Thermosets are currently once again a highly sought-after class of materials due to their numerous advantages. At the same time, their recyclability is limited. Together with partners from industry, the SKZ Plastics Center is working on the sustainability of thermosets and aims to develop bio-based thermosets in the BioDurInject project.
The SKZ’s BioDurInject project is developing bio-based thermoset molding compounds
Thermosets are used for many injection molded products due to their various advantageous properties. Among other things, the cross-linked plastics are characterized by a long service life, heat resistance, dimensional stability, good fire properties and excellent electrical insulation properties. In contrast to thermoplastics, however, their recyclability is limited due to the cross-linking. This is a disadvantage in view of the current trend towards more sustainable plastic products. The use of renewable raw materials is therefore particularly important for this material class, so that no additional CO₂ is released during thermal disposal, for example.
Development of free-flowing thermoset molding compounds based on renewable raw materials
A research project at the SKZ Plastics Center in Würzburg therefore aims to make thermosets more ecological and is already starting with the materials. The project, called BioDurInject, aims to develop free-flowing thermoset molding compounds based on renewable raw materials. This applies to the matrix material, the fillers and also the fibers. The new molding compounds are to be used for the production of technical molded parts using the injection molding process. Produced molded parts should achieve a property level that corresponds to conventional molded parts.
Synthesis of seven different bio-based unsaturated polyesters (UP) to date
As part of this project, seven different bio-based unsaturated polyesters (UP) based on renewable raw materials have been synthesized on a laboratory scale by polycondensation at the SKZ. A special condensation apparatus was set up in the chemistry laboratory for this purpose and a suitable experimental methodology was developed. As a condensation product, the researchers at the institute obtained a yellowish liquid that is viscous at 190 °C and crystallizes completely at room temperature. This has already been analytically characterized using DSC. The tendency to recrystallize was investigated in a drying oven by melting and subsequent supercooling.
Industrial applicability for industry
Once the basic properties had been clarified, the scientists were able to start the first tests with regard to practical application. At the SKZ, efforts are always made to keep real, industrial applicability for industry in mind. For example, the new UP resins were compounded with renewable fillers and fibers as well as a thermal initiator at 100 °C to 120 °C in the measuring kneader in order to investigate the wetting behavior of the melts and the thermal processing window. At the same time, guide formulations for the compounds are currently being developed. Three of the first eleven compounds have already been cured using a plate press at 155 °C – a temperature that is also common in industrial thermoset injection molding.
Initial results inspire confidence
“We hope to be able to prove that bio-based thermosets can be used as a genuine alternative to conventional thermosets. The current results give us great confidence that they can be used on an industrial scale in the future,” explains Johannes Rudloff, Head of Materials, Compounding and Extrusion at SKZ. “The active participation and support of industrial partners such as Süd West Chemie GmbH and Baumgarten automotive technics GmbH is also fundamental in this project in order to develop truly practical solutions, and we would like to take this opportunity to thank them very much.”
