APPLICATION OF THE SURFACE FREE-ENERGY CONCEPT IN POLYMER PROCESSING

The surface characteristics of variously treated carbon and glass fibres have been determined by contact angle measurements (using a capillary rise technique). inverse gas chromatography, and zeta potential measurements. The contact angles of water and methylene iodide were used to calculate the dispersive and non-dispersive components of the fibre surface free energy by applying the geometric mean approach, and the approach by Fowkes to estimate the acid-base term of the thermodynamic work of adhesion. The results obtained correlate with those of inverse gas chromatographic and zeta potential measurements. The non-polar surface character of the carbon fibre can be altered by oxidizing, or finishing the fibres with an epoxy resin. The acid base term of the thermodynamic work of adhesion, W(a)ab, and the non-dispersive component of the surface free energy, gamma(p), are increased drastically by these treatments. Treatment of the 'high-energy' glass fibre surface with an aminosilane results in a relatively low surface free energy with basic surface groups. When epoxy dispersions were used for sizing the glass fibres, the surface free energy increased without changing the basic surface character. A direct correlation between the surface-energetic properties of the fibres and the mechanical behaviour of the fibre-reinforced polyamide composites was not generally found.