Coloring Your Fabric—Without Dyes!

By convention there is color, by convention sweetness, by convention bitterness, but in reality there are atoms and space.-Democritus

With the current emphasis on coloring fabric in a more "eco-friendly" and sustainable manner, alternatives to traditional dyes and dyeing processes are being sought. Also driving these alternatives is concern that some dyes (e.g., azo dyes) produce allergic reactions when contacting the skin of sensitive individuals. But where does one find models for these new coloring schemes? Look no further than the butterfly…

Nature often provides us with inspiration that can have practical application (biomimicry). Obviously, the vibrant colors of butterfly wings are not produced by the magic of dyes. Neither are the myriad colors displayed in an opal gemstone. A butterfly's colors (as are the colors in soap bubbles) are produced by a physical process known as iridescence. The process for opal gemstones is uniquely called the play of colors. In both cases, the surface properties of these materials are responsible for producing the colors ("structural color") not a dye ("intrinsic color").

Using natural iridescent features in textiles is not a new development. For example, the wings of beetles from certain beetle families (the Buprestidae family-jewel beetles) have been used as textile embellishments in India, Thailand, Burma, New Guinea, Peru, and Ecuador for centuries.

Dyes absorb light at characteristic frequencies, allowing unabsorbed light frequencies to reach the eye as intrinsic color. The iridescent colors of specially-designed biomimetic surfaces arise from the surface's ability to behave like a diffraction grating—an optical device that acts like a flat prism by breaking up light into its component colors using a grooved surface. In butterfly wings, this is performed by an array of thin scales. The thickness and structure of its surface, and the angle at which it is viewed, determine its color. For textiles, surfaces can be engineered to have similar properties.

Fibers are now available that can add a glimmer of iridescence to fabrics without using dyes. One of these is Tenjin's Morphotex fiber. These fibers use nanotechnology to build layers of nylon and polyester, creating a difference in refractive index that leads to the creation of color through light interference.

Structural fiber development has taken another step forward with the use of variously-shaped nanoparticles to create color. Juan Hinestroza and his group at Cornell University's College of Human Ecology's Department of Fiber Science and Apparel Design have added color, as well as protective abilities, to create "nano-fashion" by applying metal nanoparticles to cotton and to electrospun nylon nanofibers. Color "tuning" depends on the metal used, its size, and shape. The incorporation of opal nanoparticles in polymers to achieve a similar effect is also under study. Although of limited practicality at present, these approaches may eventually lead to affordable alternatives to dyes for textile coloration base on the application of structural color principles.