Structural adhesives durability

Allbericci, P, Aerospace applications. In Kinlock, A.J. (Ed.), Durability of Structural Adhesives. Applied Science Publishers, London, 1983, Ch. 8. 

Effect of Surface Preparation on the Durability of Structural Adhesive Bonds... 

One of the most important requirements of a structural adhesive bond is durability that is, the ability to retain a significant portion of its load bearing capability for long periods of time under the wide variety of environmental conditions which are likely to be encountered during service life.CjJ Unfortunately, the poor durability of metal/adhesive bonds in wet, hostile environments has proven to be the major obstacle to widespread development and practical usage within many industries. 

G.D. Davis and J.D. Venables in Durability of Structural Adhesives, A.J. Kinloch, ed., 43 (Applied Science, Essex, 1983). 

The predominant applications of present day metal/polymer adhesion technology are for the development of strong metal-to-metal structural adhesive joints and durable protective coatings. 

Kinloch, A. J., Predicting and Increasing the Durability of Structural Adhesive Joints, in Adhesion, vol. 3, K. W. Allen, ed., Elsevier Science Publisher, New York, 1978. 

Oxidative stability depends on the adherend surface as well as on the adhesive itself. Some metal adhesive interfaces are chemically capable of accelerating the rate of oxidation. For example, it has been found that nearly all types of structural adhesives exhibit better thermal stability when bonded to glass or aluminum than when bonded to stainless steel or titanium.12 For any given metal, the method of surface preparation can also determine oxide characteristics, and hence bond durability. Thus, the use of primers is common practice with high-temperature structural adhesives. 

Most structural adhesives are, therefore, formulated to provide the best compromise between environmental resistance and the desired mechanical properties. Experience has generally revealed that although the moisture ingress of the adhesive or sealant does affect the durability, it is seldom the dominant factor. Generally, of greater importance is how the moisture influences the adhesive-adherend interface region. Table 15.16 summarizes the moisture resistance and performance properties of some of the more common structural adhesives. 

Extensive information on the outdoor durability of bonded aluminum joints is available in the reviews of Minford.61,62,63 Hartshorn has also provided a catalog of references to outdoor weathering of structural adhesives by adhesive class and exposure conditions.64... 

Hartshorn, S. R., The Durability of Structural Adhesive Joints, Structural Adhesives, S. R. Hartshorn, ed., Plenum Press, New York, 1986. 

Olson, W. Z., et al., Resistance of Adhesive Bonded Metal Lap Joints to Environmental Exposure, Report No. NADC TR59-564, October 1962. Also in DeLollis, N. J., Durability of Structural Adhesive Bonds A Review, Adhesives Age, September 1977. 

Sell, W. D., Some Analytical Techniques for Durability Testing of Structural Adhesives, Proceedings 19th National SAMPE Symposium and Exhibition, vol. 19, New Industries and Applications for Advanced Materials Technology, April 1974. 

Surface Treatment of Polytetrafluoroethylene Primer, Adhesive, Corrosion Inhibiting, -67 to 200°F Primer, Adhesive, Corrosion-Inhibiting, for High Durability Structural Adhesive Bonding... 

The evolution of structural adhesives will certainly continue. Each increment in strength, durability, processing speed and ease, safety, reliability and reproducibility opens new commercial markets, not only to displace older joining methods but also to allow for the manufacture of new structures not possible without adhesives. 

Phenolic resins are the oldest form of synthetic structural adhesives. Usage ranges from bonding automobile and other types of brake linings to aerospace applications. These adhesives have a reputation for providing the most durable structural bonds to aluminum. Because of volatiles, however, and the need for high pressures, the phenolic resins are used less as adhesives than the epoxy resins. 

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