduces significantly both the energy requirements and the environmental impact of the process. In the present work natural and synthetic fibres were dyed with the dyestuff isolated from Crocus sativus L., after aqueous extraction of the dried stigmas of the plant. Additionally, part of the powder was purified by using ultrafiltration technology. The saffron extract and the ultrafiltrated saffron retentate were used to dye cotton, wool, nylon and polyester, in various depths of shade and temperatures. Both saffron and ultrafiltrated saffron successfully dyed not only the natural substrates, but also the synthetic ones, while higher dyeing temperatures produced level dyeing with all substrates used. Ultrafiltrated saffron powder produced brighter and much stronger dyeing to the original saffron powder, due to the elimination of extraction by-products. Isothermal adsorptions for both colourants were performed on all substrates in order to investigate their adsorption mechanism. It was found that saffron and ultrafiltrated saffron follow a Freundlich-type adsorption isotherm on cotton, wool and nylon which is a typical mechanism for a planar-directed dye of big molecular weight. Nernst-type adsorption was found to occur on polyester which again is typical for the adsorption of disperse dyes on polyester. Thus, saffron can be claimed as a universal dye, able to successfully dye natural and synthetic substrates.