High temperature adhesives applications

Although they are not elastomers, other phosphazenes also offer potential In areas requiring heat and fire resistance. Mixed fluoroalkoxy - aryloxy substituted cyclic phosphazenes are currently attracting Interest for fire resistant fluid applications (46). In other studies, cyclophosphazene matrix resins have been prepared which have potential for high temperature adhesive applications (47) and as composite matrix materials (48). These studies serve to further demonstrate the enhanced thermal stability and fire resistance which can be achieved with these phosphorus - nitrogen systems. 

Their main applications have been in heat-resistant structural laminates, electrical laminates resistant to solder baths, chemical-resistant filament-wound pipe and high-temperature adhesives. 

Applications such as the noise attenuation panels that line engine inlets and exhausts require a special form of high temperature adhesive known as a reticulating adhesive. These bond honeycomb sandwich assemblies have inner facesheets with numerous small holes (Fig. 13). The holes and underlying honeycomb core... 

Maturation as a technology does not mean that advancement and innovation has ceased. Adhesive bonding is so essential to the aerospace field that as long as there is a desire to go higher, faster and farther more efficiently, there will be an incentive to develop new materials and processes for adhesive bonding. Areas of particular interest for future applications are high-temperature adhesives, fiber-reinforced metal laminates and more efficient bond assembly techniques. 

Metal fillers for high-temperature adhesives must be carefully selected because of their possible effect on oxidation, as indicated in the previous section. Carrier films, such as glass cloth, are generally used to facilitate the application of the adhesive, but they also provide a degree of reinforcement and lowering of the coefficient of thermal expansion. Thus, they reduce the degree of internal stress experienced at the joint s interface. 

Advantages of epoxy-based high-temperature adhesives relative to other adhesive types include relatively low cure temperatures, no volatiles formed during cure, low cost, and a variety of available formulating and application possibilities. The higher-temperature aromatic... 

This chapter will deal with the chemistry and applications of epoxies, phenolics, urethanes, and a variety of current vogue high-temperature polymers. Applications in fiber-reinforced plastics will be discussed in the individual sections on resin chemistry where appropriate. Separate sections will deal with adhesives and sealants. Adhesives are most important because, as early history demonstrates, they led the way to the application of resins in aerospace. A section is also included on silicone and polysulfide sealants. Although these materials are elastomers rather than resins, no discussion of aerospace polymers would be complete without some mention. Some major thermosetting polymers have been omitted from this review. Among these are the unsaturated polyesters, melamines, ureas, and the vinyl esters. Although these products do find their way into aerospace applications, the uses are so small that a detailed discussion is not warranted. 

Aliphatic and cycloahphatic epoxy resins have less tendency to yellow and can even be used as a basis for epoxy gelcoats. Such gelcoats are not widely available due to difficulties in application and adhesion to the substrate, as well as high costs. Use of non-aromatic anhydride curing agents such as hexahydrophthalic anhydride will produce further improvements in colour stability and these systems are suitable for high temperature curing applications. 

For adhesive applications, thermal stability alone is insufficient. Processability of high-temperature polymers is of great importance. These polymers should be processed under moderate conditions with no volatile evolution. The adhesives should be compatible with adherends and should have good, durable properties. For broader uses, the manufacturing cost should be low because cost, so far, has been the major obstacle to developing high-temperature adhesives. 

C except for small area bonding. In addition, flexible bagging material and sealants to operate at these temperatures are a problem. Those companies that have a special need for a high temperature adhesive often develop a material for that particular application and do not rely upon a commercial source. These special needs vary from the joining of electronic elements to the bonding of ceramic components in a missile. It is unlikely that a single... 

During the last decade, many high-temperature adhesives have been synthesized for aerospace applications. Supersonic cruise aircraft adhesives must be durable for tens of thousands of cumulative hours at 232 C (500 F), while spacecraft adhesives must withstand... 

The most important resins available for use as adhesives in high-temperature structural applications are polyimides (Pis) and polybenzimidazoles (PBIs), both of which are described later (see Sections 5.35 and 5.33). These resins are supplied as prepolymers containing open heterocyclic rings, which are soluble and fusible. At elevated temperatures, the prepolymers undergo condensation reactions leading to ring closure and the formation of insoluble and infusible cured resins. 

For a general discussion of these high-temperature adhesives, compared with PBI, see Section 5.5. These adhesives are synthetic thermosetting resins formed by the reaction of a diamine and a dianhydride. As with PBIs, they were developed specifically for high-temperature aerospace applications. PI adhesives are superior to PBIs for long-term strength retention, as shown in Figure 5.4. ... 

Nanoscale sihcon oxide is widely used in microelectronics, optoelectronics and electronics are parts of the means of fire protection, coatings, high temperature adhesives, paints, various mortars. Medical and biotechnology applications comprising silica nanoparticles and sorbent molecular sieves of DNA delivery vehicles, proteins, anticancer agents [17]. 

The structures given in the articles cited on high-temperature adhesives illustrate the application of these principles. They show how frequently conjugation is used to provide radical stabilization. 

Initially developed in the late 1950s and early 1960s, polybenzimidazoles are prepared by reaction of tetrafunctional aromatic amines with aromatic esters (Fig. 1). They find application as High-temperature adhesives. 

Polyimides have many applications in microelectronic industries. They are often used in the electronics industry for flexible cables, as friction elements in data processing equipment, and as insulating films on magnet wires. For example, in a laptop computer, the cable that connects the main logic board to the display (which must flex every time the laptop is opened or closed) is often a polyimide base with copper conductors. Polyimides are used as high-temperature adhesives in semiconductor industries and aerospace industries. They are used for the struts and chassis in cars as well as some... 

Materials that come close to the ideal ladder structure are thermosetting polyimides and polybenzimidazoles. These are used primarily in high-temperature aerospace applications as composites and adhesives. 

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