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 60°C, formed a separated island-phase structure with diameters of 0.4– 0.8 μ m, 3–5 μ m and 80–100 μ m 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 −196°C, 25°C, 140°C and peel strength at 25°C 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 −196°C – 140°C with good bound-strength properties.