RESILIENT

Silicone is an engineering plastic that has become increasingly important in recent years and will continue to do so, as this material can be used and processed universally. The high chemical resistance and excellent elastic properties of silicones speak in favour of their use. The material is often combined with other thermoplastic materials in order to utilise these hard/soft combinations for challenging applications, for example in the automotive, white goods or medical sectors.

There are basically different types of silicone, such as liquid silicones (LSR, liquid silicone rubber) and solid silicones (HTV, high-temperature crosslinkers) in addition to other applications such as silicone sealants. What all these applications have in common is that the basic silicone structure consists of chains based on silicon and oxygen (siloxanes). These can be built up into different molecules (determined by the chain length and the side chains or organic residues on the silicone), which are then converted from rubber to elastomer using different cross-linking mechanisms (e.g. radical for HTV silicones or via catalytic addition to double bonds in LSR). The siloxane chain or structure is responsible for the high temperature resistance, chemical resistance and biocompatibility (usually after post-crosslinking to remove the last monomers). Due to the high purity that can be achieved, silicones can be found not only in medical applications, but also in products for babies (e.g. bottle teats) or cable sheathing for e-mobility for high-voltage cables.

However, an existing problem with silicone is that the material is difficult to recycle after cross-linking, as is the case for most cross-linked plastics (elastomers and duromers). This applies both to pure silicone and to material combinations. In the case of material combinations, the effect is doubly negative, as the thermoplastic that is combined with the silicone cannot be directly recycled again and is therefore lost as a material flow for established recycling technologies. One advantage of elastomers in general, and therefore also of silicones, is that elastomers are typically more extensively cross-linked, i.e. breaking these bonds requires less chemical effort than with thermosets.

Silicone waste is produced at various points along the process chain. On the one hand, there is production waste, which is very well defined and easy to collect. On the other hand, there is also material from the production start-up and parts outside the specification, which then accumulate in the next step. Relatively pure streams can often also be recorded here (pre-consumer waste). The final step is the end-of-life waste (or post-consumer waste), which is then heavily mixed but often consists of high proportions of high-quality thermoplastics in addition to silicone.

All of this waste is made up of very high-quality (and therefore also high-priced) materials, which in combination, however, can no longer be processed or can only be processed into inferior material mixtures.
The aim of the RESILIENT project is therefore to recover such streams using a combination of different and new technologies or technology combinations and thus to recycle the materials into high-quality materials and raw materials. TCKT is working on this ambitious project as consortium leader together with the project team consisting of researchers (Competence Centre CHASE GmbH), material manufacturers (RICO Group GmbH, Gebauer & Griller Kabelwerke Ges.m.b.H.), a recycler (BERNEGGER GmbH) and a plant manufacturer (EREMA Engineering Recycling Maschinen und Anlagen GmbH).