Improving Adhesion between Epoxy Adhesive Compositions and Aluminum Using Epoxy- and Amino-Alkoxysilane Promoters
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oving Adhesion between Epoxy Adhesive Compositions and Aluminum Using Epoxy- and Amino-Alkoxysilane Promoters M. S. Fedoseeva, *, M. G. Shcherban’b, and L. F. Derzhavinskayaa aInstitute
of Technical Chemistry, Branch of Perm Federal Research Center, Ural Branch, Russian Academy of Sciences, Perm, 614013 Russia b Perm State National Research University, Perm, 614990 Russia *e-mail: [email protected] Received December 10, 2019; revised February 4, 2020; accepted February 7, 2020
Abstract—Two ways of using 3-glycidoxy propyltrimethoxycilane and 3-aminopropyltriethoxysilane promoters for improving adhesion between epoxy adhesive compositions cured using anhydride and amine hardeners and D16AT aluminum alloy are considered. The work of adhesion and free surface energy of epoxy adhesive compositions with promoters are determined. The possible reactions of the promoters to the components of the adhesive compositions and a metal surface are studied. A probable mechanism of bonding epoxy adhesives and a substrate is proposed. It is shown that preliminary treatment of the aluminum alloy surface with an aqueous alcohol solution of a promoter is the most effective way to increase adhesive shear strength. Keywords: epoxy adhesive compositions, aluminum, organofunctional silanes, work of adhesion, adhesive strength DOI: 10.1134/S1995421220040073
Polymers and composites produced by hardening of epoxy resins with diamines and acid anhydrites have become widely used in machine building, aerospace technologies, the oil and gas industry, and the construction sector [1, 2]. The process of obtaining polymers and composites is based on a polycondensation reaction that occurs without releasing by-products and with less shrinkage than in the case of phenolic and polyester binders. The polymers obtained have high strength, excellent insulating properties, good adhesion to fiber materials and metals, and high chemical durability [3]. Epoxy polymers have become widely used as adhesives in adhesive technologies. Many of them are based on fundamental approaches to the estimation of surface properties of metals and on establishing relations between acid– base parameters of an adhesive and a substrate with adhesive strength [4]. Anhydride cured polymers have an advantage to amine cured polymers: a polymerization reaction is less exothermal, occurs with less shrinkage; the obtained materials have best vibration, shock, and water resistance. Concerning the use of epoxy adhesives in the different bonding technologies, the amine cured compositions are more popular, as is stated in the published data. According to the adsorption theory, good adhesion requires a close contact between an adhesive and a substrate ensured by interatomic and -molecular interactions, e.g., hydrogen and acid–base bonds. The free surface energy of the substrate should be much higher than the free energy of the bonding agent, and the contact angle of wetting should tend to a minimum
possible value, which leads to spontaneous wetting and, thereby, makes the work of adhesion
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