Advances in Materials

CO2: In Plastics, Not the Atmosphere
Carbon dioxide (CO2) is best associated with the havoc it’s possibly wreaking on the ozone layer, so it may seem unusual that researchers at the Fraunhofer Institute for Environmental, Safety and Energy Technology UMSICHT (fraunhofer.de) have developed a process for embedding compressed CO2 into plastic parts. But there’s no need to alert Al Gore, because when it’s in a solvent-like state, CO2 can impart several positive attributes, such as non-flammability.

Here’s how the CO² impregnation is done:
• CO2 is pumped into a high-pressure container with plastic components.
• Temperature and pressure are gradually increased until the chamber reaches 30.1º C and 73.8 bar—the conditions that give CO2 solvent-like properties.
• Pressure is further increased. “At 170 bar, pigment in powder form dissolves completely in the CO2 and then diffuses with the gas into the plastic,” explains Fraunhofer scientist Manfred Renner.
Successful tests have been carried out with nylon, thermoplastic elastomers and polyurethanes, polypropylenes, and polycarbonates. The process is both quick and inexpensive.
Researchers have also found that CO2 can act as a carrier: dyes, additives, medical compounds, or other substances can be dissolved within it. “Our process allows us to customize high-value plastic components and lifestyle products,” Renner says. Potential applications range from contact lenses embedded with medicine to treat glaucoma to antibacterial door handles.

Fraunhofer researchers have developed a process that embeds CO² into plastics.

High-Strength Metallic Glass
Is it possible to engineer a glass that’s stronger than steel? If you ask researchers at the U.S. Department of Energy Lawrence Berkeley National Laboratory (lbl.gov) and the California Institute of Technology (caltech.edu), the answer is not only “yes,” but they’ll go on to claim their new damage-tolerant metallic glass is stronger and tougher than “any known material.” According to Berkeley materials scientist Robert Ritchie, strength, or material hardness, and toughness, or resistance to fracture, are typically mutually exclusive properties. For instance, hard materials are more prone to fracture than soft materials. To achieve both strength and toughness, researchers embedded a palladium-based microalloy into glass to counteract its brittle characteristics. The microalloy provides a plastic-like state to the glass, which causes it to bend, rather than break, in response to stress. Presently, the material can only be manufactured up to 6 mm thick. Applications include medical implants and orthodontics.

Self-healing Synthetics

Those sometimes tasty bivalves known as mussels generate a self-healing sticky material that allows them to stick to rocks and repair tears in their body tissue. It may seem like an unusual material to replicate, but scientists at the University of Chicago (uchicago.edu) have developed a synthetic version that could be used as an adhesive or coating in applications ranging from underwater machinery to medical implants. To create it, they developed a polymer consisting of long chains of molecules. Adding iron chloride and sodium hydroxide gives the material its gel-like, self-healing property and allows the scientists to adjust the material’s strength.

Scientists at the University of Chicago have developed a self-healing sticky gel similar to that generated by mussels.