Equilibrium contact angle measurements of natural fibers by an acoustic vibration technique

Sorption of fluids during typical wetting experiments on natural fibers produces a zero receding contact angle situation, leading to an incomplete analysis of their wetting behavior. An acoustic vibration method was used to measure "equilibrium" contact angles on natural bamboo fibers. The correctness of the technique is verified by performing the experiment with polyethylene terephthalate (PET) fibers and films, and comparing these results with the average of the cosine functions of the advancing and receding angles for a given system. Surface energies and components of the surface energies of bamboo and PET fibers were estimated using the "equilibrium" contact angle data of various test liquids by using the acid-base approach. The results are in general agreement with X-ray photoelectron spectroscopy (XPS) analysis of the fiber's surface. The findings contribute to a better understanding of the complex phenomena occurring during wetting of natural fibers and suggest that the contact angle obtained by forcing relaxation through acoustic vibration is a reliable method for study the wetting behavior of natural fibers. (C) 2014 Elsevier B.V. All rights reserved.