Scientists Use Enzymatic Polymerization Method for Furan-Based Polyester

Polyethylene terephthalate (PET) is one of the most successful plastics and is used to produce bottles and fibers for clothing. However, petroleum-based building blocks are used to produce PET.

An alternative to PET can be obtained from bio-based furan molecules; however, these furans require high temperatures and toxic catalysts in order to be polymerized. Presently, polymer chemists at the University of Groningen, headed by Prof. Katja Loos, have illustrated an enzyme-based polymerization technique. Their outcomes were reported in the journal ChemSusChem on January 29^th, 2019.

Fizzy drink bottles are manufactured using PET due to its outstanding barrier properties, which retain the fizz inside. “But furan-based polymers are a good alternative,” says Katja Loos. Furans, which are distinguished by an aromatic ring with four carbon and one oxygen atom, can be produced from biomass-derived sugars and can be polymerized into Polyethylene 2,5-furandicarboxylate (PEF). It is also possible to form other copolyesters from furans, yielding plastics with different properties.

Equilibrium

Furans are mainly produced with enzymes. But for the polymerization, the same processes are used as have been used for PET production for the last 70 years.

Katja Loos, Professor, University of Groningen.

Since this process requires high temperatures and toxic metal-based catalysts, it is not very eco-friendly.

Hence, Loos and her team sought an alternative polymerization technique which uses enzymes. “We eventually found a commercially available enzyme that would do this,” says Loos. The polymers are formed when furans are combined with linear monomers, either diacidic ethyl esters or aliphatic diols. The enzyme Candida antarctica lipase B (CALB) is a lipase that disintegrates ester bonds; however, the polymerization demands the formation of these bonds. This may look self-contradictory, but it is not, describes Loos: “Enzymes catalyze equilibrium reactions, and we simply pushed the equilibrium towards the formation of ester bonds.”

In their paper, the researchers explain how CALB and several furans and linear monomers are employed to synthesize various copolyesters. They successfully increased the content of aromatic units in the polyester to an extent where it went beyond the properties of PET. Hence, the enzymatic polymerization seems to be a feasible alternative to the traditional catalytic polymerization.

In our experiments, we used ether as a solvent, which you don’t want in a factory setting. But as the melting point of furans is quite low, we are confident that enzymatic polymerization will work in liquid monomers as well.

Katja Loos, Professor, University of Groningen.

Green Alternatives

Since the CALB enzyme is commercially available, it is shocking to know that it has not been used before by anyone to avoid the process of toxic catalysts and high temperatures. The sole reason that Loos can provide is that the majority of polyester production lines are customized to use these traditional reactions instead of the enzymatic alternative. And it is expensive to change a production line. “However, our enzymatic polymerization process would be ideal for new companies working on green alternatives to PET.”