S22 - Session O3 - Waterless dyeing with plant-based natural dyes as safe colorants

Authors: Harold Freeman, Riikka Räisänen *, Gisela Umbuzeiro

While plant-based natural dyes continue to be of interest in the coloration of various products, their low affinity for textile substrates has long limited their use in this arena. The coloration of textile fibers such as cotton, requires a mordant to bond these dyes to the fibers and employs water as the dyeing medium. Aqueous dyeing of textiles requires considerable quantities of water and substantial energy consumption for drying. The search for waterless dyeing technologies led to the use of liquid (supercritical) carbon dioxide as a medium for dyeing synthetic fibers with disperse dyes. The structural similarities between plant-based dyes and disperse dyes led us to explore textile dyeing with natural dyes in liquid carbon dioxide. In our initial studies, we found that anthraquinone dyes (e.g. Dermocybin and Emodin) extracted from macro fungi dyed polyester and nylon fibers in liquid carbon dioxide in 30 min at 4500 psi and 130 o C. We extended this work to plant extracts of madder, weld, lac, and logwood, and to carotenoids (e.g. beta-carotene and lycopene), all at 0.5n1.0% (w/w) shade depths. The best dye uptake levels were obtained using madder and logwood, while weld gave no dye uptake. To enhance color depths from weld, we treated the weld extract with amylase enzyme solution, to enhance solubility in carbon dioxide by cleaving off the glucose group(s). As anticipated, enzyme treatment led to a viable yellow shade on polyester at 1% (w/w). Regarding the carotenoids, preliminary results showed good dye uptake on polyester at 3500 psi and 110 o C, giving an especially vivid orange shade from lycopene at 1% (w/w). Coloristic data are reported in the full presentation, along with environmental data needed to ensure safe plant-based dyes for the market.