Greener high-performance polymers

High-performance polymers used in top-of-the-line aircraft can be expensive and cost the earth thanks to their huge carbon footprint. But a US team has now found a way to make fiber-reinforced polymer composites similar to those found in aircraft using just a tiny fraction of the energy.

Frontal polymerization was first discovered at the Institute of Chemical Physics in Russia in 1972, before being independently rediscovered in 1991 by John Pojman and colleagues at the University of Southern Mississippi in the US. Ideally, the monomer remains stable until heat activates polymerization at a single point. This triggers an exothermic polymerization front that spreads rapidly through the material just as knocking over the first domino can topple the rest in a run. By using the molecules’ energy of polymerization to trigger further polymerization, dramatic energy savings can be achieved.

Various monomers have been used in front polymerization, but they have generally been high-energy molecules such as acrylates. Unfortunately, these tend to polymerize spontaneously. Moreover, the resulting polymers often lack high-performance properties. ‘Mostly we’re looking for a high glass-transition temperature, high elastic modulus, high strength and good chemical resistance,’ says Nancy Sottos, part of the University of Illinois at Urbana–Champaign team behind the new work. Sottos notes that the carbon fibre–epoxy fuselage and wings of a Boeing 787 require curing for eight hours in a giant autoclave. ‘You’re just running a very large oven!’ Sottos points out.