Researchers develop green process to make bio-plastics with low waste

Polylactic acid (PLA), a bioplastic used to make biodegrade drinking cups or vegetable wrapping foil, is not yet considered a full alternative to traditional petroleum-based plastics, as it is costly to produce. However scenario could change as researchers from the KU Leuven Centre for Surface Chemistry and Catalysis in Belgium have claimed to have found a way to make the PLA production process more simple and waste-free.
 
The bioplastic PLA is derived from renewable resources, including the sugar in 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.
 
However, polylactic acid is not yet a full alternative for petroleum-based plastics due to its cost. 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. This is an expensive process. The pre-plastic – a low-quality plastic – is then broken down into building blocks for polylactic acid. 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,” said Prof Bert Sels from the Centre for Surface Chemistry and Catalysis.
 
The KU Leuven researchers developed a new technique. Michiel Dusselier, a postdoctoral researcher, explained, “We have applied a petrochemical concept to biomass. 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 polylactic acid with less waste and without using metals. In addition, the production process is cheaper, because we can skip a step.”
 
Professor Sels is confident that the new technology will soon take hold. “The KU Leuven patent on our discovery was 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 toilet drain pipes, are not meant to be biodegradable. And it is not our intention to promote disposable plastic. But products made of polylactic acid can now become cheaper and greener. Our method is a great example of how the chemical industry and biotechnology can join forces,” said Prof Sels.