Interfaces elastomer adhesion

The study of the fracture process of the elastomer-based systems containing fillers evidenced that the weakest zone is the interface elastomer-particle [1191]. The fracture occurs by the destruction of the existing bonds in the contact area, especially of the adhesive bonds. In means that the material structuration by reinforcement is intensified by the increase of adhesive forces. Therefore, using black carbon as reinforcing agent, the maximal effect is achieved whenever the elastomer is in highly elastic state [1192]. Consequently, it results that the reinforcement sensibly depends on temperature [464]. 

JKR type mea.surement.s on monolayers depo.sited on. soft elastomers. The recent interest in the JKR experiments has been stimulated by the work of Chaudhury and coworkers [47-50J. In a 1991 paper, Chaudhury and White-sides [47] reported their extensive studies on the measurement of interfacial work of adhesion and surface energies of elastomeric solids. The motivation for this work was to study the physico-organic chemistry of solid surfaces and interfaces. 

Deruelle, M., Leger, L. and Tirrell, M., Adhesion at the solid-elastomer interface influence of the interfacial chains. Macromolecules, 28(22), 7419-7428 (1995). 

Some rubber base adhesives need vulcanization to produce adequate ultimate strength. The adhesion is mainly due to chemical interactions at the interface. Other rubber base adhesives (contact adhesives) do not necessarily need vulcanization but rather adequate formulation to produce adhesive joints, mainly with porous substrates. In this case, the mechanism of diffusion dominates their adhesion properties. Consequently, the properties of the elastomeric adhesives depend on both the variety of intrinsic properties in natural and synthetic elastomers, and the modifying additives which may be incorporated into the adhesive formulation (tackifiers, reinforcing resins, fillers, plasticizers, curing agents, etc.). 

The energy release rate (G) represents adherence and is attributed to a multiplicative combination of interfacial and bulk effects. The interface contributions to the overall adherence are captured by the adhesion energy (Go), which is assumed to be rate-independent and equal to the thermodynamic work of adhesion (IVa)-Additional dissipation occurring within the elastomer is contained in the bulk viscoelastic loss function 0, which is dependent on the crack growth velocity (v) and on temperature (T). The function 0 is therefore substrate surface independent, but test geometry dependent. 

If an elastomer is bonded to a substrate such as steel, it is usual for the bond to have small areas of imperfection where the adhesive or the chemical preparation of the surface is defective. Such areas are known as holidays. In high-pressure gas environments, these holidays form nucleation sites for the growth of half-bubbles or domes, under conditions where gas has been dissolved in the elastomer and the pressure has subsequently been reduced. Gas collecting at the imperfection at the interface will inflate the mbber layer, and domes will show as bumps on the surface of the mbber-coating layer—just as a paint layer bubbles up in domes when the wood underneath gives off moisrnre or solvents in particular areas. 

Oldfield D. and Symes T.E.F., 1983, Surface modification of elastomers for bonding, J. Adhes., 16, 77-96. Romero-Sanchez M.D., Pastor-Bias M.M., and Martm-Martmez J.M., 2003, Improved adhesion between pol)oirethane and SBR rubber treated with trichloroisocyanuric acid solutions containing different concentrations of chlorine. Compos Interface, 10(1), 77-94. 

Another problem in joining elastomers with adhesives is that since they are deformable materials, it is easy to develop internal stresses at the bond interface. These stresses could adversely affect the bond strength and permanence of the joint. Minimal pressure to achieve close substrate contact with the adhesive is all that is necessary when bonding with elastomers. 

Prior to this discovery, in 1954 Silberberg and Kuhn (62) were first to study the polymer-in-polymer emulsion containing ethylcellulose and polystyrene in a nonaqueous solvent, benzene. The mechanisms of polymer emulsification, demixing, and phase reversal were studied. Wetzel and Hocks discovery would then equate the pressure-sensitive adhesive to a polymer-polymer emulsion instead of a polymer-polymer suspension. Since the interface is liquid-liquid, the adhesion then becomes one type of R-R adhesion (35, 36). According to our previous discussion, diffusion is not operative unless both resin and rubber have an identical solubility parameter. The major interfacial interaction is physical adsorption, which, in turn, determines adhesion. Our previous work on the wettability of elastomers (37, 38) can help predict adhesion results. Detailed studies on the function of tackifiers have been made by Wetzel and Alexander (69), and by Hock (20, 21), and therefore the subject requires no further elaboration. 

---