Study on the phase behavior of a toughened epoxy adhesive and its bond-strength properties at liquid nitrogen temperature

The phase behavior of an epoxy adhesive toughened with a polyether was investigated. The adhesive, cured at 60degreesC, formed a separated island-phase structure with diameters of 0.4-0.8 mum, 3-5 mum and 80-100 mum at toughener contents of 10 phr, 20 phr and 30 phr, respectively. Phase inversion occurred at a toughener content of 40 phr. The bound-strength properties of the toughened adhesive were highly influenced by this phase behavior. The measured lap-shear strengths on aluminum at -196degreesC, 25degreesC, 140degreesC and peel strength at 25degreesC for the adhesive containing 20 phr toughener and 75 phr aluminum powder were 26.5 MPa, 24.2 MPa, 11.0 MPa and 2.2 kN/m, respectively. This showed that the epoxy adhesive studied could be used in a wide temperature range of -196degreesC-140degreesC with good bound-strength properties.