Wilhelmy Technique and Solidification Front Technique to Study the Wettability of Fibres

Abstract

The strength of fibre-reinforced materials depends heavily on the adhesion between the fibre and the resin. To predict the bond strength of the adhesion, it is desirable for the surface tension of the fibre to be known. Two independent methods, the Wilhelmy balance method and the solidification front method, were investigated. The fibres used for this investigation included a carbon fibre, Thornel 300®, and an aromatic poiyamide fibre, Kevlar. In the Wilhelmy experiments three liquids, ethylene glycol, glycerol and distilled water were employed to measure the surface tensions of the test fibres. They were found to be 42.4 mJ/m² and 43.7 mJ/m² for the carbon fibre and Kevlar, respectively. These values agreed very well with the results obtained from the solidification front method, from which the carbon fibre was found to have a surface tension value of 41.8 mJ/m² while that for Kevlar was 46.4 mJ/m². Furthermore, error analysis has shown that the error limits of the experiments are within 5% of the resulting values. The reproducibility and accuracy of these two techniques indicate that they are viable for determining the surface tension of small diameter fibres.