Improvement of adhesion performance between modified phenolic and stainless steels by titanate coupling agent treatment

Compared with the phenolic, the boron phenolic has a significant advantage due to its heat resistance and toughness as adhesive. Although silane and titanate coupling agents have widely proven to improve the compatibility of fillers with resins, the detailed effects of titanate coupling agent on improving the bonding interface between boron phenolic and steel have rarely been explored in this sense. This study has explored the adhesion between the phenolic adhesive and stainless steels (SS) by the surface modification of the SS with titanate coupling agents. Contact angle test, Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS) were used to characterize the surface properties of SS. Moreover, the adhesion strength was measured by the lap-shear tensile test. The results show that the polar part of the surface energy Υsp of the SS decreases after treatment by a titanate coupling agent. The adhesive strength increases from 26.21 to 35.37 MPa with increase in the concentration of the coupling agent and exhibits its ultimate adhesion strength of 39.56 MPa at 2%. With further increase in concentration, the adhesion strength gradually decreases. The increase in adhesion could be due to the reaction of the coupling agent with iron oxide or hydroxyl on the surface of the steel sheet to form a chemical bond, and thus a 'molecular bridge' between the adhesive and the steel.