Surface treatment of alumina ceramic for improved adhesion to a glass fibre-reinforced polyester composite

The adhesion between an alumina ceramic and a glass fibre-reinforced polyester matrix composite has been investigated. The effect of various alumina surface treatments, including degreasing, etching, plasma, grit-blasting and silanisation, was evaluated. The physical and chemical surface properties were investigated by microscopy, profilometry, contact angle measurements and X-ray photoelectron spectroscopy. The analysis showed that the treatments removed organic contaminants from the alumina, resulting in higher surface free energies. Alumina/composite test specimens were prepared by a vacuum moulding technique, and the adhesive strength was evaluated using the fixed arm peel test. All surface treatments had a pronounced effect on the peel strength, and the adhesion was improved compared to the as-received alumina. This was verified by investigation of the fracture surfaces. The silane treatment produced a thin silane layer on the surface and had the greatest effect on the adhesive strength. This could be explained by the silane acting as an adhesion promoter between the alumina and the composite, better wetting of the more planar silane treated surface by the thermoplastic polyester, and a more defect-free alumina/polyester interphase.