You might think bamboo, corn and kenaf — a plant similar to jute — would make poor materials for building modern cars, but you would be wrong. These plants are helping make auto parts that are green in more ways than one.

Automakers have so far focused most of their efforts on improving the efficiency of their engines to cut emissions of carbon dioxide. Toyota Motor Corp.’s wildly popular Prius hybrid is perhaps the best-known example.

Moving out from under the hood, car companies are now working to take advantage of drivers’ growing concern for the environment to set their products apart.

Toyota’s leaf-shaped one-seat electric car, the i-unit, which it unveiled at the 2005 Aichi World Exposition, grabbed attention for its unique design.

But what most people admiring the car didn’t know was the body was made using kenaf fiber.

Toyota Auto Body Co., a Toyota affiliate which manufactured the body of the i-unit, has been studying ways to develop plant-based car bodies since 1996.

“Vehicles inevitably emit carbon dioxide. As an automaker, we thought there would be ways to contribute to reducing carbon dioxide, even if only slightly,” said Toyota Auto Body spokesman Toshikazu Muto.

Toyota Auto Body chose kenaf, because it is a fast-growing annual grass and absorbs seven times more carbon dioxide than cedar, according to Muto.

Bioplastic made from plants is already in use for some Toyota car parts such as floor mats and the spare tire cover on the Raum compact car.

Bioplastics and biofabric are “carbon neutral.” The carbon dioxide released by burning the plants used to make the parts is offset by the carbon dioxide the plants absorb as they grow.

Using plant-based materials instead of conventional metals and petrochemicals also reduces companies’ dependence on nonrenewable resources.

Although components made of plants are limited to car interiors at present, according to Muto, ‘We are studying ways to (mass-produce) outer panels such as hoods and roofs made of kenaf.”

Mitsubishi Motors Corp. has developed panels made of bamboo fiber, sugar cane and corn, and floor mats made from a combination of corn and conventional nylon resin.

“Our dream is to replace every plastic component in a car with plant-based ones,” said Isamu Terasawa of MMC’s material engineering department.

Mitsubishi Motors began research and development on plant-based materials in 2003, and is planning to use the bamboo panels for the interior surface of one model’s tailgate next year.

The biofabric floor mat will be used in a new minivehicle scheduled for release in December.

Terasawa said the company chose the minicar because incorporating the plant-based components fits the car’s concept of being “friendly to the environment and people.”

Based on an assessment of a vehicle’s carbon dioxide emissions over its entire life cycle, from manufacturing to disposal, the bamboo panels cut emissions by half, while the corn floor mats reduce them by 40 percent compared with conventional plastic components, the company said.

Terasawa said the cost of manufacturing the plant-based panels and floor mats is 20 percent to 30 percent higher than the that of conventional petroleum-based products. But he believes plant-based materials will eventually become cheaper than petroleum-based ones because oil will become scarcer, pushing oil prices higher.

Honda Motor Co., meanwhile, is working to commercialize fabric made of corn. The automaker plans to use plant-based fabric for car interiors such as seats by 2009.

Honda will first introduce biofabric car seats in a new fuel cell vehicle it plans to release within the next three years. It will then offer them on other new models starting in 2009.

“Commercializing plant-based materials has been difficult due to problems with durability, resistance to sunlight and rough texture,” said Honda spokesman Shigeki Endo.

That is why such biomaterials are usually limited to parts that customers don’t normally see, Endo said.

But the new plant-based fabric developed by Honda is soft, durable and stands up well to sunlight, he said.

Honda plans to use more plant-based fabrics for the interior surfaces of car doors, roofs and floor mats in the future.

While automakers’ efforts to use plant-based materials are starting to pay off, the next big step is to begin manufacturing commercially viable exterior panels made of plants.

Toyota Auto Body, which hopes to mass-produce a car with exteriors made of plants by next year, admits it will be tough.

Toyota Auto Body’s Muto said the company needs to secure an adequate supply of kenaf, reduce manufacturing costs and develop plant-based materials that can withstand heat, rain and other harsh weather conditions.

“Using steel is much cheaper,” and it is more durable, Muto said. “But we want to make the entire vehicle environmentally friendly.”

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