Guangzhou Longkai Chemical Co., Ltd.
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What is the effect of silane coupling agent on the durability of glass and aluminium bonding
Author:LongKom  Time:2013-10-10

1. Silane coupling agent has organic-inorganic hybrid structure, which is used to improve the adhesion between adhesives and surfaces. The earliest silane coupling agent was developed to improve the bonding between glass fibers and epoxy matrix in composites. In recent years, the use of silane in structural bonding of aluminium and glass to replace other environmentally harmful or expensive surface treatments has attracted much attention. In this paper, the effect of silane coupling agent on the durability of glass and aluminium surface is discussed from the point of view of practical application.

2. Experiments

2.1 Coupling agent is applied to glass surface in experiments. Aminopropyl triethoxysilane (APES) and propylene oxide trimethoxysilane (GPMS) are used as coupling agents. They are mixed in adhesives or dipped on glass surface with coupling agent solution. The glass samples were washed with distilled water at 50 and dried for 1 hour. Then the glass samples were soaked in different concentration of coupling agent solution for 30 mi. The mass fraction of coupling agent was 0.1%-5%. Then it was dried at 120 C for 1 h. Compared with dipping method, the coupling agent was directly mixed into the adhesive, and the mass fraction was 0.1%-5%. Float glass is bonded to tin surface with tin surface. The tin bath surface of glass sample can be distinguished from air surface under ultraviolet light. The bonding area is 20 mm x 5 mm and the thickness of the adhesive layer is 0.2 mm. The curing conditions are room temperature 24 h 120 1 h. All the bonded specimens were immersed in distilled water containing 0.15% anionic surfactant for 28 days at 40 ~C. The compression-shear strength of soaked specimens was measured on a universal testing machine with the indenter rate of 5 mm min-1.

2.2 Silane coupling agent is applied to aluminium surface. Before APES and GPMS silane coupling agent are applied, aluminium substrate is pretreated in different ways. The coupling agent was applied to the substrate by immersion in 0.5% coupling agent aqueous solution. The samples were dried at 40 C. 30 min. The adhesive is bisphenol A epoxy resin-diethylenetriamine system. The tensile and shear strength of single lap specimens were measured after 42 days immersion in deionized water at 70 C. The clamp speed was 10 mm min - 1.

3.1 The influence of coupling agent on glass bonding test results, the influence of silane content on bonding strength and durability, and the influence of non-functional silane. APES and GPMS were used in the experiment. APES is better than GPMS if silane is directly mixed in resin. This may be because alkaline adhesives accelerate the condensation of aminosilanes. On the contrary, GPMS is better than APES for glass surface pretreatment.

The strength of the joint varies with the content of coupling agent. The maximum strength is 14 MPa when the mass fraction is 0.5%. The direct mixing method yields different results. The strength of joints increases rapidly from 0.1% to 1%. The durability of glass bonding has been greatly improved: the strength of joints after aging test at 40 C. 28 d is up to 15 MPa, which is twice as high as that of specimens without coupling agent. These results show that silane improves durability. Mixing with adhesives requires more silane to achieve maximum bonding strength. The results of surface treatment with nonfunctional silane show that silane not only improves the bonding with the substrate, but also prevents the glass surface from being corroded.

The effect of 3.2 silane on the bonding of aluminium shows that the initial bonding strength and the long-term aging strength of the aluminium surface degreased by solvent are not improved by the application of aminopropyl triethoxysilane.

Compared with solvent degreasing method, the strength of aluminium surface cleaned by alkali solution treated with the same silane coupling agent has been improved both in initial bonding strength and after long-term immersion in high temperature deionized water. APES can also improve the shear strength of aluminium specimens treated by sand blasting, and the effect of GPMS with epoxy group is more remarkable. It demonstrates the importance of pretreatment of aluminium surface by appropriate chemical or mechanical methods before application of coupling agents.

4. The coupling agent with more concluding remarks can reach the maximum strength.
For aluminium bonding, the durability of aluminium sheets treated by alkali and sand blasting can be improved by coupling agent, and GPMS is more effective than APES, while solvent degreasing treatment alone has little effect.

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