German researchers advance enzymatic recycling of rubber

Halle, Germany – Researchers in Germany have reported a potentially significant advance with the development of a process for the enzymatic degradation of synthetic polyisoprene rubber. 

While enzymes are known to degrade polyisoprene occurring in natural rubber, this has not been the case for the synthetically produced polymer due to differences in molecular structure.

However, research teams at Martin Luther-University Halle-Wittenberg (MLU) and the Leibniz Institute of Plant Biochemistry (IPB), say they have found a way to decompose artificially produced polyisoprene – using an enzyme labelled LCPK30.  

Polyisoprene distributes evenly as milky-white latex in water milk, which is harvested on rubber plantations and processed into natural rubber. 

To mimic this composition, the researchers succeeded in distributing synthetically produced polyisoprene evenly in water, using a specific solvent. 

"Our assumption was that synthetic polyisoprene should be present in an emulsion so that the enzyme can work properly," explains MLU chemist Vico Adjedje said in a 9 Dec release.  

The team found that the enzyme ‘complied’ with the artificial emulsion: remaining “intact over the reaction time [and] breaking down the long molecular chains of the polyisoprene into much smaller fragments.”

"A lot happens to the starting material before it becomes a finished tire: the molecule chains are chemically crosslinked to change the mechanical properties,” said Adjedje. 

“Plasticisers and antioxidants are added. The latter in particular present a problem for the enzyme because they attack its structure,". 

The researchers used LCPK30 as it occurs in nature and are currently working on optimising the enzyme so that it becomes less sensitive to solvents and triggers further reactions. 

According to MLU, the researchers aim to apply the technology to the decomposition other similar substances from car tires in the future. 

As well as reproducing new polymers, the team also envisages the degradation products being used in the production of fine chemicals and fragrances.