Researchers at Washington University in St. Louis have found a way to create lighter, stronger carbon-fibre materials and stronger plastics with a gentler environmental impact by adding a modified form of lignin, a compound that’s essential for most plants but considered a waste product by industry.
Carbon fibre is known for being a strong and stiff, yet light – and premium – material. It’s used as structural reinforcement in everything from tennis rackets to airplanes, and carbon-fibre frames reduce weight and improve safety in high-end vehicles. It has been incorporated wherever possible in some of the fastest super- and hypercars.
Previous work carried out by the research group headed up by Joshua Yuan, professor and chair of the Department of Energy, Environmental and Chemical Engineering in Washington University in St. Louis’ McKelvey School of Engineering, revealed that there are two main roadblocks to incorporating lignin into carbon-fibre materials. First, neither lignin’s chemical structure nor its molecular weight are uniform, which makes it difficult to combine with other polymers. And second, it has a high number of -OH groups, a reactive pairing of oxygen and hydrogen that attracts water, which is far from ideal for building a rigid material such as carbon fibre.
These discoveries inspired Yuan and Jinghao Li, a senior scientist at Washington University, to redesign lignin’s structure. Having now developed a technique to do just that, Yuan said, ‘We’ve really created a type of lignin that is unique.’
The result is High Molecular Weight Esterified Linkage Lignin (HiMWELL), which, when combined with polyacrylonitrile (PAN), creates a precursor to a better carbon fibre that could also enable the development of recyclable plastics with improved properties.
When combined with PAN, the HiMWELL-based carbon fibre has a record tensile strength and shows better mechanical properties than standard carbon fibre. When it’s added to recyclable polymer blends, HiMWELL improves mechanical properties and also improves UV protection.
‘Finally, we have a technological path for lignin to be used for carbon fibres,’ Yuan said. And perhaps one day, ‘You’ll turn this waste into the shell of a car.’
The research has been published in Cell Press Matter.