Lightweight bioplastics eyed for future vehicles

New resins, such as plastics made from raw materials other than petroleum, are attracting attention as a way to help reduce greenhouse gas emissions such as carbon dioxide.

Some of the new materials have a weakness in terms of low heat resistance, but if this can be overcome in the future they may replace metals, glass and other materials.

The Environment Ministry and other entities aim to use it for parts of next-generation automobiles and other products, as they promote efforts to stop global warming through technological advances.

Improved heat resistance

"This does not melt even upon exposure to hot air at more than 300 C," said Tatsuo Kaneko, a professor at the Japan Advanced Institute of Science and Technology in Ishikawa Prefecture, showing an origami crane made of a material that resembles transparent cellophane.

Kaneko studies plastics made from materials other than petroleum, such as substances from plants. The crane is made of a thin film of biomass plastic of biological origin (bioplastic).

Conventional bioplastic has low heat resistance, and the scope of its use has been limited. However, Kaneko succeeded in producing a type of bioplastic called polyimide that is resistant to high temperatures of about 400 C.

Conventional bioplastics could only stand temperatures up to about 300 C.

Moreover, the bio-based polyimide is more transparent than conventional polyimides made from petroleum, which will allow a greater range of uses.

Kaneko started developing strong plant-derived materials in 2010 in co-operation with Naoki Takaya, a professor of microbiology at the University of Tsukuba, and realised a bioplastic with high heat resistance in 2014.

The raw material of the bioplastic is amino cinnamic acid, whose molecular structure is similar to that of the spice cinnamon.

Kaneko synthesized the highly heatproof polyimide by turning glucose extracted from plants, such as corn and other materials, into amino cinnamic acid using genetically modified Escherichia coli bacteria and then irradiating the substance with ultraviolet light to change its molecular constitution.

Kaneko expects that the bioplastic will replace metals for automobile engine cylinders and other parts.

Since it is transparent, Kaneko believes that it can be fit into window frames instead of glass or used for light covers and sunroofs.

The material will considerably reduce vehicle weight, and Kaneko said, "The polyimide could fulfil a wish to make cars as lightweight as possible to increase fuel efficiency."

Extracted from wood

Shimane Prefecture-based construction company Fujii consulting & associates is currently developing the wood-derived material lignophenol, which is expected to replace metals.

Lignophenol is a powder extracted from lignin, which is used as an adhesive when pressing bits of wood from forest thinning into fiberboard.

By mixing lignophenol with other resins, it is turned into a light, strong material that is easy to process.

Due to its high insulation and non-flammability, lignophenol can be used for parts that generate or are exposed to heat, such as a heat insulator attached to the back of a car hood or a device to connect wires.

Parts using lignophenol are 15 per cent to 50 per cent lighter than those made from metals and other conventional materials, according to the company.

"We confirmed the lightweight properties at the trial stage, so we want to continue verification of its strength and heat resistance from here on," said a Fujii employee.

If biopolyimide and lignophenol become widespread, it will become possible to reduce CO2 emissions by using them to replace metals, the production of which generates large amounts of CO2.

Combination produces effects

Last year, the Environment Ministry launched a project to verify the research findings of the Fujii company and Kaneko, and to seek ways to reduce production costs and enable a stable supply.

The ministry's goal is to produce a next-generation vehicle that is 10 per cent lighter by combining these materials with a material called cellulose nanofiber (CNF), which is derived from wood or bamboo.

Research on CNF preceded the research on the other materials.

CNF is five times harder than iron but just one-fifth its weight, drawing attention as a high-strength, lightweight material. Therefore, many paper-manufacturing companies are now putting efforts into the development of CNF.

However, CNF is heatproof only up to about 280 C, so it is difficult to use it for parts around engines and other heat sources.

Given this, the ministry is considering combining CNF with biopolyimide and lignophenol, both of which are highly resistant to heat.

"If these materials are mixed with CNF, a stronger material could be created," Kaneko said.

Meanwhile, an official at the ministry in charge of the issue said: "If they are used together with stronger CNF, all materials can exercise their own strength. We would like to use them to reduce CO2 emissions as much as possible."