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Researchers Develop Strong, Durable Bio-based Polyester

Image courtesy of Van 't Hoff Institute for Molecular Sciences, University of Amstedam tensile testing of materials
Tensile testing of bio-based polymer (left) and a sample of polymer film.
Simple method overcomes low reactivity of bio-based secondary material, resulting in high-molecular-weight polyester with mechanical and thermal properties that, in some cases, outperform fossil-fuel-based materials.

Researchers in the Netherlands have developed a method that enables the production of a strong, durable bio-based polyester. A simple synthesis strategy used by the Industrial Sustainable Chemistry group led by Prof. Gert-Jan Gruter at the University of Amsterdam reportedly overcomes the inherent low reactivity of bio-based secondary diols, resulting in a polyester with good mechanical and thermal properties as well as a high molecular weight. The research is described in a paper published in Nature Communications and an article on the University of Amsterdam website.

In general, polyester plastics are synthesized from small dialcohol and diacid molecules, explained the article on the university site. These monomers are coupled in a condensation reaction, resulting in a long polymer chain of molecular building blocks in an alternating fashion. The material properties result both from the number of building blocks that make up the polymer chain, and from the inherent properties of the monomers. In particular, their rigidity is key to a firm, strong, and durable plastic.

To achieve a bio-based material with similar properties, glucose-derived dialcohol isosorbide showed promise, as it has a very rigid molecular structure and is already industrially available. However, isosorbide is rather nonreactive, and in the past two decades it has proven quite challenging to obtain useful isosorbide-based polyesters, according to the article. It was nearly impossible to arrive at sufficiently long polymer chains (to achieve a certain ductility) while incorporating sufficiently high amounts of isosorbide (to arrive at a strong and durable material), it noted.

Daniel Weinland, PhD, first author of the paper in Nature Communications, and his colleagues found a solution by incorporating an aryl alcohol in the polymerization process. This leads to in situ formation of reactive aryl esters and a significant enhancement of end group reactivity during the final stage of polyester synthesis when the isosorbide’s low reactivity inhibits chain growth in traditional melt processes. As a result, high-molecular-weight materials could be produced with incorporation of high fractions of the bio-based, rigid secondary diol, even up to 100 mol%. For the first time, said the researchers, high-molecular-weight poly(isosorbide succinate) can be produced, the polyester obtained from isosorbide and succinic acid. The resulting strong plastics outperform existing plastics like PET in terms of heat resistance, an important attribute when washing re-usable bottles typically at 85°C (185°F). The isosorbide-based polymers also show promising barrier and mechanical properties that can outperform common fossil-based materials, according to the researchers.

The novel polymerization approach described in the paper is characterized by operational simplicity and the use of standard polyester synthesis equipment, noted the article on the university site. It suits both existing and novel polyester compositions, and the researchers foresee the application of similar methods in other classes of polymers, such as polyamides and polycarbonates.

This research was carried out within the RIBIPOL (Novel Rigid Bio-based Polyesters for potential large scale applications) project funded by the Dutch Research Council NWO with contributions from industry. The latter include Lego, which supported the project as part of its search for non-fossil alternatives for its plastic bricks, and Avantium, which is interested in bottle and film applications.

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