Exipnos and Fraunhofer IMWS optimize DCIM technology for used tire recycling

Millions of tons of scrap tires are generated worldwide every year. In Germany alone, the volume of scrap tires is around 500 kt per year. The recycling of such tires, which consist of a complex mixture of materials such as natural and synthetic rubber, fillers such as carbon black and silica, and reinforcing materials such as steel, polyester, or natural fiber-based tire cord, is playing an increasingly important role in manufacturers' efforts to achieve sustainability and meet regulatory requirements. One important approach is mechanical recycling. This involves shredding the tires to produce, for example, rubber recyclates, which are already commercially available in a wide range of qualities, or recycled fibers.

However, these recycled particles and fibers cannot be easily used in existing plants for the production of high-quality plastics. In particular, there is currently a lack of technically, ecologically, and economically efficient processes for recycling tire cord made from regenerated cellulose, a renewable raw material. Yet recovery would be particularly worthwhile because it could be used, for example, as reinforcing fibers in thermoplastic lightweight construction solutions.

In the project " DCIM4Recycling", which will run until September 2027, Exipnos GmbH, a service provider for material and technology development in the plastics industry based in Merseburg, and Fraunhofer IMWS want to develop solutions for this. They are focusing on DCIM (Direct Compounding Injection Molding) technology because it offers a further sustainability advantage in the manufacture of thermoplastic components. This involves linking a compounding unit to a conventional injection molding machine. This eliminates the need for a separate compounding step in the extruder to incorporate recycled materials and thus saves a large amount of energy that would otherwise be required to reheat the plastic melt. This reduces the energy consumption in the production of injection molded parts by about half. DCIM is also particularly suitable for the direct processing of bio-based polymer systems, biofibers, and recycled materials, as these also benefit from the lower overall thermal load.

Together, the project partners want to make this manufacturing process suitable for processing rubber recyclates and recycled fibers. The aim is to develop a DCIM add-on device that can be combined with existing standard injection molding machines. Existing systems can thus be significantly expanded in terms of functionality and the usable material selection and combination with an extruder as a side-mounted DCIM add-on module, without the need for a complete new purchase. Another major goal is to find formulations for additive mixtures for adhesion promotion that can be used in the processing of thermoplastics containing rubber recyclates.

This requires the optimization of machine configurations and processing conditions at DCIM so that they are well suited for the production of compounds with rubber recyclate powders and short tire cord fibers from scrap tires. The project partners are focusing on the machine configuration (design) as well as the processing conditions (optimal parameters for screw geometry, dosing, feeders, degassing, speed, temperature, shear input, compound composition) and the properties of the resulting plastics.

"The use of rubber recyclates in DCIM processing offers a double sustainability advantage: material from scrap tires can be reused in a meaningful way and can be processed into high-quality plastics with improved, tailor-made properties in an energy-saving and cost-effective manner," says Prof. Dr. Mario Beiner, who heads the project at Fraunhofer IMWS. "Research into fundamental process-structure-property relationships in thermoplastics containing rubber recyclates is central to enabling the targeted optimization of formulations and processing methods."

The Fraunhofer experts will investigate various model systems with suitable plastics (biopolymers as matrix) and rubber recyclates/tire recyclates, taking costs and availability into account. The focus is on particle sizes and surface properties, for example, as well as a better understanding of the kinetics of key degradation mechanisms at the molecular level in order to minimize thermal-chemical decomposition or counteract it with suitable additives. Solutions are also to be found for the selection and optimization of bonding agents that support the optimal bonding of rubber recyclate particles to the plastic matrix.

Based on this knowledge, processing trials will begin. The resulting components will be analyzed in detail at Fraunhofer IMWS with regard to their application-relevant properties and also compared with those from a classic two-stage process consisting of extrusion and injection molding. This involves comprehensive quantification of important mechanical properties such as tensile strength, impact strength, and hardness; damping properties using dynamic mechanical analysis; microstructure using (electron) microscopic methods; and crystallinity using X-ray diffractometry and calorimetric methods (DSC). Special properties such as creep or temperature and media resistance are assessed in relation to specific applications. Another scientific focus is the analysis of property-determining micromechanical mechanisms at the interfaces between recyclate and thermoplastic, as well as crack formation and propagation in the material using electron microscopic methods.

The institute can draw on its many years of expertise in the field of tire rubber as well as on materials science models for describing process-structure-property relationships for innovative, high-performance compounds made from recycled rubber and bio-based plastics. "Thanks to the capabilities of the rubber mixing room at the Fraunhofer Pilot Plant Center for Polymer Synthesis and Processing PAZ in Schkopau, we not only have in-depth experience in the compounding of silica- and carbon black-containing natural and synthetic rubber compounds, but can also develop pilot-scale solutions for our clients," says Beiner.

The thermoplastics produced using the advanced DCIM process could be used in transport infrastructure and automotive engineering, for example as damping material. "This would open up completely new possibilities both for processing thermoplastics containing recycled rubber and for the material recycling of used tires. We could produce plastics containing recycled tires with excellent, tailor-made properties and at the same time make a significant contribution to energy savings and an improved CO_₂ balance," says Beiner.

(December 19, 2025)