Mechanical and morphological investigations of reactive polysulfone toughened epoxy networks

The diglycidyl ether of bisphenol-A (DGEBA) epoxy resin was toughened by aminophenyl functional reactive polyethersulfones (R-PES) or by t-butyl terminated non-reactive polyethersulfones (T-PES). The molecular weights of PES were controlled to afford 5,000 to 20,000 g/mole and loadings were also varied from 5 to 30 wt.%. Epoxy networks cured with 4, 4'-diaminodiphenylsulfone (DDS) were subjected to Tg determinations, plane strain fracture toughness (K_1C) measurements, chemical resistance tests and morphological studies by SEM. Very significantly improved K_1C fracture toughness was obtained with reactive PES toughening without loss of chemical resistance, while non-reactive PES blended epoxy resins exhibited only slightly improved fracture toughness but poor chemical resistance. It was possible to load up to 30 wt.% of PES without utilizing solvent and the maximum K_1C fracture toughness with R-PES was around 2.2 MPa-m 0.5, which was equivalent to the neat thermoplastic resin. Ductile fracture of the PES phase is suggested as a major toughening mechanism and this is highly dependent of the excellent adhesion developed between the PES and epoxy phases due to the chemical bonds. The systems demonstrated that chemical resistance of thermosets can be combined with the tough characteristics of thermoplastics.