Epoxy adhesive disadvantages

Although the acrylate adhesives are readily available and studies have shown that they can produce reasonable bonding properties, they have the disadvantages of having high shrinkage, high fluid absorption, and low service temperatures. Acrylate adhesive applications would be limited. The development of EB-curable epoxy adhesives would have applications in the aerospace and automotive industry and potential wider uses. The most immediate application for these resin systems is composite repair of commercial and military aircraft. 

The primary advantage of solid epoxy adhesives is that they avoid the disadvantages of working with liquids. Waste and cleanup are minimized, and health problems are reduced because the end user handles only a solid substance. Since they are essentially one-component adhesives, they also eliminate the need to meter and mix individual components. 

One of the disadvantages of CTBN-epoxy adhesives has been their high viscosity, which limits additional formulation options. Recently new adducts, such as EPON 58003 and RSM-2577 from Resolution Performance Products LLC, have been introduced which have significantly lower viscosities.19 In addition, lower concentrations of these new CBTN-epoxy adducts are generally required to achieve equivalent adhesive performance. 

Fillers and extenders are used in epoxy adhesive formulations to improve properties and to lower cost. Properties that can be selectively improved include both the processing properties of the adhesive as well as its performance properties in a cured joint. However, the use of fillers can also impair certain properties. Typically, the formulator has to balance the improvements against property decline. The advantages and disadvantages of filler addition in epoxy formulations are listed in Table 9.1. Common fillers used in epoxy formulations and the properties that they are used to modify are shown in Table 9.2. 

One of the distinct advantages of epoxy adhesives is that they can be cured at room temperature or even at lower temperatures. Epoxy adhesives are often divided into room temperature curing types and elevated-temperature curing types. This chapter discusses room temperature epoxy formulations. The major advantages and disadvantages of room temperature curing epoxy adhesives are shown in Table 11.1. 

TABLE 11.1 Advantages and Disadvantages of Room Temperature Curing Epoxy Adhesives... 

Benzoquinone tetracarboxylic acid dianhydride (BTDA) has been found to provide epoxy adhesives with excellent high-temperature properties, in both the short and long terms. The formulation described in Table 12.12 provides good resistance to 260°C. This two-part adhesive can be cured 2 h at 200°C. The disadvantage of BTDA is that relatively high cure temperatures are required that result in a high degree of internal stress within the bond line. 

TABLE 13.1 Advantages and Disadvantages of Solid Epoxy Adhesives over Liquids and Pastes... 

This section reviews the chemistry behind waterborne epoxy adhesives and the formulation possibilities. The characteristics of epoxy dispersions and the performance properties of cured adhesive films are addressed. The advantages and disadvantages of these adhesive systems are discussed with the focus on determining whether waterborne epoxy systems can replace traditional epoxy adhesives. 

One of the major disadvantages of using structural epoxy adhesives is the cost and time required for long cure cycles. The number of fixtures, energy use, and production times (either at room temperature or in an oven) required have discouraged many from exploring epoxy adhesives as an alternative to mechanical fastening. 

The primary disadvantage of these processes is that they are relatively inefficient, mainly because the entire joint must be heated to cure only several mils of epoxy adhesives. The energy consumed, the time to get up to temperature, and the time to cool down to a safe handling temperature can be prohibitive in many production applications. 

The disadvantages of epoxy adhesives are the need for care in handling, as some components may be toxic, the low pot and shelf-life, and their moderate to high cost. Major uses for epoxy adhesives include aircraft manufacture, automotive, and do-it-yom elf markets. 

Advantages are similar to the epoxy system, in that these can be solventless and do not require thermal energy. Disadvantages unique to this system, however, include the need to inert the cure chamber to avoid air-inhibition of cure as well as some release instability with acrylate adhesives [72]. 

Because of the low shrinkage and the excellent adhesion, mechanical properties, and chemical resistance, epoxies have a vast variety of applications, such as adhesives (epoxyamine), structural materials in high-performance composites (epoxy-amine) (e.g., aircraft primary structure), filament wound pressure vessels, and so forth. The main disadvantage of... 

The major disadvantages of polymercaptan curing agents are their odor, skinning, and low heat deflection temperature. Progress has been made in the areas of odor and skinning through additives to the adhesive formulation. However, the low heat resistance is an artifact of the epoxy-mercaptan chemistry. 

The number of possible hybrid systems that can be manufactured with epoxy resins is nearly infinite, and many adhesive formulations have been attempted in a quest to improve the main disadvantages of a cured epoxy brittleness and rigidity. 

However, waterborne epoxy systems are not without certain disadvantages, which have limited their application as adhesives. These disadvantages include increased use of energy to evaporate the water and dry the adhesive, lower resistance of the cured film to high-humidity environments, and storage and application limitations due to potential freezing at low temperatures. 

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