by Caterina Plenzick, Anselm Wohlfahrt, Rafael Vinz & Lukas Keller

PLA has many similarities with oil-based plastics. Can you mention these and as well the main differences in terms of the materials‘ performative properties?

PLA can be produced from renewable raw materials as well as from residues from agricultural products. However, in the case of the PLA production from organic residues, one has to take a closer look at their economic efficiency. Basically, you can produce a bio-based plastic, like PLA, from sugar with a much lower carbon footprint than fossil plastics.
In terms of disposal, I can use PLA to make plastics that are biodegradable under certain conditions. However, for each product application, it should be considered individually if it makes sense to compost the plastic used in the product rather than recycle it. For instance, the consumption of coffee capsules has increased so dramatically worldwide that one should question if it was not much more reasonable to recycle the capsules than to throw them, if biodegradable, into the compost. Another point is the decomposition process of PLA in the environment, which has not yet been fully researched. Possibly, research will show in the next few years that PLA, when it enters the environment, degrades faster and is thus less harmful to the environment than comparable fossil plastics. Of course, it would be best if PLA would not enter the environment at all, but given the circumstances, such factors still need to be considered at this stage.

In your previous answer, you mentioned agricultural residues for the PLA production. How pure do the raw materials need to be in order to be suitable for the production? For example, is PLA production from organic waste possible?

The more contaminated the starting material, the more difficult it is. To produce PLA, you need lactic acid, which, in short, is produced through a bacterial fermentation process of sugar. This lactic acid must be purified very well for the final manufacturing process in order to make plastic out of it. So if I have a very poor starting material, such as organic waste, in which degradation processes have already begun, acetic acid has formed or fungi have grown, which have produced citric acid, then the fermentation process of the sugar by the bacteria becomes much more difficult due to the impurities.
However, research projects have already been undertaken on possible residues from grass-pressed juice and old bread. In the BREAD4PLA research project, old bread was soaked in water in order to be able to extract sugar for PLA production from the starch contained in the bread.
Another possibility is to process the sugar properly.
For example, the cellulose contained in straw could be chemically processed in order to obtain the glucose contained in it. The cleaner the glucose is, before it is added to the fermentation process, the better the lactic acid will be at the end. However, such a purification process would only be used if it was as profitable as producing PLA from corn starch or sugar cane.
Since maize starch is already used extensively for sugar production, it makes sense to use this sugar for the production of plastic as well. At the moment, however, 95-99% of the sugar from maize ends up in soft drinks. If we were to reduce the amount of sugar in soft drinks worldwide, we would gain huge amounts of land for the production of PLA.

So with the right know-how, can PLA plastic also be made from any lactic acid?

Basically, as I said, I have to have a very clean lactic acid at the beginning. When by-products are in there that I can’t get removed easily, it can interfere with the production of polylactic acid. A good polymerisation technique is important. I need sufficiently long chains. PLA polymers that are too short are not suitable for plastics. In addition, I need a previously identified and well-set L and D content. When such a polymer is created, that is then PLA. A few additives or fillers are then added to this base.

In the lactic acid produced via fermentation I always have proportions of L and D lactic acid, how does this distribution result?

First of all, this is defined by the bacteria. Actually, the bacteria should only produce one of the two types of lactic acid. There are strains that should really only produce L lactic acid and there are others that should only produce D lactic acid. During fermentation, a little of the other lactic acid can be produced. Unfortunately, this can also happen afterwards during the purification process. The temperatures and time involved in the processes also lead to a redistribution. That is why an additional purification step is always carried out. This is also the case with chemical recycling, for example. There, too, L still has to be separated from D in a purification operation.

If, for example, regional mechanical recycling loops are set up for individual PLA products and after a few recycling processes the quality is no longer sufficient, could this material then be processed in batches into a central chemical recycling system? Could chemical recycling be quickly adapted to different batches?

Great suggestion, I would do the same. What you said is one possibility, I take yoghurt cups today, boxes tomorrow, bottles the day after. Or I always have to make sure that about the same mixture goes in, then approximately the same comes out again. That would be two ways I could set it up, both of which are feasible, I think. Firstly, the further purification is then adjusted to the mixture, which varies as little as possible. The other time, I know the quality I will get on the different days. Then I also know what I have to do in the purification. The companies would use the version that is suitable and better and has proven itself in test campaigns. But that is fundamentally an important point; it would have to be implemented batch by batch.

In which research attempts and technological innovations do you currently see the most potential for a better functioning circular economy in relation to plastics?

If you want to have rapid improvements for the circular economy of plastics, I think you need systemic innovations above all.
Such innovations could be that the range of plastics is limited and plastics are collected more cleanly. One example is the well-functioning cycle of PET. The bottles made from this one defined plastic only contain liquids, or more precisely food, and thus end up back at the recycler with little contamination. In addition, the bottles can be conveniently returned at many places and in Germany are also linked to a deposit as an incentive system. Using the example of waste glass, 90% of which is recycled, and waste paper, 80% of which is recycled, we can also see how a circular economy can work. So the question arises why such recycling should not be possible for considerably more materials – especially for packaging.
If we take a closer look at the yellow bin, we find a mixture of materials that is both uneconomical and unattractive. Significant quantities amounting to several million tonnes are produced every year, much of which is difficult or impossible to recycle and most of which is incinerated anyway. 
At this point, „recycling“ means that the actually valuable plastic is thermally utilised or incinerated.
Why don‘t we make ourselves honest and print a brown, green or grey dot on every package? Brown could mean that the packaging is going to be composted, grey would mean that the packaging is going to be incinerated and green would mean that the packaging can be recycled. To initiate such a change, however, one would have to start with the German Packaging Legislation and define rules for recycling-friendly design.

According to your previous answer, would you say that the most important key to changing the system lies in the political sphere or which actors should be addressed in addition?

Many actors are needed for this change. Politics, the waste management industry and consumers. For example, consumers are among the best sorters in the system. If product flows are to be made more sustainable, we have to think carefully about how we can make it easier for consumers and how the product flows can then be processed more easily.

Now I wonder if something needs to be changed in the separation of plastics rather than in the establishment of new bio-plastics. If PLA is to become a bio-plastic of the future, wouldn‘t it have to be produced in much larger quantities?

That is the challenge, there is not enough at the moment. Not enough material is produced and therefore not sorted properly. 
On the other hand, there have already been experiments at larger or smaller scale events where, for example, PLA cups have been used and separated waste bins have been set up. Recycling also works well for the most part, even if a crumpled piece of paper ends up in it. After all, we‘re not talking about needing 100% sorting accuracy. Then these cups were taken afterwards and recycled. With such local cycles, it works.
In the business-to-business sector, for example, there are many cycles for products made of standard plastics. Plastic baskets in which fruit and vegetables are transported and placed directly on the shelves in supermarkets, for example. There are already very intelligent cycles today. These boxes are brought back when they are used, centrally cleaned, disinfected and then allowed to be filled again with fresh produce. If the boxes break down at some point, they are already relatively high-quality recycled material. One possibility would be to use PLA as a material in such cycles. The quantity on offer will also be a factor. If we now say overnight that we want to make all yoghurt pots in Germany out of PLA, that simply won‘t work because not that much PLA is produced. There would have to be a step-by-step process, and in my opinion it would be a good idea to start with individual „circular projects“.

If you theoretically set up a separate PLA bin for certain quantities of waste, wouldn‘t you end up with a mixture of materials in this system that can no longer be recycled into technically functioning plastics and therefore with downcycling? Shouldn‘t there be some kind of standardisation or transparency?

The comment is absolutely correct, and we are already seeing this today with some materials such as different types of polypropylene (PP), which in the mix no longer have the quality of the previous raw products.
With PET, for example, there are other products besides bottles, such as fruit and vegetable trays. These are made of slightly modified PET. If some of that gets into the bottle material, then they can‘t (re)make proper bottles. So this is nothing new for PLA, I already have this now with plastics. But they are questions that definitely have to be faced. There are always roughly similar additives, in other words stabilising agents, processing auxiliaries, which are added in the range of half a percent to maybe 2 percent. This is usually compatible with each other. But if I add 10 to 30 per cent of another polymer to PLA, which is sometimes necessary, then I have these problems. Either that has to be collected separately again, then I‘m back to my example of these transport boxes. So I try to come directly to a product-to-product recycling. That means: I can have any mixture of plastics in the boxes as long as I keep it sorted.
The problem becomes significant when I do the sorting via the consumer. Then many different types of plastic come together. This is exactly the problem we would have with the PLA bin, if 5 product types were to come in there that contain different PLA mixture qualities.

Could a PLA container be regulated or standardised to three or four „basic mixtures“ covering a wide range of applications? or are the applications so specific that this is not possible?

This is also a good approach that can certainly be applied to all plastics.
It is a possibility to limit the diversity of materials. This means not only limiting the types of polymers, but also, if necessary, what additives are contained in them or the types of polymers. The difficulty is that today every plastics manufacturer, whether large or small, produces special mixtures in order to achieve the business „unique selling point“ for itself and its products. Now the bags can be another 5% thinner and need less material, which is not bad for a start. 
The discussion at the moment is really about whether it really makes sense to build up a package of 3, 4, 5, 7 or even more layers of plastic on top of each other because it is 50% lighter than if I make it out of one plastic, or it is 20% lighter than if I make it out of two materials that I can separate from each other. These kinds of questions are only now beginning to be discussed. The entire chain, from plastic manufacturers to product designers to recyclers and reprocessors, has to come together. But the current economic approach of simply importing oil via pipelines and then exporting plastic waste again is actually nonsense from an economic point of view. This is only slowly coming into view, and it is precisely at this point that we hope to see a lot of development in the next few years.

Head of Department Circular and Bio-based Plastic Fraunhofer UMSICHT

Fraunhofer UMSICHT