Advancing Recycling Methods for Carbon and Glass Fiber Composites

Carbon fiber composites are considered an extraordinary material thanks to their high durability, weather resistance, and remarkable versatility. Over the past two decades, the global demand for carbon fiber reinforced polymers (CFRP) has experienced a substantial surge, exhibiting an approximate annual growth rate of 12.5 percent. 

 

Image used courtesy of Adobe Stock

 

However, this heightened demand has generated a considerable volume of waste associated with the production processes of CFRP. By 2030, it is estimated that approximately 500,000 tons of waste comprising carbon and glass fiber composites will originate from the renewable energy sector.

In anticipation of this challenge, researchers from the University of Sydney seek to expand recycling methods that prevent end-of-life landfill disposal.

 

Future Waste Projection

By 2030, it is projected that CFRP will become a significant global waste stream.

CFRP materials are widely utilized in various industries, such as wind turbine blades, hydrogen tanks, airplanes, yachts, construction, and car manufacturing. The annual accumulation of CFRP waste from the aircraft and wind turbine sectors is estimated to reach 840,300 metric tons by 2050.

Although recycling methods for carbon fiber composites exist, most waste is currently disposed of in landfills or incinerated. Additionally, producing new "virgin" composites has adverse environmental implications, including resource depletion and high energy consumption.

Interestingly, several recycling methods are available for carbon fiber composites that, if fully embraced, hold significant potential.

A research team at the University of Sydney suggests that these recycling techniques could reduce energy consumption by 70 percent and prevent crucial material streams from being wasted. By implementing these recycling methods, we can effectively address the environmental impact of carbon fiber composite production and the waste management challenge.

 

Carbon fiber composites. Image used courtesy of Adobe Stock

 

Material Recovery and Energy Efficiency

To address the concerns of waste accumulation, Dr. Hadigheh and Ph.D. graduate Dr. Yawning Wei from the School of Civil Engineering have devised an innovative recycling technique for carbon and glass fiber composites.

They aim to prevent these materials from being discarded in landfills as they reach the end of their life cycle. The research, published in Composites Part B: Engineering, presents an approach that enhances material recovery and energy efficiency, surpassing the capabilities of previous methods.

According to Dr. Hadigheh, kinetic analysis unveiled an additional reaction stage in pre-treated CFRP, leading to improved degradation at lower temperatures than untreated CFRP. The solvolysis pre-treatment not only enhances the breakdown process but also safeguards the mechanical properties of the fibers by reducing heat consumption during recycling.

 

 

CFRP sample preparation. Image used courtesy of Science Direct

 

The recycled fibers from pre-treated CFRP exhibited remarkable resilience, retaining up to 90 percent of their original strength. This surpassed the strength of fibers obtained solely through thermal degradation by an additional 10 percent.

The real-world viability of the method was proven through the successful recycling of bicycle frame parts and airplane scraps composed of CFRP composites using their hybrid thermo-chemical recycling approach.

 

Thermo-chemical recycling method. Image used courtesy of Science Direct

 

These achievements validate the efficacy of the chemical pre-treatment and showcase the enhanced mechanical properties of the recycled carbon fibers.

 

Reduce, Reuse, Recycle

Previously, the team conducted a comprehensive assessment of 10 distinct waste treatment systems for carbon and glass fiber composites. Their evaluation encompassed economic efficiency and environmental impact while considering the specific waste material type and geographical location.

They discovered that solvolysis, a process involving solvent under specific pressure and temperature to break down materials, proved an effective method for reclaiming carbon fiber while generating a significant net profit. Additionally, thermal recycling methods such as catalytic pyrolysis and pyrolysis combined with oxidation demonstrated high economic returns.

The research also revealed that solvolysis and electrochemical methods resulted in significantly lower CO2 emissions than landfilling and incineration.

For manufacturers, this new recycling method offers a cost-effective and eco-friendly option. The use of recycled material especially creates a huge opportunity to mitigate the effects of supply chain disruptions while supporting a circular economy.