Researchers fill plastics with compressed carbon dioxide

At a temperature of 30.1°C and a pressure of 73.8 bar, CO₂ goes into a supercritical state that gives the gas solvent-like properties. In this state, it can be introduced into polymers, or act as a ’carrier’ in which dyes, additives, medical compounds and other substances can be dissolved.

In the process developed by the Fraunhofer researchers, liquid carbon dioxide is first pumped into a high-pressure container with the plastic components that are to be impregnated, then the temperature and the pressure are increased until the gas reaches the supercritical state.

When that state is reached, the pressure is increased further and, at 170 bar, pigment in powder form dissolves completely in the CO₂ and then diffuses with the gas into the plastic. When the container is opened, the gas escapes through the surface of the polymer but the pigment stays behind.

In tests, the researchers have used the system to impregnate polycarbonate with nanoparticles that give it antibacterial properties. E.coli bacteria, placed on the plastic’s surface in the institute’s own high-pressure laboratory, were killed off completely. Tests conducted with silica and with the anti-inflammatory active pharmaceutical ingredient flurbiprofen were also successful.