Biosourced, biodegradable, biocompatible and fit for 3D printing, polylactic acid PLA seems to earn the pole position in the bioplastics market race. Yet, PLA is not yet considered a full alternative to traditional petroleum-based plastics such as Polyethylene Terephtalate (PET) or Polystyrene (PS), as it is costly to produce. Price remains a major obstacle to a widespread usage of PLA. This is why Researchers from the KU Leuven Centre for Surface Chemistry and Catalysis in Belgium decided to tackle the issue of PLA’s complex two step manufacturing process. They now present a way to make the PLA production process more simple and waste-free. Their findings were published in Science (*).
PLA is derived from renewable resources, primarily sugars extracted from maize and sugarcane. Fermentation turns the sugar into lactic acid, which in turn is a building block for polylactic acid. PLA degrades after a number of years in certain environments. If it is collected and sorted correctly, it is both industrially compostable and recyclable. In addition, PLA is biocompatible and thus suitable for medical use, for instance in absorbable suture threads. PLA is also one of the few plastics that are suitable for 3D printing.
The production process for PLA is expensive because of the intermediary steps. “First, lactic acid is fed into a reactor and converted into a type of pre-plastic under high temperature and in a vacuum”, Professor Bert Sels from the Centre for Surface Chemistry and Catalysis explains. “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. And even though PLA is considered a green plastic, the various intermediary steps in the production process still require metals and produce waste.”
KU Leuven developed a new technique. “We have applied a petrochemical concept to biomass”, says postdoctoral researcher Michiel Dusselier. “We speed up and guide the chemical process in the reactor with a zeolite as a catalyst. Zeolites are porous minerals. 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. The production process is cheaper, because we can skip a step”.
Professor Sels is confident that the new technology will soon take hold. “KU Leuven’s patent rights on our discovery were recently sold to a chemical company that intends to apply the production process on an industrial scale. Of course, PLA will never fully replace petroleum-based plastics. For one thing, some objects, such as drain pipes, are not meant to be biodegradable. And it is not our intention to promote disposable plastic. But products made of PLA can now become cheaper and greener. Our method is a great example of how chemical industry and biotechnology can join forces”.
(*) Note: The full text of the study “Shape-selective zeolite catalysis for bioplastics production” by Michiel Dusselier, Pieter Van Wouwe, Annelies Dewaele, Pierre Jacobs, and Bert Sels was published in Science (DOI: 10.1126/science.aaa7169). Copies can also be obtained from the authors.