The Race for More Sustainable Textile Fibres
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By Martin Fairbank
With a lot of attention focused on textile waste recycling (which will become mandatory in Europe in 2025) and improving the sustainability of virgin fibres, several new technologies for producing man-made cellulose fibres (MMCF) are in a race to commercialization. Unlike the “space race” between the USSR and the USA a few decades ago, this race appears to have at least five contenders from Finland and one from the US. In a moment I will list the competitors, but first let’s review the current state of MMCF.
Cotton is by far the largest source of cellulose-based textile fibre, with a 2021 world market of 24.7 million tonnes. Its cultivation uses a lot of water, agricultural land and pesticides. The MMCF textile market is 7.2 million tonnes in textiles, and non-textile markets account for another 3 million. MMCF are made with dissolving pulp, 95% by the viscose process, with toxic carbon disulfide as the solvent. The other 5% is made with the Lyocell process, using N-methylmorpholine N-oxide monohydrate (NMMO) solvent. While NMMO is not as nasty as carbon disulfide, it is expensive and has to be 99.9% recycled for the process to be economical. It can also decompose, and stabilizers need to be added to the process to prevent this. Dissolving pulp has a yield from wood of 30–35%, since all the hemicellulose has to be removed in order for the pulp to dissolve in these solvents.
The contenders:
Ioncell processThe 2022 Marcus Wallenberg Prize, awarded for scientific achievements in the field of forest products, was awarded to Professors Ilkka Kilpeläinen and Herbert Sixta at the universities of Helsinki and Aalto, respectively, for the development and use of a novel ionic liquid to dissolve cellulose, 1,5-diazabicyclo[4.3.0]non-5-enium acetate ([DBNH]OAc). Compared to the Lyocell process, the solvent is more stable and the process can operate at a lower temperature. The inventors have also shown that the Ioncell process will work with a steam-exploded, mild caustic-extracted bleached pulp with a yield of about 36%, or with recycled cotton textiles.
Biocelsol is another Finnish technology, developed at Finland’s VTT Technical Research Centre using dissolving pulp and a fairly benign solvent of aqueous sodium zincate. First developed in the 1980s, the process involves enzymatic activation of the dissolving pulp to enable dissolution. It was resurrected in the mid-2010s, when it was shown that the process could be greatly sped up and reduced in cost by applying the enzyme treatment in a twin-screw extruder.
Infinited fiber is another process developed at VTT which reacts urea with cellulose to create cellulose carbamate, targeted at post-consumer recycled textiles. The raw material is pre-treated to remove any non-cellulosic fibres, and an aqueous cellulose carbamate solution can be retro-fitted to the viscose process. Infinited is building a 30,000-tonne plant which is scheduled for startup in 2024.
Circ is the US-based contender in this race, and its hydrothermal processing technology can take in any ratio of recycled polyester/cotton fabrics. The polyester is removed as a liquid which is then hydrolyzed to its monomers and sold back to plastics producers, while the recovered cotton is re-spun into yarn for fabrics. Circ has built a 5 tonne/day pilot facility and its ambition is to get to 200 tonnes/day.
The last two contenders in this list have a lot in common. Both processes were originally developed at VTT and involve microcellulose from paper-grade kraft pulps, which have a yield of 45–50%, higher than the 30–35% of dissolving pulps.
Spinnova was mentioned in my previous blog on textile fibres. In a joint venture with Brazilian company Suzano, a demonstration plant of 1000 tonnes per year is now being built in Jyväskylä, Finland, and is slated for startup in the second quarter of 2023. Mechanical energy is used to produce microfibrillated cellulose (MFC) from eucalyptus kraft pulp, and the MFC is then spun from an aqueous suspension into yarn. Spinnova’s ambition is to build a production capacity of 1 million annual tonnes within 10–12 years. Its technology partner is Valmet, and it is working with several fashion brands to develop the market for this sustainable fibre.
Kuura is a process being developed by Metsä that uses microcrystalline cellulose to make a softwood-based spun yarn. Its technology partner is Andritz, and the demonstration plant at Metsä’s bioproducts mill in Äänekoski, Finland is a joint venture with the Japanese textile company Itochu. One advantage of its process is that it uses never-dried pulp, since the plant is integrated with the pulp mill.
