CALB enzyme for
PET is one of the most successful plastics, the polymer is used to make bottles, carpets, clothing and more. A bio based alternative is PEF, made from biomass-derived furans. But even this green alternative requires metal catalysts for polymerization. Now, University of Groningen polymer scientists have described an enzyme that can polymerize furans under mild conditions.
Furan based polyesters are already produced by companies like Avantium. Furans can be made from biomass-derived sugars, and are polymerized to polyethylene 2,5-furandicarboxylate (PEF). This polymer offers superior barrier and thermal properties, making it ideal material for the packaging of food and non-food products.
‘However, polymerization of PEF is still done in the same way that PET has been polymerized for over the last 70 years’, says University of Groningen Professor of Polymer Chemistry Katja Loos. This polymerization process requires high temperatures and uses toxic metal-based catalysts. ‘That is why we started looking for an alternative’, explains Loos.
They found a commercially available enzyme which could link the furans to PEF. The enzyme Candida antarctica lipase B (CALB) is a lipase that breaks down ester bonds. The polymerization required the creation of these bonds, but as enzymes catalyse equilibrium reactions, this only required the polymer scientists to push the equilibrium towards the formation of ester bonds.
The entire process has been published in the scientific journal ChemSusChem on 29 January 2019. It shouldn’t be too difficult to translate the process from the lab to the factory, says Loos. ‘We performed our experiments in ether, but the polymerization could easily be done in bulk material of molten monomers.’ Also, in the lab, polymerization was accomplished through an ester bond. This would require an extra step in the preparation of the monomers. ‘But that could be left out, and direct polymerization of the diacid monomer would also be possible with this enzyme.’
However, enzymatic polymerization is not a drop-in procedure, Loos acknowledges: ‘Polyester production lines are set up for the classic polymerization, so adapting them to enzymatic polymerization would require a considerable investment.’ But for new companies exploring green alternatives to PET, the enzymatic process could be very attractive.
Interestingly, five years ago a colleague of Loos at the University of Groningen, Marco Fraaije, has developed an enzymatic process to produce this diacid monomer (FDCA, 2,5-Furandicarboxylic acid) from sugar-derived Hydroxymethylfurfural (HMF). This was done in a collaboration with the Dutch biotechnology company Corbion. ‘It would be interesting to see whether we can combine both pathways to make PEF from biomass’, says Loos.
In the Chemport ecosystem, various companies are working on green alternatives for polyester, like Avantium which is building a pilot biorefinery in Delfzijl and already produces both furans and PEF. Other companies work on converting biomass into polymers, like BioBTX. They have teamed up with Cumapol to produce PET from vegetable oil.
And the bio-based furans could have more applications, says Loos: ‘Our enzymatic polymerization produced polymers with a very high aromatic content.’ This translates to strong polymers, just like the polyamides with high amounts of aromatic monomers that make up Twaron. Could the enzymatic polymerization produce polyesters of similar strength? Loos: ‘We haven’t done any mechanical measurements, but the melting point is quite high, which suggests good mechanical properties.’
Reference: Dina Maniar, Yi Jiang, Albert J.J. Woortman, Jur van Dijken, and Katja Loos: Furan-Based Copolyesters from Renewable Resources: Enzymatic Synthesis and Properties. ChemSusChem 29 January 2019.