In recent decades, there has been a lot of research into smart textiles, i.e. textiles whose functions and properties change when they react to their surroundings. But despite intensive research, relatively few products have ended up on the market. Sina Seipel wants to change that. She chose photochromic textiles, which react to UV radiation and then change colour.

"Photochromic materials can be used in a t-shirt, for example. When it changes colour, it  helps you to know that it is time to seek protection from the sun. The material could also be used in brand protection, in the form of a print that is only visible under UV light. In this way, you can show that a garment has not been plagiarised,” says Sina Seipel, who defended her doctoral thesis Ink jetting of photochromic ink – Towards the design of a smart textile sensor today. 

Conventional production processes for printing, dyeing, and curing require a lot of water, chemicals, and energy. This challenges the production of specialty textiles with rather expensive raw materials such as photochromic dyes.

"Specialty products as smart textiles are only produced in small batches. Their production with conventional technologies is so expensive that if it is realistic and economic, it must be resource-efficient," says Sina Seipel.

Exploring extremes

Her interest in sustainable textile processes was born when she was an exchange student at the Swedish School of Textiles and it felt natural to move on to this subject when she started working on her doctoral thesis.

"I chose to combine ink jet printing with UV curing to explore extremes – both of these processes use minimal resources compared to conventional methods and are well suited to producing smaller quantities," says Sina Seipel.

Ink jet printing means that small drops of ink are applied to the textile surface, as opposed to applying thick layers or dyeing the entire textile in a colour bath. When the photochromic dyes are cured with UV light, the print is dry after just a few seconds, instead of thermally curing the ink, which requires more time and energy.

"These processes are not new, but the combination of them has not been used before in photochromic materials," continues Sina Seipel.

The results she presents in her thesis show that the two processes have potential when combined and that the photochromic textiles produced in the new, more durable way behave as desired. By using a digital process, production also becomes more flexible and controllable. It is also possible to change the behaviour of the textiles; for example, to speed up the colour change.

Dyeing textile with gas

As a side project during her research studies, Sina Seipel has also tested dyeing textiles with supercritical carbon dioxide, a way to dye using gas instead of water. Immediately after the dyeing process is completed, the textile is completely dyed and dry and this is well suited to large production volumes. Ink jet and UV curing, however, are good methods for pattern printing of small quantities and individual products.

Some companies have been in contact, curious about Sina Seipel's research. She hopes that this will lead to a more sustainable textile production. As she looks ahead, she wants to continue researching processes that are resource-efficient, perhaps with other functions and materials.

"I see a great future for this and want to spread the results so that they don't just stay in the scientific community. I want to reach out to the industry and also contribute this knowledge to the educational programmes here at the Swedish School of Textiles so that the students see what opportunities there are," says Sina Seipel.

Read more

Sina Seipel's research profile

Text: Lina Färm
Photo: Anna Sigge
Translation: Eva Medin