It is estimated that by 2030 carbon and glass fibre composites (CFRP) – materials commonly used in wind turbine blades, hydrogen tanks, aircraft, yachts, construction, and car manufacturing – will be a key waste stream worldwide.

The annual accumulation of CFRP waste from aircraft and wind turbine industries alone is projected to reach 840,300 tonnes by 2050 – the equivalent of 34 full stadiums – if suitable recycling methods are not adopted.

While recycling methods do exist, most of this waste currently goes to landfill or is incinerated. The production of 'virgin' composites has further implications for the environment too, including resource depletion and high energy input during production.

This is despite the existence of numerous methods to recycle carbon fibre composites which a research team at the University of Sydney says, if fully implemented, have the potential to significantly reduce energy use by 70% and prevent key streams of materials from going to waste.

"Carbon fibre composites are considered a 'wonder' material – they are durable, resistant to weathering and highly versatile – so much so that their use is projected to increase by at least 60% in the next decade alone," says Dr Hadigheh from the School of Civil Engineering.

"But this huge growth also brings a huge increase in waste. For instance, it has been estimated that about 500,000 tonnes of carbon and glass fibre composite waste from the renewable energy sector will exist by 2030."

A new recycling method

To tackle this issue, Dr Hadigheh and his recent PhD graduate Dr Yaning Wei have developed a new recycling method for carbon and glass fibre composites in a bid to prevent from end-of-generation materials going to landfill. Published in Composites Part B: Engineering their approach ensures increased material recovery and improved energy efficiency compared to previous methods.

"Our kinetic analysis revealed that pre-treated CFRP undergoes an additional reaction stage, enabling enhanced breakdown at lower temperatures compared to untreated CFRP," says Dr Hadigheh. "The solvolysis pre-treatment not only facilitates greater breakdown but also preserves the mechanical properties of fibres by reducing heat consumption during recycling."

Recycled fibres obtained from pre-treated CFRP retained up to 90% of their original strength, surpassing the strength of fibres recovered through thermal degradation alone by 10%.

"To demonstrate the real-world applicability of our method, we successfully recycled part of a bicycle frame and aircraft scraps made of CFRP composites using our hybrid approach. These results not only validate the effectiveness of chemical pre-treatment but also demonstrate the improved mechanical characteristics of the recycled carbon fibres," says Dr Hadigheh.

Reclaiming carbon fibre

In a previous paper, the team also presented a detailed evaluation of 10 different carbon and glass fibre composite waste treatment systems based on economic efficiency and environmental effects, taking into consideration the type of waste material and its geographical location.

Dr Hadigheh's team found that solvolysis – a method whereby materials can be broken down with an application of solvent under a specific pressure and temperature – could reclaim carbon fibre while delivering a high net profit. Thermal recycling methods such as catalytic pyrolysis and pyrolysis coupled with oxidation also provided a high economic return.

Solvolysis and electrochemical methods were also shown to lead to substantially lower CO2 emissions into the atmosphere than landfill and incineration.

The researchers said that manufacturers should look beyond continuously creating virgin material and, in parallel, develop recycled products from end-of-life streams. 

Huge opportunity

"This is a huge opportunity," says Dr Wei. "And not only because various modes of recycling are cost effective and minimally impactful on the environment. In an era of mounting supply chain disruptions, local recycled products can provide a more immediate product when compared to imports and create a burgeoning advanced manufacturing industry.

"While awareness of everyday consumer recycling is increasing and plastic waste is in the spotlight, Australia must urgently consider widescale recycling of new-generation construction materials before they mount up as another waste problem and are put into the 'too hard basket'."

Dr Hadigheh's team is also developing methods for the recycling of composite materials and recently patented a machine to precisely align recycled carbon fibres, so that they can be repurposed.

The researchers conducted life cycle analysis (LCA), cost benefit analysis (CBA) and technology readiness level (TRL) assessments of the different waste treatment methods: landfill; incineration; mechanical recycling; catalytic pyrolysis; oxidation; pyrolysis combined with oxidation; fluidised bed; solvolysis using alkali and acid solvents; and electrochemical methods.