Evaluation of Dyeing and UV Protective Properties on Hemp Fabric of Aqueous Extracts from Vegetal Matrices of Different Origin

Clothes are one of the most effective measures to minimize health hazards due to the current levels of UV radiation on the earth's surface. Fabrics made of natural fibers and dyed with natural pigments are an excellent means to reduce UV exposure. In this study, the UV protection properties were tested on a vegetal fiber fabric (hemp) dyed with water extracts from madder, chestnut, onion, inula, and logwood, at three increasing concentrations. Dyeing extracts were obtained from different sources: agro-food industry residues (chestnut and onion), spontaneous (inula), and commercial dyeing plants (madder and logwood). The quantitative characterization of water dye extracts was performed to evaluate the amount of dye in pre- and post-dyeing solutions as well as the dye fastened to the fabric. The percentage values of dye fastened to the fabric, in relation to the plant dry weight, were relatively low for all the considered species. The fabric Ultraviolet Protection Factor (UPF) was evaluated using both a laboratory spectrophotometer and a spectroradiometer in outdoor conditions. A progressive increase in UPF with the increase of the dye-bath concentration was shown. Chestnut and onion, reaching the minimum protection level (UPF=15) at the highest dye-bath concentration, can be considered the most effective. The UPF persistence of the fabrics was also evaluated after sun exposure and repeated washing. Colors and UV protective properties obtained by the dyeing procedure tested in this research can provide added value to hemp fabric and meet the demands of an expanding "eco-friendly" market.