Accelerators epoxide adhesives

Novolac resins are broadly used in electronics because their functionality higher than two increases the crossimkmg density and yields cured resins exhibiting enhanced chemical and physical properties. Mixtures of epoxy resins and phenol novolacs 61 are excellent structural adhesives in the aerospace industry. However, the phenolic hydroxyl groups are not very reachve at moderate temperatures and most systems include catalysts or accelerators. Classical adhesive compositions are prepared by mixing a solid epoxy resin, t5rpicahy an epoxidized phenol novolac resin (60 parts), a phenol novolac resin (40 parts), a solvent such as 2-butoxyethanol or butylcehosolve acetate, an imidazole catalyst, and silver flakes. 

The most important inference is that Chemisorption is a direct response to carboxyl group concentration indicated by the XPS photopeak component at 288.7 eV. It seems likely that weak add functionality is of minor import to applications for surface treatments, while interfacial phenomena such as practical adhesion may be sensitive to small concentrations of very high site energies. Interphase modification in epoxy resins, for example, can occur by direct reaction of epoxide groups with surface carboxyls (17), or by accelerated cure chemistry near the surface (39). Carboxyl groups on carbon surfaces may interact with basic moieties in polymers such as polycarbonate or poly(ethylene)oxide (40=42), or promote interfacial crystallinity that improves impact strength and other aspects of composite performance (43, M)-... 

The most comprehensive treatment of wet durability is Kinloch (1983). In this Minford (1983) has compared wet durabilities of joints with phenolic and epoxide-based adhesives. Joints in aluminum have been reviewed by Brewis (1983), Mahoon (1983) has dealt with titanium and Brockmann (1983) with steel. Reviews that have provided updates are those by Critchlow and Brewis (1995 and 1996), which respectively deal with the surface treatment of titanium and aluminum, and that by Armstrong (1997). A comprehensive comparison of accelerated aging and natural aging has been made by Ashcroft et al. (2001). Modeling the environmentally induced degradation of adhesively bonded joints has recently been reviewed by Crocombe et al. (2008). 

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