Duraprint spotlight: a Q&A with Corbion on PEF and the future of bio-based plastics

Stefan: PEF is polyethylene furanoate. We see it as the counterpart to PET. PET is polyethylene terephthalic acid and is derived from petroleum sources. By substituting the terephthalic acid with FDCA, which is derived from sugars using bio-fermentation, we can make a material with very similar chemical properties to PET, but with some key differences. For example, it has a slightly lower melting point which makes it more sustainable since you don’t need to use as much heat, it has significantly better barrier properties than PET, and the tensile strength of PEF is a little higher, which means there is a possibility to make lighter-weight materials from it.

Marc: A bioplastic can be biobased so made from annually renewable resources, biodegradable or both. Biobased plastics could start from another biopolymer called cellulose, which you can then make into a glucose. At Corbion, we start from sugar (glucose or fructose) derived from plants and turn that into the building block FDCA. We then combine that with methylene glycol (MEG). If you have those two building blocks in a one-to-one ratio, you can make a100% bio-based polymer which can replace PET a 100% fossil-based, polymer.

Yes, PEF can definitely be recycled, but just as with any plastic it can not endlessly be mechanically recycled,  but you can recycle it multiple cycles. It can also be chemically recycled, and in that case, you can almost infinitely recycle the material.

Stefan: PEF can be recycled in a PET stream, up to a certain content. Although the difference in processing temperature between PEF  and PET has an impact on the mixability of the 2 polymers, in practice, the volumes of PEF are so small that you will hardly notice any impact on PET in recycling streams.

PET has the tendency to crystallize when cooling down from the melt. This phenomenon creates shrinkage during the cooling of 3D printed objects which can cause shape instability (e.g. warping of the printed object). For this reason, often not PET but PETg (glycol modified PET) is used. This copolymer does not suffer from crystallization. PETG can be recycled together with standard PET but reduces the performance of the material in e.g. bottle production hence co-recycling is unfavourable.

In this project PEF was selected not only for being not only being a green biopolymer but also for its inhibition towards crystallization similar to PEFg, making it ideal with respect to 3D printing.

Marc: Since PEF is not widely available yet when you start introducing it and it gets mixed into PET streams, you will hardly notice because the volumes are so small. However, we have been thinking about how to start a system for recycling PEF bottles. We have been looking into juice bottles and soda bottles, and in those cases, there’s already a technique you can start using today using plastic collection machines at the supermarket. About two years ago, we did some tests with these machines and found that they can be programmed to distinguish between PET bottles and 100% bio-based PEF bottles. Industrial installations could also use the same near-infrared technology at a larger scale.

Stefan: Another advantage of PEF is that it’s a one-component product. On the other hand, many PET bottles are multi-layer bottles. They often have a nylon layer in the middle to increase the barrier properties, and you cannot mix nylon into the recycling process, so that’s basically waste. But with a PEF bottle, you don’t need that additional layer.

Marc: Yes, PEF has a golden colour. It has this colour because of its sugar base. If you heat up sugar too high, you get caramel. And, in a certain way, you also notice that with PEF. However, it depends on the way you make and process the PEF. It’s important to dry it extremely well because if there’s still some moisture in it, it tends to create hydrolysis reactions during processing, which gives rise to caramelization reactions. So, if you keep it very dry when processing and don’t heat it too high, then you can control the colour more.

Stefan: The colour is also no issue for the recyclability because there’s been a shift over the last few years. In the past, PET bottles were always crisp and clean, whereas today, a lot of the bottles are a bit bluish or grayish and advertise that they are “made from 100% recycled plastic.” So, if there is some discoloration in there, it’s not a big deal anymore, customers are already getting used to this. Besides, also colour is being added to the polymer to increase the energy pickup during the bottle blowing process (this is done by IR heaters, and polymers with colour/pigment have better energy uptake, hence less energy is needed in the production process).

In thinner products such as films, it is difficult to observe any colour at all.

Stefan: PEF is ideal for bottle applications. We’ve already made countless demonstrations for carbonated and juice drinks. For juice bottles, PEF offers a big advantage because it prevents the intrusion of oxygen. This is very important since oxygen oxidizes the vitamin C in juice, making it go bad quicker. . Other ways to prevent oxygen intrusion is the application of multilayers in bottles (PET/nylon) but these are very complicated to recycle.

We have done tests with our collaborator and found that the shelf life of juice can be increased by a factor of three with PEF bottles. We are also looking at packaging applications where barrier properties are important—for instance, the lid on top of your salad package. These are similar to the applications for PET. Other possible applications could be for instance medication packaging.

We have not disclosed our official LCA data yet as it would involve disclosing production secrets. What we can share is that a CO₂reduction of around 50% compared to PET is achievable.

Marc: By comparing it to PLA growth rates, I would say that we are still five to seven years away. It took about 20 years to get PLA to the level it is now — and that’s still only a fraction of a percentage of total plastic production.

Marc: There are two parts to it: the production of glucose and FDCA and the polymerization step. To make the glucose components, you just need sunlight and plants, which will take up the CO₂from the air:  so that step is carbon negative. Producing FDCA can also be done with a very low carbon footprint if you make use of renewable electricity. But at this stage, water is the most important environmental consideration, rather than energy use, because to create the FDCA from glucose, we use bacteria that survive better in water. That means we have to recycle a lot of process water to keep the system going. Then comes the polymerization step. You cannot avoid higher energy use here because you need the higher temperatures to get the chemical reaction for polymerization. Perhaps this can be reduced in the future by using more efficient catalysts.

Marc: Currently the amount of land used for bioplastic production is very minimal, it accounts for less than 0.015% in 2020  – and it’s expected to only slightly increase in the years to come (2025 = 0.020%). Nevertheless, the use of next-generation (or alternative) carbohydrates such as organic waste as a biomass source for bioplastics presents a valuable potential additional feedstock source. We looked a lot at forestry residual material or agricultural material like stems and leaves. That works as it contains cellulosic material because it has the glucose and fructose we need. People have also been looking at wastewater treatments. However, we cannot use that. That type of input is too low in sugar content and has a lot of other processing problems. For us, using organic waste material is a second step. There’s currently no factory from which you can order the sugars coming from organic waste or cellulosic waste.

Marc: The ultimate dream is to phase out fossil-based plastics wherever possible and have different kinds of biobased plastics for different purposes. If you want to design a solar panel or a wind turbine, it requires different plastics than what you would need to make packaging or fibres. The chemical polymer industry only started around 100 years ago, and then it started evolving with new applications and new polymers for niche markets. So, I think it will also take a lot of time to develop different kinds of biopolymer materials for different kinds of purposes. In the UK, you have the supermarket Tesco. Their ideal world would probably be to simply have one type of biopolymer for everything so that they could make a salad dish and bottle packaging from one type of plastic, but that’s simply not possible because they require different properties. I think there will be different types of bioplastic for different types of application purposes made from different types of feedstocks, and I think that’s a good thing.

Stefan: I agree with Marc that every polymer has its own strength, but I would like to see every polymer that can be biodegradable is used for biodegradable applications. Also, if it can be made from renewable feedstock, then it should be. For instance, polyolefins can also be made from renewable feedstock, and there’s nothing wrong with polyolefins because you can recycle them many times. Every polymer has its purpose, but they aren’t always being used smartly. Another example is that you can use biobased polyethylene to make a plastic bag, but today, plastic bags often have more than 10 multi-layers, making them impossible to recycle.

Besides the chemical part of the story, the technology development part is huge. If you compare PET from 30 years ago to bottles produced today, you see a gigantic leap in improvement, mainly in how the material is processed. Bottle manufacturers have made it into an art to produce lightweight, sturdy, drop-resistant bottles, at immense production speeds by years and years of development efforts. We can of course learn from the past but any new type of polymer (bio or fossil fuel-based) will have to go through a similar learning process before it can replace the currently applied polymer. This will be true for bottles but also for other applications such as films, fibres and the newer 3D printing.