**3. Solubility of functional agents in scCO2**

The most important property for the design of processes in scCO2 medium is the solubility of the compounds in scCO2 fluid. For this reason, solubility data of many compounds including dyes are available in the literature [12–14]. The properties of the compounds such as molecular structure, size, and polarity are the main factors determining their solubility in scCO2 solvent. The solvent character of scCO2 is very much like a hydrocarbon solvent such as n-hexane [15], in which polar compounds are poorly soluble and nonpolar molecules such as disperse dyes have relatively higher solubility [16, 17]. To improve the solubility, polar co-solvents (also called entrainer or modifier), such as acetone or alcohols, are usually added to the scCO2 bath. Furthermore, the solvent power of scCO2 is a function of its density, and this density can be fine-tuned by changing the pressure and temperature of the system [18]. Disperse dyes are among the most investigated compounds, owing to acceptable solubility and suitable molecular size for dyeing polyester and other synthetic fibers in scCO2 [13]. However, the solubility data of functional finishing agents commonly used for textile finishing are still scarce in the literature. According to reports, several non-ionic, low molecular mass organic materials are soluble in scCO2, but only two classes of polymeric materials such as fluoropolymers and silicones showed appreciable solubility in scCO2 at a readily accessible temperature and pressure [19]. Thus, future research should focus on studying the solubility of functional compounds in scCO2.
