Mechanically bonding adhesives general properties

The phenolic family of adhesives are very diverse in their formulations and uses. Some are filled or modified with other polymers (vinyl, nitrile or epoxy). The composition depends largely on the intended use, e.g. for temperature and chemical resistance, or for water-proof wood bonding (phenol-resorcinol-formaldehyde). The majority are heat-curing although some wood-bonding adhesives can be cured at room temperature (RT). The comparison table includes Typical Use to differentiate between the types of adhesives. Phenolic adhesives are generally poorly represented by mechanical property data. 

Adhesion is the interaction that develops between two dissimilar bodies when they are contacted. Adhesion is thus a multidisciplinary science dealing with the chemistry and physics of surfaces and interfaces as well as the mechanics of deformation and fracture of adhesive joints. In this overview, these various aspects of adhesion are discussed. We begin by describing the general types of adhesive bonds. This is followed by sections on solid surfaces and their characterization, interfacial properties, surface treatment, and finally a discussion of the mechanics of adhesive joints. 

The nature of bonding is not only dependent on the atomic arrangement, molecular conformation and chemical constitution of the fiber and matrix, but also on the morphological properties of the fiber and the diffusivity of elements in each constituent. It follows therefore that the interface is specific to each fiber-matrix system (Kim and Mai, 1991). Adhesion in general can be attributed to mechanisms including, but not restricted to, adsorption and wetting, electrostatic attraction. 

When sand molds or cores made with low ratio (<3.5) silicate binders get dry either by exposure to a dry atmosphere or by heating, they become harder. On the other hand, when sand molds or cores made with very high ratio silicate as binders get dry either by exposure to a dry atmosphere or by heating they tend to become weak and friable. This is because the overall strength of the mold or core is primarily dependent on the mechanical properties of the solid film formed by the silicate adhesive when it sets. The separation of adhesive bonds is rarely the breaking away of the solid-hquid interface but more generally a rupture either within the adhesive film or within the body of the material to which the adhesive was apphed. Cracks or other faults within the adhesive film are more likely to account for low bond strength than mpture at the interface. 

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