Structural adhesives advantages

Methacrylates possess many advantages, and alternatives to them are rarely seen in the marketplace. An early example using styrene in a structural adhesive has been reported [26]. The combination of styrene with unsaturated polyester is commonly used as a filler and bonding putty. 

Most of the raw materials used in large quantities in structural adhesives are used because they are widely available, relatively safe, and inexpensive. Quite often they are made in large quantities for uses other than adhesives and the adhesive manufacturers have taken advantage of supply and price. Few new basic raw materials are being developed specifically for the adhesive industry although the traditional raw materials are being combined in new ways to enhance desired adhesive properties. New initiators, adhesion promoters, primers, and specialty chemicals are being developed for use in small quantities to provide wider application latitude and improved performance. 

Urethane structural adhesives have been very popular for bonding of plastics to plastics and plastics to metal by the transportation industry. As an example, more than 90% of the bonds in Fords experimental graphite car were urethane adhesives rather than rivets or welds. Urethane structural adhesives have been used by the transportation industry since 1969. It is estimated that 5 million pounds of urethane structural adhesives were used in the transportation industry in the United States in 1979. Some of the advantages of urethane adhesives as used by the transportation industry are shown in Table IX. 

Adhesive materials will continue to have a significant part to play in the construction industries, and the contribution of structural adhesives can only expand in the future. Additionally, engineers will need to develop some understanding and expertise in the field of adhesion science and technology if greater advantage is to be taken of the potential waiting to be exploited. 

Many opportunities exist currently in the remedial markets, in the fabrication of aluminium and steel assemblies and, in particular, for stiffened plate structures. Great advantages can be derived from combining material combinations and, indeed, from combining adhesive bonding with some form of mechanical attachment to create composite harmony. 

In the aerospace, aircraft, automotive, electrical, instrument, construction and marine industries, among others, modified acrylics offer distinct assembly advantages over high performance epoxies and urethanes, as well as anaerobic structural adhesives and cyanoacrylates. 

In cured and curing properties, aerobic acrylic adhesives have a clear advantage for use as a structural adhesive. 

Some elastomeric adhesives are supplied in film form. Most of these adhesives are solvent dispersions of water emulsions. Temperature environments up to 66-204°C are practical. Elastomeric adhesives never melt completely. Bond strengths are relatively low, but flexibility is excellent. These adhesives are used in unstressed joints on lightweight materials, so they cannot be considered structural adhesives. They are particularly advantageous for joints in flexure. Most of these adhesives are modified with synthetic resins for bonding rubber, fabric, foil, paper, leather, and plastic films. They are also applied as tapes. Examples of elastomeric adhesives are shown in Table 4.3. 

A number of high-strength structural adhesives are currently supplied in film and tape form. Although the bond strengths provided by both film and tape and one-component pastes are generally similar, there are several advantages of using film and tape "... 

Structural bond—A bond that stresses the adherend to the yield point, thereby taking full advantage of the strength of the adherend. On the basis of this definition, a dextrin adhesive used with paper (e.g., postage stamps, envelopes) which causes failure of the paper, forms a structural bond. The stronger the adherend, the greater the demands placed on the adhesive. Thus, few adhesives qualify as structural for metals. A further requirement for a structural adhesive is that it be able to stress the adherend to its yield point after exposure to its intended environment. 

Table 5.17 Advantages and limitations of some widely used chemically reactive structural adhesives (reference 5.20).

---