Vitrimer composites game changing super materials

Since their discovery in 2011, self-healing vitrimer polymers have been shown to address the limitations of both thermoset and thermoplastic materials.

Vitrimers exhibit the strength and stiffness associated with thermosets at normal working temperatures, but can be "rebirthed" (reshaped, healed or recycled) when heated.

DSTG chemist Dr Ashleigh Farnsworth has been awarded a Chief Defence Scientist Fellowship to investigate the use of vitrimers in fibre-reinforced composites. It's an application that is not well understood and offers exciting opportunities for Defence.

In particular, Dr Farnsworth will focus on developing novel methods to link vitrimers between a base resin and carbon fibres yielding high stiffness structural composites resistant to delamination. Such vitrimeric composites are of interest to Defence as they can be essentially 'rebirthed' to remove any in-service induced cracks or damage in carbon-reinforced polymer composite structures such as those in land systems, military aircraft, UAVs, naval vessels, and weapons.

Recent literature has shown that vitrimers can also have superior shock wave energy distribution compared to their non-vitrimeric counterparts; their chemical bond structure dissipates energy very effectively. For Defence, this desirable damping behaviour could mean stealthier platforms. Research has also shown that vitrimers can absorb energy continuously and reversibly without generating heat, meaning they may also have good resistance to impact and fatigue. As part of her fellowship, Dr Farnsworth will submit her vitrimer samples to high levels of strain to assess their resistance to delamination and failure compared with conventional composites.

Dr Farnsworth manages DSTG's spectroscopy and thermal analysis lab at the Fishermans Bend site, leading the material characterisation program in support of failure analysis and for research and development purposes.

In her role at DSTG analysing material failures, Dr Farnsworth noticed commonalities in the failures. In her fellowship she will use some of the sophisticated organic chemistry techniques developed during her PhD to create the self-healing vitrimer networks and then conduct mechanical testing to characterise the potentially game-changing vitrimer composites.

Rebirthing vitrimers

'Basically, vitrimers can be heated up, at which point the chemical bonds realign, self-heal and then cool down into a new shape,' explains Dr Farnsworth. 'The required temperature depends on the polymer a little bit. It can't be at a point where it's going to degrade the polymer, so this can be a challenge for polymers that have a very high glass transition temperature. Interestingly, the vitrimer's exchangeable network property doesn't necessarily have to be triggered by heat.'

'The end game is that you could have these materials on a Defence platform like an aircraft and use something a bit more sophisticated than a hair dryer or microwave oven to reach the temperature where you get these exchangeable bonds activated. The bonds exchange partners, and then self-heal into new material that retains the original mechanical properties.'

During her fellowship, Dr Farnsworth will collaborate with Monash University chemistry researcher Dr Joel Hooper who is a leader in the development of new organic synthesis and catalysis techniques. Most usefully for this research, Dr Hooper has developed novel methods to graft amorphous carbon with polymers.

Dr Farnsworth will also work with Monash University engineer Dr Matthieu Gresil who has specialist vitrimer fabrication equipment at hand, as well as Deakin Univerty's Professor Luke Henderson who is an expert on carbon fibre and carbon fibre functionalisation.

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