Circular economy: Researchers show how synthetic rubber raw material can
be degraded

Date:
December 9, 2021
Source:
Martin-Luther-Universita"t Halle-Wittenberg
Summary:
Enzymes are capable of degrading synthetic polyisoprene. The
specific conditions for that have now been created and
exploited. Polyisoprene is the principal component of natural rubber
and of many types of rubber also used in car tires, for example. Up
until now, it has only been possible to degrade polyisoprene, with
a composition similar to naturally occurring rubber. The present
research could provide important insights toward a circular economy.



FULL STORY ========================================================================== Enzymes are capable of degrading synthetic polyisoprene. The specific conditions for that have now been created and exploited by researchers at Martin Luther-University Halle-Wittenberg (MLU) and the Leibniz Institute
of Plant Biochemistry (IPB). Polyisoprene is the principal component of
natural rubber and of many types of rubber also used in car tires, for
example. Up until now, it has only been possible to degrade polyisoprene,
with a composition similar to naturally occurring rubber. The present
research could provide important insights toward a circular economy. The
study appeared in the journal Green Chemistry.


========================================================================== Natural rubber is used to make polyisoprene, which in turn enables the production of many types of rubbers and plastics. Polyisoprene is a
long-chain molecule formed by linking hundreds or thousands of smaller
isoprene molecules.

"Various bacteria are able to degrade natural polyisoprene with the help
of enzymes," says MLU chemist Vico Adjedje. Enzymes are biomolecules
that make chemical reactions possible in all living organisms -- from
simple single- celled organisms to humans. Since global demand for
rubber products is greater than can be satisfied by existing stocks of
natural rubber, the starting material is mainly produced by chemical
synthesis. Natural and synthetic variants have similar properties,
but exhibit a number of differences in the structure of the molecules
of which they are composed.

The research teams of Prof. Dr. Wolfgang Binder at MLU and Jun.-Prof. Dr.

Martin Weissenborn at IPB and MLU have now found a way to decompose artificially produced polyisoprene using the enzyme LCPK30. "We are the
first to have succeeded in getting the polyisoprene into a form that the
enzyme can also work with," says Binder. In doing so, the researchers took inspiration from nature: "Our assumption was that synthetic polyisoprene
should be present in an emulsion so that the enzyme can work properly,"
Adjedje says.

Milk, which consists largely of water and fat, provides a typical
example of an emulsion. It forms globules a few micrometers in size,
and its fine distribution in water lets the milk seem cloudy. Just like
fat, polyisoprene is virtually insoluble in water. Nature nevertheless
manages to distribute it evenly in water: as milky-white latex milk,
which is harvested on rubber plantations and processed into natural
rubber. Inspired by this latex milk, the researchers succeeded in
distributing synthetically produced polyisoprene evenly in water, using
a specific solvent. The enzyme complied with the artificial emulsion
and thus remained intact over the reaction time, breaking down the long molecular chains of the polyisoprene into much smaller fragments.

The researchers' goal is to be able to break down other similar substances
from car tires in the future. "A lot happens to the starting material
before it becomes a finished tire: the molecule chains are chemically cross-linked to change the mechanical properties. Plasticizers and
antioxidants are added. The latter in particular present a problem for the enzyme because they attack its structure," says Adjedje. The results also provide important impetus toward a recycling economy. "We could further
process the degradation products into fine chemicals and fragrances --
or reproduce new plastics," explains Binder. The researchers used LCPK30
as it occurs in nature. Weissenborn's research team is currently working
on optimizing the enzyme so that it becomes less sensitive to solvents
and triggers further reactions.

========================================================================== Story Source: Materials provided by Martin-Luther-Universita"t_Halle-Wittenberg. Note: Content may be edited
for style and length.


========================================================================== Journal Reference:
1. Vico K. B. Adjedje, Eugen Schell, Yannick L. Wolf, Annegret Laub,
Martin
J. Weissenborn, Wolfgang H. Binder. Enzymatic degradation
of synthetic polyisoprenes via surfactant-free polymer
emulsification. Green Chemistry, 2021; 23 (23): 9433 DOI:
10.1039/D1GC03515K ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2021/12/211209095608.htm

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