# Green-Dyeing Processes of Plant and Animal Fibers Using Folium, an Ancient Natural Dye
###### Abstract  
In recent decades, fabric-dyeing processes involved greener processes because, since ancient times, dyes used mordants based on metals to make the color better adhere to the textile fibers, but this is the reason for their increased pollution. To develop new strategies, attention was focused on finding the best condition for a dyeing method for natural fibers of vegetable and animal origin (cotton and wool) using an ancient natural dye known as folium. Folium was used mostly in miniature painting in an attempt to avoid the use of classical mordants and solvents. To this purpose, plasma treatment and chitosan coating were employed. Firstly, the textile fibers were analyzed through infrared spectroscopies to verify surface modifications; subsequently, the post-treatment morphological variations were observed via scanning electron microscopy. Both techniques highlighted a significant variation of the surface functional groups due to plasma treatments with He-O\({}_{2}\) mixtures, which allowed a greater adhesion of chitosan on the fiber's surface. Finally, the color strength of samples dyed with folium was tested through fiber optic reflectance spectroscopy, and the folium absorbance peaks were still detected after fabric washing. It is thus shown how an ancient, traditional raw matter has become relevant for developing new modern technologies. dyeing process; natural dye; folium; natural fibers; chitosan mordant; plasma treatment; spectroscopic characterizations; scanning electron microscopy; fiber optic reflectance spectroscopy 20242 However, if compared to synthetic dyes, natural dyes present several problems in the dyeing stage, such as lower fiber-affinity of the dye, the need for pre-treatments of the textiles, lower color strength, and chromatic range [3; 5; 7]. To overcome these issues, plasma treatment and chitosan coating were chosen for this study. Plasma is ionized gas consisting of ions, electrons, photons, and other chemical species able to roughen the substrate surface without the need for any wetting process [9; 10]. Furthermore, plasma modifies and functionalities the fiber surface without altering the bulk properties; this seems to increase the dyeability and wettability of the textile, as well as color fastness [9; 10; 11]. Plasma based on He or a He and O\({}_{2}\) mixture (He-O\({}_{2}\)) allows for the formation of binding sites for chitosan molecules. Chitosan is a polysaccharide which bears positive charges (e.g., NH\({}_{3}\)+) at low pH; because of this characteristic, it can be easily protonated in the presence of acids such as lactic acid, formic acid, acetic acid, malic acid, and citric acid [12; 13]. Upon plasma-treatment, chitosan coatings can interact with its cationic components onto the fiber, thus increasing their affinity for anionic dyes. With the aim of finding a natural, more sustainable material, in this study, the dye known as folium was used; it is a purple dye extracted from the fruits of _Chrozophora tinctoria_ (L.[PERSON], a plant of the Euphorbiaceae family, common in geographic areas with mild and dry climates such as Southern Europe or Near- and Middle East Asia. The plant has been known since antiquity; [PERSON], in his _Naturalis historia_[14], mentions it as _Heliotropium tricoccum_. The dye is extracted from the trilobate fruits of _Chrozophora_, more specifically from the external cucticles that envelope the seed [15; 16], by means of simple extraction in water. The color of the external cuticle changes depending on the ripening stage; in fact, it gradually shifts from green to blue and finally to purple color. Therefore, different hues can be obtained from the fruits, even if the final stage of ripening, being the purple fruits, generate a stable color, while the other colors are not stable.