Polylactic acid (PLA) is a biodegradable bioplastic that is already used to produce a variety of everyday items, such as cups, trays, bowls and vegetable wrapping foil. Unfortunately, the current PLA production process is expensive and produces waste. Researchers at the KU Leuven Centre for Surface Chemistry and Catalysis in Belgium have now developed a new production technique that is cheaper and greener and makes PLA a more attractive alternative to petroleum-based plastics.
PLA boasts a number of advantages over petroleum-based plastic. It is one of the few plastics suitable for use in 3D printers, it is biocompatible, making it suitable for medical use, and it biodegrades in a few years in certain environments, and is industrially compostable and recyclable. But when it comes to cost, PLA can't compete with petroleum-based plastics due to the intermediary steps required to produce it.
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As its name suggests, lactic acid is a main building block of PLA. This can be obtained by the fermentation of sugar that can be sourced from renewable resources such as corn starch, tapioca and sugarcane.
"First, lactic acid is fed into a reactor and converted into a type of pre-plastic under high temperature and in a vacuum," explains Professor Bert Sels from the Centre for Surface Chemistry and Catalysis. "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."
To develop a more efficient and economical route to PLA, the researchers have borrowed a petrochemical concept that uses a zeolite (a porous mineral composed of aluminium, silicon, and oxygen) as a catalyst in the reactor to guide the chemical process that converts lactic acid into lactide.
"By selecting a specific type [of zeolite] 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,” said postdoctoral researcher Michiel Dusselier.
In practice, this means the intermediary steps that require metals and produce waste are eliminated from the production process, while providing higher yields of lactide. A patent for the new technique has already been bought by a chemical company that intends to scale up the production process to an industrial capacity.
While admitting that biodegradability isn't a desirable property for all plastics, (toilet drain pipes, for example), and the team isn't aiming to promote disposable plastic, Dusselier says that products that are made from PLA have the potential to become cheaper and greener thanks to the this new technique.
Details of the team's research were published in the journal Science.
Source: KU Leuven