Carbon Nanotubes: The Key to Low-Cost Fabrication of Strong Carbon Fiber Composites

16 Nov 2023

As the world deals with climate change and carbon emissions, there is a growing demand for renewable energy sources and policies promoting sustainable practices. One of the essential elements driving this shift towards a greener future is large tow carbon fibers, as they are lightweight, durable, and have high strength.

However, it can be expensive to produce due to its limited supply and sourcing. Researchers have been exploring using carbon nanotubes (CNTs) to develop a cost-effective and strong composite carbon fiber to address this issue.

A study published in the journal Composites Part B: Engineering in December 2022 has shown promising results in creating these composites with exclusive and advanced properties at low cost.

What are Carbon Nanotubes (CNTs)?

Carbon nanotubes (CNTs) are one-atom thick cylindrical structures made of carbon atoms. They are intricate, with diameters ranging from a few nanometers to several micrometers but with lengths reaching up to several centimeters.

CNTs are considered one of the strongest high-performance materials with a tensile strength 100–200 GPa range, making them ideal for various applications in electronics, energy, and biomedical industries. CNTs can be either single-walled (SWCNTs), made of a single layer of carbon atoms rolled into a cylinder, or multi-walled (MWCNTs), made of several layers of carbon atoms.

Moreover, CNTs possess high thermal and electrical conductivity, making them suitable for creating carbon fiber composites. These composites combine carbon fiber's superior mechanical properties with carbon nanotubes' electrical conductivity, resulting in a material with exceptional performance.

Carbon fiber composites that incorporate CNTs can exceed the capabilities of current carbon fibers, making them a promising material in the aerospace, military, and transportation fields. Nonetheless, it is challenging to maintain the exceptional attributes of CNTs in fibers, and the high cost of CNTs poses a significant obstacle to their commercialization.

Way to Affordability

Two research teams, Bon-Cheol Ku from the Korea Institute of Science and Technology (KIST), Jeonbuk Institute of Advanced Composite Materials, and Professor Han Gi Chae from the Ulsan National Institute of Science and Technology (UNIST) collaborated to drive innovation. The study aimed to create an affordable fabrication method for composite carbon fibers using carbon nanotubes.

Carbon fibers are usually produced using polyacrylonitrile (PAN) polymer or pitch derived from pyrolyzed fuel oil. The former produces high-strength fibers, while the latter produces highly modulus fibers.

However, the research team took a different approach and employed carbon nanotubes and polyimide (PI) to develop a new technology for producing composite carbon fibers. The research team utilized PI as the matrix material and incorporated CNTs to enhance the mechanical properties of the fibers.

The CNTs are highly conductive and have a high aspect ratio, which allows them to act as reinforcing agents in the PI matrix, resulting in a significant improvement in the modulus of the fibers while maintaining their high strength.

The experimentation focused on a wet-spinning process that produced fibers by extruding a polymer and carbon nanotube solution through a spinneret and solidifying it in a coagulation bath.

The researchers used a liquid crystalline solution to align the carbon nanotubes within the polymer matrix and improve the orientation of the composite fibers, which improved modulus, strength, and electrical conductivity. Furthermore, the resulting fiber had a high modulus of 528 GPa and a high strength of 6.2 GPa, which is remarkable considering the material's low density.

Compared to commercially available carbon fibers with a modulus of around 320 GPa, the new composite fiber developed by the research team was proven to be 1.6 times more potent. The microstructure analysis of the fabricated material revealed that the void content was reduced, and the presence of the polyimide matrix improved the carbon nanotube orientation.

The team's cost-effective approach using low-cost polyimide to replace up to 50% of the carbon nanotubes demonstrated the potential of the developed technology for the large-scale production of composite carbon fibers with superior mechanical properties.

The study and the practical innovation will significantly drive growth in high-performance material markets such as the large tow carbon fiber market.

According to BIS Research, the global large tow carbon fiber market was valued at $0.57 billion in 2021, and it is expected to grow at a CAGR of 13.43% and reach $1.96 billion by 2031.

 The Future of Carbon Nanotubes

The above research by KIST and UNIST shows the significance of the developed technology and its potential to address the challenges of producing high-performance composite materials at a lower cost. Using low-cost polymers to produce these fibers makes them accessible for large-scale production, crucial for meeting the growing demand in the industrial sector, such as aerospace, military, and future mobility.

The success of research conducted by KIST and UNIST paves the way for future developments and innovations in material science, providing new possibilities to produce lightweight, high-strength materials that can withstand extreme conditions.

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