Control of morphologies and mechanical properties of thermoplastic-modified epoxy matrices by addition of a second thermoplastic

Ternary mixtures based on stoichiometric mixtures of the diglycidyl ether of bisphenol-A (DGEBA) and 4,4'-diaminodiphenyl sulfone (DDS) and two miscible thermoplastics, poly(methyl methacrylate) (PMMA) and the poly(hydroxy ether of bisphenol-A) (phenoxy), were investigated by optical microscopy (OM), atomic force microscopy (AFM) and dynamic mechanical analysis (DMA). Mechanical testing was used to study the ultimate behavior. All the modified epoxy mixtures were heterogeneous. DMA has been shown to be an excellent technique for detecting the morphologies generated after curing when the loss modulus is used for analysis. Morphology varied with the thermoplastic content on the mixtures. The addition of a second thermoplastic in small amounts changed the morphological features from particulated to co-continuous and from that to phase-inverted morphologies. A significant increase in fracture toughness was observed above all for the mixtures with some level of co-continuity within the epoxy-rich matrix. Phase inversion led to poor strength and also fracture toughness. (C) 2003 Society of Chemical Industry.