To provide laundry with fragrances without the effect disappearing after the first laundering is quite a challenge. Empa researchers have now developed fibers that release the scent of roses or cloves - permanently. What’s more, the hollow fibers can also be equipped with other active ingredients.
Core-sheath fibers are produced from two components in the melt spinning process. The picture shows a textile polymer fiber with a central core. Scanning electron micro-scope image, magnified 1,200 x, colored.
A sensitive nose can pick up a wide range of aromas. In our perception, we often associate exquisite scents with fond memories, for instance of an excellent wine, an adventurous journey or first love. Equipping textiles with pleasant fragrances is not a new demand: Cleopatra is said to have had the sails of her ships soaked with the finest essences. Today, curtains for offices with an invigorating fragrance, flowery bouquets for bed linen or spicy aromas for neckerchiefs and ties are in demand.
Empa researcher Rudolf Hufenus from the "Advanced Fibers" laboratory in St. Gallen has, therefore, developed a process, by which so-called liquid-core fibers are produced, filled with, for example, flowery rose scent or cloves essences. Thus far, it has only ever been possible to fill hollow fibers of limited length in a complex 2-step process. Using a continuous melt-spinning process, Hufenus is now able to produce longer fibers that are being filled during production. The bi-component fibers can then be processed into textiles. "We have successfully demonstrated the desired mechanical properties for textiles as well as the dye-ability and wash-ability of the scented fibers," says Hufenus. The fragrances are released slowly and continuously through the gas-permeable sheath of the polymer fibers, so that the textiles have a fragrant effect over numerous washing cycles.
The selection of essences and polymers is crucial in order to achieve a perfect interaction for the diffusion of the fragrance. Since the spinning parameters can be precisely controlled, additional properties have already been integrated into the fibers, such as flame retardancy.
To ensure that textiles release a lasting fragrance, the essences can be packaged in tiny capsules (orange), which are strung together to form pearl string-like fibers (green) during electrospinning, (confocal microscopy image).
Another novel technology that is suitable for a variety of active ingredients to be incorporated into textiles is the electrospinning of polymer fibers with scent-capsules. "Fragrances, because of their volatility, are a particularly tricky class of substances," explains Empa researcher Giuseppino Fortunato from «Biomimetic Membranes and Textiles» Lab in St. Gallen. For one thing, they should diffuse evenly in the environment to achieve their desired effect; on the other hand, they should remain in the textile for as long as possible. To achieve sustainable fragrance results, Fortunato and Nicolas Luisier confine the essences into tiny capsules made of skin-friendly polymers in accordance with Oekotex Standard 100.
In cooperation with various industry partners, including Cilander AG in Herisau, Bachmann Krawatten AG in Zurich and Swifiss AG in Urnäsch, Fortunato and his team developed fragrance capsules that can be used to treat textiles. Using this process, which is patent-pending, textiles were finished, washed and stored - with lasting effects. In standard olfactory tests with researchers from the University of Applied Sciences in Rapperswil, the fragrant textiles scored well with test subjects. After all, the ensemble of the first perceived top note, the longer-lasting heart note and the final base note of the fragrance composition must harmonize perfectly.
Fortunato is now developing ultra-fine membranes based on degradable biopolymers, in which the fragrance capsules are lined up like a string of pearls. "With this ’beads on a string’ structure, the fibers release only very tiny amounts of fragrance over months," explains the researcher. In future, the membranes produced by electrospinning could be included in sportswear, for instance. Fortunato does not want to limit the process to fragrances, though. The capsules could also contain active ingredients that soothe the skin or support wound healing. "Once we have succeeded with volatile substances like fragrances, active ingredients that are quite a bit more stable should be a piece of cake," he says.