Epoxy adhesives applications

Physical chemistry is an important factor, which leads to the exceptionally good performance properties of epoxy adhesives. Physical chemistry deals with the physiochemical and surface chemistry aspects of the system. Here system is defined as the adhesive, its constituents, the substrates, and the interface region of the joint. The physical chemistry can determine the success or failure of an epoxy adhesive application. 

In order to eomplement their knowledge, the engineers who work with structural materials in automotive, aerospace, bonding of metals, plastics, and composites should also, of course, read the chapters Design and calculation of bonded parts , Physics and chemistry of adhesion , Surface preparation before bonding , Metal bonding , Bonding composites , and also Epoxy adhesives , Application equipment , etc. 

Two wooden beams are butt-jointed using an epoxy adhesive (Fig. A1.3). The adhesive was stirred before application, entraining air bubbles which, under pressure in forming the joint, deform to flat, penny-shaped discs of diameter 2fl = 2 mm. If the beam has the dimensions shown, and epoxy has a fracture toughness of 0.5 MN mT , calculate the maximum load F that the beam can support. Assume K = cT Tra for the disc-shaped bubbles. 

Elevated temperatures are necessary for cure and the chemical resistance of the laminates is inferior to those from unmodified resins. Because of problems in handling, the polyamides have found only limited use with epoxy resins, mainly for coating and adhesive applications. 

Direct bonding. In many high-volume production applications (i.e., the automotive and appliance industries), elaborate surface preparation of steel ad-herends is undesirable or impossible. Thus, there has been widespread interest in bonding directly to steel coil surfaces that contain various protective oils [55,56,113-116], Debski et al. proposed that epoxy adhesives, particularly those curing at high temperatures, could form suitable bonds to oily steel surfaces by two mechanisms (1) thermodynamic displacement of the oil from the steel surface, and (2) absorption of the oil into the bulk adhesives [55,56]. The relative importance of these two mechanisms depends on the polarity of the oil and the surface area/volume ratio of the adhesive (which can be affected by adherend surface roughness). 

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. 

We have also looked at the lap shear strength of selected EB-ciirable epoxy adhesives. Because the adhesives being developed were being used for both aluminum-to-aluminum and composite-to-composite applications the lap shear strengths for both adherends was measured. Aluminum adherends were T2024 phosphoric acid anodized according to ASTM 3933. The composite adherends... 

Though toughened phenolic adhesives remain in use for specific applications, toughened epoxy adhesives have dominated metallic bonding on civil aircraft since their development in the 1960s. Advances since then have been incremental and mostly revolving around manufacturing issues such as handleability and allowed out-time. 

Condensation polymers, which are also known as step growth polymers, are historically the oldest class of common synthetic polymers. Although superseded in terms of gross output by addition polymers, condensation polymers are still commonly used in a wide variety of applications examples include polyamides (nylons), polycarbonates, polyurethanes, and epoxy adhesives. Figure 1.9 outlines the basic reaction scheme for condensation polymerization. One or more different monomers can be incorporated into a condensation polymer. 

Adhesive applications, thermosetting epoxy resin based on N-cyanourea-terminated oligomer, 107... 

Adhesives have been classified according to their applications. Epoxy is a compatible adhesive for stainless steel and ceramics, as used in the piezoelectric motor industry. Epoxy adhesives of different characteristics are found. Epoxy-polysulfone and epoxy-phenolics both exhibit thermosetting properties, providing stronger bonding properties with ceramics. 

Tetrahydrofurfuryl alcohol is used in elastomer production. As a solvent for the polymerization initiator, it finds application in the manufacture of chlorohydrin mbber. Additionally, tetrahydrofurfuryl alcohol is used as a catalyst solvent-activator and reactive diluent in epoxy formulations for a variety of applications. Where exceptional moisture resistance is needed, as for outdoor applications, furfuryl alcohol is used jointly with tetrahydrofurfuryl alcohol in epoxy adhesive formulations. 

Epoxy resins are also used in special applications, such as an ovedaying procedure requiring a durable, heat-resistant bond of a difficult-to-bond oveday on a wood-base panel substrate. Metal sheets used as ovedays, for example, often require an epoxy adhesive. 

The commercial possibilities for epoxy resins were first recognized by DeTrey Fmres in Switzerland and DeVoe and Raynolds in the United States (1,2). In 1936, DeTrey Fmres produced a low melting bisphenol A-based epoxy resin that gave a thermoset composition with phthalic anhydride. Application of the hardened composition was foreseen in dental products, but initial attempts to market the resin were unsuccessful. The patents were licensed to CIBA AG of Basel, Switzerland (now CIBA-GEIGY), and in 1946 the first epoxy adhesive was shown at the Swiss Industries Fair and samples of casting resin were offered to the electrical industry. 

Requirements of adhesives vary with the application but most epoxy adhesives have the following properties [151] ... 

Epoxy adhesives are chemical compounds used to join components by providing a bond between two surfaces. Epoxy adhesives were introduced commercially in 1946 and have wide applications in the automotive, industrial, and aerospace markets. Epoxies are probably the most versatile family of adhesives because they bond well to many substrates and can be easily modified to achieve widely varying properties. This modification usually takes the form of... 

Such modification is commonly described as formulating or compounding. Formulating is necessary to achieve an adhesive that will yield the desired application characteristics and end-use properties at an acceptable cost. As a result, an enormous number of epoxy adhesive formulations are possible. 

Therefore, it is a mistake to describe epoxy adhesives in a generic manner as if all these formulations had similar properties. Depending on the type of resin and curing agent used and on the specific formulation, epoxy adhesives can offer the user an almost infinite assortment of end properties as well as a wide diversity of application and curing characteristics. 

Commercial epoxy adhesives are composed primarily of an epoxy resin and a curing agent. Various additives and modifiers are added to the formulation to provide specific properties. Example trade names and suppliers of these ingredients are included in App. A. The curing agent may be incorporated into the resin to provide a single-component adhesive, or else it may be provided in a separate container to be mixed into the resin immediately prior to application. 

Secondary ingredients in epoxy adhesives include reactive diluents to adjust viscosity mineral fillers to lower cost, adjust viscosity, or modify the coefficient of thermal expansion and fibrous fillers to improve thixotropy and cohesive strength. Epoxy resins are often modified with other resins to enhance certain properties that are necessary for the application. Often these modifications take the form of additions of elastomeric resins to improve toughness or peel strength. 

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