Mechanism of adhesion

The mechanisms whereby adhesion is obtained between textiles and rubber can be considered in two separate areas, namely the interfaces between the textile and the dip layer, and between the dip and the rubber matrix. 

With cotton-based fabrics, the basic adhesion is achieved purely by mechanical means, due to the embedding of the individual fibre ends within the rubber matrix [3]. On peeling the bond, it is necessary either to pull these fibre ends out of the rubber or, if this force is greater than the tensile strength of the fibres, to break the fibres. This mechanical adhesion applies basically to all staple fibre-based fabrics, where there is no additional adhesive treatment. However, in the case of the synthetic staple fibres, the individual fibres are smooth and cylindrical, compared with the rougher surface produced by the scales on the cotton fibre surface. The adhesion levels obtained with these yarns are significantly lower than with cotton. 

Considering the treated fabrics, the adhesion between the dip film and the rubber matrix is derived mainly from the direct crosslinking of the latex polymer component with the rubber in the matrix compound. There is also some slight contribution from purely mechanical action, due to the penetration of the rubber matrix into the weave structure of the fabric, but this is minimal with all but the most open weave structures. Similarly, there is a small contribution from interaction between the resin component of the dip and the rubber in the matrix compound. 

In order to achieve the direct crosslinking between the dip latex rubber and the matrix polymer, it is, of course, necessary for the curatives, sulphur and accelerator (or active groupings derived from them), to migrate from the matrix into the dip film. Consequently, the actual formulation of the curing system can have significant effects on the levels of 

As can be seen from these results, the curing system exerts a significant effect on the adhesion levels. As the speed of cure increases (as shown by decreasing cure time), so the levels of adhesion fall although the scorch time of CBS systems are greater than with MBTS alone, the cure is faster and the adhesion achieved is reduced. With the activated 

The previous chapter considered the various aspects involved in the attainment of intimate molecular contact at the adhesive/substrate interface. As discussed, the attainment of such interfacial contact is invariably a necessary first stage in the formation of strong and stable adhesive joints. The next stage is the generation of intrinsic adhesion forces across the interface, and the nature and magnitude of such forces are extremely important. They must be sufficiently strong and stable to ensure that the interface does not act as the weak link in the joint, either when the joint is initially made or throughout its subsequent service life. The various types of intrinsic forces which may operate across the adhesive (or primer)/substrate interface are commonly referred to as the mechanisms of adhesion, and they are discussed in this chapter. 

As shown in Chapter 2, the molecular forces in the surface layers of the adhesive and substrate greatly influence the attainment of intimate molecular contact across the interface and such molecular forces are now frequently the main mechanism of adhesion, and this is called the adsorption theory of adhesion. However, this is only one of the four main mechanisms of adhesion which have been proposed, namely  

Some years ago many workers searched for the mechanism of adhesion , but more recently it has become generally accepted that, whilst the adsorption theory has the widest applicability, each of the others may be appropriate in certain circumstances and often make a contribution to the intrinsic adhesion forces which are acting across the interface. As discussed below, much of the confusion that has arisen in the literature concerning the mechanisms of 

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Fig. 6. Four mechanisms of adhesion, (a) The adsorption mechanism (contact adhesion), (b) The diffusion mechanism (diffusion interphase adhesion), (c) The mechanical interlocking mechanism. (d) The electrostatic mechanism.

Fitzpatrick et al. [41] used small-spot XPS to determine the failure mechanism of adhesively bonded, phosphated hot-dipped galvanized steel (HDGS) upon exposure to a humid environment. Substrates were prepared by applying a phosphate conversion coating and then a chromate rinse to HDGS. Lap joints were prepared from substrates having dimensions of 110 x 20 x 1.2 mm using a polybutadiene (PBD) adhesive with a bond line thickness of 250 p,m. The Joints were exposed to 95% RH at 35 C for 12 months and then pulled to failure. 

Fitzpatrick and Watts [57] also applied imaging TOF-SIMS to deteiTnine the failure mechanisms of adhesively bonded, phosphated hot-dipped galvanized steel... 

Theoretically, these intermolecular interactions could provide adhesion energy in the order of mJ/m. This should be sufficient to provide adhesion between the adhesive and the substrate. However, the energy of adhesion required in many applications is in the order of kJ/m. Therefore, the intermolecular forces across the interface are not enough to sustain a high stress under severe environmental conditions. It is generally accepted that chemisorption plays a significant role and thus, physisorption and chemisorption mechanisms of adhesion both account for bond strength. 

A detailed study of adhesion or design of the adhesive performance of a silicone adherent material requires that all possible mechanisms of adhesion be evaluated. The following section focuses on the mechanisms of adhesion that affect Go-... 

The theories proposed for the mechanisms of adhesion have been reviewed in detail elsewhere [44,45,55-58]. However, for the purpose of this chapter, we are presenting them in the context of silicone adhesion. The various theories underlying each mechanism will be briefly outlined and qualitatively illustrated with specific examples. 

Since the locus of failure can clearly distinguish between adhesive and cohesive failures, the following discussion separates loss of adherence into loss of adhesion and loss of cohesion. In the loss of cohesion it is the polysiloxane network that degrades, which can be dealt with independently of the substrate. The loss of adhesion, however, is dependent on the cure chemistry of the silicone, the chemical and physical properties of the substrates, and the specific mechanisms of adhesion involved. 

An investigation of the mechanism of adhesive failure of polydimethylsiloxane elastomers was conducted [75]. The study showed that the total adhesive failure energy could be decomposed into energies for breaking chemical bonds, breaking physical bonds and deforming the bulk viscoelastic elastomer. 

Schultz, J. and Naidin, M., Theories and mechanisms of adhesion. In Mittal, K.L. and Pizzi, A. (Eds.), Adhesion Promotion Techniques — Technological Applications. Dekker, New York, 1999, pp. 1-26. 

Volume I of Adhesion Science and Engineering dealt with the mechanics of adhesive bonds and the rheology of adhesives. Volume II deals with the other two disciplines that make up adhesion science, surfaces and chemistry. In addition, this volume describes several applications of adhesion science and engineering. 

The mechanisms of adhesion are explained by four main theories mechanical theory, adsorption theory, diffusion theory, and electrostatic theory. 

The improved adhesion of rubber soles treated with TCI solutions are due to the contribution of several mechanisms of adhesion ... 

Pastor-Bias M.M., Martfn-Martfnez J.M., and Boerio F.J., 2002, Mechanisms of adhesion in surface chlorinated thermoplastic rubber/thermoplastic pol3uirethane adhesive joints. Rubber Chem. Technol., 75(5), 825-837. 

In order to elucidate the mechanism of adhesion of ionomer-carboxylate cements, Wilson and his coworkers have carried out several studies on the adsorption of carboxylates - aliphatic, aromatic and polymeric-on hydroxyapatite (Skinner et al., 1986 Scott, Jackson Wilson, 1990 Ellis et al., 1990). 

The bond strength to enamel (2-6 to 9-9 MPa) is greater than that to dentine (1-5 to 4-5 MPa) (Wilson McLean, 1988). Bond strength develops rapidly and is complete within 15 minutes according to van Zeghbroeck (1989). The cement must penetrate the acquired pellicle (a thin mucous deposit adherent to all surfaces of the tooth) and also bond to debris of calciferous tooth and the smear layer present after drilling. Whatever the exact mode of bonding to tooth stmcture, the adhesion is permanent. The principles and mechanism of adhesion have already been discussed in Section 5.2. 

Wilson, A. D., Prosser, H. J. Powis, D. M. (1983). Mechanism of adhesion of polyelectrolyte cement to hydroxyapatite. Journal of Dental Research, 62, 590-2. 

The mechanism of adhesion to various substrates has not been fully explained. Brauer Stansbury (1984b) consider that bonding to composite resins occurs by the diffusion of methacrylate polymer chains into the resin. Bonding to base metals is, perhaps, by salt or chelate bridges. Here it is significant that ZOE cements do not bond, so perhaps bonding is due to the action of free EBA on the substrate. The adhesion to porcelain is surprising. Porcelain is inert so that the attachment can hardly be chemical. Also, it would be expected that if a cement adheres to porcelain then it should adhere to untreated enamel and dentine, but this is not so. 

Unfortunately, although EBA cements have been subjected to a considerable amount of development, this work has not been matched by fundamental studies. Thus, the setting reactions, microstructures and molecular structures of these EBA cements are still largely unknown. In addition, the mechanism of adhesion to various substrates has yet to be explained. Such knowledge is a necessary basis for future developments. 

The symposium on which this book is based was organized to provide a forum for discussion of recent advances in the use of polymeric materials in corrosion control. Most of the papers presented in the symposium are included in this volume. Several chapters have been added. These include an introductory overview as well as separate review chapters on how organic coating systems protect against corrosion, on mechanisms of adhesion loss of organic coatings, and on the interfacial chemistry of adhesion loss in aggressive environments. 

Basic Mechanisms of Adhesion Acid-Base Interactions. The understanding of polymer adhesion has been greatly advanced in recent years by the recognition of the central role of acid-base interactions. The concept of an acid was broadened by G. N. Lewis to include those atoms, molecules, or ions in which at least one atom has a vacant orbital into which a pair of electrons can be accepted. Similarly, a base is regarded as an entity which possesses a pair of electrons which are not already Involved in a covalent bond. The products of acid-base interactions have been called coordination compounds, adducts, acid-base complexes, and other such names. The concept that... 

Locus and Mechanism of Adhesion Failure during Corrosion Effects of Adhesive Chemistry. In previous studies (4- on the corrosion induced adhesion loss of coatings from steel surfaces, a primary mechanism for coating deadhesion was polymer degradation at the coating/metal interface by corrosion reactions that generate hydroxide ion ... 

Deo, N. Nataragans, K.A. Somasunda, P. (2001) Mechanisms of adhesion of Paeniba-cillus polymyxa onto hematite, corumdum and quartz. International J. Mineral Processes. 62 27-39... 

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