Adhesive bonding enhancement

Surface treatment of the composite can have a significant effect on adhesion. Surface treatment enhances one or more of the mechanisms described previously. Wu et al. [15] studied the effects of surface treatment on adhesive bonding for AS-4/APC-2 laminates. They found that the greatest bond strength was achieved from acid etching and plasma etching the composite surface. Table 1 summarizes the various surface treatments that were evaluated. 

Reactive species can be generated prior to monomer exposure (preirradiation grafting), during contact with monomer, or, after the polymer surface has been saturated with monomer and isolated (postirradiation grafting). The radiation-induced (y-ray and EB) graft copolymerization of AA and vinyl acetate monomer onto PE surface has been reported [170]. The grafted sheets show excellent bonding with an epoxy adhesive and enhanced adhesion with aluminum. 

Apparently, the chemical bonding present at the paint/adhesive interface is much stronger than that occurring at either the phosphate/adhesive or the phosphate/topcoat interfaces. In the case of ZM, phosphating to improve durability is not necessary, and in fact, was proven to be detrimental. The paint provides a moisture resistant barrier layer which reduces the activity of water at the interface providing for a surface receptive to the chemical and physical bonds necessary to promote good adhesion and enhance durability. 

Since water exposure has been shown 86) to have no substantial short-term effect on adhesive bonds in which a large degree of mechanical interlocking is present, these pretreatments have the potential to enhance the durability of aluminum/polymer adhesion systems. 

Abstract—The effects of metal alkoxide type and relative humidity on the durability of alkoxide-primed, adhesively bonded steel wedge crack specimens have been determined. Aluminum tri-sec-butoxide, aluminum tri-tert-butoxide, tetrabutyl orthosilicate, and titanium(IV) butoxide were used as alkoxide primers. Grit-blasted, acetone-rinsed mild steel adherends were the substrates bonded with epoxy and polyethersulfone. The two aluminum alkoxides significantly enhanced the durability of the adhesively bonded steel, while the titanium alkoxide showed no improvement in durability over a nonprimed control. The silicon alkoxide-primed samples gave an intermediate response. The failure plane in the adhesively bonded samples varied with the relative humidity during the priming process. 

Woo et al. (1994) studied a DGEBA/DDS system with both polysul-fone and CTBN. The thermoplastic/rubber-modified epoxy showed a complex phase-in-phase morphology, with a continuous epoxy phase surrounding a discrete thermoplastic/epoxy phase domain. These discrete domains exhibited a phase-inverted morphology, consisting of a continuous thermoplastic and dispersed epoxy particles. The reactive rubber seemed to enhance the interfacial adhesive bonding between the thermoplastic and thermosetting domains. With 5 phr CTBN in addition to 20 phr polysul-fone, Glc of the ternary system showed a 300% improvement (700 Jm-2 compared with 230 J m 2 for the neat matrix). 

The fact that covalent bonding can be an important, and possibly necessary, contribution to water-proof adhesive bonds to wood has convinced many scientists to study methods of enhancing adhesion by increasing the probability of covalent bonding between wood and adhesive, or directly between wood particles. This subject is still in its infancy with solid wood, although pulp and textile fiber scientists have produced an enormous volume of literature from which wood scientists can draw. 

Many wood species, both hardwoods and softwoods, are used for particleboard however, the density of the particleboard should be higher than the density of the raw material to efficiently utilize the adhesive system. The compression of the particles, which is required for consolidation into the finished product, enhances the particle-particle contact, producing more inter-particle adhesive bonds as well as reducing the total void volume in the panel. With wood of density higher than the finished particleboard, the compression of the particles is lower and the resultant reduced interparticle contact and higher void volume adversely influence the physical and mechanical properties of the parti cleboard. 

Adherend stresses in weldbonded joints are lower and more uniform than those for comparable spot welded joints. This provides increased in-plane tensile shear and/or compressive buckling load-carrying ability for a given joint design. The presence of the spot weld provides enhanced out-of-plane load-carrying capability compared to adhesive bonding only. 

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