A LIQUID DROPLET MEASUREMENT TECHNIQUE AS A MEANS OF ASSESSING THE INTERLAMINAR SHEAR-STRENGTH OF FIBER-REINFORCED COMPOSITES

A liquid droplet measurement technique was used to measure the contact angle for low modulus, medium modulus and high modulus pitch-based carbon fibres. A phase transfer catalytic oxidation treatment and an electrochemical oxidation treatment both resulted in falls in the observed glycerol contact angle. Increases in surface energy values were estimated using an equation-of-state approach. The electrochemical oxidation treatment increased the concentration of oxygen- and nitrogen-bearing groups on the fibre surface (as shown by Auger electron spectroscopy), resulting in a fall in the surface energy values estimated using the droplet measurement technique, and corresponding improvements in composite interlaminar shear strength (ilss) were observed. Thus it was shown that the surface energy values determined using this method could be used to assess changes in ilss due to surface treatment of the fibre, provided only chemical changes resulted from the fibre treatment. © 1990.