Heat-triggered polymerisation method saves energy

L. Brian Stauffer

A NEW polymer manufacturing process that uses the energy from the internal polymerisation reaction rather than high-temperature curing ovens, can save ten orders of magnitude of energy, according to researchers at the University of Illinois.

Conventionally, the lightweight and heat-resistant components that are vital for vehicles such as aircraft require the liquid monomer to be cured for several hours at high temperatures in order to produce a hardened polymer through cross linking of polymer chains. This involves large amounts of energy along with an oven that scales with the size of the component. For example, curing a small section of a Boeing 787’s fuselage requires around 350 GJ of energy over eight hours, and produces around 80 t of CO₂.

The new curing method reduces the cost, time, and energy needed, by using only the exothermic heat from the reaction, cutting energy requirements by around ten orders of magnitude.

Known as frontal polymerisation, an external heat source is used to trigger polymerisation at a point, and then the heat drives further polymerisation in a reaction wave. The frontal ring-opening metathesis polymerisation (FROMP) process uses a thermally-activated ruthenium catalyst, although previously this reaction was occurring too quickly. By adding an inhibitor, the team extended the reaction time at room temperature from 30 minutes to 30 hours.

This means that the liquid monomer used in the study – dicyclopentadiene (DCPD) – slowly transforms into a gel at room temperature, but does not polymerise until heat is applied via a soldering iron. This allows the gel to be moulded or 3D-printed before being polymerised to polydicyclopentadiene (pDCPD).

The high-performance thermoset components used in vehicle manufacturing are made of fibre-reinforced polymer composites (FRPC). The researchers created FRPC panels by infusing carbon fibres with the monomer solution and FROMP was triggered via an embedded heating wire. They were able to cure a 900 cm² FRPC panel in five minutes using just 750 J of energy.

The FROMP-cured polymers and carbon fibre-reinforced polymers have the same mechanical properties as those cured in a conventional oven.

"This development marks what could be the first major advancement to the high-performance polymer and composite manufacturing industry in almost half a century," said research leader Scott White.

The team envisions that the process could be used in large-scale production due to its compatibility with techniques like 3D-printing. “We are in very early phase discussions about commercialisation and intrigued by several interesting enquiries,” said Jeffrey Moore, professor of aerospace engineering at Illinois.

Nature http://doi.org/gdjt9r