Technological watch

The circularity of polystyrene has been in the spotlight for industry initiative Styrenics Circular Solutions (SCS).

At its K2019 event in October last year,  SCS invited a series of players from across the value chain to discuss how the misperceptions that polystyrene is not recyclable differ from the reality that the material is highly recyclable even to food grade standards. 

In an interview with SCS Jürgen Priesters, SVP, Circular Economy at Tomra, discusses polystyrene’s recyclability from a sorting perspective.


Jürgen Priesters, just how recyclable is polystyrene?

When it comes to recycling, everything starts with the design of the packaging. Polystyrene has some clear advantages in this area. The first is that most polystyrene packaging, like yoghurts cups, are well designed and do not have complicated, multiple layers. Secondly, polystyrene packaging is highly suited to near-infra-red sorting technology and can be sorted very precisely into the different styrenic materials, such as into high impact polystyrene (HIPS) or general-purpose polystyrene (GPPS) or, styrene acrylontrite copolymer (SAN). The reason is that styrenic compounds have a unique signal that enable easy and very precise sorting, an advantage which some of the other polymers do not have. Thirdly, it is easily washable, so that you can get rid of all the inks, glues and lids. The same applies at the sorting step, because on a flake level, we can really ensure we have 99.9% plus quality. 

We at Tomra were pleasantly surprised that polystyrene is such a fantastic material for the entire process. It is far from being an ugly duckling. It is in fact a swan in terms of recycling and circularity.


What should be done to increase the amount of polystyrene that gets recycled?

The answer lies in the collection and sorting of mixed plastics. Here in Europe we can fortunately say that almost all waste is collected and we lose only a fraction of a percent to littering. The real issue then is, in which of the 20 waste bins does the end consumer actually place the plastic product after its use? 70% of the plastic packaging ends up in the wrong bin. But we should focus on the fact that it is at least collected, so there is a chance to take it out, to sort and to recycle it, if we start to sort other waste streams which many European countries do already. 

There is no rule that states we must concentrate only on taking out one type of plastic material. Why not try taking several plastics, for example polypropylene and polyethylene together with polystyrene and then concentrate large volumes and separate them again? This would make more financial sense than having a sorting system in each and every hub. Such a sorting of mixed plastic waste streams with several plastics at the same time, makes a lot of financial sense and would lead to a dramatic boost in the recycling rates of polystyrene, but of other plastics, too. 

Tell us more about design for recycling. What improvements could be made?

There is a very simple example of a step that could easily be taken. It is well known in our field of expertise that all the sorting units, near-infrared technology have a problem with carbon black. Avoiding the use of carbon black would solve the problem worldwide as it increases sortability. 

Another example of a simple step to take is the avoidance of paper being used for sleeves or layers. This is because we cannot look through the paper to see what is beneath. But with any kind of plastic sleeve or layer thinner than 50 microns for example, we always see, if it is polypropylene or PET or polystyrene below. 

The reduction of multi-material- multi-layers, although not possible in every single case, would also have a great impact. There are some applications where it is definitely possible to use the same material instead of 13 different materials. We do recommend that companies take that approach wherever possible.  

These all are simple steps that allow us to easily increase the sorting efficiency, the washing efficiency, the yield, everything. For polystyrene and other plastics alike.


How else can we increase recycling rates for polystyrene?

In Europe, we have more than 10 million tons of plastic that we burn or we landfill. This is a feedstock that needs to be accessed. There are some countries in Europe where waste streams must be sorted by law before they can be burned. This means that recyclable items, whether aluminum cans, glass or any kind of polymers or plastics then come out in pre-sorted streams for onward recycling. It is with this approach that we can truly fulfill European recycling targets. If we acknowledge that people put 70% into the wrong bins or containers, it becomes rather difficult to achieve a European 50% recycling rate. Consequently, it is essential that the rest of Europe moves to a system where waste streams are sorted before incineration or landfilling. Extraction of polystyrene before incineration is perfectly possible – we see it done in Stavanger, Norway and several plants in Poland.


Is there a viable market for recycled polystyrene?

The short answer is yes. Why would someone decline a perfect monomer or a perfect 99.9 plus percent pure quality flake or granule that is not more expensive than virgin? The demand is there - among brand owners for millions of tons. Maybe there is some work to be done to show brand owners that they will be receiving perfect quality. But once they see such high quality recyclates, that in the case of polystyrene even have a high potential to have food contact quality, there will be no problem selling them. 

For plastics in general, the current situation, at least in Europe, is that plastic is separately collected and when it is recycled, tends to be for lower-value products, such as composting systems or black tubes. We know that top quality is possible and that food contact standards are possible. Brand owners will drive this demand. We know they need hundreds of thousands of tons. Together, we must support recycling companies to better understand the market for top quality applications and find commitments from brand owners or virgin plastic producers to push needed investments. 


Tell us about the parts you have already produced from recycled polystyrene?

Just recently we produced takeaway coffee cups out of 100% post-consumer  polystyrene material from Norway.  Together with partners, we produced the granules. The converter produced film from the recycled granules and then undertook the thermoforming. We did not encounter any issues. The producer simply stopped using virgin polystyrene and switched to recycled polystyrene without any issue. It was a drop-in solution. We said we wanted to make High Impact Polystyrene and test its chemical and mechanical properties. We even brought the cups to the K2019 trade fair and handed them out so everyone could see for themselves what was achieved. First laboratory results confirmed the high purity of the recycled material, fully equivalent with virgin material due to the absence of any substances related to post-consumer waste. This is achieved by the very high cleaning performance of the recycling process and helped by the low diffusion property specific to polystyrene which means organic contaminants do not enter the polymer matrix.So, it really looks very promising. 

Polystyrene is a natural for recycling. It is highly sortable and washable. Recycled polystyrene can achieve 99.9% plus purity, enabling food contact. We have seen that for convertors, recycled polystyrene is a simple, drop-in solution and we know the demand is there from the brand owners.