Selection of adhesives

The term all-purpose adhesive requires a more critical examination. This term often suggests a universal adhesive suitable for any application and any stress of most different materials. The reader will understand why such adhesives are suitable for special applications, however, not for all purposes, in particular after having studied the explanations regarding the selection of adhesives in Chapter 8. 

Figure 8.1 shows the determining factors to be generally observed in the selection of adhesives. 

The basics and criteria for the selection of adhesives discussed in Chapter 8 refer, to a large extent, to process applications on an industrial scale. Experience shows that when choosing adhesives, users in the nonindustrial sector orientate themselves more on the bondable materials and their adhesive properties. For this reason, the following descriptions of the materials include information on the recommended or even not recommended adhesives with the respective justifications. In addition, it has to be mentioned that a large part of the explanations in Section 8.3 are of universal validity. 

Once the fluoropolymer sheet, film, etc., has been etched, it is an adherable surface. The choice of adhesive depends on the required service conditions and, to some extent, the substrate. Some of the considerations in the selection of adhesive include chemical resistance, flexibility, and temperature resistance. 

For polar substances, the types of interactions, as well as their strength, becomes significant, and selection of a proper adhesive by solubility parameter alone does not always work well. A more general, simple rule for selection of adhesives is like sticks to like. In other word, the greater the chemical similarity between two materials, the larger will be the intermolecular forces between them. 

Besides an understanding of the basic failure modes and mechanisms, important in the initial selection of adhesives, qualification and strict adherence to materials and processes specifications and work instructions are an integral part of the rehability process. The process begins with the design guidelines and requirements for a specific application. Qualification criteria and test specifications must then be generated and the adhesives selected must be qualified. In addition, materials specifications or... 

Selection of adhesives depends on many requirements, particularly the nature of the materials to be bonded, the function of the bond. 

Selection of adhesive, surface preparation, cleaning and bonding should follow the same principles as applicable for the replacement of decayed beam ends. This technique has low intrusiveness and visual impact, and although not reversible, it allows keeping in place the original element that would otherwise have to be replaced. 

The basic requirements for a good bond to plastic substrates are surface cleanliness, wetting of the surface by the adhesive, solidification of the adhesive, and proper selection of adhesive and joint design. These requirements are briefly defined here and then more thoroughly discussed in following sections. 

Sometimes, these organic layers will be removed, or at least reduced, by a Pre-treatment, but on many occasions, the substrates will be used as received . With suitable selection of adhesives, paints and printing inks, good adhesion can often be achieved with these as-received surfaces. For example, oily steel can be bonded satisfactorily with some Acrylic adhesives, hot curing Epoxide adhesives and Solvent-based adhesives see Selection of adhesives. 

Information on particular types of adhesive may be found in articles cited above and in the following entries Hot melt adhesives. Selection of adhesives. Silicone adhesives addition cure. Silicone adhesives condensation cure. Toughened adhesives. 

Selection of adhesives D M BREWIS Setting time, initial performance, durability, cost... 

Every discipline develops its own specialized vocabulary and that of adhesion and adhesives is no exception. The terms relating to adhesives can be found in the glossaries of several handbooks on adhesives " the definitions most often used are based on those given in ASTM standard D-907, reproduced in Appendix I." In addition to terminology, there are a number of other topics that require some comment and these will be discussed in this introduction. They are the classification of adhesives, the selection of adhesives, and the choice of units. 

In a study of nine commercially available acrylic adhesives, Wilkinson and Tyler found a considerable variation in the resistance to environmental exposure. The tests employed were 1,000-h water soak, 30 days at 125°F/100% RH, and 1,000-h 5% salt spray at 95°F aluminum adherends were used. The nature of the alloy was also a factor in determining joint durability. The authors concluded that excellent durability can be obtained with the proper selection of adhesive and alloy. A similar study by Zalucha using recently developed high-performance acrylic adhesives also indicates excellent performance for many acrylic-bonded assemblies. Minford has conducted weathering tests on both the early formulations and the more recently introduced second generation acrylics." He found that the durability of the earlier products was generally poor in both water soak and... 

And of course, the selection of adhesives and sealants will be another very important chapter, it will be studied later in this Handbook, because it is important to gain the basic knowledge of adhesives and sealants before we explain how to select the adhesives and sealants and the equipment. 

The performance of today s highly sophisticated adhesives can be very specific, not only in terms of the materials to be joined, but also with reference to the design of a joint and its intended requirements. There are two very useful databases to facilitate the selection of adhesives EASel , developed by the Design Council, and PAL from Permabond Adhesives Ltd (Eastleigh, Hampshire), which is not confined to adhesives supplied by Permabond. 

Apart from demonstrating the validity of the theory, this work has proved of great value in the selection of adhesives for practical applications. It focuses attention on the need to maximize w, either by optimizing the chemical match between adhesive and substrate (by, e.g., adjusting the polarity of the adhesive) or by building stronger bonds into the interface by chemical reaction. 

The basic requirements for a good adhesive bond are cleanhness, wetting, sohdification, and proper selection of adhesive and joint design. 

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