Adhesion between elastomers

Naturally occurring fibers such as cotton, cellulose, etc., have short whiskers protruding from the surface, which help to give a physical bond when mixed with rubber. Glass, nylon, polyester, and rayon have smooth surfaces and adhesion of these fibers to the rubber matrix is comparatively poor. In addition, these synthetic fibers have chemically unreactive surfaces, which must be treated to enable a bond to form with the mbber. In general, the fibers are dipped in adhesives in the latex form and this technology is the most common one used for continuous fibers. The adhesion between elastomers and fibers was discussed by Kubo [128]. Hisaki et al. [129] and Kubo [130] proposed a... 

The complexity of the phenomenon of adhesion, as well as the diversity of materials capable of adhesive interaction, mean that a whole series of monographs would be required to constitute a comprehensive treatise. The purpose of this paper is more modest. We aim to present simple views on polymer adhesion to readers who are not familiar with this field. We choose to do so on a specific example, namely the adhesion between two cross-linked elastomers (a cross-linked elastomer consists of long, flexible chain-like molecules which are interconnected at various points by cross-links to form a molecular network the polymer medium is locally fluid but the macroscopic flow of the material is prevented by the cross-links). This choice is motivated by a number of reasons (a) the possibility of describing the fracture of the adhesive junction between the two elastomers in terms of a simple model, (b) the existence of controlled experiments that can be compared with the predictions of the model, (c) the possibility of introducing concepts that are of interest for other polymer adhesion problems, and, finally, (d) the fact that adhesion between elastomers is a technologically important field. Several texts on polymer adhesion are avaible (Wu, 1982 Kinloch, 1987 Lee, 1991 Vakula and Pritykin, 1991). A good reference for the results of the last few years is the review article by Brown (1991). 

Thermoplastic polymers, such as poly(styrene) may be filled with soft elastomeric particles in order to improve their impact resistance. The elastomer of choice is usually butadiene-styrene, and the presence of common chemical groups in the matrix and the filler leads to improved adhesion between them. In a typical filled system, the presence of elastomeric particles at a level of 50% by volume improves the impact strength of a brittle glassy polymer by a factor of between 5 and 10. 

Since most polymers, including elastomers, are immiscible with each other, their blends undergo phase separation with poor adhesion between the matrix and dispersed phase. The properties of such blends are often poorer than the individual components. At the same time, it is often desired to combine the process and performance characteristics of two or more polymers, to develop industrially useful products. This is accomplished by compatibilizing the blend, either by adding a third component, called compatibilizer, or by chemically or mechanically enhancing the interaction of the two-component polymers. The ultimate objective is to develop a morphology that will allow smooth stress transfer from one phase to the other and allow the product to resist failure under multiple stresses. In case of elastomer blends, compatibilization is especially useful to aid uniform distribution of fillers, curatives, and plasticizers to obtain a morphologically and mechanically sound product. Compatibilization of elastomeric blends is accomplished in two ways, mechanically and chemically. 

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. 

Figure 15.4 gives the stress-strain diagrams for a typical fiber, plastic, and elastomer and the average properties for each. The approximate relative area under the curve is fiber, 1 elastomers, 15 thermoplastics, 150. Coatings and adhesives, the two other types of end-uses for polymers, will vary considerably in their tensile properties, but many have moduli generally between elastomers and plastics. They must have some elongation and are usually of low crystallinity. 

In the literature, there are several reports that examine the role of conventional fillers like carbon black on the autohesive tack (uncured adhesion between a similar pair of elastomers) [225]. It has been shown that the incorporation of carbon black at very high concentration (>30 phr) can increase the autohesive tack of natural and butyl rubber [225]. Very recently, for the first time, Kumar et al. [164] reported the effect of NA nanoclay (at relatively very low concentration) on the autohesive tack of BIMS rubber by a 180° peel test. XRD and AFM show intercalated morphology of nanoclay in the BIMS rubber matrix. However, the autohesive tack strength dramatically increases with nanoclay concentration up to 8 phr, beyond which it apparently reaches a plateau at 16 phr of nanoclay concentration (see Fig. 36). For example, the tack strength of 16 phr of nanoclay-loaded sample is nearly 158% higher than the tack strength of neat BIMS rubber. The force versus, distance curves from the peel tests for selected samples are shown in Fig. 37. 

The degree of toughness is determined by the crosslink density of the matrix, the elastomer particle size and size distribution, the volume fraction of the elastomeric phase, and the degree of adhesion between the epoxy matrix and the particle. The formulating procedure was found to have as strong an effect on the fracture toughness as the materials themselves.16... 

These characteristics indicate in particular that one can improve the adhesion between the brush or the pseudo-brush and the elastomer by decreasing the number of monomers between crosslinks, Nc. This result, which is a direct consequence of the de Gennes analogy between a network and a melt (see Sect. 4.1), cannot be correct for too small values of Nc, that is for too highly reticulated networks. For pseudo-brushes, it has been conjectured [107] that Eqs. (20) and (21)... 

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