Mechanical properties and thermal ageing of a perfluoroether-modified epoxy resin in castings and glass fibre composites

Castings from a bisphenol epoxy resin cured with methyl nadic anhydride, and containing varying amounts of a miscibilized carboxy-terminated perfluoroether oligomer (CTMF), were produced in such a manner as to display two different morphologies: one consisting of fine heterophase interpenetrating networks (IPNs) and the other comprising precipitated dispersed particles. High-temperature accelerated ageing showed that compositions containing 15% CTMF exhibit higher flexural strength and ductility than unmodified resins, irrespective of the type of morphology. Castings of CTMF-modified resin with an IPN morphology, however, displayed superior property retention characteristics with respect to thermal ageing and consequently were chosen as the matrix for the production of unidirectional fibre composites. The composites, on the other hand, were found not to exhibit the same improvements in heat ageing resistance as the castings. The cause has not been established but the increase in peak tan δ temperature over that exhibited by the castings suggests that the matrix is more highly crosslinked.