KYOTO – The global push among carmakers to make ever lighter vehicles is leading some auto suppliers in Japan to turn to what seems like an unlikely substitute for steel — wood.
Japanese researchers and auto component makers say a material made from wood pulp weighs just one fifth the weight of steel, and can be five times stronger.
The material — known as cellulose nanofiber — could become a viable alternative to steel in the decades ahead, they say, although it faces competition from carbon-based materials and remains a long way from being commercially viable.
Reducing the weight of a vehicle will be critical as manufacturers move to bring electric cars into the mainstream. Batteries are an expensive but vital component, and a reduction in car weight means fewer batteries are needed to power the vehicle and running costs can be reduced.
“Lightweighting is a constant issue for us,” said Masanori Matsushiro, a project manager overseeing body design at Toyota Motor Corp.
“But we also have to resolve the issue of high manufacturing costs before we see an increased use of new, lighter-weight materials in mass-volume cars.”
Together with major parts suppliers such as Denso Corp. (Toyota’s biggest supplier) and Daikyo-Nishikawa Corp., researchers at Kyoto University are working on plastics with incorporated cellulose nanofibers — which are made by breaking down wood pulp fibers into fragments several hundredths of a micron (one-thousandth of a millimeter) in size.
Cellulose nanofibers have been used in a variety of products, ranging from ink to transparent displays, but their potential use in cars has been enabled by the “Kyoto process,” under which chemically treated wood fibers are kneaded into plastics while they are simultaneously being broken down into the nanofibers. The method slashes the cost of production to roughly one-fifth that of other processes.
“This is the lowest-cost, highest-performance application for cellulose nanofibers, and that’s why we’re focusing on its use in auto and aircraft parts,” said Kyoto University professor Hiroaki Yano, who is leading the research, during an interview.
The university is also currently working with auto parts suppliers to develop a prototype car using cellulose nanofiber-based parts, set to be completed in 2020.
“We’ve been using plastics as a replacement for steel, and we’re hoping that cellulose nanofibers will widen the possibilities toward that goal,” said Yukihiko Ishino, a spokesman at Daikyo-Nishikawa, which counts Toyota Motor Corp. and Mazda Motor Corp. among its customers.
Automakers are also using other lightweight substitutes. BMW uses carbon fiber reinforced polymers for its i3 compact electric car and for its 7 series, while high-tensile steel and aluminium alloys are currently the most widely used lightweight options because they are cheaper and recyclable.
Yano said he was inspired in his research by a photo of the “Spruce Goose,” a cargo plane made almost entirely of wood in 1947 by U.S. billionaire entrepreneur Howard Hughes. At the time, it was the world’s largest aircraft.
“I thought that if Howard Hughes could find a way to use wood to build a massive plane, why not use wood to make a material that was as strong as steel,” he said.
The cost of mass producing 1 kg of cellulose nanofiber is currently around ¥1,000.
Yano aims to halve that cost by 2030, which he says will make it an economically viable product since it will be combined with plastic. That will make it competitive against high tensile steel and aluminium alloys, which currently cost around $2 per (about ¥220) per 1 kg.
Industry experts anticipate that carbon fiber prices will fall to around $10 per kg by 2025.
Analysts still say high-tensile steel and aluminium will be the more popular alternative for many years to come, mindful that parts makers would need to overhaul production lines and figure out ways to fasten new materials like cellulose nanofiber onto other car parts.
Anthony Vicari, an applied materials analyst at Lux Research in Boston, said it “would be a big deal” if Yano’s projections prove to be correct.
For now, he said, it remains “a very big ‘if.’ “
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