The influence of silane coupling agent on the durability of glass and aluminum bonding
1. Introduction: Silane coupling agents have an organic-inorganic hybrid structure and are used to improve the adhesion between adhesives and surfaces. The earliest developed silane coupling agent was used to improve the adhesion between glass fibers and epoxy matrix in composite materials. In recent years, the use of silane for structural bonding of aluminum and glass to replace other environmentally harmful or expensive surface treatments has attracted attention. This article focuses on the impact of using silane coupling agents to treat glass and aluminum surfaces on the durability of adhesion from a practical application perspective.
2. Experimental section
2.1 Application of Coupling Agents on Glass Surfaces In experiments, aminopropyltriethoxysilane (APES) and glycidoxypropyltrimethoxysilane (GPMS) were used as coupling agents, which were mixed in adhesives or dipped in coupling agent solutions and applied to glass surfaces. After cleaning the glass sample with distilled water, dry it at 50 ℃ for 1 hour, and then immerse it in coupling agent solutions of different concentrations for 30 minutes, with a coupling agent mass fraction of 0.1% to 5%. Then dry at 120 ℃ for 1 hour. Compared with the dip coating method, the coupling agent is directly mixed into the adhesive with a mass fraction of 0.1% to 5%. Float glass is bonded with tin on the tin surface, and the tin bath surface of the glass sample can be distinguished from the air surface under ultraviolet light. The bonding area is 20mm&Times: 5mm, adhesive layer thickness is 0.2mm. The curing condition is room temperature for 24 hours↠ 120 ℃, 1h. All adhesive specimens were soaked in distilled water containing 0.15% anionic surfactant at 40 ℃ for 28 days. The soaked specimen is tested for compressive shear strength on a universal testing machine with a head rate of 5mm· Min-1.
2.2. Silane coupling agents are applied to aluminum surfaces. Before applying APES and GPMS silane coupling agents, the aluminum substrate is pre treated using different methods. Soak the coupling agent in a 0.5% aqueous solution and apply it to the substrate. The sample was dried at 40 ℃ for 30 minutes. The adhesive is a bisphenol A epoxy resin diethylenetriamine system. The tensile and shear strength of the single lap joint specimen was measured after immersion in deionized water at 70 ℃ for 42 days, with a clamp speed of 10mm· Min-1.
3. Results and Discussion
3.1 Test results on the effect of coupling agents on glass adhesion. Explain the effect of silane content on adhesive strength and durability. Explain the impact of non functional silane groups. APES and GPMS were used in the experiment. If silane is directly mixed into the resin, APES has a better effect than GPMS. This may be because alkaline adhesives accelerate the condensation of aminosilane. On the contrary, for glass surface pretreatment, GPMS yields better results than APES.
It can be seen that the strength of the joint varies with the content of the coupling agent, and reaches a maximum value of 14 MPa at a mass fraction of 0.5%. The direct mixing method yielded different results. The quality score increased rapidly from 0.1% to 1%, and the joint strength increased rapidly. The durability of glass bonding has been greatly improved: after 28 days of aging test at 40 ℃, the joint strength reaches up to 15MPa, which is twice as high as the specimen without coupling agent. These experimental results indicate that silane improves durability. Mixing with adhesive requires more silane to achieve maximum bonding strength. The results of surface treatment with non functional silane indicate that silane not only improves the adhesion with the substrate, but also prevents corrosion of the glass surface.
3.2 The effect of silane on aluminum bonding indicates that the application of aminopropyltriethoxysilane on solvent degreased aluminum surfaces does not improve the initial bonding strength or the strength after long-term aging.
Compared with the solvent degreasing method, the aluminum surface cleaned with alkaline solution is treated with the same silane coupling agent, which improves both the initial bonding strength and the strength after long-term immersion in high-temperature deionized water. APES can also improve the shear strength of sandblasted aluminum specimens, while GPMS with epoxy groups has a more significant effect. It highlights the importance of pre treating the aluminum surface with appropriate chemical or mechanical methods before applying coupling agents.
4. Conclusion
More coupling agents are needed to achieve maximum strength. For aluminum bonding, coupling agents can improve the durability of aluminum sheets treated with alkali and sandblasting, and GPMS has a more significant effect than APES, while solvent degreasing treatment alone has little effect.
