As demand for more natural materials and processes grows, so does interest in alternative and plant-based dyes. From natural indigo to recycled agricultural or industrial waste, this new outlook is fuelling experimentation and expectations.

Whether based on recycled textile waste or natural indigo, these alternative dyes are, for now, just that, alternative. Very few can equal the scale and performance of synthetic indigo. When more sustainable practices are called for, chemicals companies have, or develop, solutions. The introduction of pre-reduced or liquid indigo some 20-odd years ago significantly improved the environmental profile of denim dyeing. An aniline-free solution, developed by chemicals company Archroma, is considered a further step in the right direction. These are without question better and welcome, but they don’t address the rumblings for more natural solutions.

The reintroduction of natural indigo in industrial processes is the mission that Stony Creek Colors, a company based in Springfield, Tennessee, is pursuing with dedication. Its innovative dry leaf extraction process, in operation since 2019, is ready to be scaled up and should be patented this year. The company founded in 2012 has faced many challenges in its drive to make the natural dyestuff suitable for today’s industrial needs. “We looked to improve each stage of the process, from seed to mill, and believe it is possible to disrupt each one,” company founder Sarah Bellos tells Inside Denim.

The crop itself had faded from the agricultural landscape, and had therefore not benefitted from modern farming techniques. To improve yields and consistency, it was first necessary to identify and breed new indigo plants. “We are at a stage where it is possible to make giant leaps in indigo yields, as opposed to other crops that have been optimised for decades,” says Ms Bellos, citing corn and cotton having been incrementally improved over many years. 

The perishable nature of the leaves, from which the dye is extracted, was another challenge. Their shelf life is in the order of 4 to 5 hours, she says. To address this issue, which is the crux of its extraction innovation, the company developed a process that involves the stabilisation of the leaves to limit their perishability and allow year-round extraction. This solved the issue of scaling up production and, even more critically, provides batch-to-batch consistency.

For Stony Creek, the reintroduction of indigo crops supports the growing trend towards regenerative agriculture. “Our indigo plants partner with bacteria in the soil to extract nitrogen from the air and use it to grow the plant. Nitrogen cycles are critical to agriculture, as they are a source of fertilisers,” says Ms Bellos, who adds that tropical indigo is a legume crop. “Leaves are composted after extraction and stems and roots are left in the field, which improves carbon sequestration and helps soil regenerate,” she adds. The company says that this makes its agricultural practices not just climate neutral but climate positive, while offering the market a bio-based chemical.

Stony Creek Colors is currently supplying textile dye partners and denim mills in the US, Mexico, Turkey, Italy and China, and selectively integrating new partners. It claims that its natural dye can be used as a drop-in solution. “The purity of our plant-based indigo dye is still somewhat lower than that of petroleum-based dyes, but the unwanted elements are non-toxic,” says Ms Bellos. Current production is consistently sold out,  but the company’s goal is to make it available season after season without disrupting a brand’s supply chain. “We know now that our plant-based indigo solution works at industrial mills and will work with those companies that see the value of using natural indigo."

Changing views

Natural indigo may in time find its place on the market, agrees Ali Tekin, head of R&D for Pakistan-based AGI Denim. He compares its evolution to that of organic foods and organic cotton. “At first, they were much more expensive than their conventionally grown equivalents but with time, quantities increased and prices went down. I think natural dyes will follow a similar path. They require more effort at first, and not all brands and consumers are ready to make the shift. But if there are enough that are willing, it can turn into a viable market,” he says.

With regards to processing, whether synthetic or natural, indigo needs to be made soluble. “But each solution has its advantages and disadvantages,” says Mr Tekin. Besides its steeper price, natural indigo lacks the uniformity of synthetic dyes and often requires longer production times. “There is no standard recipe for natural indigo,” he says, and depending on weather conditions, the plant will produce a greener or yellower shade. Among its advantages, he lists its renewability, biodegradability, non-toxicity and skin friendliness. Ideally, plant-derived indigo should be processed using natural and non-toxic chemistry, but it may require the addition of synthetic chemistry to obtain better results or brighter colours. “We are working on all of these issues today, so as to be ready for the future,” says Mr Tekin. He believes that natural indigo could make up 15% to 20% of the market in five years. Other sustainable processes, such as waterless dyeing, he points out, went from virtually zero to mainstream in five to six years. As part of its strategy to favour more sustainable processes, AGI has introduced a natural, organic reducing agent, which replaces salt with glucose and eliminates hydrosulphites, leaving no toxic residue in wastewater.

In its exploration of alternative dyes, AGI is also working with Nature Coatings. The California-based company founded by Jane Palmer uses FSC-certified wood waste to make a high-performance black pigment. “This solution solves the issue of petrol-based carbon black which has many health concerns,” says Mr Tekin. Nature Coatings’ closed-loop manufacturing process is very clean, requires no external source of energy and emits only steam. It is also easy to process, resists humidity and UVs, and is a cost-neutral high-performance dye, he says.

Plants and agricultural waste are not the only source of novel pigments in the denim industry. Using old clothes to dye new ones is the innovative and sustainable solution invented and patented by Andrea Vernier, CEO of Officina +39. The process known as Recycrom starts with leftover fabric scraps in cotton or cellulosic fibres (tolerance for other fibres is low, in the order of 3% to 5%), these are sorted by colour and ground into powder using an eight-step process that is mainly mechanical, he tells Inside Denim. And, he says, it is growing demand for natural dyes that first inspired him to seek a more sustainable solution.

Recycrom is now reaching industrial scale. The company recently dyed 150,000 pieces with pre-consumer waste for G-Star and OVS, and produced Recycrom dyes from unsold Inditex group garments to make a capsule collection. The company is now looking into the possibility of recycling fabrics made in other fibres into dyes and is stepping up trials with second-hand clothing. Through its participation in the Fashion For Good incubator programme, Officina +39 is working with Reverse Logistics and I:CO on these projects. The company has also expanded the options, introducing Recycrom for screen printing. It is working on developing solutions for fabric dyeing and for coatings.

A shift to natural processes

Heightened interest in natural or plant-based chemicals can be seen throughout the denim industry and not only in dyes. Italian mill Candiani introduced a chitosan-based alternative to PVA with Kitotex, and then a plant-based solution known as V-sizing.

Italian laundry specialist Tonello is developing dyes made from vegetable food waste, using a natural mordant, in its Wake process. Though processing is faster than that of indigo, not all shades offer the performance levels of synthetic dyes, the company says. A fixing agent can be added, but that will go against the “all-natural” claim, R&D team member Carlo Reniero told Inside Denim.

Archroma was a precursor in the recycling of agricultural waste into colourants when it introduced its EarthColors dyes for cotton and cellulose fabrics and garments. Coming from a well-established supplier of chemicals, they may help change the industry’s views on plant-based chemistry. The company’s latest development, an indigo that is near aniline-free (the presence of aniline is below limits of detection by standard test methods), has been adopted by Soorty.

With its Smart Indigo technology, the Pakistan-based denim manufacturer uses electricity instead of chemistry to reduce liquid indigo. This, the company says, removes many of the harmful chemicals that end up in wastewater. Soorty is experimenting with natural indigo, another process that discharges cleaner wastewater, it claims.

The optimisation of dyeing operations is an ongoing process at Sharabati Denim. The Egypt-based company has focused on the automation of the dyeing machines themselves, enabling the company to increase quality, efficiency and production capacity. The Sahara process it developed uses a new chemical to improve indigo uptake on warp yarns and reduce the number of washes needed to remove unfixed dyestuff. Foam and nitrogen dyeing processes are other more sustainable measures in development.

Iskur Denim has recently focused on reducing the amount of dyestuff needed to make very dark shades of blue. The result, Blue Zircone, is said to cut water use by 95% and offer long-lasting colour that does not fade, even after 40 home laundries. The Turkey-based company introduced We Are Water (WAW), a certified water-saving indigo dyeing technology in 2017, which will be rolled out across all of its denim pieces by the end of 2021.

Finding the right balance

Without denying that demand for more natural products is up, Günther Widler, DyStar’s head of technology for denim, believes the market needs to find the right balance between natural and synthetic indigo. He points out that it may be difficult for plant-based indigo to reach the level of performance and optimisation that synthetic indigo has benefitted from since it was first invented 125 years ago. In 2017, the chemicals company introduced Cadira Denim, a resource-saving concept based on its pre-reduced Indigo Vat 40% Solution combined with a biodegradable organic reducing agent (Sera Con C-RDA), which, he says, “does the job without the negative effects of the salt.” It is part of the company’s focus on reducing the footprint and side effects of indigo chemistry, furthered by the launch of indigo spray in 2018.

DyStar is now testing the possibility of filtering out indigo pigments after dyeing so as to release cleaner wastewater, which Mr Günther says could be reused in some processes such as pre-treatments, leading ultimately to a closed loop use of water and indigo in factories. “We are working with chemists to find the best and most environmentally-friendly solution. It is our responsibility to use the right chemistry in the right quantities,” he says.

Providing sufficient quantities of plant-based dyes for an industry that currently consumes in the order of 50,000 to 70,000 tonnes a year of synthetic indigo is not feasible and not in the interests of the industry nor, for that matter, the world. “The surfaces required to grow the amount of dyestuff the denim industry uses would be gigantic, possibly the size of Bangladesh, and would replace food crops,” he posits. It is not possible to rely entirely on natural indigo, he insists, other than for special collections and capsule lines. “In the future, the situation may change with the development of biotech dyes. But these processes require sugar, and may lead to the same discussion with regards to land use. The question would then be: should sugar be used to make dyes or to feed people? Food for thought,” he says.

Plant-based dyes may require extra processing steps in the backend of the supply chain, which may offset the sustainable nature of these products, as a spokesperson for Sharabati Denim points out. “Natural dyestuffs are not yet perfectly suited to industrial processes,” agrees Ali Tekin at AGI Denim, but he believes they could, in time, become a viable solution and could address market demand for more natural and sustainable jeans.

The outlook for bio- and plant-based chemicals is mostly positive. Some solutions, such as Nature Coatings’ bio-black, tick all of the boxes with regards to performance and price. But blue is another story, and natural indigo faces the daunting task of competing with synthetic indigo, whose market dominance has been largely unchallenged, until now.

The development of a dry leaf extraction process allows Stony Creek Colors to scale up production of its natural indigo dyes .  
PHOTO: Stony Creek Colors

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