Bonding of elastomers

In the rubber industry, a fundamental distinction is drawn between bonding and adhesion . Whereas the adhesion of generally vulcanized rubber articles to one another or to metals or plastics is solely a function of the adhesive used, bonding is a process in which vulcanization of the rubber and, at the same time, adhesion between rubber and substrate are obtained by the action of heat and pressure. 

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Although the elastomer phase is essentially in particulate form, the tensile strength of the blend can be increased five-fold by increasing the cross-link density from zero to that conventionally used in vulcanisation processes, whilst tension set may be reduced by over two-thirds. Since the thermoplastic polyolefin phase may be completely extracted by boiling decalin or xylene, there is apparently no covalent chemical bonding of elastomer and thermoplastic phases. 

Rubber-like polymers (made of polychloroprene, polybutadiene copolymers, SIS, SBS for adhesive bonding of elastomers and as substitutes for solvent-based adhesives)... 

These observations do not allow the full refutation of chemical reinforcement theory. Chemical bonding by acidobasic reaction is clearly rejected, but, following Medalia and Kraus (1994), other chemical reactions could occur in carbon black mixes. For example, elastomeric chain breaking during mixing can lead to radicals that could react with carbon black surface (Le Bras and Papirer, 1979) sulfur-direct bonding of elastomer and carbon black could also be envisaged (Rivin et al., 1968). 

Similarly, ingredient sources can be examined to establish compounds that are more cost effective. Operational information gained by the use of these techniques over more than two decades is discussed in the ensuing chapters. It deals with many aspects of the production of vulcanised elastomeric engineering automotive components and includes bonding of elastomers to various substrates. 

Accepting the formation of strong bonds of elastomer-ingredient particle type, L. Mullins proposed the modification of the kinetic theory of elasticity for adequately describing the behaviour of filled elastomers [1196]. 

Examples and data are then prepared to show that the same mechanisms of migration and chemical interaction are operative in various approaches for vulcanization bonding of elastomers to textiles. The systems discussed are the work-horse RFL (resorcinol-formaldehyde- latex) dips, self-bonding elastomers (via two different approaches), and a versatile proprietary bonding agent. 

Ozone reacts with and cleaves the double bonds of elastomers. Under strain, this causes cracks to form and propagate, leading ultimately to product failure. Elastomers are subjeet to ozone attaek in proportion to their level of imsaturation. Highly imsaturated rubbers (natural, SBR) are readily cracked. Rubbers with low imsaturation (butyl) or a deactivated double bond (neoprene) are moderately ozone resistant. Saturated elastomers (EPDM) are totally resistant. 

Cyanoacrylates are often the first choice for the bonding of elastomers, especially where the application is essentially non-structural. For the bonding of small, coloured-plastic assemblies, cyanoacrylates also show excellent adhesion (Figure 7.2). 

Bond, R. (1990) Tire adhesion role of elastomer characteristics, in Supplementary Volume 2 of the Encyclopedia of Materials Science and Engineering, ed. Cahn, R.W. (Pergamon Press, Oxford) p. 1338. 

I.H. Gregory and A.H. Muhr, Stiffness and fracture analysis of bonded rubber blocks in simple shear, in Finite Element Analysis of Elastomers, ed. by D. Boast and V.A. Coveny, Professional Engineering Publications, Bury St. Edmunds, United Kingdom, 1999, pp. 265-274. 

Femandez-Garcfa J.C., Orgiles-Barcelo, and A.C., Martm-Martmez J.M., 1991, Halogenation of styrene-butadiene rubber to improve its adhesion to polyurethanes, J. Adhes. Sci Technol, 5, 1065-1080. Oldfield D. and Symes T.E.F., 1983, Surface modification of elastomers for bonding, J. Adhes., 16, 77-96. Pastor-Bias M.M., Ferrandiz-Gomez T.P., and Martm-Martmez J.M., 2000, Chlorination of vulcanized styrene-butadiene rubber using solutions of trichloroisocyanuric acid in different solvents, J. Adhes. Sci. Technol, 14, 561-581. 

Polyepichlorohydrin (PECH) is well known as a reactive elastomer. Displacement at the carbon-chlorine bond of PECH has been accomplished with a wide variety of nucleophilic reagents, for the purposes of polymer modification, grafting and crosslinking (1, 2). On the other hand, the PECH structure (1) is hardly optimal from the point of view of its reactivity as a substrate for nucleophilic... 

The 1,4-polymers of isoprene and 1,3-butadiene and some of their copolymers (Butyl, SBR, NBR) comprise the largest group of elastomers. Commercial vulcanization is achieved almost exclusively by heating with sulfur. The reaction mechanism is probably ionic and involves both sulfur addition to the double bonds in the polymer chains and substitution at the allylic hydrogen... 

Conjugated dienes such as 1,3-butadiene very readily polymerize free radically. The important thing to remember here is that there are double bonds still present in the polymer. This is especially important in the case of elastomers (synthetic rubbers) because some cross-linking with disulfide bridges (vulcanization) can occur in the finished polymer at the allylic sites still present to provide elastic properties to the overall polymers. Vulcanization will be discussed in detail in Chapter 18, Section 3. The mechanism shown in Fig. 14.3 demonstrates only the 1,4-addition of butadiene for simplicity. 1,2-Addition also occurs, and the double bonds may be cis or trans in their stereochemistry. Only with the metal complex... 

Stadler R, Burgert J. Influence of hydrogen-bonding on the properties of elastomers and elastomeric blends. Makromol Chem Macromol Chem Phys 1986 187 1681-1690. 

Most thermoplastics, such as PVC, have relatively high moduli at their useful temperatures, which are below the Tr The intermolecular forces of plastics are much stronger than those of elastomers and are usually weaker than the intermolecular hydrogen bonds characteristic of most fibers. Figure 5.2 describes the idealized behavior of a thermoplastic as a function of chain length and temperature. 

Anderson [25] determined the distribution of olefinic bonds in elastomers after derivitization with 2,4-dinitrobenzenesulfonyl chloride using a gel permeation chromatograph equipped with a photometer operating at 254 nm. It is also possible to determine olefinic linkages with a preliminary epoxidation, followed by a method to analyze for the epoxy [26],... 

There are a large variety of elastomers based on a chain -Si-O-Si- with different groups attached to the Si atom, that affect the properties of the polymer. Technologically, the most widely used silicone elastomers are those with all methyls on the silicone atoms, i.e., polydimethylsiloxanes (PDMSs), or ones with less than 0.5 mol% of vinyl substitution for the methyls. Irradiation of PDMS produces hydrogen, methane, and ethane. The gas yield at room temperature correlates with the concentration of cross-links formed. This can be expected since double bonds cannot be formed. 

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