Greener dyes of every colour for fabric and food | Business

Redwan Rahman grew up in Bangladesh, one of the world’s biggest textile producers. He used to see people in his community dealing with illnesses that he believes came from drinking and using river water polluted by nearby textile dyeing and finishing plants releasing petrochemical-derived dyes and waste into the water. ‘I said: “We need a solution, and that solution should come from nature”,’ Redwan tells Chemistry World. Redwan therefore co-founded Brilliant Dyes during his PhD, a spin out from Imperial College London, UK, which has developed a low-energy, closed-loop way to harvest organic dyes from algae.

Redwan first started working with these single-celled, photosynthetic organisms during his PhD, where he developed techniques to mass-produce algae. He optimised the algae’s growth conditions and scaled up production to a 120-litre bioreactor. ‘We can also grow [the algae] under sunlight, using industrial flue gas which contains CO₂, and wastewater,’ he explains.

‘Interestingly, there are over 70,000 different species of algae,’ he says, adding that these have various shapes, sizes and – importantly for Brilliant Dyes – different colours. Pre-treating the algae and then passing it through the team’s automated extraction platform can produce a wide range of colours at high purity – from red to blue to green – by varying the species of algae.

The benefit of using photosynthetic algae, rather than using those that ferment sugars, is that the process uses fewer resources and less energy. The excess biomass (mostly proteins) and nutrients can also be sold to the animal feed industry, for example, reducing waste from the process.

Aside from producing dyes, the team has also developed a strategy to fix the dyes to fabrics using less energy and water than conventional methods, while also producing less waste. Dyeing and finishing fabrics currently accounts for 3% of global CO₂ emissions, says Redwan. To overcome this, the team pre-treats the material’s surface, to produce functional groups that can then react with the dyes to form robust bonds. This reaction happens at around 40°C, which is round 30–100°C lower than fixing processes currently used by industry, which also use chemicals such as per- and polyfluoroalkyl substances (PFAS). Cutting reaction temperatures significantly reduces the energy needed.

Redwan says that the dyes are currently at Technology Readiness Level 5 – meaning they have been validated in an industrially relevant environment – with plans for a pilot plant next year that will produce around 10 tonnes of dyes per year. However, Redwan notes that there needs to be different conditions depending on the exact dye and materials.

He also adds that the natural dyes start fading after around 15 washes with strong detergent. As such, the team is currently targeting the high-end textile market to dye fabrics such as wool, cotton and linen where the performance is near to reaching industry standard. Consumers tend to wash clothes made from these natural materials less frequently, without strong detergents, which will help the dyes last longer, says Redwan.

Companies also often sell these textiles at a premium price, meaning that they could absorb the higher cost of Brilliant Dyes’ natural pigments, compared to existing alternatives. Scaling production will lower costs, explains Redwan, which will then allow the team to expand production. Alongside, the company is also developing technology and products for premium cosmetics and food.