Next generation thermoplastic polyester elastomers

Plastic products are under criticism. In the future, truly sustainable plastics must be built exclusively from renewable carbon (rC) ¹. Plastic recycling as an rC source will play an essential role but will not be sufficient under the assumption of constant plastic production. Therefore, virgin material from biomass is also needed!

This is because the return of plastic products to equivalent economic cycles by means of mechanical and chemical recycling technologies is already an enormous technical challenge in principle - but it is not possible without losses. In mechanical recycling, this results from the fact that (i) the collection and sorting systems are not perfect and (ii) quality losses occur due to thermal stress or impurities. In chemical recycling, losses are caused by the necessary purification processes of the resulting basic chemicals, among other things. According to the rC guiding principle, these losses can only be compensated by biomass or CO2 utilization  (CCU) if the goal of net CO2 emissions close to zero is to be achieved.

Following this guiding principle, a team at Fraunhofer IAP has developed new thermoplastic polyester elastomers (TPEE) based on biogenic raw materials. Instead of the commonly used terephthalic acid, we use the biogenic building block 2,5-furandicarboxylic acid (FDCS), since the production of terephthalic acid from renewable carbon sources is currently not foreseeable. As our investigations show, substitution by FDCS can be a clear prospect here. Although the production of FDCS-containing plastics (as also widely documented in the literature²) presents several process-related difficulties, we have succeeded in identifying a suitable process window for the synthesis of high-molecular-weight bioTPEE.

The synthesis process developed at the Fraunhofer IAP, which can also be implemented industrially, delivered initial samples. These are currently being used to investigate and modify basic properties. One important goal is, among other things, to adapt the crystallization behavior to commercial petro-based TPEE grades so that their established applications can also be addressed by the bioTPEEs.

_{1) The major goal is to stop taking fossil carbon from the earth. Unlike the energy sector, which is aiming for decarbonization, the chemical industry cannot be made carbon-free. Since plastics are made up of significant amounts of carbon, it must therefore come from alternative carbon sources, which include biomass, CO2 utilization and recycling. Carbon obtained from these sources is referred to as renewable carbon.}

_{2) Refer to e.g. G.-J. M. Gruter et al., DOI: 10.1021/bk-2012-1105.ch001}