Strength of the adhesive

Neoprene—phenohc contact adhesives, known for thein high green strength and peel values, contain a resole-type resin prepared from 4-/-butylphenol. The alkyl group increases compatibiHty and reduces cross-linking. This resin reacts or complexes with the metal oxide, eg, MgO, contained in the formulation, and increases the cohesive strength of the adhesive. In fact, the reactivity with MgO is frequently measured to determine the effectiveness of heat-reactive phenoHcs in the formulation. 

Film Adhesion. The adhesion of an inorganic thin film to a surface depends on the deformation and fracture modes associated with the failure (4). The strength of the adhesion depends on the mechanical properties of the substrate surface, fracture toughness of the interfacial material, and the appHed stress. Adhesion failure can occur owiag to mechanical stressing, corrosion, or diffusion of interfacial species away from the interface. The failure can be exacerbated by residual stresses in the film, a low fracture toughness of the interfacial material, or the chemical and thermal environment or species in the substrate, such as gases, that can diffuse to the interface. 

According to [116], the relationship between tensile strength and the strength of the adhesion bond between the filler and polymer may be estimated as ... 

The model proposed by Bowden and Tabor has been regarded as the most successful one for presenting a simple and logical theory capable of explaining the Amontons friction law. However, suspicions concerning the two fundamental assumptions in the model were gradually aroused over past years. Friction has been attributed, in Bowden and Tabor s model, to the adhesion between asperities in contact and torn-off of the adhesive junctions when the shear stress exceeds a critical value. This implies that plastic flow and surface destruction may occur at the moment of slip, and that friction is dominated by the shear strength of the adhesive conjunctions, which is material dependent. 

The copolymer-silica adhesives also follow a similar trend but fail much earlier than the terpolymer-based adhesives. This is because of two factors (1) the increase in the inherent strength of the adhesive due to more favorable terpolymer rubber-silica interaction and (2) chemisorption in much higher magnitude between the polar substrates and the nanocomposites. 

Finally, an important feature of gels made of adhesive emulsions arises from the deformation of the droplets. Indeed, as the temperature is lowered the contact angles between the droplets increase [27,28] (see Chapter 2, Section 2.3). Consequently, the structure of the final floes depends on the time evolution of the strength of the adhesion. Initially, the adhesion results in the formation of a random, solid gel network in the emulsion. Further increase of adhesion causes massive fracturing of the gel, disrupting the rigidity of the structure and leading to well separated, and more compact floes [27,28]. 

Adhesion is created by primary and secondary forces according to the theory of adsorption interaction. This theory is applied the most widely for the description of interaction in particulate filled or reinforced polymers [30]. The approach is based on the theory of contact wetting and focuses its attention mainly on the influence of secondary forces. Accordingly, the strength of the adhesive bond is assumed to be proportional to the reversible work of adhesion (W ), which is necessary to separate two phases with the creation of two new surfaces. 

The strength of the adhesive bond is described acceptably by the reversible work of adhesion values calculated by the above theory in most cases. Often, especially in apolar systems, a close correlation exists between and the mac-... 

The results are summarized in Table II. The bond strength of the adhesives from the methylolated SEL expectedly exhibit poor adhesion as compared to the phenolated SEL adhesives, especially after repeated boil. 

In order to obtain water resistant materials the curing temperature should be raised to 130 °C or more, because this increases the strength of the adhesion layer. But the presence of dressing formulations reduces the temperature of the hardening reaction, while retaining the degree of conversion, and this simplifies the technology... 

The purpose of this paper has been to present a short overview of the recent advances that have been made in determining particle charge and mobility in nonaqueous suspensions. Clearly the nature of the charge on the particles plays a major role in determining the strength of the adhesion of these particles to an electrode and the electrical transient methods described here may be used to determine the force of that adhesion. In this respect the reader is referred to three recent papers by Vincett (15, JJ3, 17). This work was oriented towards... 

These properties have a profound effect on the processing properties of the uncured adhesive and on the end properties of the fully cured product. The properties determined by physical chemistry affect both the cohesive strength of the adhesive film as well as the degree of adhesion to the substrate. They also affect the permanence and durability of the adhesive bond once it is placed into service. 

The viscosity increase in a epoxy resin-curing agent system could result in poor wetting of the substrate surface, resulting in suboptimal adhesion. Several reaction mechanisms can also occur to an epoxy adhesive once it is mixed and applied to a substrate but before the substrates are mated. These mechanisms can result in a weak boundary layer, which will prevent optimal wetting and reduce the strength of the adhesive. 

Epoxy resins may be blended with certain vinyl polymers to improve the impact strength and peel strength of the adhesive. Polyvinyl acetals, such as polyvinyl butyral and polyvinyl formal, and polyvinyl esters are compatible with DGEBA epoxy resins when added at concentrations of 10 to 20% by weight. The addition improves the resulting impact resistance and peel strength of the cured adhesive. However, temperature and chemical resistance are sacrificed by the addition of the low-glass-transition-temperature vinyl resins. 

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