微小時間におけるパルプ繊維のぬれの測定

抄録

An optical technique to measure directly the contact angle of liquid against a single wood-pulp fiber has been developed for characterizing fiber-liquid interactions. A fiber was contacted with liquid by partially immersing the fiber in a drop of the liquid. The contact angle was determined from a series of photographs of the liquid drop silhouette at the point of contact. The contact line and profile history were continuously photographed in every 0.2 seconds after the initial contact. The direct contact angle measurement was carried out by a system consisting of an automatic rewinding camera with two bellows, an intervalometer and a stroboscope. Contact angle of a water drop on handsheet surface were also measured as a function of time according to that for single pulp fibers. The measurement on single pulp fibers by this technique did not deviate significantly from data previously reported by the wilhelmy method. Because of appropriate reproducibility with small standard deviation, this technique was considered to be suitable for measuring the contact angle on fibers of small cross section. Contact angle of water on single pulp fibers showed a rapid decrease with time in the initial 1 second and then was settled after 5-15 seconds.
Softwood bleached kraft pulp fiber and its handsheet showed fairly low contact angle of water.
On the other hand, contact angle of single fiber and handsheet from thermomechanical pulp was higher. This can be interpreted as being due to higher lignin and extractives content. For softwood bleached kraft pulp fiber, water showed lower contact angle compared with methylene iodide. But there was little difference between water and methylene iodide in case of thermomechanical pulp fiber. In order to determine surface properties of single pulp fiber of kraft and thermomechanical pulps, the dispersion and polar components to the surface free energy were calculated. The similar values for the dispersion component were obtained, whereas the polar component of kraft pulp fiber was greater compared with thermomechanical pulp.