Epoxy adhesives Adhesive-sealants

Frihart, C., et al., Less Odor and Skinning with Stabilized Mercaptans for Curing Epoxies, Adhesives and Sealants Industry, January 2001. 

Coal tar pitch is the most widely used resinous extender for epoxy resins. It is primarily used in surface coating formulations, but can also be used as a cost reducer and flexibi-lizer in epoxy adhesives and sealants. In addition to the increase in flexibility (and reduction in thermal and chemical resistance), coal tar pitch extenders provide excellent water resistance. Their primary applications, therefore, are often in the marine, pipe, tank, and general industrial maintenance areas. 

Fumed silica is often used in 100 percent solids, liquid polymers. With epoxy adhesives and sealants only a few percent by weight of the additive will eliminate common problems such as slumping and separation. The fumed silica also raises the effective viscosity of the base resin to prevent other components from settling while the extrudability or spreadabil-ity is unaffected. Also note that fumed silica provides a surface that is free of texture. This is important in architectural-grade paints and sealants. 

Talc is also often used as an extender in epoxy adhesives and sealants, but it also has flow control properties. Talc is used in higher-solids, high-viscosity applications such as caulking compounds, automotive putties, mastics, and sealants. Talc is a hydrophobic and organophilic material. 

Epoxy adhesives and sealants are generally not significantly affected by simple outdoor weathering. However, there are certain circumstances that could affect the permanence of joints exposed to outdoor service, ft is important that these be considered early in the design of the adhesive joint and selection of materials. 

Calbex. [Calbar] Epoxy coatings, adhesives, sealants. 

Reshveld . [H.B. FuUer] Epoxy for adhesive, sealant concrete patching qrplics. 

ANSWER The usual type of sealant for this application is a silicone, polyurethane or a silyl-terminated polyether sealant. However, 1 would also suggest that you consider a flexible two-component epoxy adhesive or sealant. Concrete does not expand or contract very much with temperature changes, and you do not really need a sealant with high flexibility. 

Uses Accelerator for dicyandiamide in epoxies adhesives, automotive sealants, powd. coatings, prepregs, elec, encapsulants, printed circuit boards... 

PU, polyester or epoxy adhesives and sealants for naval construction (bonding deck to hull in yatchs, bonding stiffeners to hull in larger ships). 

Sprenger S, Eger C et al (2004) Nano-modified ambient temperature curing epoxy adhesives. Adhesion. Adhes Sealants 2003/2004 20-23 Umemura K, Inoue A et al (2003) Development of new natural polymer-based wood adhesives I dry bond strength and water resistance of konjac glucomannan, chitosan, and their composites. JWood Sci 49 221... 

A.dhesiveslCements Sealants j Coatings. Excellent adhesives of high strength and high oil resistance can be prepared using nitnle mbber (25). Many references have discussed the use of nitnle mbber—phenoHc and nitnle mbber—epoxy adhesives for printed circuit boards. 

Cationic photoinitiators are used in coatings, printing inks, adhesives, sealants, and photoresist applications. Most of the applications involve vinyl ether polymerizations or ringopening polymerizations of epoxy monomers (Sec. 7-2b). 

Construction. Polymeric materials such as adhesives, sealants, and composites have been used considerably in the last several decades for the construction, repair, and rehabilitation of our transportation infrastructures. Even though most processes were experimental until recently, they have evolved to the point where many are now standardized and well accepted. Table 1.6 hsts several common applications for advanced polymeric materials (as well as the polymeric resins that are most commonly employed). In the construction or repair of roads and bridges, epoxy adhesives have primarily been used for bonding concrete and for bonding stiffening members or repair structures to degrading concrete facilities. 

The job of the adhesive formulator has been made particularly difficult by the lack of practical information on the topic. There are only several forums that provide an introduction to adhesive formulating. One such forum is the Adhesive and Sealant Council, which offers short courses on adhesive formulating. There are also a few books that offer information and guides on adhesive formulations.23-27 Information specific to epoxy adhesives is usually found in a chapter or section within the work. There has been no book devoted solely to epoxy adhesive formulations, although several have focused on the more general topics of epoxy resins and their applications.28,29... 

The adhesive base or binder is the principal component of an adhesive. The binder provides many of the main characteristics of the adhesive such as wettability, curing properties, strength, and environmental resistance. The binder is often by weight the largest component in the adhesive formulation, but this is not always the case, especially with highly filled adhesives or sealant systems. The binder is generally the component from which the name of the adhesive is derived. For example, an epoxy adhesive may have many components, but the primary material or base is an epoxy resin. Once the binder is chosen, the other necessary ingredients can be determined. Chapter 4 describes in detail the various polymeric resins that are commonly used as bases or binders in epoxy adhesive formulations. 

Behm, D. T., and Gannon, J., Epoxies in Adhesives and Sealants, vol. 3, Engineered Materials Handbook, ASM International, Materials Park, OH, 1990. 

Nearly all polymeric materials (including adhesives and sealants) shrink during solidification. Sometimes they shrink because of escaping solvent or volatile by-products, leaving less mass in the bond line. Even 100 percent reactive adhesives, such as epoxies, with no formation of by-products during cure experience some shrinkage because their sohd polymerized mass occupies less volume than the liquid reactants. 

Epoxy-polysulfide Epoxy-polysulfide adhesives and sealants have a very high degree of elongation but poor tensile strength compared to unmodified epoxies. They are used primarily as sealants or coatings in die building and construction industries. 

Polysulfide resins combine with epoxy resins to provide adhesives and sealants with excellent flexibility and chemical resistance. These adhesives bond well to many different substrates. Tensile shear strength and elevated-temperature properties are low. However, resistance to peel forces and low temperatures is very good. Epoxy polysulfides have good adhesive properties down to -100°C, and they stay flexible to -65°C. The maximum service temperature is about 50 to 85°C depending on the epoxy concentration in the formulation. Temperature resistance increases with the epoxy content of the system. Resistance to solvents, oil and grease, and exterior weathering and aging is superior to that of most thermoplastic elastomers. 

An interpenetrating polymer network (IPN) consisting of an epoxy and an elastomer has been developed by Isayama.29 This is a two-component adhesive-sealant where the components are simultaneously polymerized. It consists of the MS polymer, developed in Japan by Kanegafuchi and commonly used in sealant formulations, with the homopolymerization of DGEBA using a phenol catalyst and a small amount of silane as a graft site to connect the MS polymer and epoxy homopolymer networks. 

Polymerized epoxy adhesives are amorphous and highly crosslinked materials. This microstructure results in many useful properties such as high modulus and failure strength, low creep, and good chemical and heat resistance. However, the structure of epoxy resins also leads to one undesirable property—they are relatively brittle materials. As such, epoxy adhesives tend to have poor resistance to crack initiation and growth, which results in poor impact and peel properties. In sealant formulations, epoxy resins do not often provide the degree of elongation or movement that is required for many applications. 

Farris, R. D., and Steward, S. L., New Epoxy Tougheners Widen the Adhesive Formulation Window, Adhesives and Sealants Industry, January 2002. 

Fumed Silica. Today colloidal silica (fumed silica) is the most common thixotropic agent in epoxy resins. Fumed silica, an amorphous silicon dioxide, is a versatile, efficient additive used for flow control and thixotropy. Fumed silica has long been the dominant thixotrope employed in the adhesive and sealant industry. 

Conventional silanes are limited to high-solids and solvent adhesive and sealant applications in which moisture is not encountered until use. However, water-stable epoxy silane promoters have recently been developed to enhance the wet strength of waterborne adhesives and sealants.17... 

Epoxy-based primers are commonly used in the aerospace and automotive industries. These primers have good chemical resistance and provide corrosion resistance to aluminum and other common metals. Primer base resins, curing agents, and additives are much like adhesive or sealant formulations except for the addition of solvents or low-viscosity resins to provide a high degree of flow. 

The room temperature cured epoxy adhesives discussed thus far exhibit a general lack of flexibility, especially when considered next to elastomeric sealants. Flexibility is generally desired when the performance requirements include high peel strength, impact strength, and resistance to thermal shock or thermal cycling. 

For an adhesive or sealant bond to be useful, not only must it withstand the mechanical forces that are acting on it, but also it must resist the service environment or the chemical forces that are applied. Thus, one of the most important characteristics of an epoxy adhesive or sealant is its endurance to the operating environment. 

Pyrolysis is simple thermal destruction of the molecular chain of the base polymer in the adhesive or sealant formulation. Pyrolysis causes chain scission and decreased molecular weight of the bulk polymer. This results in reduced cohesive strength and increased brittleness. Resistance to pyrolysis is predominantly a function of the intrinsic heat resistance of the polymers used in the adhesive formulation. As a result, many of the aromatic and multifunctional epoxy resins that are used as base resins in high-temperature adhesives are rigidly crosslinked or are made of a molecular backbone referred to as a ladder structure, as shown in Fig. 15.4. 

A typical formulation for a metal-to-metal adhesive-sealant that is cured with a combination of phthalic anhydride and pyromellitic anhydride is shown in Table 12.6. Table 15.9 shows the high-temperature properties of another epoxy formulation cured with pyromellitic dianhydride. Epoxy formulations cured with pyromellitic dianhydride (PMDA) show good short-term thermal stability in the temperature range of 150 to 230°C. 

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