Colouring Plastics

At a temperature of 30.1^oC and a pressure of about 73.8 bar, carbon dioxide goes into a super critical state that gives the gas solvent-like properties. In this state it can be introduced into polymers, acting as a "carrier" in which dyes, additives, medical compounds and other compounds can be dissolved:

• liquid carbon dioxide is pumped into a high-pressure container with the plastic components to be impregnated
• temperature and pressure are increased steadily until carbon dioxide reaches its supercritical state
• pressure increased to 170bar and the powdered pigment dissolves completely
• the dissolved pigment diffuses with the carbon dioxide gas into the plastic
• high-pressure container is opened, the carbon dioxide gas escapes but the pigment remains attached to the polymer

Tests have shown that nanoparticles of antibacterial agents can be impregnated into polycarbonate and that E-coli bacteria placed on the surface will be killed. Tests conducted with silica and with the anti-inflammatory active pharmaceutical ingredient flurbiprofen were also successful.

The process is suitable for use with amorphous or partially crystalline polymers such as nylon and polycarbonate, but cannot be applied to crystalline polymers.

Reference
Fraunhofer-Gesellschaft (2011, January 4). Impregnating plastics with carbon dioxide. ScienceDaily. Retrieved January 10, 2011, from http://www.sciencedaily.com­ /releases/2011/01/110103110206.htm

Further Reading
Temperature Conversions
Chemical and Physical Changes
Lewis Structures
Molecule Polarity
Intermolecular Forces
Ideal Gas Law

Study Questions:

1. Convert the information provided in the dot points in the article into a flow chart.
   
2. Give the molecular formula for carbon dioxide.
3. Draw a Lewis Structure (electron dot diagram) for carbon dioxide.
4. Is carbon dioxide a polar or non-polar molecule? Explain your answer
5. What type of solvents would be the best to use to dissolve carbon dioxide?
6. What type of solutes do you expect to dissolve in carbon dioxide? Explain your answer.
7. Given that 1bar is equivalent to 100kPa, convert the following pressures in bars to pressures in atmospheres:
   
   • 73.8bar
   • 170bar
8. At 25^oC and 1 atmosphere pressure, 1 mole of gas has a volume to 24.47L. Assuming ideal gas behaviour, what volume would this gas occupy at 30.1^oC and 73.8bar?
9. Calculate the volume of gas above at the same temperature but at a pressure of 170bar.
10. Calculate the volume per molecule of carbon dioxide gas in question in 9.
11. Do you think it is reasonable to assume ideal gas behaviour at this temperature and pressure? Explain your answer.
12. What do you think the term "supercritical state" as used in this article might mean?