3dpbm recently caught up with Jason Rolland, the Senior Vice President of Materials at Carbon, regarding the development of EPU 44, a bio-derived, 3D printable elastomer, with performance-enhancing qualities. A polymer scientist by training, Jason Rolland joined Carbon at a very early stage – as the eighth employee at the company. Carbon is now hovering around 500 employees, globally.
From the very beginning, Carbon wanted to do something different within the world of additive manufacturing. When the company questioned why the technology was not used more widely within production, the conclusion was that two main issues were causing this lack of adoption – print speed and materials.
Print speed was important in order to be relevant enough for production in industries such as footwear, where the speed of manufacturing significantly affects the final costs of the product.
With regard to materials, the problem was, specifically, “around the material selection relative to what people would do with molding technologies. With foams, for example, in particular with elastomers, there were very few relevant technologies for elastomers and 3D printing, and a lot of work was needed to get it to the point where you could build a performance elastomer for use in a running shoe that would meet all the requirements of durability, et cetera. And so that’s what we set out to build the company on – let’s try to solve these problems.”
Carbon had developed a breakthrough in resin-based printing that allowed for the printing of products at a much faster speed – “greatly reducing the adhesion forces between the building part and the bottom of the cassette by leveraging oxygen permeability of certain materials – the oxygen can quench the polymerization at that interface and give you much lower adhesion forces.”
Carbon realized that “we were sort of in this box of UV curable materials and traditional UV curable materials” – materials stemming from the coatings and inkjet printing industries, that were not designed for use as performance materials for running shoes, or automotive applications.
“And so we developed this platform of dual-cure materials – to expand the palette of materials in the formulation space so that we could achieve the necessary properties. And, what I mean by that is, basically, we have UV curable resins that react with UV light and solidify with UV light, and then we have thermally curable resins. People are familiar with this where you go to the hardware store and buy a two-component epoxy resin, or a two-component silicone resin, or a two-component polyurethane resin. We can take those chemistries and blend the UV chemistry with the thermally curable chemistry and then mix them just before going into the printer. We then use the printer to solidify the part through the UV chemistry. So we form an initial network with the UV printing, and we basically entrap that thermal chemistry into that part. And we then take the part out of the printer, clean it, and then it goes into an oven where you now activate that thermally curable chemistry that’s now embedded within your initial print. And that is what really opens up this huge property space for us.”
Carbon had eyes on making footwear, as the team knew the industry had huge potential volumes for resins and production. The initial dual-cure elastomer concept allowed Carbon to make true polyurethane elastomers that have the properties required for footwear. Considering that a lot of the newer shoes were made using polyurethane foams – Carbon knew that achieving polyurethane properties would be a step in the right direction.
This initial ‘Gen One’ material is what Carbon used to launch the Future Craft 4D shoes with Adidas, in 2017. And although the material met all of the requirements around durability, UV stability, hydraulic stability, color, printing speed, etc – the shoes were heavier than desired. Carbon also wanted to move away from Adidas’ Originals line (a product line focused more on lifestyle, novelty, and, ‘coolness’) and towards the performance side of Adidas’ business – to enhance the products and “take it to the next level”.
If this was to happen, Carbon realized the need for a ‘Gen Two’ material – a material that was to become EPU 44. Of the several problems Carbon was trying to solve, one was that “in order to pull weight out of the shoe…. one way to do that is to make the struts on the lattice thinner, but that makes the shoe softer. And so, you need a stiffer material that can compensate for that reduction in strut size. So we need to make a stiffer elastomer that also still had a high-energy return and high durability, and all those requirements to make a performance product. So that was one thing that we did.”
The second thing is the property known as “green strength” – when, in the dual-cure process, the part has just been printed, and has only been activated by the UV network. “The material in that green state has a set of mechanical properties that are important for dictating what types of geometries you can print. The stiffer you can make that material in the green state – the easier it is to make some of these more complex lattice geometries.”
When summarising approximately five years’ worth of work, Jason Rolland explained how Adidas had a concept of a forward displacement running shoe. Which was, essentially, a lattice that was able to convert vertical force into horizontal motion – giving a small, two millimeter or so, pulse of forward-moving motion with each step. Carbon worked in tight collaboration with Adidas for approximately three years to make sure that the ‘Gen Two’ material met all of the requirements. “We needed a material that had a high enough green strength to enable these sorts of really cool geometries. Now that we have a new material that is lighter – we’re taking advantage of the fact that you can make these 3D printed lattices and do things that you couldn’t do with a foam, like this forward displacement concept.”
Adidas did a test, when Boost, a foam sole made of expanded thermoplastic polyurethane (eTPU), was released – Adidas put it to the test by dropping a steel ball onto flat mats of the foam, in an attempt to prove the physical properties of the material. When dropped, the ball bounced higher than it did without the foam – proving that the material provided a higher energy return. When Adidas repeated the test, with flat mats of EUP 44, the ball actually bounced forward, slightly.
Another problem was that of sustainability – an area where both Carbon and Adidas aligned. Some of Adidas’ previous sustainability-focused projects include the company’s Parley line – where the company used recycled ocean plastic to spin polyester yarn – and the ‘Made to be remade’ fully recyclable running shoes, made fully from recyclable materials.
Carbon prioritized creating a polymer derived from plants, instead of polymers derived from petroleum, to create the necessary building blocks for the soon-to-be EPU 44. One of these materials, known as PO3G, is a shorter polymer, and the backbone of the long polyurethane chain.
The monomer for this material, Susterra, made by DuPont Tate & Lyle, is derived from corn sugars and can be used to build the PO3G polymer. Carbon can then take this PO3G molecule, and add functionality to it that allows for it to be used in the company’s polyurethane system.
“The really cool thing here is that you have a much lower carbon footprint in the generation of your material because you’re using, basically, CO2 from the air and sunshine to make plants. And then the plants are making the building blocks of your polymer – versus extracting petroleum and then using the petroleum byproducts to make the building blocks of your polymer.”
Fortunately, the use of this bio-derived polymer for EPU 44 actually resulted in a much lower viscosity of the resin – reducing the print time and making the production more cost-effective.
“It was one of those moments where the sustainability requirements were lined up with the economic incentives, and the performance incentives. And so we made the decision to use this bio-derived material in our product and yes, it turned out to work really well.”
Thanks to the development of EPU 44, Carbon has been able to significantly increase the printing speed of Adidas’ printed soles. Jason Rolland also noted that “the ‘Gen One’ material didn’t have the right green strength to actually even print these new types of lattices. So in some respects, it’s not even a fair comparison.
Now, after 12 months of development with Adidas, Carbon is making the use of EPU 44 available to other companies, mostly targeting performance-based industries (with a need for lighter, more breathable, and more customized parts), many of which Carbon has catered to in the past. For example, in 2019, Carbon printed lattices that were designed to absorb impact, for the lining of Riddell’s football helmets – using a “completely different material that’s still an elastomer, but it’s an energy-absorbing elastomer”, instead of an energy-returning elastomer. As well as bicycle saddles – also an industry Carbon has catered to in the past – when the company collaborated with Specialized, in 2020, to digitally print lattice bike saddles, for the same reason as the football helmets, and the backpacks the company created with Osprey – providing a new level of breathability.
Carbon may be focused on sports performance, but the company has not limited itself to this domain. “It’s certainly a focus, but I think it could be useful for almost anything that uses a polyurethane foam… It [printed latices] allows you to really finely tune the energy attenuation and the cushioning throughout a given part.” The company is currently exploring other applications, ranging from wheels to wheelchair cushions.
Carbon’s technology, and expertise, is also available to small and medium-sized businesses – not only industrial-sized businesses like Adidas. “It’s probably one of my favorite things about Carbon and about 3D printing, in general, is the spread of different industries and different types of companies that you get to engage with… Some of our most important customers in the space are small businesses all over the world that just make parts for a living… I can’t think of an industry that isn’t impacted by, or doesn’t have opportunities for, additive manufacturing.”
Carbon’s strategy, with regards to material development, seems to be one of jumping straight into the deep end. “I think the bet is if you solve for footwear, then that material is probably good enough to be used in bike saddles and other applications. Or if you solve for electrical connectors (a notoriously challenging area of application for materials – considering the thermal and vibrational requirements, as well as the retention of force throughout) and there’s a bunch of other adjacent applications that are like ‘okay, you can solve for that, then that will work for my application’.”
“Right now, it’s a significant portion of our overall business, the EPU family of materials, I should say. But I also think we’re just scratching the surface of what’s possible. I think that there’s a whole lot more to do.”