Performance meets circularity: fibre-reinforced plastics become recyclable

Recycled plastics are often less efficient than new plastics. But they can be upgraded - namely by using fibre composites. In turn, they make the plastics difficult to recycle. The All-Polymer project shows how both are possible: high-performance materials and a closed cycle.

In an interview with K-MAG, Prof. Dr. Silke Rathgeber talks about the All-Polymer project, Röchling Automotive's participation in it, and the extent to which fibre-reinforced plastics can save material and energy.

To what extent is there still a need to catch up when it comes to recycling fibre-reinforced plastics?

Prof. Dr. Silke Rathgeber: Secondary plastics often have poorer mechanical properties than primary materials. This means that the recycling of plastics is in most cases inevitably associated with downcycling. Plastic composites are generally not recyclable. This does not correspond to the goal of a resource-efficient Circular Economy, in which raw materials should remain in the cycle for as long as possible without loss of value. Nevertheless, due to their properties (low density, design flexibility, media stability, energy-efficient processing, durability), plastics offer many advantages in terms of resource efficiency compared to other material classes, such as metal or even wood, especially in lightweight construction, logistics, the construction industry, etcetera. The goal must therefore be to upgrade recycled secondary plastics through new design concepts and to process them into new products that are 100 percent recyclable.

In the All-Polymer project, you researched exactly that. What were the goals?

Rathgeber: The goal of All-Polymer is to add value to secondary plastics by means of cost- and energy-efficient unidirectional (UD) fibre-reinforced tapes (UD tapes), which are either applied to a component using an additive tape-laying process for local reinforcement or integrated into a component as inserts in injection moulding or compression moulding processes. Instead of using energy- and cost-intensive glass and carbon fibres, the innovative approach is to use plastic fibres. These can be produced in an extraordinarily energy-efficient way, are sorted according to type and are completely recyclable.

How did you go about your research?

Rathgeber: The potential to use recyclates from one application in another high-value application was investigated using use cases from different industries. Here we focused on important key industries such as automotive (Röchling Automotive), logistics (Infinex Holding) and agriculture, forestry and construction (Hahn Kunststoffe). The start-up A+ Composites produces UD tapes with the plastic fibre Dyneema®, which are unique worldwide according to the fibre manufacturer DSM.

By investigating the tape-component adhesion as well as by means of mechanical characterisation, the requirements for the various applications could be identified and the UD tapes and component properties adapted. The connection between the component and the UD-Tape was made using a welding or pressing process, depending on the application. Both processes could be significantly improved through the cooperation and adapted to the requirements of the components. Stable processes leading to well adhering tapes were realised.

An examination of the ecological and economic framework conditions by the Technical University of Kaiserlautern (Chair of Sustainability Management) supported the technical development. The status quo of the participating companies in the Circular Economy could be recorded through an accompanying circularity assessment. In addition, potentials were identified through which the project participants can position themselves even more sustainably in the future. For one of the use cases, a life cycle analysis including a CO2 balance was also prepared.

You were also provided with a prototype by Röchling Automotive. What was the basic idea here? What were the results of the investigations?

Rathgeber: Röchling Automotive was involved in the project as an associated partner. The company has set itself the strategic goal of acting in a sustainable and value-conscious manner. This includes supporting new developments in the plastics processing industry that aim at increased resource efficiency, recycling of plastics and more recycling. Several series of tests were carried out with different car parts. The aim was to use the fibre-reinforced tapes to compensate for a drop in performance of the components with recycled material and to reduce or make obsolete the proportion of long fibres or the insertion of glass or carbon layers by using completely polymer-based unidirectional fibre reinforcements. The feasibility could be demonstrated in a prototype.

To what extent can the results of the All-Polymer project contribute to more sustainability in the plastics industry?

Rathgeber: The technical, ecological and economic results have shown that several types of upgrading can be realised. By using fibre-reinforced tapes, the recycled content can be increased and a loss of performance due to the use of recycled material can be compensated for. This can open up new, demanding areas of application for components that are 100 percent recyclable. Another possibility is to reinforce components, which can thus be made lighter in construction. This not only saves material, but also energy in the life cycle of the product during every transport process.