Checkerspot has developed a biotech platform that uses microalgae to create polyols with chemical structures that can be tailored to tweak polyurethane properties. It’s also putting the polyols to practical in high-performance lightweight skis. Sarah Houlton finds out more.
The appeal of plant-based raw materials in place of petroleum sources in the production of polyurethane is obvious. But there are drawbacks, not least that they compete with food crops for land and other resources, and the chemistry of the polyols is limited.
US biotech company Checkerspot is taking an alternative approach: using microalgae to produce the oils that yield polyols with a wide range of chemical structures. The company has also developed a practical PU application to prove the polyols’ potential – skis.
The company’s founders and other key members of the team previously worked together at Solazyme, which developed an industrial oils platform using a microalgal approach. ‘I left the company in 2016, but was captivated by the utility of microalgae as robust industrial microbes,’ Checkerspot CSO and co-founder Scott Franklin said.
Biopolyols are commonly made from oils extracted from seeds such as soyabeans, while Checkerspot’s microalgae are single-cell organisms that are grown in a fermentation vessel. At the start of the process, they are fed both sugar and a nitrogen source. If the nitrogen source is shut off while there is still sugar present, a stress response is initiated, and the microalgae start to lay down a lot of triglyceride oil. ‘They can accumulate 70 or 80% oil on a dry cell weight basis,’ Franklin said. ‘The oil is entrained in the cell, similar to a seed.’
The same technique used for oilseeds is applied to processing the triglycerides out of the microalgae cells. After this mechanical extraction, the oil is refined, bleached and deodorised. ‘We have scaled this to 625,000 litre fermenters,’ Franklin said. ‘These are very large tanks, and it’s a very robust industrial process.’ The fermentation within those reactors takes about 120 hours, depending on the strain. Each reactor can yield between 90 and 110 tonnes of triglyceride oil.
The algae angle
Importantly, there are far fewer limitations on the chemical structures of the oils than there are on those produced by seeds. And because of the speed of reproduction of the cells – they double every about every four hours – it is feasible to make genetic modifications, or use classical strain improvement, to change the nature of the triglycerides the cells make, and also improve productivity.
‘We can make a lot more progress in tailoring these outputs in a much shorter timeframe than we can in a higher plant system like canola or soybean,’ he said.
Different aspects of the company’s work are carried out in different places. At its Berkeley, California headquarters, the focus is on a molecular foundry for strain development and improvement. In Salt Lake City, Utah, a design lab that carries out manufacturing and formulation applications development. A lot of the polymer chemistry is done in collaboration with the team at the Kansas Polymer Reseach Center in in Pittsburg, Kansas, and the large-scale manufacture takes place in Brazil.
As well as improving the microalgae’s performance, the molecular foundry aims to broaden the palette of monomers the company can manufacture. Importantly, modern genetic engineering techniques accelerate the process of strain development. What would be an 8–12 year proposition with plant breeding can now be done in as little as five days, Franklin said.
Ah, Sugar, Sugar
‘We feed the organisms nitrogen and sugar, grow them in 96-well blocks, and test them [for what they make and how much of it],’ Franklin said. ‘We can do about 3000 of those tests in a week. The best of those may get another round of genetic modification, or if they are close, go into classical strain improvement. We are looking for productivity in grams per litre and yield on sugar. Our record for engineering and scaling up a commercialisable product to a 500 m3 scale is about five months. It’s an incredibly efficient process.’
The ability to scale it is simply limited by that four-hour doubling time of the organism. ‘It’s pretty rapid,’ he said. ‘You don’t need to make seeds, or build a seed bank to plant next year, and you are not limited by seasons. You are just limited by access to fermentable sugar.’
These organisms had not been grown on a very large industrial scale before, but a platform process has now been built, with five 625,000L fermenters in use in Brazil, in which the microalgae can generate more than 200g/L of oil. The solid waste from the process is fed into a co-generation plant that helps power the sugar mill, while the wastewater is either recycled or used for irrigation. ‘It’s a really nice closed loop process,’ Franklin said.
This is the key to financial viability: siting the industrial fermenters close to the source of the sugar feedstock. ‘We work with contract manufacturers located in Brazil next door to a sugarcane mill,’ he said. The oils produced in Brazil are then imported into the US, where they are processed.
Make it flexible
Checkerspot makes its polyurethanes using diisocyanates. ‘We require a relatively quick cure, and non-isocyanate chemistries can be limiting,’ Franklin said. ‘We use a variety of isocyanates depending on the end application.’ MDI and derivatives are used for hard applications, he said.
Then there is the chemical structure of the polyol, which will have an impact on the nature of the final polyurethane material. He cites two ways in which the material can be tailored by altering the structure of the polyols. Functionality such as hydroxyl groups can be engineered into the molecules, and any unsaturation in the fatty acids can be exploited, perhaps by epoxidation. Either way, it is fairly simple to produce polyols with different activity profiles.
In contrast, the structures of seed-derived polyols are much more limited. They are 18 carbons long, with double bonds only appearing at positions 9, 12 and 15. Castor oil, for example, has a hydroxyl at position 12. ‘This is a very narrow monomer universe,’ he said. ‘With natural oil polyols, the ability to do chemistry is very restricted.’ He believes the microalgal polyols have huge wider potential in polyurethanes, whether for TPUs, dispersions or elastomers. ‘Because of our ability to tailor and get very high purity of specific monomers in the oil, it allows us to do different things than when working with a traditional seed oil.’
Creating a market
However good the sustainability story, it remains a price-sensitive market. ‘One of the challenges in this field is that if you are simply making monomers and trying to sell them to large chemical companies, you have to compete on price,’ Franklin said. ‘The challenge as a small start-up is that you do not yet have the scale or a market. The challenge is getting people to do applications development work, because the first thing they focus on is how much will it cost?’
So they looked to prove the concept themselves, developing a brand early on that would allow them to take the monomers and create materials that would solve specific problems. Franklin stresses the importance of having a product to show potential investors and partners. ‘We are trying to animate the technology, which creates value for the company,’ he said. ‘We can demonstrate what we can do with the monomers, and the polymers we create, and the kind of problems they can address. A finished good carries huge weight, particularly if there are a lot of data to show how it performs.’
The first products marketed using their Wonder Alpine brand are backcountry skis; this form of skiing involves a fair amount of climbing, and therefore lightweighting is important. ‘We have done a lot of work around high-density and low-density foams. We engineered a ski that uses a formulation for a high-density foam that we incorporated into the core of the ski,’ he said.
This first product, the Intention 110 ski, was launched in July 2019. It uses Algal Core, a vertically laminated composite of biobased high-density PU and aspen wood, which the company says makes skis that are lighter than those with a traditional solid wood core. The biobased content of the PU is 41%.
But even as that ski was launched, they were already thinking about how else they could use the new polyols, as skis are multi-material products. ‘In a ski lay-up, the top sheet is typically a nylon material, there’s a bottom sheet of ultra-high-density polyethylene, and the sidewall material is typically ABS, plus epoxy resin, rubber and steel,’ Franklin said. A year after the first ski, a second product was launched. In these skis, marketed as Vital 100, the polyols are also used to make a PU sidewall in place of the ABS. ‘When we characterised the urethanes physically, we noticed that, unlike ABS, they provide significant damping properties, mitigating vibration,’ Franklin said. This will improve comfort for the skier.
The location of the company’s design lab in Salt Lake City allows prototype skis to be made and tested very rapidly on the nearby slopes. ‘We do a lot of physical measurements on the skis, and can check their flexural characteristics whenever we change anything-,’ he said. ‘But getting people who understand skiing on the skis rapidly is key.’
Another project that is currently in the pipeline is a textile finish. For this the company is working with Swiss company Beyond Surface Technologies and WL Gore. The aim is to create a fluorine-free textile finish that gives comparable performance to fluorinated chemistries. ‘That’s an incredibly high bar,’ he said.
Franklin admitted that it’s unusual for an industrial biotech company to put its initial focus on outdoor recreation, but they felt it was important to work on something they personally cared about, and where the ultimate consumers really care about what they buy. ‘People will spend hours fretting over a ski, and how it is built and the materials that go into it,’ he said.
These consumers also tend to be concerned about sustainability, which chimes with the company’s aims. About 2kg of material goes into building a pair of skis, but the final product weighs maybe 1kg, Franklin explained. ‘Within the brand Wonder Alpine, we have a very focused effort on the sustainability of the triglyceride oils we use when replace petroleum incumbents,’ he said. ‘We are also looking to repurpose the waste products that come out of ski manufacture.’