Phenolic adhesives introduction

Although the phenolic adhesives have been used to bond metals for many years (and are still used for this purpose in the bonding of brake linings to brake shoes), it was really the introduction of epoxide resins that made possible metal bonding on a large... 

This might be explained with failure to crosslink sufficiently. Sano et al. have also reported that phenolysis of hardwood lignin sulfonates enhances adhesion properties (22). It is thus clearly demonstrated that the introduction of phenol into lignin improves adhesion properties. 

Various attempts have been made to prepare adhesives from lignin. The preparation of resol resin adhesives has been studied especially extensively. The introduction of phenols into the a or /2-position of the sidechain of the phenylpropane unit (phenolation of lignin) has been considered a key reaction for the formulation of these types of adhesives with adequate glu-ability. 

Polyacrylamides 562 are second in importance only to alkyl phenols. Their water solubility as well as ionogenic power arc increased by the introduction, through Mannich reaction, of the dimethylamino group, which allows better adhesion to the surface of suspended micelles and hence an improvement of the precipitating action. 

As discussed in the Introduction, in addition to hot-melt adhesives, one of the most important forms of adhesives for the future is the waterborne system. In general, an advantage of the waterborne system is that it is free from the solvent-pollution problem. For this reason, we shall describe several new waterborne systems in detail acrylics, modified ethylene-vinyl acetate, polyurethanes, phenolics, epoxies, isocyanates, and tackifiers. Applications of these systems range from PSA s contact adhesives, and laminating adhesives to wood adhesives. 

The use of adhesives can be traced back many centuries, while the production of adhesives, on an industrial scale, started about 300 years ago. The birth of modern structural adhesives can be dated from about 1910, with the introduction of the phenol-formaldehyde resins.Table II summarizes the historical development of structural adhesives, with the dates referring to the approximate time period during which each adhesive became commercially available. The introduction dates for the high-temperature polymers (polyimide, polybenzimidazole, and polyquinoxa-line) have been included for reference, although, as previously mentioned, there are presently few commercial products based on these polymers. 

It is vital to understand that each kind of test evaluates only one factor. The shear test cannot assess durability, and the peel test cannot ensure complete cross-linking of the resin. Perhaps the worst violation of this principle is the use of ultrasonic inspections to over-rule failure to pass the coupon tests for parts that are deemed too expensive to scrap. There are never any written specifications allowing this, but there are also no written instructions prohibiting material review boards from making such decisions. Fortunately, since the introduction of phosphoric-acid bonding and phenolic-based adhesive primers, the processes have become more robust than the testing techniques and such decisions have not created a safety problem. 

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