Cheaper, greener biodegradable plastic

Researchers from KU Leuven have developed a way to produce polylactic acid (PLA) — a bioplastic used in products such as biodegradable drinking cups and vegetable wrapping foil — in a simpler and more waste-free way.

Writing in the journal Science, the researchers explained that PLA is a benign alternative to petrochemical-based plastics. It is derived from renewable resources, including the sugar in maize and sugarcane. Fermentation turns this sugar into lactic acid, which in turn is a building block for polylactic acid.

Suitable for both medial use and 3D printing, PLA degrades after a number of years in certain environments. However, it is not yet a full alternative for petroleum-based plastics due to its costly production process.

“First, lactic acid is fed into a reactor and converted into a type of pre-plastic under high temperature and in a vacuum,” explained study co-author Professor Bert Sels. “This is an expensive process. The pre-plastic — a low-quality plastic — is then broken down into building blocks for PLA. In other words, you are first producing an inferior plastic before you end up with a high-quality plastic.”

Corresponding author Michiel Dusselier said the researchers developed a new technique in which they “applied a petrochemical concept to biomass”. He said, “We speed up and guide the chemical process in the reactor with a zeolite [a porous mineral] as a catalyst.

“By selecting a specific type on the basis of its pore shape, we were able to convert lactic acid directly into the building blocks for PLA without making the larger by-products that do not fit into the zeolite pores. Our new method has several advantages compared to the traditional technique: we produce more PLA with less waste and without using metals. In addition, the production process is cheaper, because we can skip a step.”

Professor Sels revealed that the patent on the discovery was “recently sold to a chemical company that intends to apply the production process on an industrial scale”. And while he admits PLA will never fully replace petroleum-based plastics — “For one thing, some objects, such as toilet drain pipes, are not meant to be biodegradable” — he is pleased that products made of PLA can now be cheaper and greener.

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