While more and more cars are becoming electric, they are still essentially made from metal and conventional engineering plastics. Carbon and aluminium are lightweight, but use six times more energy to produce than steel, which goes some way to cancel out the energy they save in use after production. But researchers are driving innovation to biocomposite cars.

The idea of manufacturing a car from plants broke the headlines earlier this year when students from Eindhoven University in the Netherlands came up with a novel design and have begun to display it round the globe at a handful of high-profile events, including Dutch Technology Week and the Shell Eco marathon in London.

Flax is an interesting alternative. It grows everywhere and costs less energy to produce than aluminium and carbon, and it is a renewable material. What’s more, it is lightweight and can be recycled.

Flax has a very strong structure: when the fibres are stacked crosswise and compressed, panels made from it have a similar strength to carbon and aluminium, which are materials widely used in the car industry.

Meet Lina, the world’s first biocomposite car

Lina, the biocomposite car, features a complete chassis, the body of the car and the interior are all made of bio-based materials. The chassis is made of a combination of biocomposite and bioplastic. The honeycomb structure bioplastic, or PLA (polylactic acid), is a 100 percent biodegradable resin derived from sugar beet and supplied by a company called NatureWorks. It is enveloped in biocomposite sheets with a flax foundation. In terms of its strength-weight ratio, the biocomposite is comparable with familiar fibreglass composites but manufactured in a sustainable way. The bodywork is also flax-based.

EconCore’s ThermHex technology for cost-effective, continuous production of thermoplastic honeycomb core materials was used to manufacture the honeycomb based on PLA from NatureWorks.

ThermHex is a continuous process for the production of thermoplastic honeycombs integrated with in-line lamination of skin layers, by successive in-line operations, either directly from the extruder or from a roll of material. The versatile technology allows direct lamination of thermoplastic skins, as well as other facing layers (including, for instance, composites and metal) onto the thermoplastic honeycomb core to offer lightweight sandwich panels suitable for different applications.

The core is produced from a single sheet by a thermoforming, a folding and a bonding operation. ThermHex honeycombs have closed skin strips, allowing perfect bonding of skins onto the core. The process enables the cost-efficient production of honeycomb cores from a wide range of thermoplastic polymers with a large variation in cell size, density and thickness. In-line post-processing to panels and parts leads to further cost reductions.

The Lina is electric-powered and has a total weight of 300kg. Lina is certified by the Netherlands Vehicle Authority as roadworthy and can carry four people. It is a city car, reaching speeds up to 85km/hr. It only needs a licence plate before it can drive on public roads.

Prius lightens its load with biocomposite parts

While the students have shown that it is possible to build a car from bio-based materials, it is unlikely the car industry will pick up the idea immediately. However, more conventional honeycomb materials are very much in the thinking of Japanese automotive OEM Toyota, which has adopted an interior part using honeycomb material for its new hybrid model Prius PHV launched earlier this year.

The part is the boot (trunk) cover of the car. It was again achieved using ThermHex technology licensed from EconCore by Gifu Plastic Industry of Japan. Due to its combination of strength, rigidity and ultra-low weight, the honeycomb delivers weight savings of 50 percent compared to previous conventional material set-ups based on metal.

Gifu Plastic started to use the ThermHex process to make thermoplastic honeycomb products for packaging and logistics applications. Recently the company has extended to automotive interiors, where light, rigid and easy-to-thermoform honeycomb core materials have attracted interest in Europe and North America.

Folded honeycomb

The range of conventional engineering polymers suitable for use with ThermHex includes:

• PP (Polypropylene)
• PE (Polyethylene)
• PS (Polystyrene)
• PET (Polyethylene terephthalate)
• PA (Polyamide)
• PC (Polycarbonate)
• ABS (Acrylonitrile-butadiene-styrene)
• PPS (Polyphenylene sulfide)
• PEI (Polyetherimide)