A promising partnership between two Finnish companies could supply denim manufacturers with a high-performing, pre-dyed warp yarn, allowing them to skip the indigo dyeing process altogether and go straight to weaving.

A partnership announced last year between fibre producer Spinnova and dyestuffs manufacturer Kemira has the potential to make an impact on the environmental footprint of the denim industry. The companies, both from Finland, have been working together on a method for “inherent” dyeing that they say could be “disruptively sustainable” for the textile and apparel industry, including denim.

Key to this is the fibre that Spinnova produces. The company, launched as a spin-off from the VTT Technical Research Centre of Finland in 2014, turns wood fibres into yarn “without complex chemical processes” and without dissolving anything. Its feedstock is micro-fibrillated cellulose (MFC) from paper-grade wood pulp. Its technique is based on fibre-suspension flows, mechanically pulping the fibres and controlling the flow in such a way as to form a yarn. After going through a drying process, the yarn is ready for spinning.

“It’s very simple,” says chief technology officer and co-founder, Juha Salmela. “It’s the combination of those two factors, the raw material sourcing and the technology we use, that makes this work.” It is, however, clearly more difficult to achieve than he makes it sound; otherwise all fibre producers would become “disruptively sustainable”.

In addition to sustainability, he insists that Spinnova has always sought to provide products that work. Rather than making fibres with special properties such as those of spider silk or carbon fibre, the company set out to make a difference to the mainstream, global textile industry by producing a fibre with properties like cotton’s and a price-point like cotton’s.

Early adopters

Fashion retail groups H&M and Bestseller have been among the early adopters that have given Spinnova confidence that it is on the right track. Bestseller, the parent group of brands such as Jack & Jones, Vero Moda, Selected and Mamalicious, has described the materials that its textile manufacturing partners can produce from Spinnova yarns as “revolutionary”. For its part, H&M has recognised the role Spinnova’s products can play in blends with other fibres, including cotton.

These big-name partnerships are the fruit of years of proof-of-concept work. Lifecycle assessment results show figures for carbon footprint and water consumption that are “minimal compared to anything else”, Mr Salmela says. Plus, tests have shown that fabrics made from the company’s fibres have additional benefits, including high levels of thermo-insulation, moisture management and antimicrobial properties.

The process remains the same

Its work with Kemira shows that it’s possible to incorporate dyeing “in the main colours” into the Spinnova process seamlessly. Juha Salmela, making it sound simple again, describes it as being “like dropping an ink pellet into a big tank full of MFC and mixing it a little”. All the dye is absorbed into the fibrils of the MFC and the fibre then goes through exactly the same extrusion and drying process as non-dyed fibre. A small amount of curing time is necessary, but other than that the process is the same, with no extra energy and no extra water required.

“It’s the same method as Kemira uses to dye pulp and paper in an environmentally friendly way,” he says. Spinnova’s fibre is particularly suited to bringing this into textiles because it is made without dissolving anything. Mr Salmela explains that manmade cellulose production usually requires the raw material to be dissolved back to the polymer stage first, with regeneration of the fibres taking place after that.

Dyeing the polymers is not possible and, therefore, dyeing in these mainstream processes normally takes place at the fabric stage. Some manufacturers have begun dope-dyeing at the regenerated fibre stage. They are making a great success of this, Mr Salmela points out, particularly in applications such as intimate apparel, but this comes at the cost of extra washing cycles. “They cannot do it at the stage at which we do it,” he says, “the raw material stage.”

Even though the Spinnova fibre will, after this, be dyed a particular colour, the fibre will keep its mechanical properties and preserve another of the benefits Spinnova claims – recyclability. “In some cases, the quality of our fibre can even improve with recycling,” the chief technology officer says.

Indigo included

Although the range of colours that Spinnova can use with the Kemira inherent dyeing technique is limited, indigo dyeing is one of the possibilities. For this reason, Dr Shahriare Mahmood, who became the sustainability director of Spinnova in 2020, says he believes there is good potential for using the company’s fibre and the new inherent dyeing method to make a positive impression on the denim market.

His previous roles include working in the denim industry in research and development and sustainability positions. “It will work,” he says. “There is no question about it.” The indigo idea has now progressed to testing the colour-fastness and rub-fastness of the resulting fabric, and examining any impact on knitting or weaving.

Straight to weaving

He foresees savings for denim manufacturers in time, money, energy, water and chemicals. They can use a Spinnova fibre that is already indigo-dyed as the warp yarn, and combine it effectively in the weft with a fibre of their choice, including cotton. “Manufacturers will go straight to weaving with the dyed Spinnova warp yarn, completely skipping the indigo-dyeing process,” he says. “This will have a really significant environmental impact.”

In terms of look and feel, fabric development tests so far show that denim made using Spinnova has what Dr Mahmood refers to as the right level of “roughness” and an absence of the shininess that many lyocell and viscose fibres have, making it better able to emulate cotton or linen. It will be no more than a matter of months now before Spinnova-based fabrics are available for denim brands to try for themselves in sample collections of jeans, he says. He believes the idea of using Spinnova in this way will be ground-breaking.

Photo: A visual of Spinnova’s new factory, currently under construction in the university city of Jyväskylä. This facility will help the company increase its production capacity to one million tonnes of fibre per year. Credit: Spinnova

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