Styrene-butadiene rubbery adhesives substrates

Figure 6.9 Cohesive and adhesive joint tensile fracture stresses plotted against effective rate of extension, kaj, at 23 °C (styrene-butadiene-rubbery adhesive bonding poly-(ethylene terephthalate substrates) [43]. A Cohesive tensile strength of adhesive. Cohesive-in-adhesive failure of butt joints. O Interfacial failure of butt joints.

For example. Fig. 7.9 shows the results from studying crack growth in a simple-extension joint (Fig. 7.7) consisting of a crosslinked styrene-butadiene rubbery adhesive (a non-linear-elastic material) adhering to a rigidly supported poly(ethylene terephthalate) substrate [103]. From Equation 7.44, with ks = 7T, the data is plotted as t/dc versus and the linear relationship which is... 

This concept is illustrated in Fig. 8.11 for a poly(ethylene terephthalate) substrate and a mild steel (ferric oxide) substrate with, in both cases, water as the hostile environment. Values of y and yl of the various adhesives may be measured, as described in Chapter 2, or extracted from the literature (see Table 2.3) for example, considering a styrene-butadiene rubbery adhesive the values are 27.8 and 1.3 mJ/m, respectively, and for a typical epoxy adhesive they are 41.2 and 5.0 mJ/m, respectively. Hence, it is evident that these (and most other) adhesives will form an environmentally water-stable interface with the poly(ethylene terephthalate) substrate but an unstable interface with mild steel. Indeed, the data confirm that if only secondary molecular forces are acting across the interface then water will virtually always desorb organic adhesives, which typically have low surface free energies of less than about 60 mJ/m, from a metal oxide surface. Hence, for such interfaces, stronger intrinsic adhesion forces must be forged which are more resistant to rupture by water. 

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