A new chemically designed lignin leads to stronger, lighter carbon fiber and better recycled plastics

Research from Washington University in St. Louis may soon lead to lighter, stronger carbon fiber materials and stronger plastics with a gentler environmental impact. The main ingredient necessary for these improvements is lignin, a compound that is essential for most plants but considered a waste product by industry.

The key to opening up lignin’s potential was chemically altering some of its properties. High Molecular Weight Esterified Linkage Lignin (HiMWELL)  was designed by the group of Joshua Yuan, professor and chair of the Department of Energy, Environmental & Chemical Engineering at Washington University in St. Louis’ McKelvey School of Engineering.

The research was published Aug. 11 in the journal Cell Press Matter. 

Researchers knew that, combined with polyacrylonitrile (PAN), the newly designed HiMWELL lignin could become a precursor to a better carbon fiber and that it could enable the development of recyclable plastics with better properties, as well.

Already, carbon fiber is known for being a strong and stiff, yet light — and premium — material. It is used as structural reinforcement in everything from tennis rackets to airplanes, and carbon fiber frames reduce weight and improve safety in high-end vehicles. It has been incorporated anywhere possible in some of the fastest super and hypercars.

Yuan’s previous work identified three main roadblocks to incorporating lignin in the equation: neither lignin’s chemical structure nor its molecular weight is uniform, which makes it difficult to combine with other polymers. And it has a high number of OH groups, a reactive pairing of oxygen and hydrogen that attracts water — not ideal for building a rigid material like carbon fiber. These discoveries inspired Yuan and Jinghao Li, a senior scientist at Washington University, to redesign lignin structures.

By developing a technique to chemically alter these properties, Yuan said, “We’ve really created a type of lignin that is very unique.” 

When combined with PAN, the HiMWELL-based carbon fiber had a record tensile strength and showed better mechanical properties than standard carbon fiber. When it was added to recyclable polymer blends, HiMWELL improved mechanical properties and also improved UV protection.

“Finally, we have a technological path for lignin to be used for carbon fibers,” Yuan said. And perhaps one day, “You’ll turn this waste into the shell of a car.”

The U.S. Department of Energy’s Office of Energy Efficiency & Renewable Energy and Bioenergy Technologies Office supported the work.

The research is supported by the U.S. Department of Energy, grant # EE0008250

The McKelvey School of Engineering at Washington University in St. Louis promotes independent inquiry and education with an emphasis on scientific excellence, innovation and collaboration without boundaries. McKelvey Engineering has top-ranked research and graduate programs across departments, particularly in biomedical engineering, environmental engineering and computing, and has one of the most selective undergraduate programs in the country. With 140 full-time faculty, 1,387 undergraduate students, 1,448 graduate students and 21,000 living alumni, we are working to solve some of society’s greatest challenges; to prepare students to become leaders and innovate throughout their careers; and to be a catalyst of economic development for the St. Louis region and beyond.

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