Why lignin might just be a miracle manufacturing material
One day we could be riding bicycles and driving cars made from wood. We aren’t talking about eccentric steampunk contraptions, but high-tech, lightweight machines of carbon fibre made from lignin, a complex carbon polymer abundant in nature. The foam in bike saddles and car seats could also be derived from lignin, as could the glue holding it all together. Lignin could even be the biocarbon alternative to graphite in the lithium-ion battery. This is the vision of Stora Enso – a renewable materials company and one of the largest private forest owners in the world.
“[The amount of lignin needed for] your new car will be able to regrow in a Scandinavian forest in about one-tenth of a second,” says Lauri Lehtonen, head of innovation in the Biomaterials division at the Helsinki-based company.
Currently, the manufacture of carbon fibre – increasingly in demand for use in wind turbines and electric vehicles – necessitates an expensive, energy intensive and toxic chemical process using petrochemicals as building blocks. Conversely, lignin is a fully renewable, non-toxic resource. Found in almost all plants, humans consume it daily in fruit and vegetables, where it’s a source of dietary fibre. Now it is being transformed into high grade carbon materials. Stora Enso has partnered with the German industrial rayon producer Cordenka to turn lignin into carbon fibre precursors and carbon fibre.
Lignin, with its complex carbon-rich, chemical make-up and natural abundance – the second most plentiful macromolecule on the planet after cellulose – offers a broad green highway out of our reliance on fossil-based carbon.
This promise is huge. Fossil-based materials literally surround us. The foam in your sofa, the glue holding your furniture together, the paint on your walls, the plastic in your laptop and water bottle, the threads in your clothes are all – more than likely – derived from oil, from life-forms that died millions of years ago.
Scientists are fast-forwarding that process. “We’re basically taking a shortcut past the hundreds of millions of years needed to turn biomass – trees and other organisms – into oil and gas,” says Mojgan Nejad, an assistant professor in green bioproducts at Michigan State University, whose research is transforming lignin into foams for use in insulation, car interiors and furniture. She is also developing lignin-derived paints and adhesives.
“Not only are we replacing expensive toxic petrochemicals with lignin, which is renewable and biodegradable, but the products we’re making have natural anti-microbial and flame retardant properties,” she says. “In nature, lignin acts as a ‘glue’ holding cells together so why not use it to make adhesives.”
This property of lignin partly explains its suitability as a replacement for the bitumen derived from crude oil that is used in road surfacing and roofing. In Sweden and the Netherlands, roads have been surfaced with asphalt made from Stora Enso’s powdered lignin.
For decades lignin has been used in a multitude of low-cost, high-volume chemicals in agriculture and construction, and even to make synthetic vanillin, the essential constituent of vanilla. However, it’s only in the last 10 years that a technique has been developed to extract a cleaner form of lignin from wood that can more readily be used as a chemical building block for higher value products such as polyurethane foams, adhesives, bioplastics, electrolytes in batteries, graphite anodes in lithium-ion batteries, carbon fibre and even graphene. But while there is an abundant supply of lignin available globally for potential commercial use, the industry does not yet have the capacity needed to replace fossil fuel based materials in large quantities.
Since 2015, Stora Enso has been the world’s biggest producer of this lower sulphonate form of lignin – which it sells as a dry brown powder under the brand name Lineo by Stora Enso – with a production capacity of 50,000 tonnes annually from the company’s Sunila mill in Finland. In January, a Swedish company, RenCom, will begin using Lineo in the commercial manufacture of a bioplastic for use in plastic bags, packaging, artificial football pitches and car interiors. The plant will be able to produce 2,000 tonnes of biodegradable Renol bioplastic annually.
Using inexpensive plant-based alternatives to petrochemicals is essential if we are to reach ambitious zero-carbon targets. “If we can substitute non-renewable fossil-based materials with these bio-based renewable materials we do two things: we reduce the amount of emissions from below the ground [from fossil fuels] and we increase the carbon capture of forests as we will need more trees to supply these materials,” says Lehtonen.
Lignin, primarily produced in the form of “black liquor”, a tarry liquid byproduct of paper and pulp mills, has for over a century simply been burnt, a non-fossil fuel energy source powering the mills and local electricity and heating networks. An estimated 80m tonnes of lignin is produced worldwide annually, 98% of which is burnt as bioenergy.
“It’s better to take the lignin and use it to convert into products that we use in the home rather than just burn it and release the carbon into the atmosphere,” says Nejad. “Pulp and paper plants have become more efficient and they make a lot more black liquor than they need for power,” she says.
At a time when paper sales are declining, adding value to lignin also offers a new income stream, as well as facilitating the transition to our future free from petrochemicals. “We need to begin to live from above the ground as opposed to below the ground,” says Lehtonen.
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