Organic adhesives

A variety of organic adhesives which are capable of forming strong bonds between a polymeric (acrylate) restoration and the hydrophilic tooth material have recently been developed. A number of these monomers, which possess a pendent ionizable group, are polymerized in the mouth to form an adhesive layer. Alginates, which are used as impression materials, are formed by the reaction of the sodium salt of anhydro-beta-d-mannuronic acid with calcium sulfate. Calcium ions crosslink the linear polymer to form a gel. This reaction is carried out inside the mouth, and the gel formed retains the shape of the oral cavity. 

In 1983 a new class of metal organic adhesion promoters—the zircoaluminates— emerged. Evaluations by all of the major glass manufacturers ultimately provided compelling evidence that zircoaluminate application to fiberglass did not result in the sine qua non for success, that is, the irreversible attachment to the glass surface in the presence of moisture. (Note Irreversible is not intended to mean the... 

Zircoaluminates are predominantly inorganic (50-75 wt%) metal organic adhesion promoters in contrast to the silanes (< 50%). As such, they are highly polar and do not dissolve appreciably or disperse easily in resin/solvent-based media. Thus, the user must employ a high shear mixer (Cowles in paint manufacture, Banbury in rubber manufacture) to achieve as fine and homogeneous a dispersion of ZA as possible within a given system. 

Most common adhesive liquids readily wet clean metal surfaces, ceramic surfaces, and many high-energy polymeric surfaces. However, epoxy adhesives do not wet low-energy surfaces such as polyethylene and fluorocarbons. The fact that good wetting requires the adhesive to have a lower surface tension than the substrate explains why organic adhesives, such as epoxies, have excellent adhesion to metals, but offer weak adhesion on many untreated polymeric substrates, such as polyethylene, polypropylene, and the fluorocarbons. 

Organic titanates and zirconates have been found to provide several important functions as additives for organic adhesives and sealants. At least eight primary functions have been proposed.18 Organic titanates and zirconates can be used as... 

Many organic adhesives tend to be susceptible to chemicals and solvents, especially at elevated temperatures. Most standard tests to determine chemical resistance of adhesive joints last only 30 days or so. Unfortunately, exposure tests lasting less than 30 days are not applicable to many service life requirements. Practically all adhesives are resistant to these fluids over short time periods and at room temperatures. Some epoxy adhesives even show an increase in strength during aging in fuel or oil over these time periods. This effect is possibly due to either postcuring or plasticizing of the epoxy by the oil. 

Epoxies are commonly used to bond nickel substrates. However, the nickel alloys often find applications at temperatures higher than most organic adhesives are capable of resisting. 

Once properly treated, there are practically thousands of organic adhesive compounds that are available for bonding steel alloys. Epoxies are the most common of structural adhesive for bonding steel. Figure 15.15 shows the effect of humidity on the adhesion of two structural epoxy adhesives used to bond stainless steel. 

The specific surface preparation can be checked for effectiveness by the water-break free test. After the final treating step, the substrate surface is checked for a continuous film of water that should form when deionized water droplets are placed on the surface. A surface that is uniformly wet by distilled water will likely also be wet by the adhesive since the specific surface energy of water is 72 dyn/cm and of most organic adhesives is 30 to 50 dyn/cm. However, this test tells little about weak boundary layers or other contaminants that may be present on the substrate s surface but still be capable of wetting with water. 

Errors associated with impurities introduced into or present in the ivory matrix, e.g., inorganic salts from groundwater replacing collagenous material during burial or organic adhesive materials used in the field or... 

The properties described above and the thermal stability up to 150 °C, which is derived from the inorganic backbone, make these materials superior to common organic adhesives such as epoxy resins. 

Poor metal organic adhesion. This may be caused by (or facilitated by) the following ... 

CS181-52, Water-Resistant Organic Adhesives for Installation of Clay Tile, 1952. 

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