Researchers at the Germany-based Fraunhofer Institute for Applied Polymer Research have developed a new polylactide (PLA) material for flexible film applications.
PLA is a popular bio-based, biodegradable alternative to fossil-based polymers. Due to its high stiffness, it is suited for rigid packaging such as disposable cups, but not for flexible disposable packaging such as shopping bags, one of the main sources of plastic waste.
To address that shortcoming, scientists at Fraunhofer coupled polyether plasticisers directly to the polymer chain to make the PLA more flexible in the long term. Unlike usual additive manufacturing processes which mix plasticisers into PLA, Fraunhofer’s method ‘anchors’ the polyethers into the PLA chain which slows down molecular motions.
“Until now, plasticisers have been mixed into PLA as additives,” Dr. Benjamín Rodríguez said. “However, the plasticiser molecules migrate out of the material over time, making the PLA stiff and rigid again. To prevent this migration, we anchored the polyether to the polymer. To achieve this, we synthesised PLA-based block copolymers in which the polyether chain segment is covalently linked to PLA chain segments at both ends,” he explained.
Polyethers are non-toxic, commercially available, and can be produced from bio-based raw materials. Fraunhofer’s new material is at least 80% bio-based and the team believes it may be able to increase that proportion to almost 100%.
The team of three researchers, which also includes Dr. Antje Lieske and André Gomoll, has won the Joseph von Fraunhofer Prize for their invention. The €50,000 prize is awarded to Fraunhofer employees for outstanding scientific achievements in developing solutions for practical problems.
Another benefit of the new PLA-based material is that it can be produced cost-efficiently from commercially available raw materials in medium-size companies.
“Until now, PLA could only be produced profitably in continuous large-scale plants, which excluded smaller companies as manufacturers,” Gomoll said. “Finally, the new PLA material can also be processed into plastic films using conventional processing equipment in a similar way to LDPE - and it can be chemically recycled with considerably less energy input than LDPE,” he added.
Last year, SoBiCo GmbH, a subsidiary of the Fraunhofer Polymer Group, commissioned a production plant for the new PLA block copolymers in Pferdsfeld, Germany. It produces 2,000 tons of the new bioplastics per year under the name Plactid. Going forward, the company wants to increase production to 10,000 tons of the new flexible PLA material per year.