Methods of Improvement of Dyeability of Wool with Natural Dyes

Nowadays, Due to the environmental pollution associated with synthetic dyes, the attention to the application of natural dyes in the textile industry is growing. Natural dyes are environmentally friendly and possess some advantages and disadvantages in comparison with synthetic dyes. One of the main drawbacks of natural dyes is the low exhaustion of textile fibers. To improve the dyeing of textiles with natural colorants, several methods, including metal mordanting, bio-mordanting, treatment with nano-clay, ultrasound, microwave, plasma, ultraviolet, and enzyme, besides the attachment of chitosan, cyclodextrins, and dendrimers to the fibers have been employed. Due to the toxicity of the majority of metallic mordants, the use of bio-mordants and surface modification of fibers by physical and chemical methods are considered as alternative strategies for promoting the natural dyeing of wool fibers. These methods usually improve the sorption of natural dyes by wool fibers and improve the fastness properties of the dyed fibers in most cases. In this paper, the different methods employed to enhance the dyeing of wool fibers with natural dyes are discussed and summarized.