Cyanoacrylic adhesives structures

Epoxy adhesives represent a significant part of the overall structural adhesives market (about 1.8 bihion). The main competitors to epoxy adhesives are polyurethanes however, thermosetting acrylics and cyanoacrylate adhesives are also strong challengers in certain market segments. 

The chemistry of cyanoacrylate adhesives contains no co-reactants but can polymerise at room temperature on any substrate that is exposed to atmospheric moisture or alkaline surfaces. Synthesised cyanoacrylate esters can be methyl, ethyl, n-propyl, n-butyl, allyl, ethoxyethyl and methoxyethyl. The basic structure of the cyanoacrylate monomer is ... 

Acrylic structural adhesives have been modified by elastomers in order to obtain a phase-separated, toughened system. A significant contribution in this technology has been made in which acrylic adhesives were modified by the addition of chlorosulfonated polyethylene to obtain a phase-separated structural adhesive (11). Such adhesives also contain methyl methacrylate, glacial methacrylic acid, and cross-linkers such as ethylene glycol dimethacrylate [97-90-5]. The polymerization initiation system, which includes cumene hydroperoxide, IV,AT - dimethyl-p- toluidine, and saccharin, can be applied to the adherend surface as a primer, or it can be formulated as the second part of a two-part adhesive. Modification of cyanoacrylates using elastomers has also been attempted copolymers of acrylonitrile, butadiene, and styrene ethylene copolymers with methylacrylate or copolymers of methacrylates with butadiene and styrene have been used. However, because of the extreme reactivity of the monomer, modification of cyanoacrylate adhesives is very difficult and material purity is essential in order to be able to modify the cyanoacrylate without causing premature reaction. 

The term cyanoacrylate comes from the chemical structure of these materials. Figure 1 depicts the general formula for cyanoacrylates. As the figure shows, cyanoacrylate adhesives are made up of carbon, hydrogen, oxygen, and nitrogen. The way these atoms are... 

The cyanoacrylate adhesives sold today are quite similar to the first product, Eastman 910. This is due to the fact that changes in the structure of the monomer have dramatic effects on the adhesive properties, and because there are very few modifying monomers which will successfully coreact with the cyanoacrylates under normal application conditions. Also, the monomers with the best adhesive properties were discovered early in the development of cyanoacrylates. Finally, research toward improving the deficiencies of these products had a slow start owing to the early manufacturing problems. Beginning in the late 1970s, however, a number of adhesives with improved performance were introduced. 

The properties of cyanoacrylate adhesives have been discussed in detail in the previous sections of this chapter. The evaluation of these adhesives is complemented in this section by comparisons with other structural adhesives. A specific comparison has been made of cyanoacrylate adhesives with a two-part epoxy, EC 2216 B/A, and a two-part polyurethane, EC 3549 B/A, all sold by 3M. The substrates on which the adhesives were tested were aluminum, polystyrene, and chloroprene. The results for room temperature water immersion, 90°F/90% relative humidity, and 150°F oven aging are shown in Tables XVI and XVII. 

The patent literature discloses that several speciality-type acrylate monomers, such as /3-hydroxyethyl acrylate,2-acrylyloxyethyl phenyl carbonate,vinyl acrylate,2,2,2-trifluoroethyl acrylate, N,N-dimethylaminoethyl acrylate,glycidyl acrylate,cyanoacrylates,and several diacrylates,have been copolymerized with MA. These copolymers were shown to exhibit properties which allowed the materials to be useful for polymeric emulsifiers, adhesives, " printing pastes,fire retardant textile coatings, and fibrous structural materials.Maleate and fumarate copolymers with acrylates also show possible utility in coatings, dispersants, adhesives, and other applications. Cyanoacrylate adhesives have much improved heat resistance... 

Anyone who has used cyanoacrylates on a continuous basis in an area with poor ventilation is familiar with the pungent, irritating, acrylic-type odor. The relatively high vapor pressure of the cyanoacrylate monomers which contributes to the odor can also cause evaporation from uncured fillets the vapors precipitate as a white haze on surfaces adjacent to the bondline. On bright, decorative, or transparent parts this may be unacceptable, often requiring the use of an alternative adhesive. Good ventilation helps, but not universally. This has led to the development and marketing of alkoxyalkyl cyanoacrylate adhesives, which structurally are merely ethyl cyanoacrylates with methoxy or ethoxy... 

The general structure of cyanoacrylate esters is H2C=C (CN) (COOR). Most cyanoacrylate adhesives are based on either methyl-2-cyanoacrylate or ethyl-2-cyanoacrylates. Methyl cyanoacrylates yield better strengths when bonding metals or other rigid surfaces. In addition, impact resistance is slightly hetter. Ethyl cyanoacrylates are stronger and more durable when bonding rubber or plastic substrates. 

Any epoxide adhesive Any cyanoacrylate adhesive Loctite Structural Adhesive 326 Loctite Multibond 330 Permabond F... 

Adhesives come in several forms and include pressure-sensitive adhesives (which must have characteristics of both a liquid and a solid), mbber-based adhesives (essentially all mbbers can be used with solvent natural mbber based, neoprene based, styrene butadiene rubber (SBR) based), hot melt adhesives, and natural produce adhesives. Structural adhesives require high-strength materials and are often used instead of welding or other methods of joining. For example, structural adhesives are used to attach bodywork to automobile chassis in some makes of car. Epoxy-based thermosets, phenolics, polyurethanes, acrylics, cyanoacrylates. 

The outermost skin layer, the stratum corneum (SC), consists of corneocytes embedded in lipid layers and represents the main barrier for skin penetration of xenobiotics. Its thickness in healthy adults may vary from 5 to 20 /um, except in the palm and sole where it is much thicker. SC can be removed sequentially by repeated application of appropriate adhesive tapes.1 This technique, commonly known as SC tape stripping, is a relatively noninvasive method to investigate the structure, properties, and functions of SC in vivo2 and is the most frequently used for such purposes. Other techniques to remove SC are skin surface biopsy using cyanoacrylate strips and skin scraping. 

Cyanoacrylates and Light-Curing Acrylic Adhesives - These types of adhesives have achieved widespread acceptance in high-speed manufacturing because they cure rapidly, offer high bond strength to many substrates and are easy to dispense 9. (See Reference 189 for the structure of these chemicals.)... 

Alkyd parts are generally very rigid, and the surfaces are hard and stiff. Surface preparation for alkyd parts consists of simple solvent cleaning and mechanical abrasion. Epoxies, urethanes, cyanoacrylates, and thermosetting acrylics are commonly used as structural adhesives. 

Acrylic Adhesives. Acrylic structural adhesives can be classified into three major types the surface-activated acrylics (anaerobics), the surface-activated second-generation acrylics, and the cyanoacrylates. 

Most current applications for reactive adhesives are as structural adhesives (16). They compete with high performance epoxies and urethanes and, in certain cases, with anaerobics and cyanoacrylates - in stringent aerospace, aircraft, electrical, electronic, marine, instrument and other uses (1,2,14). The reactive adhesives do not require the sophisticated fixturing usually needed... 

The structural adhesives discussed in this section are acrylics, anaerobics, cyanoacrylates, and epoxies. Among them, epoxies still are the most important. With new innovations, epoxies will be more readily cured at room temperature to compete with cyanoacrylates and anaerobics. In the following sections, we shall discuss several new forms of adhesives, e.g., hot-melt adhesives, film adhesives and waterborne adhesives. Several structural adhesives will be discussed again in relation to new forms of adhesives. 

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