Resole resin as sizing agent for aramid fibres

A comparative study was made in order to evaluate the interfacial characteristics of treated aramid fibres and epoxy resins. Surface treatment by coating with phenolic resins was performed using the following two systems: a) alkaline aqueous solution of resole resin and b) solution of novolac resin containing hexamethylene-tetramine as cross-linking agent. After these treatments, the modified aramid fibres were used for the preparation of reinforced epoxy specimens. The flexural properties of these specimens were determined and the results were discussed taking into consideration the surface characteristics of the modified fibres, as derived from pull-out tests and contact angle measurements. It was shown that both coatings are adequate to promote interfacial adhesive bonding to epoxy matrices due to the chemical reactivity of phenolic resins to the epoxy matrix as well as to their affinity with the aramid fibre surface. Resole appeared more efficient than novolac as it produces uniform continuous films, shows increased reactivity due to its higher hydroxyl content and can be easily processed because it is soluble in alkaline water solutions.