Excess carbon dioxide in the atmosphere has certainly become an environmental concern in recent years, but researchers from Germany’s Fraunhofer Institute for Environmental, Safety and Energy Technology are now experimenting with a process that uses CO2 to process plastic products in an environmentally-friendly fashion. They have discovered that by compressing the gas, it can be used to impregnate plastic objects with dyes, antibacterial compounds, or other substances. Traditionally, toxic solvents have been used for coloring plastic items.
The Fraunhofer team pump CO2 into a high-pressure container already containing the plastic parts and powdered pigment, then heat it to 30.1C (86.18F) and compress it to 73.8 bar. At this point, it goes into a supercritical state and takes on solvent-like properties. The team then continue to increase the pressure, until at 170 bar the pigment dissolves into the CO2, and then proceeds to diffuse into the plastic. The whole process only takes a few minutes, and while the gas itself escapes from the plastic afterward, the pigment stays in and cannot be wiped off.
The researchers have also successfully impregnated plastics with antibacterial nanoparticles, silica, and the anti-inflammatory active pharmaceutical ingredient flurbiprofen.
The process is said to work on partially crystalline and amorphous polymers (such as nylon and polycarbonate), but not on crystalline polymers. Unlike some traditional plastic impregnation technologies, it doesn’t cause dyes to change color, heat-sensitive substances (such as fire retardants or UV stabilizers) can be introduced, and the plastic comes nowhere near its melting point.