Washington, D.C. — Millions of consumers love the "softness" of their clothing after using liquid fabric softeners. Scientists from the Kao Corporation in Japan have unlocked the mechanism describing how these products work effectively on cloths and yarns, which could pave the way to more effective softening products.
Their research was honored with the American Cleaning Institute (ACI) Distinguished Paper Award, recognizing the most outstanding research to appear in 2016 in the Journal of Surfactants and Detergents.
"The reason why fabric softeners can soften fabrics likes towels had been conventionally understood by the simple keyword of ‘sliding’, where the product slides between fibers or yarns by lowering the friction between them," said Ms. Takako Igarashi, a Kao scientist and paper co-author.
Photo courtesy of the American Cleaning Institute"When we observed the cotton towel which was naturally dried before the treatment by fabric softeners, however, the texture of this dried towel gave us the impression of not only stiffness but ‘hardness,’ as if it was glued by something. This hard texture was not related to ‘sliding’ or friction."
In their research, Ms. Igarashi and her colleagues first focused on understanding why a fabric hardened when a fabric softener wasn’t used.
"We concluded that this hardening phenomenon is because of ‘hydrogen bonding,’ in which the non-frozen bound water plays the main role of the formation of cross-linkage between the cotton fibers. We proposed the new theory that the softening effect of fabric softener was considered to be mainly caused by the inhibition of the formation of the hydrogen-bonding-based cross-linkage by non-frozen bound water between single fibers.
"We also found that the softening agent has a tendency to adsorb preferentially to the more exposed part of yarns through several unique observation methods. This means that the role of fabric softeners at the unexposed point on the yarns is less important to cause the feel of softness."
Researchers found that the concentration of softening agent decreases from the outer to inner part of the yarns; this outer part loses its hardness and the inner part maintains the hardness caused by the abovementioned hydrogen bonding. With these findings, this particular uneven adsorption of softening agent is regarded as the key phenomenon to give proper softness together with bouncy feel to fabrics such as cotton towels.
"With these new understandings and theory, we can test new possibilities and may be able to design new effective softening agents, formulations or systems," said Ms. Igarashi.
The paper, Elucidation of Softening Mechanism in Rinse-Cycle Fabric Softeners. Part 2: Uneven Adsorption-The Key Phenomenon to the Effect of Fabric Softeners appeared in the Journal of Surfactants and Detergents, July 2016, volume 19, Issue 4, pp 759-773. It is authored by Takako Igarashi, Koichi Nakamura, Masato Hoshi, Teruyuki Hara, Hironori Kojima, Masatsugu Itou, Reiko Ikeda, and Yoshimasa Okamoto.
ACI’s Distinguished Paper Award is presented at the Annual Meeting of the American Oil Chemists’ Society, during a luncheon of the group’s Surfactants and Detergents Division.