Although - contrary to what some think - polystyrene can be mechanically recycled, post-consumer polystyrene waste is often too contaminated to make this a truly feasible option. This is largely due to the low quality of the recyclate, which can therefore not find application in the kind of products this resin would ordinarily be used for.
As the transition to the circular economy starts to take shape, a different approach to end-of-life polystyrene is urgently needed. The ResolVe project was set up to explore whether chemical recycling offered a possible solution.
Established as a joint project, with partners from various German research institutes and facilities, funded by the German Federal Ministry of Education and Research (BMBF) and led by Ineos Styrolution, the ResolVe initiative sought to develop technology that would enable the commercial use of post-consumer polystyrene waste as a raw material to produce high-quality plastics. The styrene monomer, the main component of depolymerisation, would subsequently be used by Ineos Styrolution in its own production process.
Next to studying the technical feasibility of depolymerizing polystyrene, the project also developed a conceptual layout of an entire recycling concept, including the contributions of recycling companies.
The ResolVe initiative developed a method for thermally induced depolymerisation. In this process, the polymer is split thermally into low-molecular substances, such as monomers and oligomers. The monomers are then used to produce polymers that have identical properties to polymers from conventional feedstock.
The so-called “downcycling”, that takes place in mechanical recycling, is therefore avoided.
The project also included a commercial and an ecological evaluation of the recycling process.
The final report on the ResolVe research has now been completed by the team, coordinated by Franziska Nosić, of Ineos Styrolution. The conclusion is clear: depolymerisation is a highly appropriate recycling solution for polystyrene in combination with distillation of the output for further polymerisation. The process promises to produce recycled polystyrene meeting food contact standards.
The research carried out with the scope of ResolVe revealed that up to 75 percent of the output can be fed into the purification step and subsequently back into the production of new polystyrene. A broad variety of feedstock materials could be processed using the depolymerisation process, although lightweight packaging and expanded polystyrene (EPS) waste were proven to be the most suitable.
It was also possible to largely eliminate the “legacy” flame retardant HBCD (hexabromocyclododecane), although some bromine-containing traces remained.
For Norbert Niessner, Global R&D/ Intellectual Property Director at INEOS Styrolution, the project has made a dream come true.
“The results demonstrate that polystyrene and depolymerisation fit perfectly to the concept of a circular economy,” he said.
Moreover, in addition to contributing to offering a solution to reduce the accumulation of post-consumer polystyrene waste and making it possible for valuable resources to be recovered, the approach is a sustainable one.
A life cycle assessment of the production process for polystyrene revealed that the production with previously depolymerised material requires less energy and produces less CO2, than conventionally produced polystyrene.