Carbon dioxide is present in the air at over 400ppm. Familiarly, it is also dissolved in beer. It is a gas at room temperature, but by pressurizing it, it can be liquefied even near room temperature and used as a solvent. Carbon dioxide is widely used as an extraction solvent for functional components. Recently, there have been examples of using supercritical carbon dioxide for anhydrous dyeing of polo shirts. The features and merits of supercritical carbon dioxide treatment are as follows.
Solvent
Easy solvent removal after treatment
Room temperature treatment
- Processing of food and heat sensitive materials
Physical properties can be controlled
- Variable density (generation of fine particles)
- Variable dielectric constant
- Variable solubility
- Low surface tension (no gas-liquid boundary)
Both gaseous and liquid characteristics
- Low molecular weight, low viscosity
- Low surface tension (surface tension free drying)
- High diffusion/high permeability (CVD)
- High heat flux (supercritical plasma)
Others
- Density fluctuation and clustering
- Multipole moment (chemical interaction of polymer chains, plasticizing effect)
