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The right recycling method for all plastics

Reading time: 5 min

Not all recycling is created equal. While chemical recycling is the best option for food packaging and medical products, many plastics can also be recycled using mechanical recycling. The common goal for every method: Turn plastic waste into a valuable resource and keep plastics in the loop – think Circular Economy. Günter Stephan is on hand to explain what makes mechanical recycling special and how it works.

“Plastic is too valuable to dispose of after use. And that’s why we give it a second life”, says Günter Stephan, responsible for mechanical plastics recycling at OMV subsidiary Borealis. Borealis is a leader in this sector. “Back in 2014, we got together with the automotive industry to start producing plastic from recycled car bumpers that is then used to make new car bumpers”, he recalls. “But the plastic waste problem is first and foremost a packaging problem”. That is why, in 2016, Borealis invested in a mechanical recycling plant – incidentally becoming the first plastics producer to do so – a plant that also recycles plastic waste from households. Today Borealis operates three mechanical recycling plants: mtm plastics, Ecoplast and a pilot plant for innovative sorting in Lahnstein, Germany.

Plastic waste as a raw material: This is how mechanical recycling works

“The principle is simple: Waste is sorted, shredded, cleaned and melted into tiny balls that can then be processed into new plastics”, is how Günter Stephan puts it in a nutshell. But it is trickier in practice. “Household waste is more difficult to recycle as on the one hand it comes from many different locations, namely homes. On the other hand, the waste consists of different types of plastic like PVC, PET, polypropylene, polyethylene, and it is usually dirty as well”. So, it not only requires a lot of effort in terms of logistics, but it’s especially challenging when it comes to sorting and cleaning.

Plastic is too valuable to dispose of after use. That’s why we give it a second life in our mechanical recycling plant and make new plastic out of it.
Günter Stephan, Head of Mechanical Recycling, Borealis

Proper sorting is half the battle


“First the waste is presorted. There are different methods for this. Metal parts, for example, are removed using magnets or induction technology. The sink-float method can be used to separate plastics according to their density – lighter types of plastic float to the top, while heavier ones sink to the bottom. Optical processes such as cameras or infrared scanners are also used”, says Günter Stephan. Sorting is the crux of mechanical recycling, after all: “With mechanical recycling, what I put in is what comes back out. I don’t change the plastic molecule or the properties and color. It’s like a meat grinder: I can’t make pure beef mince from a mix of pork and beef”, he concludes.


Please wash and dry…

“Even though the waste is often presorted and is more or less split by type when it arrives in the recycling plant, we sort it yet again, by color for example. Before this sorting step, the plastic has already been roughly shredded.

Now it is shredded again or ground, making it easier to clean”, he explains. During the washing process, dirt and elements like labels, adhesive residue and foreign plastics are removed. Finally the plastic, that now looks like a kind of mush, is dried again.


…and then to the extruder

"The dried plastic particles then go to the extruder, a device that looks like a corkscrew", says Günter Stephan. Here the used plastic is processed into pellets at temperatures of between 200 and 240 degrees Celsius. This results in what's known as recyclate - plastic pellets sorted by color. This recyclate can then be used to produce an array of high-value plastic products. This closes the loop, creating the circular economy in which old plastic becomes new plastic.

Mechanical or chemical plastics recycling? The secret’s in the combination

As a manufacturer of polypropylene and polyethylene, Borealis has long specialized in recycling these types of plastic as well. In essence, almost any type of plastic can be recycled with mechanical recycling. “Deciding whether chemical or mechanical recycling is the better choice depends on multiple factors”, says Günter Stephan.


Mechanical recycling is a tried-and-tested technology that can be used relatively easily compared to chemical recycling to get the same type of plastic again from a certain type of plastic. “Basically, polypropylene becomes polypropylene again, PET becomes PET again, the waste used in the process must be properly sorted by type. One advantage of mechanical plastics recycling is that all the energy that has already gone into the production of the plastic is retained, because it is only cleaned and melted”, he explains. Chemical recycling, on the other hand, changes the chemical structure of the molecule and turns the used plastic back into synthetic crude oil. This makes sense first and foremost where the recovered crude can be processed into new plastics, like in a refinery or petrochemical plant”, adds Günter Stephan.

In theory, there is no limit on the number of times plastics can be mechanically recycled. “But in practical terms, it is hard to sort the waste streams that perfectly. Especially in terms of color, there is more and more mixing happening over time. “In the end then it will all be gray”, sighs Günter Stephan. So for the plastics where it does not make sense anymore to recycle them mechanically, for example because producers and consumers also care about the color of their packaging, these plastics can still be chemically recycled: “This means that dark gray can become bright yellow again if I want it to”.

If the issue is food and drinks packaging or plastics products for the hygiene and medical sectors, then we go straight to chemical recycling. “While the recyclate from mechanical recycling cannot be used because of the strict hygiene regulations in the food and medical sector, the sphere of application for chemical recycling is unlimited as I can make any kind of plastic I want from synthetic crude oil”, he says. “In mechanical recycling we have to pay attention to where the plastic waste originates. There’s no way to make sausage packaging out of a used paint bucket”.

This is why a true circular economy needs both chemical and mechanical recycling – two technologies that complement each other perfectly”, concludes Günter Stephan.

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