Dispersants bond strengths

Thus, as the substrate changes from a hydrocarbon non-reactive surface (ethyl) to a hydrocarbon surface capable of entering into coupling reactions with the elastomer layer (vinyl) the strength of adhesion increases in the ratio of covalent bond strengths relative to dispersion bond strengths, to reach the same level as the cohesive strength of the elastomer. 

Pentaerythritol in rosin ester form is used in hot-melt adhesive formulations, especially ethylene—vinyl acetate (EVA) copolymers, as a tackifier. Polyethers of pentaerythritol or trim ethyl ol eth an e are also used in EVA and polyurethane adhesives, which exhibit excellent bond strength and water resistance. The adhesives maybe available as EVA melts or dispersions (90,91) or as thixotropic, one-package, curable polyurethanes (92). Pentaerythritol spko ortho esters have been used in epoxy resin adhesives (93). The EVA adhesives are especially suitable for cellulose (paper, etc) bonding. 

Adhesives. Contact adhesives are blends of mbber, phenoHc resin, and additives suppHed in solvent or aqueous dispersion form they are typically appHed to both surfaces to be joined (80). Evaporation of the solvent leaves an adhesive film that forms a strong, peel-resistant bond. Contact adhesives are used widely in the furniture and constmction industries and also in the automotive and footwear industries. The phenoHc resins promote adhesion and act as tackifiers, usually at a concentration of 20—40%. In solvent-based contact adhesives, neoprene is preferred, whereas nitrile is used in specialty appHcations. The type and grade of phenoHc resin selected control tack time, bond strength, and durabiHty. 

ABS plastic, a polymer consisting of polybutadiene spheroids is dispersed in a continuous phase of poly(styrene—acrylonitrile). The chromic acid attacks the polybutadiene at a much higher rate than the continuous phase. This gives an excellent microroughened surface with superior metal-to-plastic bond strength. A typical recommended formulation consists of 20 vol % sulfuric acid, 420 g/L chromic acid, and 0.1—1.0% of a fluorocarbon wetting agent. The plastic is treated with this formulation for 6—10 min at 60—65°C. 

The most common use of curing agents is with carboxylic latices. Isocyanates and melamines can be used but zinc oxide is the most common curing agent. Zinc oxide cross-links carboxylated latices and improves bond strength by ionomer formation [78]. Carboxylated polychloroprene reacts slowly with zinc oxide in dispersed form, causing a gradual increase in adhesive gel content. This can lead to restricted adhesive shelf life. Resin acid sites compete with the polymer acid sites for Zn(II). The more resin acid sites, the more stable the adhesive. 

The general structure of this class of materials can, therefore, be summarized as a fine dispersion of metal oxide in a polymer matrix very similar to plasma polytetrafluoroethylene and in principle any metal should be able to be incorporated. Clearly, if the films are protected from the atmosphere, for metals which form involatile fluorides having a relatively weak metal-fluorine bond strength, it should be possible to produce films having metal atoms dispersed in the matrix. It is expected that these films will have many interesting chemical, optical, electrical and magnetic properties., ... 

T is the defining parameter of both the thermodynamic and kinetic states of polysaccharide dispersions. With declining T, T increases and vf decreases until Vj = 0 when all macromolecular motion ceases and the dispersion becomes essentially frozen with the onset of brittleness. With increases in T, the hydrogen-bond strength decreases, a poor solvent may become good, and a good solvent may become better. The strength of the hydrophobic bond increases with T (Ben-Naim, 1980). 

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