08. Jul 2022
The Fraunhofer Institute for Structural Durability and System Reliability (Fraunhofer LBF – Darmstadt, Germany) and Ansmann AG (Assamstadt, Germany), a leading manufacturer of lithium-ion batteries, have developed organosheets with flax fibres in the "BioBattery" project. The sheets were incorporated into a battery housing for e-bikes for reinforcement.
Better mechanical properties, lower weight
Organosheets are fibre-reinforced thermoplastics that can be processed in a similar way to sheet metal. Their strength is in no way inferior to that of classic sheet metal components, while being lighter at the same time.
The continuous manufacturing process adapted by the Fraunhofer LBF for the natural fibre organosheets opens the door to serial, industrial production. Due to its mechanical properties and low weight, the new material is particularly suitable for lightweight construction applications with high requirements.
Organosheets with natural fibres are hardly commercially available on the market so far. The reason for this is the sensitivity of natural fibres to high temperatures, which makes impregnation with the thermoplastic matrix difficult. On the other hand, fibres made from, e.g. hemp are characterised by a low tendency to splinter and high elasticity, which promises materials with unprecedented impact strength. They could improve crash behaviour and reduce risks from battery housing breakage in e-vehicles.
In the BioBattery project, the Fraunhofer LBF has adapted a melt impregnation process developed in-house so that it is suitable for the continuous production of organosheets from natural fibres. The Fraunhofer team used flax fibres, which have a higher thermal stability than other natural fibres, and polypropylene (PP) as the materials matrix. The researchers also conducted tests with biobased PA11 as a matrix. In the long term, this could be the more interesting raw material, as its mechanical properties still exceed those of PP.
An e-bike battery housing from the company Ansmann, which was reinforced with the flax PP organosheets, served as a demonstrator. In tests, samples of these housings showed better mechanical characteristic values than comparative materials while at the same time reducing weight.
The organosheets were joined to the battery housing in an injection moulding process. After cooling, a slight, undesired curvature of the manufactured components became apparent, which the researchers attribute to a different expansion of the matrix and the organosheets. They now want to test possible solutions. If the process can be optimised, the industrial use of natural-fibre-based organosheets will be within reach.
The project "Large-scale lightweight construction with natural fibre-reinforced biobased plastics using the example of lithium-ion battery housings" was funded by the German Federal Ministry of Food and Agriculture (BMEL) through the project management agency Fachagentur Nachwachsende Rohstoffe e.V. (FNR – Gülzow, Germany).