Polyurethane foam is a big challenge for recyclers. It’s bulky, and its thermoset nature makes it difficult to reuse. Sarah Houlton takes a look at some of the initiatives that are under way to create a useful future for old foam
Recycling is now routine for many types of plastic, particularly those such as PET and HDPE commonly used as packaging. The same is not true for polyurethane foam. The fate of a large proportion of end-of-life foam is to rot – very, very slowly – in landfill. While some is burnt, only a very small fraction is currently reused or recycled. If the dream of a circular economy for furniture is going to become a reality, some significant advances in PU foam recycling will be required.
Without legislation that mandates some form of recycling, the sheer difficulty in recycling bulky items such as mattresses and sofa cushions is likely to mean landfill will continue to predominate. France is ahead of the game, where the Extended Producer Responsibility scheme has already been implemented, and its Eco-mobilier scheme organises collection and recycling services for furniture. There will be similar EPR implementation rules in Belgium and the Netherlands next year.
Recticel, for one, is planning ahead. ‘We don’t want to wait until the directives come or wait for legislation,’ said Bart Haelterman, innovation manager for corporate sustainability at the company.
In Belgium, he said, about a million mattresses are discarded every year. But with foam products, it’s not just the weight, it’s the volume that creates an issue – piled on top of each other, this would create a 90km high tower, he said. Around Europe, the total is more like 30m every year; in landfill, he added, this would fill the Great Pyramid of Giza twice over.
We need to move from a linear economy to a circular one, Haelterman said. And there are many elements on the circular economy ‘wheel’ that can be addressed. ‘We are working on all the elements in parallel,’ he said.
For waste foam, there are several potential recycling streams that can prevent the foam from ending up in landfill, but currently mechanical recycling is the only realistic option other than incineration. Haelterman cited figures from 2016 indicating that, of the 160kT of mattresses that were discarded in the year, a whopping 60% ended up in landfill. Of the rest, 39% was incinerated, and just 1% was mechanically recycled. There have been improvements since then – landfill is reducing while mechanical recycling has increased to 5–10% – but there is a limit to how much can be usefully repurposed in this way. Chemical recycling will also be required.
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Mechanical recycling broadly encompasses two separate processes: bonded foam and fibre-bonded foam. The bonded foam process has been used for at least a couple of decades, he claimed, and Recticel has two facilities that does this. ‘At first, this was only trimmed foam waste from production, but as of the middle of last year we started using end-of-life foam too,’ he said. The new products are typical used for acoustic insulation in buildings, and in industrial and automotive applications.
In the bonded foam process, the foam is first shredded into flakes, and then it is glued together to create a new material. In fibre-bonded foam, instead of using a glue, a polyester fibre is added in which a middle core confers strength, and the outer layer becomes soft and acts as the glue. ‘We acquired an industrial line in Angers in France in 2017 with a 3 kT capacity ahead of the start of the French Ecomobilier scheme,’ he said. They have since installed a pilot facility at the facility in Wetteren, Belgium, in advance of a similar scheme starting in the country in 2021.
Taking the initiative
There are various initiatives looking at different aspects of the problem. One of these is the PUReSmart project, which is backed by EUR 6m of funding from the EU’s Horizon 2020 Research and Innovation scheme. It is being coordinated by Recticel, with Haelterman as project coordinator. The consortium has eight other members, including chemical producers Covestro and WeylChem, recycling specialist Redwave, consultants and project managers Eco Innovazione and Ayming, and three academic centres: KU Leuven, Ghent University and the Universidad de Castilla La Mancha.
One of the biggest challenges that needs to be addressed is sorting the foam. ‘We need to sort the foams for chemical recycling, mechanical recycling, or to be burned,’ Haelterman said. It’s not as simple as the sorting process for materials such as PET bottles. End-of-life foam from mattresses and sofa cushions is bulky, and needs to be shredded. But whereas PET or HDPE shreds still have some weight to them and move in a fairly stable fashion on a conveyor belt, foam shreds are light and bouncy. This motion makes it difficult to scan them to determine their chemical composition – something that will be essential for chemical recycling.
Sorting is being addressed by Redwave, as R&D specialist Katharina Ander explained. ‘Redwave has the key role of ensuring there is a well-defined input to the chemical recycling,’ she said. ‘We need high quality of foam to go into chemical recycling, and with sorting, we can do that.
When you transport mattresses, you are transporting a lot of air
The different types of polyurethane have to be separated before they can be chemically recycled. While it is still very early days for the project, and intellectual property considerations limit what can be disclosed at this stage, Ander is optimistic that a solution will be possible.
The material detection is done via sensors, without touching the material. It is irradiated with a suitable light source, and the sensor detects the reflection, essentially like a large spectrometer.
‘At the outset, no-one knew how we would be able to distinguish between the different foams,’ she said. ‘We tested different sensors, and worked in cooperation with the universities in the consortium, who have different types of sensors from the ones we use. We tried to find the best solution, and we are still working on this. We have made good progress, but there is still some way to go.’
‘Material handling gives us headaches,’ she added. ‘Usually, the sorting machines for plastic applications are like a conveyor belt which passes the sensors, the material is detected, and it either passes or is rejected. That movement on the conveyor belt is quite tricky [for foam shreds] as it can jump up and down, moving with the air not the belt.’
Another important question that will have to be addressed is where the separation should be done. ‘When you transport mattresses, you are transporting a lot of air,’ Ander said. ‘Looking at the whole process chain, you have to look at where it makes sense to put the sorting and recycling. Is it best where the mattresses are collected, or is it best where the chemical recycling is done? Do you try to minimise the transporting of materials? That is a big question mark.’
Haelterman explains that one of the other aims is to invent a new kind of chemistry that bridges the worlds of thermoset and thermoplastic material. ‘Packaging is thermoplastic: you can remelt it and make something else out of it,’ he said. ‘Polyurethane is thermoset; you cannot remelt it and reshape it as it burns.’
Would it be possible to build in chemistry that allows a thermoset material to be temporarily turned into a thermoplastic one, so that it can be melted and then ‘refrozen’ to a thermoset? ‘This is the most challenging and high-risk part of the consortium,’ he said. It’s also likely to have the longest timescale, and it’s not even clear if it will be possible.
They are also looking at splitting the PU into smaller chemical components that can be reused. ‘The chemolysis route we are following was first explored by Huntsman in the 1990s, but they never succeeded in making it happen industrially, and there was no interest in recycling PU then,’ Haelterman said. ‘We are building on that knowledge.’
Since that early work by Huntsman, Rampf and H&S have developed ways of using acidolysis to chemically recycle PU and create new polyols from it. However, he said, mass balance is a problem. ‘From 1kg of PU they make 3kg of polyol, which makes 30kg of foam,’ Haelterman explained. ‘What we want to do is go from 1kg foam to 1kg of [new] foam. We don’t make a new polyol: we recycle the polyol and the isocyanate that were put in originally.’ The ability to recycle the isocyanate part of PU, not just the polyol, will have a real impact on the circular economy, he added.
Another potential route to recycling comes in the form of pyrolysis. This is not just burning waste to generate energy: it can be done in a less destructive manner to create useful chemical fragments more upstream than polyols.
The goal of PUReSmart was to have a pilot plant running as an outcome, but the pilot will be there this year, so we are two years ahead of schedule.’ For chemical recycling, he believes, there will be a solution within four to seven years, and for new chemistry, within a decade. As Haelterman concluded, there will not be a single solution to the foam recycling dilemma. ‘We believe that in the future, there will be a combination of solutions,’ he said. ‘We are not looking at one element of the circular economy.’
In the longer term, there is an initiative in the Netherlands looking at ‘passports’ for mattresses, so that at the point of dismantling there is a label that includes information about the type of foam included. Clothing labels routinely include details of the material from which they are made, and programmes such as Certipur-US involve labelling foam products that meet certain production standards. Why not expand this to material composition? ‘In my opinion, that could be a solution,’ he believes.
Another recycling option
A way of up-cycling polyurethane foams has been developed by scientists at Northwestern University and the University of Minnesota in the US. They take waste polyurethane foam, and mix it with a solution of a carbamate exchange catalyst that renders the foam more malleable. It is then fed into a twin-screw extrusion process that removes the air from the foam, and creates a new material. This can be either a hard, durable plastic, or a soft, flexible film.
Previous upcycling efforts relied on simply compressing the foam to remove the air. However, the result was cracked or unevenly blended materials. By using two intermeshing, co-rotating screws to simultaneously mix and remould the foam, the result was better mixing and air removal.
These new materials have many potential uses. They could be used as cushioning in shoes, as wristbands for watches, or as hard, durable wheels for skateboards and shopping trolleys. They might even have automotive applications, such as bumpers.
‘Polyurethane foam waste has historically been landfilled and burned or downcycled for use in carpeting,’ said Northwestern's William Dichtel, who co-led the research. ‘Our latest work effectively removes air from polyurethane foams and remoulds them into any shape. This could pave the way for industry to begin recycling polyurethane foam waste for many relevant applications.’
The extrusion process removes air simultaneously, as the catalyst enables the polyurethane to flow like a liquid, added Christopher Ellison, one of the University of Minnesota authors of the study. ‘This reactive process is similar to those already used in the plastics industry for other purposes meaning the technology could have impact quickly,’ he said.
Marc Hillmyer, director of the Center for Sustainable Polymers based at the University of Minnesota, is excited about the research because of the potential for recycling PU materials that are typically considered waste. ‘It also demonstrates how the powerful combination of polymer chemistry and polymer processing can be applied to help solve environmental problems,’ he said.