Adhesion mechanical bonding

Adhesion, mechanical Bonding between two surfaces caused by interlocking action of molecules. 

Lamination. la lamination a film is prepared by caleaderiag or extmsioa (see Laminated materials, plastic). It is thea adhered to a textile at a laminator by either an adhesive or sufficient heat which partially melts the film to obtain a mechanical bond. There are a variety of adhesives available for lamination, including solvent systems, water-base latex systems, and various forms of hot melt adhesives (qv). 

Simply bonding a stiffener to a panel with adhesive is certainly a very feasible and natural procedure with typical composite structure construction. We have not discussed any procedure for joining parts except co-curing. Alternatively, to use film adhesive for bonding parts together, we simply cut a sheet or film of adhesive to the proper size, place it between the two parts that we wish to bond together, and then go through a cure cycle that causes the adhesive to adhere to both the stiffener and to the panel itself. We can also mechanically fasten any stiffener we like to a panel. 

TABLE 1 Single Chemical Bond Forces (in pN) for Every Tip-Substrate Combination, Calculated on the Basis of the JKR Theory of Adhesion Mechanics ... 

In general, both physical and weak chemical bonds are responsible for mucoadhesion. Physical/mechanical bond formation can be explained as the entanglement of the adhesive polymer and the extended mucin chains. When this diffusion is mutual, it leads to maximum bioadhesive strength. 

The silicon substrate is removed while the temporary substrate provides mechanical support. Next, the substrate is bonded to a final carrier substrate 54 with a layer 52 of epoxy adhesive. The bonding layer 48 is removed, which also removes the temporary carrier substrate 50. The final carrier substrate is chosen according to the same criteria as described in the first embodiment. Processing continues by forming indium interconnects 34b for later hybridization of the read-out integrated circuit assembly with a detector array. 

Although the mechanisms of polyimide/metal adhesion remain to be fundamentally elucidated, it is generally accepted that the interfacial diffusion of metallic entities into the polyamic acid plays a key role at the interface [156-158]. Two main theories have been reported explaining the adhesion of the Pl/metal bond chemical and mechanical bonding [159]. Initial work emphasized mechanical bonding and most efforts were dedicated to the physical roughening of the substrate by different abrasive methods as well as chemical treatments in order to improve metal to polyimide adhesion by increasing the metal surface area [156,160-164]. 

The hydrophilic groups on mucoadhesive polymers and the large amount of water associated with mucin present two possible adhesion mechanisms (i) hydrogen bonding and (ii) interpenetration of a swollen gel network with hydrated mucin. Many methods have been used for the assessment of bioadhesive properties, including fluorescent techniques and tensile tests. By using these methods, a number of natural and synthetic polymers have been discovered possessing mucoadhesive properties. 

Since slower-curing epoxy adhesives systems flow over and wet high-energy surfaces very well, there is little chance for air to become trapped at the interface. As a result, mechanical abrasion is often recommended as a substrate surface treatment prior to application of the epoxy adhesive. The added surface area and the mechanical bonding provided by the additional peaks and valleys on the surface will enhance adhesive strength. If the adhesive does not wet the substrate surface well, such as in the case of epoxy resin on polyethylene, mechanical abrasion is not recommended since it will only encourage the probability of gas voids being trapped at the interface. 

Low-viscosity primers can also easily fill the irregularities on the substrate surface and displace air and fill hollows. This can improve the wetting properties of the adhesive system. For example, if the adhesive is a hot melt and it is applied to a bare metallic surface, the adhesive will gel before it gets a chance to efficiently wet the surface and mechanically interact with any surface roughness. However, if a dilute primer were first applied to the substrate and dried, the hot-melt adhesive could bond directly to the primer that in turn has bonded to the interstices of the substrate, thus providing excellent adhesion. 

As a result of their properties, melamines are often used as decorative laminates. The melamine resins cure via an addition reaction mechanism so no reaction by-products can be produced on postcure as with the phenolic resins. The specific surface preparation for adhesive bonding and the preferred adhesives for bonding melamine and urea parts are similar to those suggested for phenolic resins. 

Adhesives commonly used on concrete must be formulated so that they cure well in the presence of moisture. The adhesive should have a viscosity that allows it to penetrate the concrete for mechanical bonding. Epoxy and epoxy-polysulfide adhesives are especially effective adhesives for concrete. The starting formulations given in Table 16.16 are for an ambient cure 100 percent solids epoxy and a waterborne epoxy adhesive. 

By far the dominant adhesion mechanism, particularly in the absence of covalent linkages, is the electrostatic attraction of the polar groups of the adhesive to polar groups of the adherends. These are mainly forces arising from the interaction of permanent dipoles, including the special cases of hydrogen bonding (10-25 kJ/mol) and Lewis acid-base interactions (<80 kJ/mole).25 26 These forces provide much of the attraction between the... 

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