Carbon dioxide as a filler for plastic

We have all heard that carbon dioxide is responsible for global warming. However, this gas also has several advantages. Researchers have now succeeded in infusing compressed carbon dioxide into plastic using a new process that could lead to the development of diverse applications ranging from colored contact lenses to bacteria-resistant doorknobs.

Carbon dioxide is more than just a byproduct. In fact, it has multiple uses: the chemical industry uses this colorless gas to produce urea, methanol and salicylic acid. Urea is used as a fertilizer, methanol is a fuel additive and salicylic acid is a starting material for the preparation of the drug aspirin.

Researchers from Oberhausen University in Germany are trying to promote their new idea that explores the possibility of injecting carbon dioxide into plastic. At a temperature of 30.1 degrees Celsius and a pressure of 73.8 bar, carbon dioxide goes into a special aggregation state (The term in Wikipedia, supercritical state) which gives the gas properties that make it solvent-like. In this state it can be injected into polymers, or used as a carrier in which dyes, additives, medical compounds and other substances can be dissolved.

"We introduced carbon dioxide into a high-pressure container containing the plastic components and then gradually increased the temperature and pressure until the gas reached its liquid state. At this point we further increased the pressure. At a pressure of 170 bar, a powdered dye completely dissolved in the carbon The dioxide and then enters the plastic itself. The whole process lasts only a few minutes. When the container is opened, the gas is released from the surface of the polymer, but the dye remains inside the plastic without being able to be released from it," explains Manfred Renner, one of the researchers.

In laboratory experiments, the researchers were even able to inject nanoparticles with antibacterial properties into polycarbonate plastic. Escherichia coli bacteria, which were established on the surface of the plastic, were completely destroyed - an important ability that could be applied to door handles containing the same nanoparticles. Experiments conducted for silica and for an anti-inflammatory pharmaceutical substance (flurbiprofen) were also successful.

"Our process is suitable for partially crystalline and amorphous polymers such as nylon, polycarbonate, TPE (Thermoplastic elastomers), TPU (Thermoplastic polyurethanes) and PP (Polypropylene)," notes the researcher, "However, it is not suitable for fully crystalline polymers."

The process has tremendous potential due to the fact that carbon dioxide is non-flammable, non-toxic and cheap. Although it exhibits solvent-like properties it lacks the harmful health and environmental effects of the solvents used in industry today. Normal processes for introducing defined materials into plastic and the possibility of giving them new and desirable properties have several disadvantages. Injection molding, for example, does not allow the introduction of heat-sensitive materials such as flame retardants or ultraviolet stabilizers. Many dyes change color over time.

"Our method makes it possible to provide important customized plastic components as well as convenience products such as covers for mobile phones. The most important feature of our method lies in the fact that the dye, additive or active substance is inserted into the layers near the surface of the plastic at temperatures that are well below the melting point of the plastic, in an environmentally friendly way and without any need for strong solvents," adds the lead researcher.

The process could, for example, be used for coloring contact lenses and even to enrich them with pharmaceutical compounds that will be slowly released into the eye during the day - an alternative to the repeated dripping of eye drops in the treatment of glaucoma. The researchers note that this insertion method is suitable for a wide variety of new applications.

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