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"Biodegradability needs to have an additional benefit"

Dr. Michael Thielen had worked in the plastics industry for many years before he entered the realms of journalism in 2006, the year in which he created the “Bioplastics Magazine”, the only worldwide journal that focuses exclusively on bioplastics. In an interview with Christoph Bächtle, Thielen spoke about polylactide, biodegradability, the properties of bioplastics and their role in comparison with traditional petrol-based plastics.

Dr. Thielen, the Thai government has declared that it wants Thailand to become the major producer of biobased materials, notably polylactide, in East Asia by 2021. Is this a good decision?

Basically, polylactide is a material that can be used for a broad range of applications, thanks mainly to the fact that it can be combined with filler materials such as natural fibres or additives. Therefore, I think the Thai government has made a good decision.

However, it is also worth taking other aspects into account. Does the Thai government have this objective to produce plastics from regenerative resources with a view to substituting fossil-based plastics? Or are they mainly seeking to market biologically degradable and compostable plastics? In the latter case, the question arises as to whether the infrastructure required to compost the material is in place.

Let’s look at the EU. The EU’s objective is for ten per cent of all plastics produced to be made from biological materials by 2020. Do you envisage a special role for polylactide?

Dr. michael Thielen: "I believe that by 2020 we will have a completely biobased PET available." © privat

It's difficult to say. On the one hand, polylactide is one of those plastics that have played an important role in the initial phase of the bioplastics boom. Polylactide was available in large quantities very early on, it can be used for a broad range of applications, it has achieved a certain level of publicity and it is possible to expand its application range by combining it with other materials. On the other hand, there are interesting approaches that focus on producing standard plastics, i.e. well-known plastics such as polyethylene, polypropylene, PVC, polyamide and PET from regenerative materials. For example, monoethylene glycol, which is an important constituent of PET, can already be produced from renewable resources and is already available on the market for certain applications.

Other research focuses on terephthalate, which is another major constituent of PET. I believe that by 2020 we will have a completely biobased PET available. A Brazilian company is set to market biobased polyethylene from 2011 onwards, and biobased polypropylene is already in the pipeline. I think polylactide has an excellent chance of success, but it remains to be seen whether it will still be as important in 2020 as it is today.

We will also have to see how prices develop. In the case of what is known as drop-in-solutions, i.e. bioplastics produced from renewable materials, but which are standard plastics and are not biologically degradable, it is important to focus on the longevity of the goods. In this case, the idea of "renewability" should be seen as more important than "biological degradability".

Biobased and biodegradable – these two terms sometimes cause confusion. How are the two terms connected to one another?

They are not. Biodegradability depends solely on the molecular structure of a plastic. Traditional plastics such as polyethylene, polypropylene and others cannot be biologically degraded, no matter whether they are biobased or produced from fossil fuels. It is also very difficult to differentiate them from biobased plastics, for example when the age of carbon is determined using the radiocarbon dating method. In the field of bioplastics, there is a trend that is moving towards long-lived biobased plastics. Biological degradability plays a major role in cases where this special property generates an additional benefit.

Some people have a tendency to throw away their plastics waste in the countryside. However, the majority of plastics are very stable and take decades or centuries to degrade. Can biodegradable plastics contribute to solving this problem, at least partially?

I am sure they can. But I believe that this is the wrong path to pursue. The topic of littering, which is the specialist term used to describe this kind of behaviour, actually has nothing to do with the materials themselves, but with education. Effort should be made to prevent biological degradability being regarded as a potential solution for littering. Let’s take polylactide as an example: this is a biologically degradable material that can be composted in industrial composters within a set time period. In the countryside, this process does not happen so easily. Until polylactide is fully degraded, it is a visual blot on the landscape and potentially also a danger for animals that might feed on it. Littering is and will remain a matter of education.

For polylactide to be effectively and rapidly composted, much higher temperatures are required than can be achieved with a garden composter. It is therefore necessary to use industrial facilities. Would this not require entire waste flows to be reorganised in order to be able to exploit the potential of biodegradability and compostability?

Biobased plastics are already used for a broad range of products. © BIOPRO/Bächtle

This is a very complex issue. There is a broad range of industrial composting plants that can use compostable plastics packaging, in particular films and bags. However, municipal composting is not the right way to dispose of bottles because of their large volume. Much more space would be required and the large quantities would potentially also lead to problems. Therefore, it is necessary to find out what infrastructure is available and calculate the potential quantities, a procedure that has to be gone through with any type of material and packaging.

The Columbian airline company Avianco was the first to use polylactide cups to serve cold beverages. The cups are collected by the Avianco personnel and then picked up in Bogotá by a company that crushes them and sends them to a composting facility. This is an excellent procedure, which is known as a closed-loop system. And there are many more examples that illustrate the use of polylactide products.

Such examples show that solutions are available. But it is necessary to look at individual applications in any country, find out about the infrastructure and find solutions that can be adapted to specific applications.

But biodegradability is worth nothing if it cannot be implemented. This requires politicians or other stakeholders to put the necessary conditions in place.

There are two major aspects here. I believe that it is not sensible to promote the large-scale use of biodegradable packaging as long as the waste industry, i.e. composting facilities, is not part of the cycle. It is no doubt a problem when composting facilities of certain administrative districts refuse to accept biodegradable packaging. But efforts are currently being made to deal with this particular issue.

The second major aspect is that there is no point using biologically degradable plastics for just any packaging. I would only use biodegradable plastics where it is possible to achieve an additional benefit. An example of an additional benefit would be the ability to plough mulch film used on agricultural land into the soil rather than having to go through the costly process of collection and disposal after the harvest.

Tomato plants are another example. In greenhouses, tomato plants are fixed with plastic clips to wires to support the upward growth of the plants. After the harvest, it costs tomato growers a great deal of money to dispose of the plant residues because the polypropylene clips contaminate the biological waste. If these clips were produced from compostable plastics, they could be sold at a higher price than traditional polypropylene clips because tomato breeders would still save money in the disposal process.

Another example is big catering projects. At the Catholic World Youth Day held in Cologne in 2005, the organisers used seven million compostable catering dishes. If such catering dishes could be disposed of along with food leftovers, then compostability would truly make sense.

Which properties differentiate PLA from other bioplastics?

PLA is a versatile plastic whose properties can be constantly improved.. © BIOPRO/Bächtle

For example, the permeability of water vapour. This is a problem with bottles. However, this is a property that is highly desirable for vegetable and bread packaging because it helps keep vegetables and bread fresh much longer. PLA is highly transparent and therefore can be used to create very attractive packaging. PLA can be pressure moulded, especially when combined with additives and natural fibres.

Standard PLA is not heat stable, but this can be changed by combining PLA with additives and by using new processes. Special PLAs, for example stereo complex PLAs that have an excellent thermostability are now available. All in all, PLA is a very versatile material. A major advantage of PLA is its availability: no other bioplastic is currently available on the market in the same high quantities as PLA.

Other bioplastics also have certain special strengths: polyhydroxyalkanoates, PHAs, can be produced with a broad range of properties, from viscoplastic to very hard. Cellulose-based bioplastics or those made from modified starch and mixtures of different materials all have their specific property profile.

There is a broad range of different bioplastics. It is necessary to focus on application and make sure that the chosen property spectrum fits the application/product the bioplastic is designed for and chose the bioplastic accordingly.

The plastics market is a mass market. Approximately 280 million t of plastics are produced every year. But it is also a market with a long tradition, a market that is dominated by petrol-based technologies and products. Do biobased plastics have to fight enormous opposition?

Classical plastics are well established. They have all gone through several decades of development and are fully mature. It took thirty years to develop polypropylene and 50 years to develop PVC. When bioplastics are compared with established standard plastics and all the disadvantages are listed, one must be careful not to throw out the baby with the bathwater. The production capacities of PET, polypropylene, polyethylene, PVC and polyamides have completely different dimensions to bioplastics. Huge facilities are available to produce such plastics at low cost.

At some stage a break-even point will be reached, which will be due to a combination of rising oil prices and falling bioplastics prices as a result of technological progress and larger facilities. Biobased plastics will then become a lot cheaper. This might already be the case for one or two applications in 2011, others might take two or even five years before they have reached this degree of maturity. In the case of biodegradable biobased plastics it is necessary to take into account the end-of-life scenario – here I’m referring back to my comments on mulch film and tomato clips.

Nobody would want to put a Herculean effort into squeezing classical products out of the market and replace them with biobased plastics. This will happen over time, and in relation to market and price development. Therefore, the big chemical plastics producers are also part of the game, partly as observers, and partly as the producers of new goods. When oil becomes extremely expensive some time in the future, we will all be pleased that alternatives made from renewable resources are available.

Further information:

Dr. Michael Thielen
Bioplastics Magazine

Phone: +49 (0)2161 - 664864
E-mail: mt(at)bioplasticsmagazine.com

Website address: https://www.biooekonomie-bw.de/en/articles/news/biodegradability-needs-to-have-an-additional-benefit