Applications in the Adhesives and Construction Industries

Adhesives are high-molecular-weight substances which bond materials to one another without significantly changing their structure. The action of adhesives is based on two key properties they must firstly wet solid surfaces and adhere to them, and secondly, they must be cohesive, i.e. have internal strength. 

Adhesives of natural origin were mainly used prior to the beginning of the 20th century and by early civilizations as long ago as 2000 BC. These included animal glue, casein, natural rubber and starches. Today, specially developed adhesives based on semi- or fully synthetic products are used for a wide variety of bonding applications (Fig. 8-1). 

The development of synthetic adhesives paralleled the development of plastics which began in 1845 with the nitration of cellulose to give cellulose nitrate, the first semi-synthetic plastic, whose ethereal solution was used by the shoe industry in 1910 for bonding leather. The products discovered in 1872 by Adolf Baeyer by polycondensation of phenol with formaldehyde were the basis for the first firlly synthetic plastic, Bakelite, which was obtained by Bakeland in 1909 by thermally curing reactive phenolic pre-condensates. But it was not until 1930 that phenol-formaldehydes and urea-formaldehyde condensates developed by C. Goldschmidt in 1896 (Kaurit) were used widely as adhesives. 

Polymerization processes discovered in the 1920s resulted in a large number of new thermoplastics and elastomers, of which, in particular, polychloroprene, and polyisobutylene were used as the basis for new adhesive technologies. Polyurethanes and epoxies - developed in the mid-1930s - further broadened the range of adhesive raw materials. 

Thermally stable plastics were more recently developed which enable adhesive bonds that withstand temperatures up to 350 °C. Concurrent development of new bonding technologies (e.g. sandwich construction) now makes it possible to adhere a multitude of various materials to one another. As such, classical connection meth- 

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I 8 Applications in the Adhesives and Construction Industries 2. AU-temperature paper label (non-taddfied)... 

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