| Water is increasingly being recognized as a valuable raw material, the availability of which is not unlimited, and must be protected by appropriate legal measures. Up to the present day, the dyeing of textiles depends on water as solvent or as transport medium for the dyestuffs. Take synthetic fibers as an example, polyester fabrics, which are dyed with disperse dyes, require chemical auxiliaries such as surfactants, dispersing agents, etc., in the aqueous dye liquor, owing to the low solubility of dyes in water. However, these auxiliaries and unused dyestuffs still remain in the dyeing liquor after dyeing, and cause pollution. The waste water problem is, therefore, one of the most urgent issues of the textile finishing industry.This is where the idea of dyeing in supercritical carbon dioxide comes from. Dyeing with supercritical carbon dioxide was developed to completely avoid the use of water during dyeing, thus creating no pollution. This novel technique offers many additional advantages including: complete elimination of water pollution; energy savings in drying textiles; a high degree of dye levelness and exhaustion; any residual dyestuff is easily recovered; dyeing in supercritical system requires shorter time; for PET, no aftertreatment such as reductive washing is required; carbon dioxide is nontoxic and easily obtained, and it can easily be recycled in a dyeing process.A set of dynamic supercritical carbon dioxide dyeing equipment was successfully designed and constructed in this lab.The effect of variables, such as temperature, pressure, dyeing time etc, to the uptake (measured as K/S) of PET fabrics was studied. It was foundthat after the dyeing temperature reached 110℃, the dye uptake increased significantly, and it increased initially on increasing the pressure to 20 MPa, but increased very slowly after 20 MPa. The dye uptake approach equilibrium after dyeing 60min in supercritical carbon dioxide at 120~130℃ with C.I. Disperse Blue 79, the fastness of the dyed PET fabric was very good. Supercritical CO2 dyeing had no significant influence to the strength of PET fabric.The diffusion model of the dyes to PET fabric in supercritical CO2 was obtained. The diffusion coefficient and the activation energy of the dye in PET fabric in supercritical CO2 and water were discussed respectively (the activation energy of the dye in PET fabric in supercritical CO2 was 67.47J/mol and that of the dye in PET fabric in water was 187.02J/mol),The PET fabrics and the dyes were treated under model supercritical CO2 dyeing conditions. X-ray diffraction, differential scanning calorimetry, Scanning electron microscopy, infrared spectrum and so on were used to characterize fiber and dyes morphology, properties and structure. It could be concluded that the chemical structure of the PET fiber was not influenced by supercritical CO2, the crystalline forms of the dye and PET fiber did not change. However, the crystallinities of the dye and the fiber were affected by treatment conditions in supercritical CO2, the melting temperature of the dye increased on increasing the pressure and temperature and the melting temperature of PET fabric had not any changes on the whole.
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