Water absorption in a rubber-modified epoxy resin, carboxy terminated butadiene acrylonitrile-amine cured epoxy resin system

Gravimetric and dielectric measurements of water uptake by a series of carb oxy terminated butadiene acrylonitrile (CTBN) -amine cured epoxy resin syst ems are reported. The amount of water absorbed and rate of diffusion increa ses up to approximately 15 w/w% CTBN content. Anomalous behaviour is observ ed around a composition of approximately 20% CTBN which is coincident with the occurrence of a co-continuous phase structure in the resin. Dynamic mec hanical analysis and atomic force microscopy studies provide evidence for p hase separation and inversion of phase structure at 20% CTBN. The increase in the water uptake with increasing CTBN content reflects the ability of th e highly polar acrylonitrile group to bind water. The general increase in t he diffusion coefficient is consistent with CTBN being initially dispersed in the epoxy matrix tending to a lowering of the effective segment density inhibiting mobility of the water molecules. In the co-continuous region sub tle effects of mutual solubility of components and generation of a long per colation path leads to the observed anomalous behaviour, Dynamic mechanical thermal analysis (DMTA) indicated that water absorption suprisingly leads to an increase in the glass transition temperature and is associated with a densification of the matrix structure. Atomic force microscopy measurement s reveal that the surface roughness changes with composition with a marked increase in the surface roughness at 20% CTBN. (C) 1999 Elsevier Science Lt d. All rights reserved.