Chemical composition, classification adhesives

The chemical composition classification broadly describes adhesives as thermosetting, thermoplastic, elastomeric, or combinations of these. There are then many chemical types within each classification. They are described in Table 7.5. 

There are a large number of adhesives on the market. It is helpful to organize these adhesives in groups with common characteristics to facilitate their understanding and use. Adhesives can be classified in a number of ways, although no one classification is universally recognized. Classifications include source, function, chemical composition, physical form, and application. 

Chapters 4-6 describe the adhesives available from a materials standpoint. In Chapter 4, adhesive classification in a number of ways has been described according to the source, function, chemical composition, physical form, and application. Chapter 5 discusses individual adhesive types in detail. As a matter of convenience, the adhesives have been arranged in alphabetical order. Chapter 6 describes adhesives for specific adherend types. 

Adhesives may be classified by various methods such as function, chemical composition, mode of application and setting, physical form, cost, and end use. The most common methods of adhesive classification are summarized in Table 7.6 (p. 7.22). 

Adhesives can be classified on the basis of chemical composition [29], setting mechanism [30], and adhesion mechanism as pressure-sensitive, adhesion, and diffusion adhesives [31]. Lucre [32] proposed a flexible classification in which each adhesive is characterized and classified according to various characteristic features, such as chemical basis, form of application, application temperature, thermal behavior, and uses. A classification such as this provides for very detailed coverage of the individual features of an adhesive and is a helpful guide for industrial users. However, it is extremely comprehensive and goes beyond the scope of this treatise. For this reason, a classification based on the setting mechanism is given here [30]. 

Adhesives can be broadly classified as being thermoplastic, thermosetting, elastomeric, or alloy blend. These four adhesive classifications can be further subdivided by specific chemical composition as described in Tables 7.20 through 7.23. The types of resins that go into the thermosetting and alloy adhesive classes are noted for high strength, creep resistance, and resistance to environments such as heat, moisture, solvents, and oils. Then-physical properties are weU suited for structural-adhesive applications. 

Proteins are natural, renewable, and biodegradable polymers which have attracted considerable attention in recent years in terms of advances in genetic engineering, eco-friendly materials, and novel composite materials based on renewable sources. This chapter reviews the protein structures, their physicochemical properties, their modification and their application, with particular emphasis on soy protein, zein, wheat protein, and casein. Firstly, it presents an overview of the structure, classification, hydration-dehydration, solubility, denaturation, and new concepts on proteins. Secondly, it concentrates on the physical and chemical properties of the four important kinds of proteins. Thirdly, the potential applications of proteins, including films and sheets, adhesives, plastics, blends, and composites, etc. are discussed. 

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