A novel measurement of contact angle on cylinder-shaped lignocellulosic fiber for surface wettability evaluation

Abstract

Lignocellulosic fiber, composed of hydrophilic component (carbohydrates, including cellulose and hemicellulose) and hydrophobic component (lignin), is widely used in bio-composites, paper and paperboard products, and other fiber-based bio-products. The surface wettability of cylinder-shaped fibers, focusing on the liquid spreading ability on fiber surface, essentially has an important effect on many kinds of fiber properties. A novel measurement of contact angle (“liquid-bridge” testing) was utilized for the calculation of surface free energy, expressed as the evaluation of fiber surface wettability. The results showed that the fiber contact angle determined by the “liquid-bridge” testing was quite similar to that measured by the traditional sessile drop technique. The fiber surface free energy increased dramatically from 46.63 mJ m−2 to 54.45 mJ m−2, calculated by the fiber contact angle with water (74.30 ° to 43.24 °) and glycerol (64.50 ° to 49.41 °), when the PFI mechanical treatment was strengthened up to 15,000 rev. This novel method has also been applied to test the positive variation and sensitivity of surface wettability with the increase of fiber surface roughness and surface pore size.