A plastic part colored using the CO2 impregnation process
(Photo: Fraunhofer)
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.
The CO2 itself is non-flammable, non-toxic and inexpensive.
While the
Fraunhofer process doesn’t capture carbon dioxide,
there are
experimental plastic production systems that do – perhaps
the escaped gases from the one could find their way into the
other.
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