Chitosan pre‐ and post‐treatments for improving the fastness and UV protection of wool fabrics dyed with Datisca cannabina L . via sonication

This study investigates the influence of chitosan pre‐ and post‐treatments on the fastness properties and ultraviolet protection of wool fabrics dyed using an ultrasonic‐assisted process with a natural dye extracted from hemp ( Datisca cannabina L.). Dyeing was performed under pre‐ and simultaneous mordanting conditions with varying alum concentrations. Chitosan was applied either before or after dyeing to enable a systematic comparison of treatment routes. Dye composition was analysed by HPLC‐DAD, while structural characteristics were examined using FTIR spectroscopy. Colour properties were evaluated in the CIELab system, and colour strength (K/S) values were determined. Fastness properties, including washing, rubbing, light and saliva resistance, together with ultraviolet protection factor (UPF), were assessed according to relevant standards. The results indicate that chitosan post‐treatment provides superior performance compared to pre‐treatment, significantly enhancing dye uptake, colour strength and overall fastness behaviour. UPF performance was strongly dependent on mordant concentration and treatment stage. The combined approach improved colour durability and functional performance, demonstrating the effectiveness of integrating ultrasonic‐assisted natural dyeing with bio‐based finishing strategies.