Epoxy structure

Some graphite-epoxy structures can be tailored to have a zero coefficient of thermal expansion, a big advantage for large antennas that must pass in and out of the sun, yet maintain dimensional stability for accuracy of pointing the signal. For example, a graphite-epoxy truss is used to stabilize and support the Hubble Space Telescope. 

Conventional machining operations are used preferably from the same plastic to be used in the product (Chapter 8, SECONDARY EQUIPMENT). Different casting techniques are used that provide low cost even though they are usually labor intensive. The casting of unfilled or filled/reinforced plastic used include TS polyurethane, epoxy, structural foam, and RTV silicone. Also used are die cast metals. 

Figure 7.38 Epoxy structures (1) bisphenol-A-based epoxy, (2) brominated bisphenol-A-based epoxy, and (3) siloxane epoxy.

Epoxidized novolacs, 411 Epoxy -phenol networks, 411-416 properties of, 413-416 Epoxy-phenolic reaction kinetics of, 413 mechanism of, 411-412 Epoxy structures, 414 e-Caprolactam, 174... 

A nltrlle-modlfled epoxy structural adhesive (American Cyanamld FM 123-2)... 

The value of the epoxy resins lies in their reactivity with a variety of chemical groups. This enhanced reactivity also means that the surface chemistry of the reinforcement which the epoxies are cured against, can alter the local structure in the interphase regionJl). The most common reinforcement surfaces cured in contact with the epoxies are carbon/graphite fibers, glass fibers, aramid fibers and metal oxides. The surface chemistry of these reinforcement surfaces is quite diverse and in many cases can be the reason for alteration of the interphase epoxy structure as compared to the bulk. 

Alteration of this epoxy structure is the result of the fact that the epoxy molecules are both reacting and diffusing at the same time. This process forms a concentration gradient with a high epoxy monomer concentration at the surface which gradually reduces to the bulk concentration away from the surface. The properties of an epoxy with an excess of resin can be quite different from the stoichiometric amount. Figure 2, for example, illustrated the alteration of cured epoxy mechanical properties with epoxy/amine ratio. Excess epoxy or less than the stoichiometric amount of amine produces a brittle material if the mixture is cured in the same manner as the stoichiometric amount (Fig. 2). The stoichiometric sample has the lowest modulus while excess amine produces increased brittleness. The potential for variation in local properties within the epoxy due to the presence of a 200 nm or less layer must be considered. 

In measurements of physical properties of epoxy resins - and the epoxy-polyim-ide system will be included in this general categorization - the method of failure is of considerable interest. Gross flaws in the epoxy structure act as initiation points for cracks which typically propagate by the breaking crosslinks. Therefore the level of crosslinking and cure will have a significant influence on the physical properties determined. The incorporation of additives that typically... 

Just as their counterparts rejuvenated the aircraft industry decades ago, modem epoxy structural adhesives are providing automobile designers and manufacturers with innovative possibilities that could not have been considered only a short time ago. As a result, structural automotive adhesives will have an average annual growth rate of greater than 7 percent over the next 5 years.15 This growth rate is additive to any growth that will occur in the automotive industry itself. 

The type of epoxy group and its location within the molecule influence reactivity. Some epoxy resin structures prefer to react with acid curing agents, and others with basic curing agents. Certain epoxy structures are extremely reactive with specific catalysts, and others are virtually inactive. Several types of epoxy resins are reactive with almost all classes of curing agents. 

The functionality of an amine is determined by the number of reactive hydrogens present on the molecule. The amines typically have greater than three reactive sites per molecule that facilitate the formation of the crosslinked epoxy structure. The difference between primary, secondary, and tertiary amines is reflected by the number of hydrogens that are bound to each nitrogen atom ... 

Aromatic amines are widely used as curing agents for epoxy resins. However, they are not used as widely in adhesive formulations as they are in composites, molding compounds, and castings. They offer cured epoxy structures with good heat and acid resistance. 

Polymercaptans and poly sulfides are aliphatic oligomers containing sulfohydro (-SH) groups that will react with epoxy groups at room temperature to form cured epoxy structures and epoxy adducts. A generalized structure is shown in Fig. 5.11. 

Novel, toughened one-component epoxy structural adhesives based on epoxy-terminated polyurethane prepolymer incorporating an oxolidone structure were developed to provide improved toughness, fracture resistance and adhesive properties with good chemical and moisture resistance.21 The hybrid resin cures with a standard latent curing agent/accelerator. 

By adding flexible chemical groups to the cured epoxy structure, via either the epoxy base resin or the curing agent... 

By introducing long-chain, flexible molecules into the epoxy structure that remain unreacted after cure... 

Wright, C. D., and Muggee, J. M., Epoxy Structural Adhesives, Chapter 3 in Structural Adhesives, S. R. Hartshorn, ed., Plenum Press, New York, 1986. 

Because of their ease of use and overall good adhesive properties, epoxy structural adhesives often find themselves in these types of applications. 

TABLE 15.15 Effect of Water on Mechanical Properties of Epoxy Structural Adhesives33... 

Epoxy adhesives command a large portion of the structural adhesives market. Many people are probably familiar with epoxy structural adhesives, as these are the typical two-part adhesives found in hardware stores and supermarkets. Epoxy adhesives owe their popularity with both the general public and industry to their ease of use, their relative safety, and their compatibility with many adherends (Fig. 14.3). The various chemical reactions involving the epoxy ring provide a fertile field for the development of a wide range of properties.29 Even a half century after the first epoxy patents were issued,30 new patents on epoxy adhesive technology continue to appear every month (Fig. 14.1.)... 

Various aliphatic and aromatic mono-glycidyl ethers are available that can be used as reactive diluents of many formulated epoxy structural adhesives. They are... 

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