Why are towels that are naturally dry so hard

A new study conducted by Kao and Hokkaido University shows that the “bound water” remaining on the surface…

A new study conducted by Kao and Hokkaido University shows that the “bound water” remaining on the surface of cotton can make the single fibers of cotton cross-bond, which makes the cotton products harder after drying naturally. This discovery provides new ideas for us to understand the special performance of water on the surface of materials, and it can also provide new ideas for the development of clean technologies.


If there is no softener when washing, and the naturally dried cotton towels will often become very hard, this is a common life phenomenon, but the mechanism behind it has always been a mystery. In previous research, Kao’s research team believed that the binding water is the reason for stiffening the towel. The binding water is a special kind of water that exists on the surface of the material. The team proposed a theoretical model that the bound water remaining on the surface of the cotton caused a cross-bonding between the single fibers through a phenomenon called capillary adhesion.

Why are towels that are naturally dry so hard
Why are towels that are naturally dry so hard

In a new study published in The Journay of Physical Chemistry C, the researchers published direct observations of the water bound on the surface of cotton, supporting the model proposed by Kao. Kenichiro Murata of Hokkaido University participated in this research. They used special analysis techniques of atomic force microscopy (AFM) and infrared spectroscopy (AFM-IR) based on atomic force microscopy to analyze the bound water on the cotton surface from the molecular level.

Atomic force microscope observations show that there is a non-cellulose sticky substance on the surface of cotton, and cellulose is the main component of cotton. This result strongly suggests that there is viscous bound water, which causes capillary adhesion. In the spectrum experiment, two peaks appeared on the surface of naturally dried cotton, which further proved the existence of bound water. After completely removing moisture from the cotton surface, no peak was observed. In addition, the spectrum also shows that the bound water shows different states at the air-water junction and the water-cotton junction.

Kenichiro Murata said: “Experiment shows that there is obvious binding water on the surface of cotton. The binding water helps to form specific dynamic properties, such as the drying effect caused by capillary adhesion. In addition, the binding water itself also shows different The unique hydrogen bonding state of ordinary water. ”Kao ’s Takako Igarash added:“ In the past, people believed that the softener worked because it reduced the friction between cotton fibers. But our research results show that water binding is involved. The hardening process of cotton gives us a better understanding of how softeners work and can help us better study the formula and system of softeners. “

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