They eventually found an answer in a chemical process that transforms polyethylene waste into diacids that could be used to make polyols instead of petrochemicals or crop-derived oils. ‘It was not an obvious chemical invention,’ Wang said; as a linear carbon chain, PE is devoid of functional groups that could be used as a synthetic handle. ‘We recognised diacids as being particularly versatile and useful to target as an intermediate. The two of us came from biochemistry and molecular biology backgrounds, and we noticed that diacids were potentially useful for polyols and performance materials, even in synthetic biology.’
The diacids are made via an accelerated thermal oxidative decomposition process, using nitric acid. ‘The conditions are not harsh at all,’ she said. ‘The reaction happens in an acidic environment below 200°C, and can be run in standard chemical reactors,’ she said. The process scaled up well, and they are currently working with a commercial toll manufacturer in the US to increase the batch size. They should soon have reached 60kg batches, she said, with a goal of one tonne batches by 2022.
From polyol to TPU
Going from diacids to PUs was an exploratory process, Wang explained. ‘We identified the possible materials we could synthesise from it sustainably, and which would be comparable to virgin plastic,’ she said. And, of course, it would have to be affordable and scalable. TPU provided the perfect place to start.
Currently, the TPU they developed, branded as Xirc, is made using both aliphatic and aromatic isocyanates from virgin sources, but Wang said they are looking at renewable and sustainable sources for this, too. ‘We have gone end-to-end with the process, and the scale-up for the TPU is also happening now,’ she said. ‘We are producing samples, and there is a lot of customer interest.’
Third-party tests carried out by SGS Intertek have studied several of the material’s key properties, including melt flow index, hardness, abrasion resistance, tensile strength, and both UV and hydrolytic stability. ‘It is comparable to industrial grade virgin TPUs and, in some cases, a little better,’ she said. Xirc is designed as a drop-in replacement for current virgin and bio-grade TPUs. As well as footwear, the initial target markets are apparel and automotive, where there is already demand for green consumer products, she said.
Recycling – or upcycling?
Technically, Wang believes the process is more upcycling than recycling, because of the huge amount of value that is added in transforming PE waste into a material that can be used in a running shoe, for example. The ultimate aim, she said, is to create materials whose performance is indistinguishable from virgin polymer. ‘People shouldn’t be choosing between sustainability and performance,’ she said. ‘Performance is something that has to be achieved, but sustainability has to be meaningfully more significant.’ Something with a lower carbon footprint is unlikely to meet overall sustainability goals if it has a much greater water footprint, say, or pesticide footprint.
Affordability is another important factor. ‘Because we take PE waste and go straight to the diacids in one step, we are saving compared to virgin fossil fuels, skipping steps like cracking and the chemical synthesis to go from simple monomer up to a diacid – that’s six steps,’ she said. ‘This is why our carbon footprint is about half of that of virgin polyol.’
While she is unable yet to talk pricing, Wang says that what is important to customers is not so much the cost of the resin itself, but the cost per SKU that they produce. ‘Even if you have a $1 or $2 increase per kilo on the raw material, that might sound like a big%age increase, but there are a lot of things they can do at the shoe level,’ she said. ‘For example, if it has slightly higher performance, they might be able to use less of it in the shoe.’
It could also save wastage, she said – synthetic rubber creates up to 30% waste in the workshop, she said, and as it’s not meltable it cannot be recycled. ‘TPU can be melted and remoulded at least six times,’ she said. ‘The brand might actually be economising by using a TPU instead, and even if it is already being used but this one has a slightly higher bulk price on the raw material, at the shoe level the brand won’t feel it very much. And also what we are seeing now is that everybody wants to get in first. They want to have this material and get it into their products to show their customers they are meeting their commitments.’
An interesting prospect
As a novel material that works in the same way as an established one, but with added sustainability credentials, it’s perhaps unsurprising that Wang reports good levels of interest. ‘We have people approaching us for making all parts of the shoe with it,’ she said. These types of products are already appearing in the marketplace, such as the Adidas Futurecraft Loop shoe that was launched in 2019, and will be far easier to recycle at end of life than a product made with mixed materials. ‘We want to provide them with the materials to make a full-cycle shoe,’ she said. ‘TPU is one of those unique materials where you can really do that.’
TPU is the first of a whole suite of products Novoloop plans to introduce based on its diacid platform, and demand for sustainable performance materials is skyrocketing, Wang said. ‘Everybody wants sustainable content, not only in their packaging but in their products, and it’s one of the success metrics that companies are being measured by,’ she said. ‘But the actual amount of sustainable supply in this material [is low], with biobased about 1% compared to virgin production. This has to be changed, and is ready for disruption. We’re going through a generational shift – millennials and Gen Zs don’t want to stick with virgin materials any more. For every kilogram of TPU that we produce we’re offsetting more than 5kg of CO2. This is the kind of sustainable manufacturing that we have to adopt in the next couple of years.’