Study on Modification of Epoxy Resin Reinforcing Adhesive Commonly Used in Aerospace Applications

Epoxy resin reinforcing adhesive has become the most commonly used reinforcing adhesive in the aerospace field because of its wide bonding range, high bonding strength, small coefficient of thermal expansion, and no volatile substances after curing. At present, the mainly used epoxy adhesives, such as DG-4, HY-916, etc., are all two-component adhesives, which need to be mixed before use. However, due to the good fluidity after preparation, and the need to restrict the flow of adhesive under typical working conditions, the adhesive could not be dispensed until the viscosity of the glue is suitable by standing at room temperature for a period of time. In this study, DG-4 epoxy resin adhesive was selected for doping modification. Three doping species were selected, namely polyamide wax, modified hydrogenated castor oil and hydrophobic nano-SiO2. And the optimal doping method of the adhesive was obtained by adjusting the doping species and the doping amount. Through the kinetic viscosity test and shear strength test, the glue doped with 5% (mass fraction) polyamide wax has the best performance. The thixotropic coefficient of the glue increased from 0.864 to 1.093, while the shear strength increased slightly, which was because that the polar groups on the surface of the doped material were fully activated in the adhesive environment to form swelling particles, and the hydrogen bonds between the swelling particles and the interaction force between the doped material and the epoxy resin matrix could bear a certain load, which was conducive to stress transmission. In addition, there were no significant changes in the glass transition temperature (T
g
), coefficient of thermal expansion (CTE) and thermal vacuum outgassing properties of the doped glue. Furthermore, the doped adhesive has passes the reliability assessment and can be used in aerospace products. In general, this study improved the operating performance of adhesive under typical working conditions. The proposed modification method not only ensured the microscopic immersion, but also avoided adhesive flow at the macroscopic level, which reduced the difficulty of operation and improved production efficiency while ensuring product quality.