Adhesives unreactive surfaces

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... 

To explain the adhesion of isocyanate-based adhesives to impervious, apparently unreactive surfaces such as glass and metals, it is considered that isocyanate groups react with the molecular film of tightly absorbed water always present on such surfaces, the reaction of the isocyanate groups with the oxyhydrate layer on metal surfaces and isocyanate polymerization on (alkaline) glass. All of these processes provide intimate contact if not actual chemical bonds between adhesive and adherend. 

Mechanical adhesion. Cracks and pits are produced on the treated rubber surface which favor the mechanical interlocking with the adhesive. Eurthermore, unreacted solid prismatic TCI crystals on the treated rubber surface can be dissolved by the organic solvent into the adhesive, favoring the reaction with the adhesive. 

Obviously, one requirement for an adhesive is that it flow easily to cover a surface. This is a more complex business than it first appears. One might naively think that the governing feature is whether we are dealing with a thin or a thick liquid, but this is not the case. If we put a drop of oil in an iron skillet, it spreads, but on a Teflon surface it beads up. The explanation revolves around surface energies, which are a measure of the relative strengths with which atoms on the surface of a material are attracted to atoms inside the bulk of the material. In a sense, this determines how much attraction these surface atoms can spare for other substances. In the case of Teflon, very little. Teflon is composed of long chains of carbon atoms, with each carbon also joined to two fluorine atoms. The fluorines, which stick out from the carbon skeleton, represent the exposed part of the molecules, the part that could potentially interact with other molecules. Fluorine, once it has bonded to carbon, is notoriously unreactive, and it is not interested in forging other... 

Table 2. The two failure surfaces are denoted as A and B In the case of the A1TSB and A1TTB pruned samples, the atomic concentration of carbon was about 60% on both sides and is possibly due to carbon originating from partially unreacted alkoxide or residual adhesive. The concentration of oxygen was about 25%. Very little iron was detected on either side, which indicates that Mure did not occur close to the steel substrate. The atomic concentration of sulfur for the A1TSB case is not high enough to conclude that failure occurred primarily within the adhesive. The atomic concentration of aluminum was about 14% on each of the surfaces of both samples. The XPS results support the assignment that failure occurred mainly within the alkoxide layer. The Ti(IV)B primed and TBOSi primed samples also failed mainly within the alkoxide layer.

Coatings failure occurs by delamination (separating by layers) or by peeling (separating from the concrete). The latter happens most frequently when the adhesive bond with the concrete is lost. This type of failure occurs when coatings are applied without first removing the surface contaminants and laitance. Laitance, a film which can form on the surface of the concrete, is unreacted cement or cement which has risen to the surface of the concrete surface due to over-working fresh concrete. 

Compared with mechanical and physical mechanisms, chemical mechanisms are slow and may not be detectable until well after the product has been in use, at which point the failures may be catastrophic. One chemical mechanism involves the formation of an oxide layer at the die-epoxy interface. A poorly alloyed gold-backed surface has been identified as one cause of degraded interfacial resistance. Although this is one cause, adhesives formulations also may play a role. For example, adhesives having excess (unreacted) curing agent absorb large amounts of water, thereby... 

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