Work of adhesion and local bond strength in glass fibre-thermoplastic polymer systems

The microbond test was employed to determine the interfacial shear strength (IFSS) in glass fibre-polypropylene and glass fibre-polystyrene systems. The experimental IFSS values were analyzed as a function of embedded length. The local bond strength in both systems was calculated as a limit value of IFSS at zero embedded length. For the same systems, the reversible work of adhesion, WA, was determined from wetting angles of polymer melt on single glass fibres and using the Owens-Wendt approach. A method for WA determination from the microbond test data based on the Nardin-Schultz hypothesis and the concept of local bond strength is proposed. This method, applied to the calculation of WA in composites of a non-polar polymer polypropylene (PP) with glass fibres showed a good agreement with the results obtained from wetting measurements. At the same time, the calculated WA value for a polar polymer polystyrene (PS) is much higher than that obtained using wetting data. Besides, bond strength in the glass fibre/PS system is strongly influenced by the contact forming temperature. These results lead to the assumption that an increased number of the local bonds at the interface can contribute to an improved adhesion between a fibre surface and a polar polymer.