Valorization of natural dye extracted from date palm pits (Phoenix dactylifera) for dyeing of cotton fabric. Part 2: Optimization of dyeing process and improvement of colorfastness with biological mordants

This paper investigates the feasibility of dyeing cotton fibers with solution extracted from date pits which are abundant vegetal material. The extraction step and its optimization were conducted in the first part of this paper. This second part studies the influence of the main dyeing conditions on the color yield K/S and the CIELab coordinates. The studied parameters are pH of the dye bath, temperature and duration of dyeing. Experiments were carried out using Box-Behnken experimental design to be able to analyze the main effects of each parameter, to detect interactions between these parameters and to deduce optimum conditions for dyeing process. The fastness properties of dyed samples were also evaluated. Obtained results indicate interesting sweat, washing and rubbing fastness in the range of 4-5. Three metallic mordants (Alun, ZnSO4 and CuSO4) and three biological mordants (gall nuts, chlorophyll (a) and green almond shell) were used to improve the degree of absorption as well as the color fastness of cotton fabrics dyed with aqueous extract from date pits. The obtained results showed high improvement of fastness (sweat, friction, washing and light fastness) for biological mordants than the metallic ones.