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Epoxy resins are robust and versatile polymers. Together with glass or carbon fibers, they’re used, for instance, to fabricate elements for plane, vehicles, trains, ships and wind generators. Such epoxy-based fiber-reinforced polymers have wonderful mechanical and thermal properties and are a lot lighter than steel. Their weak point: They aren’t recyclable — at the least not but.
Now Empa researchers led by Sabyasachi Gaan at Empa’s Superior Fibers laboratory have developed an epoxy resin-based plastic that’s totally recyclable, repairable and in addition flame retardant — all whereas retaining the favorable thermomechanical properties of epoxy resins. They’ve printed their findings within the Chemical Engineering Journal.
Recycling epoxy resins is something however trivial, as a result of these plastics are so-called thermosets. In this sort of polymer, the polymer chains are intently crosslinked. These chemical crosslinks make melting inconceivable. As soon as the plastic has hardened, it will probably now not be reshaped.
This isn’t the case for thermoplasts, akin to PET or polyolefins. Their polymer chains lie shut collectively however are usually not chemically linked to one another. When heated, these polymers might be melted and fashioned into new shapes. Nevertheless, due to the shortage of crosslinks, their mechanical properties at elevated temperatures are usually not so good as these of thermosets.
A brand new form of polymer
The distinctive epoxy resin that the Empa researchers have developed in collaboration with nationwide and worldwide companions is technically a thermoset — however not like different thermosets, it may be reshaped like a thermoplast. The bottom line is the addition of a really particular practical molecule from the category of phosphonate esters into the brand new resin matrix. “We initially synthesized this molecule as a flame retardant,” says co-inventor of this know-how and Empa scientist Wenyu Wu Klingler. Nevertheless, the bond the molecule types with the polymer chains of the epoxy resin is dynamic and might be damaged beneath sure circumstances. This loosens the crosslinking of the polymer chains in order that they are often melted and reshaped.
Such supplies, also called vitrimers, have solely been recognized for about ten years and are thought of notably promising. “Right this moment, fiber-reinforced composites are usually not recyclable in any respect, besides beneath very harsh circumstances, which injury the recovered fibers,” explains Wu Klingler. “As soon as they’ve reached the tip of their service life, they’re incinerated or disposed of in landfills. With our plastic, it could be attainable for the primary time to carry them again into circulation once more.”
“Our imaginative and prescient for the long run,” provides group chief Sabyasachi Gaan, “is a composite materials, through which each the fibers and the plastic matrix might be utterly separated and reused.” The researcher sees a chance in carbon-fiber-reinforced plastics specifically, as they’re generally used within the building of airplanes, trains, boats, vehicles, bicycles and extra. “The manufacturing of carbon fibers requires a variety of power and releases an infinite quantity of CO2,” he explains. “If we may recycle them, their environmental footprint can be rather a lot higher — and the worth rather a lot decrease.” Furthermore, the restoration of worthwhile parts like phosphorus related to the matrix polymer can be attainable.
A fabric made to measure
Fiber-reinforced composites are usually not the one utility for the brand new polymer. For instance, it might be used to coat wood flooring, as a clear, resistant layer that has good flame-retardant properties — and the place scratches and dents might be “healed” with a bit stress and warmth.
“We did not develop a single materials for a selected goal, however quite a toolbox,” Gaan explains. “Flame retardancy, recyclability and repairability are a given. We are able to optimize all different properties relying on the supposed use.” For instance, he says, stream traits are notably necessary for the manufacturing of fiber-reinforced plastics, whereas exterior wooden coatings must also be weather-resistant.
To pursue these and different purposes of the fabric, the researchers at the moment are searching for industrial companions. The possibilities of industrial success are good: Along with all its different advantageous properties, the modified epoxy polymer can be cheap and simple to fabricate.
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