The adsorption and diffusivity behavior of supercritical CO ₂ fluid in cellulose acetate fiber

The adsorption and diffusion behaviors of subcritical and supercritical CO ₂ (SCF-CO ₂ ) on cellulose diacetate (CDA) and cellulose triacetate (CTA) fibers were investigated using a magnetic suspension balance at temperatures of 40–100°C and pressures of 40–240 bar. The goal was to analyze the factors influencing the adsorption and diffusion behavior of SCF-CO ₂ in acetate fibers, aiming to enhance its application potential in dyeing and functional finishing processes. The real adsorption amount ( M _ra ) was calibrated by calculating the volume of CO ₂ adsorbed by cellulose acetate fibers (CAFs) using isothermal linear regression. It was found that M _ra decreases with increasing SCF-CO ₂ temperature but increases with pressure, remaining nearly constant at pressures above 120 bar. Below 80 bar, higher fluid temperatures result in higher CO ₂ diffusion rates into CAFs, whereas above 80 bar, lower fluid temperatures lead to faster diffusion rates. The value of M _ra of CO ₂ in CDA, which has a higher proportion of amorphous regions, is generally less than that in CTA, which has more carbonyl groups. The diffusion behavior of CO ₂ in CDA and CTA is similar at pressures of 40 bar and 80 bar across different temperatures. Under other pressure conditions, the diffusion rate of CO ₂ in CDA is slightly greater than that in CTA at 40°C, while at temperatures above 80°C and pressures above 120 bar, the diffusion rate in CDA becomes slightly less than that in CTA. These results provide a scientific basis for processing functional or dyed CAFs using SCF-CO ₂ technology.