Rubbery adhesives

Introduced successfully for tires in 1967, glass fibers had properties that made them very attractive for use in tires (5,8). The britdeness of glass fibers, however, imposed some limitations on the final tire cord properties because of the requirement that each fiber be individually coated with a rubbery adhesive to avoid interfilament damage during fabrication and use. This additional treatment step is introduced at the fiber manufacturing stage. For several years fiber glass was used extensively in bias-belted and radial tires, but was ultimately replaced by steel belts in radial tires. 

Peel test Assuming the strain in the tab is negligible (e.g. if (1) the peel forces are very low or (2) a fabric- or plastic-backed rubbery adhesive or a relatively thick metallic substrate is the peeling member) and plastic bending of the tab does not occur, then adhesive fracture energy (critical strain energy release rate) is given by... 

This theory allows the design of adhesive joints with resistance to internal stress. The most important objective is to minimize shrinkage by appropriate choice of polymer. An alternative approach is to add filler to the polymer to reduce shrinkage (see Filler-matrix adhesion). Use of a compliant or rubbery adhesive reduces the internal stress. Weakening of the joint is minimized by using the smallest possible volume of adhesive when making the joint. 

Peel tests are generally used for elastomeric or rubbery adhesives. A typical version of this test would be the T-peel test in which two strips of a rubber would be bonded together, face to face, and the force required to puU the strips apart would be recorded. The name of the test derives from the shape of the test piece during testing when the top of the T are the two loaded arms and the vertical of the T is the remaining bonded length. 

Rubber-to-metal bonding Specifically for rubbery adhesives Cross-lap specimen specifically for glass substrates... 

Gc. These studies are described in detail in Chapter 7, but essentially from experimental and theoretical considerations it was demonstrated that the adhesive fracture energy, Gc, for a crosslinked rubbery adhesive/rigid plastic interface could be divided into two major components ... 

Thus, in the central region of the joint, the rubbery adhesive is subjected to a hydrostatic tensile stress, a feature which has been recognized for many years [24-28] and which has important consequences, as discussed below. 

Hence, for example, for a rubbery adhesive bonding two metal substrates with a ratio of ro. /za of 20 the measured value, Ea, is over two orders of magnitude greater than the true Young s modulus, E. ... 

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.

Strength of rubbery adhesive/rigid substrate joints tested in tension, shear... 

Other geometries have also been developed to determine Gc for rubbery adhesives and include a cone-test specimen [69], a torsion test which results in mode III failure [66] and the adherence of spheres to rubbers [77-80]. 

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... 

In the case of a rubbery adhesive the work of Gent and Kinloch [11] has shown that the adhesive fracture energy, Gc, is independent of the type of specimen. They used several of the joint geometries illustrated in Fig. 7.7 and confirmed that the value of Gc, when measured for a given value of temperature and crack velocity, is independent of the details of the test specimen. 

In the case of rubbery adhesives values of the adhesive fracture energy measured under different modes of loading are shown [69,70] in Table 7.4. As expected the order of values for Gc is mode I < mode II < mode III. 

Gent and Petrich have explained the transition which is observed at lower rates by considering the viscoelastic behaviour of the rubbery adhesive. The... 

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