About David

David is a polymer engineer with a strong multidisciplinary background within polymer physics, chemistry and process technology. During his master studies at University of Leoben in Austria he conducted research within the Simulation and Modeling group at the Polymer Competence Center Leoben GmbH in the field of heat transfer analysis.

He joined KraussMaffei Extrusion GmbH in 2021 as a process engineer in the field of Compounding and Recycling, where he was responsible for conceptual design, technical specification and evaluation of novel technologies for large scale recycling projects, mostly focused on twin-screw extrusion.

In 2022 he picked up his doctorate studies at the University of Hanover at the Institute of Plastics and Circular Economy in the field of advanced physical recycling concepts for post-consumer polyolefins, leading various development projects.

Since 2023 he has the technical responsibility for Extrusion based Recycling applications at KraussMaffei, for which he leads a team of process engineers.

What are the main benefits of using twin-screw extruders in chemical recycling compared to other technologies?

Extruders generally process polymers through friction-heating, mixing, conveying, and degassing. Specifically, intermeshing co-rotating twin-screw extruders are ideal for chemical recycling due to their unique processing characteristics. They generate high shearing rates on a small diameter, enabling polymer melting and heating through mechanical energy dissipation. This results in no need for a heat transfer medium, low losses, high energy-efficiency, and excellent scalability. They are underfed systems that allow stoichiometric addition of reagents or catalysts and prevent fouling through self-cleaning. With the flexibility to independently vary throughput and screw speed, they handle fluctuating input material robustly. A wide range of screw elements allows us to customize process sections to control temperature, residence times, and pressure. Our high-volume, high-torque BluePower series is particularly suitable for process-specific adaptations. Twin-screw extruders are perfect for leveraging established, configurable equipment to create scalable continuous processes requiring intensive mixing, substance addition, degassing, or high temperatures.

Can you provide examples of how KraussMaffei's products have improved chemical recycling for automotive or packaging clients?

We actively engage in PET chemical recycling for packaging clients, using glycolic degradation to partially depolymerize PET into shorter chain oligomers with co-rotating twin-screw extruders. This is followed by filtration and a polycondensation reactor to repolymerize the PET, producing essentially virgin FDA-grade polymer. Our customers can flexibly integrate our extruders within existing setups. This method allows beverage companies to add recyclate content to their PET bottle material streams without quality restrictions. This is just one example where the extruder functions as a depolymerization reactor, we are working on different projects to establish other fully continuous depolymerization processes. Some engineering plastics that can be yielded will be of interest to automotive clients. More recently, our extruders are also used for melt preparation in pyrolysis processes – which ultimately yield polyolefins for the packaging value-chain. Expect to hear more from KraussMaffei in this domain in the future.

How do KraussMaffei's new investments in plants and modernisation help support circular economy efforts and the demand for recycled materials?

We have invested in our new Innovation Center (IC) in Laatzen, which stands as a unique R&D hub for extrusion technology. It houses 18 operational lines across a 10,000 m² space for all of our applications including recycling. The IC mirrors large-scale production plants, showcasing our solutions integration into customer layouts. We see ourselves as a solution provider, aiming to maximise our products positive impact on customers and the environment. The facility is key for developing and validating advanced recycling processes - be it through challenge tests for food-grade recyclates, evaluating extrusion technology for solvent-based processes or using the extruder as a reactor for depolymerization. We are equipped to handle explosive substances and solvents, densify low bulk density material, test different filtration systems and are generally operating independently of suppliers for up- & downstream equipment to be able to freely combine and evaluate the ideal solutions for any given process.

David Rapp will be speaking on Day 2 at the Innovation and Extrusion Theatre.