Study On The Toughening For Epoxy Resin Structural Adhesive

This paper investigates the toughness of the epoxy structure adhesive by adding nano materials, rubber elastomers, interpenetrating polymer network structure and flexible chain section curing agent. Two toughness indexes (impact strength and T impact peel strength) of toughening epoxy adhesive are studied. Besides, tensile, compressive and shear properties are tested. Based on SEM morphology analysis of impact section, different toughening mechanisms are found. Finally, this paper puts forward an optimal compounding which reaches the requirement of A grade adhesive. Specific research results are as follows:As for nano materials, 3% nano SiO2 improves the tensile properties of adhesive, but has no significant effect on improving the impact strength and T impact peel strength. Nano CaCO3 improves impact peel strength of adhesive greatly. The effect of the toughening mainly depends on the dispersion of nano materials and the bubbles remained in the system of adhesive. The better nano materials mixed and the less bubbles remained in system, the better toughening effect will be.As for rubber elastomers, the effects of RA (homogeneous system after curing) and RB (heterogeneous system after curing) are studied and compared. Tensile and compressive properties of adhesive drop with the increasing of flexibilizer, especially for RA. This two kinds of flexibilizers can obviously increase the impact strength. The adhesive toughened by RA has little T impact peel strength, but T impact peel strength of adhesive toughened by increasing RB firstly but then decreases with the increase of RB, the main reason is that "island structure" formed by RB induces yield and energy dissipation in resin, which can greatly improve toughening effect. It is also found that impact strength has a lot to do with the elasticity modulus of adhesive, the smaller modulus is, the bigger impact strength is; T peel strength has a lot to do with section energy consumption, the larger section energy consumption is, the greater T impact peel strength is.Network interpenetrating structure of interpenetrating polymer reduces the inner stress of system and increases the movement space of molecules, so it improves impact strength. However, this method has little effect on T impact peel strength due to the energy consumption of section not improved.Epoxy curing agent with flexible segments mainly improves the impact strength, but not the T impact peel strength. This toughening way has no much effect on other mechanical properties of adhesive system.Based on the above four toughening way, an optimal compounding is raised. Other mechanical properties of this compounding are studied. It is found that by adding 25% RB and 50% silica powder, the performance of epoxy structure adhesive is optimal.