Model of the heavy duty bicycle

Cargo bike containers made of flax fibers

March 14, 2023, Nr. 14

A project that involves the University of Stuttgart is making heavy-duty cargo bikes lightweight and sustainable
[Picture: IFB, Silvio Facciotto]

Electric cargo bikes are increasingly being used as a climate-friendly means of transportation not only for shopping or on the way to the daycare center, but also for deliveries. Every kilo counts in order to reduce the burden on the driver and save the battery. In cooperation with the company Radkutsche in Nehren, researchers at the University of Stuttgart have developed an interchangeable container system for cargo bikes that relies on flax fibers and bio-based plastic and is particularly lightweight and sustainable.

The “CoaLa” project (a bio-based container system adapted to a new, driver-supporting cargo bike for last mile delivery) aims to make inner-city delivery traffic more sustainable. To this end, a system was developed at Radkutsche GmbH whereby containers with the capacity of a euro pallet are deposited at a central location and delivered using a specially developed bicycle. After distributing the cargo, the empty containers are returned to the depot. There, the battery is recharged while the next container is being delivered using the cargo bike.

The heavy-duty cargo bike developed by the University of Stuttgart and the company Radkutsche is intended to make inner-city delivery traffic more sustainable.

A new manufacturing process for more sustainability

At the same time, researchers at the Institute of Aircraft Design (IFB) at the University of Stuttgart were concerned with the sustainability of the materials and the manufacturing processes for the containers. “It was particularly important to us to achieve the highest possible proportion of renewable raw materials while keeping the weight to a minimum,” explains Mathias Engelfried, project manager at the IFB. “Therefore, we chose flax fibers combined with a bio-based plastic. In this way, we can achieve mechanical properties comparable to those of fiberglass.”

A container made of flax fibers in combination with a bio-based plastic and with an integrated solar panel.

However, compared to conventional reinforcing fibers such as glass or carbon fibers, plant fibers have special properties, such as their swelling behavior. These can lead to problems during production, such as the formation of pores or too high a proportion of plastic. In addition, the conventional production of fiber-reinforced composites generates a considerable amount of waste. The researchers at the IFB therefore developed a new manufacturing process. The new process allows the flax fiber composite material to be produced with higher quality, while using simpler manufacturing equipment and generating a significantly reduced amount of waste. To exploit the full lightweight potential of the container, a sandwich material was developed, for which the researchers examined a wide variety of core materials, such as honeycomb cardboard, cork, balsa and paulownia wood, in combination with the flax fiber composite plastic.

Based on the results of the research on the optimal process parameters and material combinations, the IFB and the company Radkutsche made an interchangeable container out of bio-based material. In doing so, it was demonstrated that the new manufacturing process is also suitable for larger components and small batches.

The sandwich material of the container exploits the potential of lightweight construction.

Flexible charging during transportation and storage

The energy concept developed by the company Radkutsche in the course of the project and the attachment points to the cargo bike were integrated into the container. Due to the fact that the battery is integrated into the container, the cargo bike will be supplied with a full battery at the same time it is loaded with a new container. An additional solar module on the container ensures a longer range and self-sufficient charging away from a power connection, while the container is ready to be used. Furthermore, the container was designed in such a way that it can be changed without assistance, which makes the system particularly flexible.

“In the future, we want to further develop the production process so that there will be no waste at all,” says Engelfried. In addition, the core system is to be made from 100 percent plant-based raw materials in the future, making it ever more sustainable.

About Coala

The CoaLa project was funded by the Federal Ministry for Economic Affairs and Climate Action (BMWK) with EUR 360 000 within the framework of the Central Innovation Program for SMEs (ZIM). The funding period was two and a half years.

Expert Contact:

Mathias Engelfried, University of Stuttgart, Institute of Aircraft Design, Phone.: +49 711 685 60341, E-Mail 

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