Study On Sorption And Mass Transfer Characteristics In Polymer With SCF

The technology of SCF assisted permeation brings new ideas to the traditional polymerprocessing techniques, which promotes many of them to development and innovation. Thesupercritical fluid dyeing (SFD) process is the typical application of that technology. Atpresent, there are a large amount of researches on the feasibility of SFD process. However, itis still necessary to descript the models of the phase equilibrium and mass transfer of thisprocess for providing the optimization design with theoretical basis.In this paper, the isothermal sorption curves and diffusion coefficients of supercriticalCO2 in polymers with the SCF were first measured. Then, the thermodynamic behaviors andmass transfer kinetics of the small molecules in polymer were preliminarily investigated,which would be the theoretical basis for industrializing this process for the future.Because the solubility of supercritical CO₂ in the polymers is very little, it has beendifficult to accurately measure the sorption amount of supercritical CO₂ in the polymers. Aftersummarizing the experimental techniques proposed by other scholars at home and abroad, anew set of equipments based on the principle of pressure decay were bulit to meaure thesorption amount of supercritical CO₂ in the polymers.By adding a comparison vessel themaximum operating pressure of the equipment can be up to 30MPa with enough precision andaccuracy.Isothermal sorption curve and the curve of sorption amount against the sorption time forsupercritical CO₂ in PET, PVC and PS were measured. According to that, the sorption amountand diffusion coefficients at different conditions can be calculated. The results show thattemperature has two counteractive effects on the sorption amount: (â…°) at the lowertemperatures, the increase of temperature will lead to the increase of the sorption amount; and(â…±) at the higher temperatures, the increase of temperature will suppress the increase of thesorption amount. The diffusion coefficient increases with the increase of the temperature. Thesorption amount increases at elevated pressure, but the changing trend of the diffusioncoefficient with the pressure is different at various range of temperatures, At the lowertemperatures, the diffusion coefficient increases first and then decreases at elevated pressure.However, at the higher temperatures, the diffusion coefficient increases with the increase ofpressure. The solubility of supercritical CO₂ in the polymers was predicted by the S-L lattice fluidmodel. The predicted values are in good agreement with the experiment datum.The maximumerror is less than 5%.At the last in this paper the "film roll method", which has been applied in water dyeingsystem, was used to evaluate the diffusion coefficient of dyes in polymers with supercriticalCO₂ environment. The results show that the "film roll method" can be successfully used inhigh pressure SFD technology. The effects of temperature and pressure were discussed...