Assessing and improving bonding in wet conditions
Water is ubiquitous in any uncontrolled setting and affects world wide commerce by instigating device and structural failures. This can be a result of corrosion, electrical shorting, or adhesive failure. For adhesive failure, the environmental attack of water leads to significant depreciation in joint strength and subsequently to premature failure of the adhesive bond. Water, in either liquid or vapor phases, penetrates the adhesive and causes great problems in both durability and reliability of adhesive joints. Since water molecules exhibit a strong dipole, they interact with charged or polar surfaces such as high surface energy substrates, and can permeate most polymers. This significant susceptibility to moisture has led to significant efforts to evaluate the effects of moisture on adhesion and to the development of better understanding of the mechanisms of water attack. It is well documented that the presence of moisture in joints may not only weaken the physical and chemical properties of a bulk adhesive itself via plasticization, swelling, degradation, cracking and crazing, etc. (Weitsman, 1977; Sargent and Ashbee, 1981; Bowditch, 1986; Gazit, 1978; Su et al., 1992; Xiao and Shanahan, 1997; Wylde and Spelt, 1998; Loh et al., 2002), but also attack the interface between the adhesive and the substrate. Hydrolysis of secondary interfacial bonds, hydration of substrate oxide layer, and cathodic delamination are several key problems caused by wet conditions at the interface (Watts and Castle, 1984; Venables, 1984; Watts, 1989; Brewis et al., 1990; Kalashikova et al., 1996; Kinloch et al., 2005; Nguyen et al., 2005; Kinloch et al., 2007). Additionally, in some cases, the moisture degradation of substrates, including gross corrosion or dimensional changes of substrates, also may occur if a hydrolytically unstable substrate, such as wrought iron, is utilized. With such potential deleterious effects of water, many adhesive joints are unlikely to reach their anticipated service life. Because knowledge of the durability of adhesive joints exposed to moisture is limited, adhesive bonding is not widely used in load-bearing primary structures. Research undertaken during the past decade, however, has provided significant progress in understanding the effects of wet conditions on bonding, and has helped develop measures to improve the bonding in wet conditions. The present chapter is devoted to consideration of the durability of structural adhesive joints.
Vogt, Bryan, "Assessing and improving bonding in wet conditions" (2010). Polymer Engineering Faculty Research. 995.