A novel method for contact angle measurements on natural fibers

Abstract

Natural fibers typically vary in cross-sectional shape, dimensions and physical properties. They have rough surfaces and a hollow structure to conduct water and nutrients. During contact angle measurements, the liquid is often absorbed by natural fibers. As the result, the common drop-on-fiber and tensiometric methods are unsuccessful in measurements of contact angles. In this study, a novel method of contact angle measurements is presented that reduces the flaws of previous methods. The method relies on calculation of the contact angle from a spherical liquid meniscus of the liquid column formed in between two parallel fibers separated by a small spacing. The accuracy of the method was confirmed through advancing water contact angle measurements on synthetic fiber made of nylon 6,6. Using this novel approach, both advancing and receding water contact angles were measured for commercially available fibers of hemp (Cannabis sativa), curaua (Ananas erectifolius), fique (Furcraea andina), jute (Corchorus capsularis), piassava (Attalea funifera), pineapple (Ananas cosmosus), ramie (Boehmeria nivea) and sisal (Agave sisalana). All natural fibers were found weakly hydrophilic with advancing water contact angles in the range of 40–50°. The receding water contact angles were typically a few degrees smaller although fibers with a rougher surface demonstrated a 22–30° contact angle hysteresis.