Polyamines, base strength

Table 1.1 presents information on the effect of additives upon the adhesion strength of an adhesive based on ED-20 resin cured hy polyethylene polyamine (PEPA). It is evident that the lowest adhesion strength is exhibited by the adhesive based on the unpurified resin. The sorption of low-molecular weight fractions of an epoxy resin from the interphase boundary caused by addition of alcohols to this adhesive, i.e. resin purification, results in increase of the adhesion strength. Adding further alcohol to a purified resin results in formation of a weak layer on the interphase boundary, producing some decrease of the adhesion strength. 

The hyper-branched aromatic polyamine system not only enhances the rate of the cross-linking reaction of poly(ester amide) resins, but also improves the performance characteristics of cured films, especially those of thermostability, flame retardancy, hardness, impact strength and chemical resistance. A short list of vegetable oil-based poly(ester amide)s with some of their properties is given in Table 5.2. 

Figure 105 (Wake, 1982) illustrates the temperature limitations of epoxy resins based on bis-phenol A. The two component polyamine cure shows relatively poor performance but these figures refer to torsional shear and the two one-component epoxies here exhibit strengths which would cause gross distortion of lap-shear test pieces of the usual thickness. None is usable above 120°C. By contrast, Fig. 106 (Wake, 1982) shows the very different behaviour of an epoxy-phenolic adhesive supported on a glass cloth carrier. There are two features to be reckoned with when considering the use of adhesives at elevated temperatures. There is the temperature at which they can be used continuously and at which the joint will retain adequate strength...

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