As one of the most widely used bioplastics in the world, polylactic acid (PLA) degrades very little outside of industrial composters. Researchers have developed an enzyme and then integrated it into PLA so that it helps degrade the plastic and withstand the high temperatures of enzymatic plastic manufacturing.
Published in
Nature, this work allows PLA to disintegrate in less than twenty-six weeks in a home composter.
Derived from plant materials, PLA can now degrade in less than 26 weeks thanks to an enzyme directly embedded into the plastic and capable of withstanding the temperature of its formulation.
© Guicherd et al.
Synthesized from plant materials, polylactic acid (PLA) is a biosourced polymer highly prized for food containers. Its biodegradability is also highlighted, but this only occurs if the temperature exceeds 140°F (60°C) for an extended period. While this partially corresponds to the conditions in industrial composters, PLA discarded elsewhere will degrade far too slowly to be considered environmentally friendly.
Enzyme integration directly into the material could facilitate its biodegradation, but industrial PLA processing occurs at no less than 340°F (170°C), a temperature too high for molecules derived from living organisms.
Researchers from the Toulouse Biotechnology Institute (
TBI, CNRS/INRAE/INSA Toulouse), the company
Carbios (France), and the universities of
Kasetsart (Thailand) and
Mons (Belgium), have developed a solution to integrate enzymes that retain their effectiveness after the formation of PLA.
The enzymatic plastic disintegrates in less than twenty-six weeks, which is faster than the maximum legal time allowed for home composting, and it also disappears, although more slowly, if left out in the open. In a dedicated facility, the modified PLA also generates more biomethane, providing an additional way to valorize waste.
This research was primarily conducted at the INSA/Carbios PoPlaB cooperative laboratory (Polymers, Plastics, and Biotechnology) located at TBI. The scientists first searched for the most appropriate enzymes and selected a protein, named PAM, produced by the thermophilic bacterium
Actinomadura keratinilytica.
As its properties were interesting but not sufficient, the team relied on bioinformatics approaches to search for a new thermostable enzyme, called ProteineT, and optimized its properties using molecular engineering techniques. The team then created an enzyme that withstands high temperatures, efficiently degrades PLA, and blends well with the plastic.
The enzyme is then integrated into a stabilized pre-mixture, a form in which the molecule can be stored long-term. It is only when the enzymatic PLA is placed in composting conditions that the enzyme begins to degrade it, making it an ideal material for flexible food packaging.
The scientists are now exploring enzymatic solutions for other polymers, such as polyamide.
Reference:
An engineered enzyme embedded into PLA to make self-biodegradable plastic.
Nature 631, 884-890 (2024).
https://doi.org/10.1038/s41586-024-07709-1