Three unprinted tea bags with clip-on cards

The new, more sustainable bags from EN Tea are unprinted and come only with a clip-on collectible card featuring a botanical motif. Image: EN Tea

Compostable biopolymer PBS replacing fossil plastics

Bioplastics are becoming increasingly well-established on the plastics market. Many can be processed just like classic petroleum-based plastics and are suitable for a wide range of applications. One important type of bioplastic is PBS. The biopolymer is plant-based, biodegradable and recyclable. A Japanese tea manufacturer is now using PBS in the packaging for its tea bags.

PBS stands for polybutylene succinate. It is made from succinic acid and 1,4-butanediol, both of which can be obtained today usingrenewable materials. The bioplastic can be turned into a wide variety of different versions and has good processing properties, making it suitable for a diverse range of applications in sustainable products. As a current example, one of the materials Japanese tea brand EN Tea now uses in the packaging for its tea bags is BioPBS from the Mitsubishi Chemical Group. The tea itself is already sealed in bags made of Soilon, a starch-based, biodegradable mesh. On the unprinted packaging, fossil plastics are now replaced by a sealing layer and a zip closure made of compostable BioPBS from the Mitsubishi Chemical Group. The biopolymer is highly heat-sealable at low temperatures and is already used in a multiplicity of applications – in particular as packaging material for food. Mitsubishi’s BioPBS is used, for example, as a coating for cardboard to-go cups, allowing them to be composted or recycled via the waste paper stream unlike conventional cardboard cups coated with LDPE.

Coffee cups coated with BioPBS can be composted or recycled with the waste paper. Image: Anna Pascale/Unsplash

With the use of BioPBS in the sealing layer and the zip fastener, EN Tea’s tea bag packaging, including barrier layer and adhesives, is now made entirely of compostable materials. Mitsubishi Chemical obtains its bio-based polybutylene succinate from renewable materials such as sugar cane, cassava or corn and offers both certified industrially compostable and home-compostable types. The biopolymer can be processed using conventional systems without the need to modify or replace existing equipment and is compatible with natural fibres and other biopolymers such as PLA.

Major need for development in PBS segment

Rethinking plastics is also a key motivation for research at the German Fraunhofer Society. Consistently making progress with bioplastics such as PBS is an important area of focus in this context. The organisation states that there is a major need for development in this area. Polybutylene succinate is a promising base material available on the market that is made from bio-based raw materials and is biodegradable. But to cover a broad range of different properties, as is possible with the large number of different types of polyethylene (PE), application-specific PBS types will also need to be developed.

This is exactly the task that the Rubio Project sets out to accomplish. The undertaking is funded by the German Federal Ministry of Education and Research (BMBF) and will run until August 2024. In pursuing the research project, 18 partners want to make the vision of a sustainable plastics industry a reality. Their aim is to use locally available plant residues to crate versatile, sustainable products that are recyclable and biodegradable. As part of the project, the Fraunhofer Institute for Applied Polymer Research (IAP) is developing novel types of PBS so that the bioplastic can be used for significantly more applications. Along with German company Polifilm Extrusion GmbH, the institute has developed a first marketable product: a PBS sheet that can be used for postal bags.

The bioplastic sheeting made of PBS and developed as part of the Rubio Project is recyclable, biodegradable and can be processed on widely used extrusion lines. Image: Polifilm

"Depending on the application or process at hand, the plastic used may need to be hard or soft – perhaps it may also need to be high or low-viscosity. However, there are only three types of PBS on the market, and these are suitable only for a limited number of processing methods and applications."

Dipl.-Ing. Thomas Büsse, head of Processing Pilot Plant for Biopolymers, Fraunhofer Institute for Applied Polymer Research

For this reason, Fraunhofer IAP is developing completely new types of PBS that can be put through a significantly broader range of processes – from blow moulding to injection moulding. In doing so, the research team is also expanding the range of potential applications. And it tests for biodegradability, printability, sealability and machine compatibility – criteria that the scientists can set on an individual basis at the customer’s request.

Use of local plant residues

Development work is ongoing, as the bioplastic is not yet based on local raw materials. But this should change as the collaborative effort unfolds. In principle, all materials containing cellulose or lignocellulose can be recycled. These include unrotted digestate from biogas plants, residues from farming activities or even, in theory, waste from paper production.

"One of the great advantages of this idea is that the raw materials used in the first instance are readily available plant residues. This means there is no competition with food, such as with sugar cane-based bioplastics. In addition, if we achieve our goals, PBS can be used in a wide range of processes with comparatively low energy consumption. In that scenario, it should be possible to fine-tune the desired material properties for the relevant task with a high degree of precision."

Dr. Patrick Hirsch, Rubio Project coordinator, Fraunhofer Institute for Microstructure of Materials and Systems