“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,” said Loos. Toxic metal-based catalysts and high temperatures that are needed for this process mean that it is not very environmentally friendly.
That is why Loos and her colleagues looked for an alternative polymerization method, one that uses enzymes. “We eventually found a commercially available enzyme that would do this,” said Loos. The polymers are made by combining furans with linear monomers, either aliphatic diols or diacidic ethyl esters. The enzyme Candida antarctica lipase B (CALB) is a lipase that breaks down ester bonds, but the polymerization requires the creation of these bonds. This may seem counter-intuitive, but it is not, explains Loos: “Enzymes catalyze equilibrium reactions, and we simply pushed the equilibrium towards the formation of ester bonds.”