Types of Cyanoacrylate

There are many different types of cyanoacrylate and so when designers are contemplating the use of an adhesive for specific project, they have to consider which type is most 

Alkoxy ethyl. Surface insensitive. Toughened, Thermally resistant. Flexible, and UV-curing grades. 

The ethyl cyanoacrylates are probably the most common of all the standard cyanoacrylates and the most widely used. The ethyl cyanoacrylates are best suited for bonding most plastics and elastomers to themselves and have excellent adhesion to polycarbonate, acrylonitrile butadiene styrene, poly(vinyl chloride) (PVC) and butyl rubber amongst many. 

With a smaller molecule size the methyl cyanoacrylates have better affinity to metals and can sometimes offer better resistance to solvents. The methyl grades of cyanoacrylate would often be specified for bonding plastic to metal or rubber to metal applications. The basic monomer is a very thin (low viscosity) liquid typically around 3-5 mPa-s. These methyl cyanoacrylate adhesives can be used to wick-in to pre-assembled items such as for locking small adjustment screws or for increasing the strength of two press-fitted components. 

Ethyl and methyl cyanoacrylates have a sharp odour and are eye and nasal irritants, especially in enclosed spaces or where large volumes of cyanoacrylate are present. 

There are three major chemical types of cyanoacrylate adhesives. The major distinguishing feature between these three is the size of the molecule. 

The ethyl cyanoacrylate ester molecule is slightly larger than the methyl ester molecule although adhesive properties are very similar. However because of their larger size, the number of molecules per given area is less than that for methyl adhesives. This results in a less rigid adhesive and is more suited to bonding rubbers and plastics. 

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Typical free radical inhibitors added as hydroquinone monomer acrylether (HQ), or other hindered phenolics, etc., are employed at concentrations from 0.2 to 0.5% depending on the type of cyanoacrylate ester and its additives. 

The fourth type of cyanoacrylates presented in Fig. 2 are the alkoxyalkyl esters. Methoxyethyl cyanoacrylate and methoxyisopropyl cyanoacrylate esters have all the desirable properties of the methyl, ethyl, and allyl cyanoacrylates, with the added advantage of low vapor pressure. As a result, these monomers have little or no odor, which makes them popular for use in environments where ventilation is a problem. The low vapor pressure also reduees the fogging of adjaeent parts so often seen with regular cyanoaerylates on damp days, a problem discussed in more detail below. 

In general, standard industrial cyanoacrylates do not operate effectively above 180°F (see Fig. 4). However, the new allyl types of cyanoacrylates can operate as high as 480°F before the bond loses sufficient strength to be operationally effective (see Table 2). Allyl cyanoacrylates for metal-bonding applications have proven effective in wave solder and under-hood (automotive) applications. In Fig. 4, bonded assemblies are cured at room temperature for 24 h. The assemblies are heated for 2 h and tested hot. 

Owing to unique manufacturing processes and chemical reformulations, cyanoacrylates can now be completely odor free. These products, which have almost no detectable odor, improve worker comfort and acceptance. Also, there is no unsightly fogging (chlorosis) of expensive parts adjacent to the bond line as can be seen with other types of cyanoacrylate adhesives on hot, humid days. This improves production rates of acceptable parts. 

Bond stresses, materials, type of cyanoacrylate, surface preparation, method of application and production requirements should all be considered in relation to each other at the... 

Figure 4c illustrates interfacial polymerisation encapsulation processes in which the reactant(s) that polymerise to form the capsule shell is transported exclusively from the continuous phase of the system to the dispersed phase—continuous phase interface where polymerisation occurs and a capsule shell is produced. This type of encapsulation process has been carried out at Hquid—Hquid and soHd—Hquid interfaces. An example of the Hquid—Hquid case is the spontaneous polymerisation reaction of cyanoacrylate monomers at the water—solvent interface formed by dispersing water in a continuous solvent phase (14). The poly(alkyl cyanoacrylate) produced by this spontaneous reaction encapsulates the dispersed water droplets. An example of the soHd—Hquid process is where a core material is dispersed in aqueous media that contains a water-immiscible surfactant along with a controUed amount of surfactant. A water-immiscible monomer that polymerises by free-radical polymerisation is added to the system and free-radical polymerisation localised at the core material—aqueous phase interface is initiated thereby generating a capsule sheU (15). 

Reactive adhesives Reactive adhesives are either low molecular weight polymers or monomers that solidify by polymerization and/or cross-linking reactions after application. Cyanoacrylates, phenolics, silicon rubbers, and epoxies are examples of this type of adhesive. Plywood is formed from impregnation of thin sheets of wood with resin, with the impregnation occurring after the resin is placed between the wooden sheets. 

An alternative hydrophobic microparticulate dosage form can be produced using poly(alkyl cyanoacrylates) also referred to as simply poly(cyanoacrylates) (PCAs) (Table 11.3). Poly(cyanoacrylates) are a class of addition polymers that undergo polymerization under mild conditions, and even upon the addition of water or ethanol. Poly(cyanoacrylates) have been widely investigated for delivery of biomacromolecules. Due to their properties, cyanoacrylates can easily be formed into two types of particles spheres (Couvreur et al. 1982) or capsules (Al-Khouri Fallouh et al. 1986), both of which can be used to deliver biomacromolecules. The most used of the poly(cyanoacrylates) is poly (isobutyl cyanoacrylate) (PBCA). The reason... 

Cyanoacrylate adhesives are the most widespread type of adhesive that are applied today for glueing traumatized tissues. They have been subjected to long-term improvement by introducing different alkyl substituents and even fluorine atoms5,6). 

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.)... 

Different aromatic residues have been substituted for the pyrazine and phenyl groups in 9 in order to undertake a systematic investigation of this type of compound. Nakanishi et al. have examined the solid-state photochemistry of l,4-bis[p-pyridyl-(2)-vinyl]benzene (10), p-phenylenediacrylic acid dimethyl ester (11), diethyl ester (12) and diphenyl ester (13), and p-phenylenedi[a-cyanoacrylic... 

Huang, C.-Y., and Lee, Y.-D. (2006), Core-shell type of nanoparticles composed of poly[( -butyl cyanoacrylate )-co-(2-octyl cyanoacrylate)] copolymers for drug delivery... 

Alternatively, different types of glue, including epoxy or cyanoacrylate-based glues, can be used. Care has to be taken to avoid sample contamination. In particular, cyanoacrylates must not be covered during curing as they outgas material that deposits on the sample if covered. 

Materials are indexed quite adequately. The broad MeSH heading Biomedical and Dental Materials includes such narrower terms as Alloys, Biocompatible Materials, Polymers, and Tissue Adhesives. More precise narrower terms au-e also provided, for example, the many different types of polymers (e.g., cyanoacrylates, elastomers, plastics, and silicones). 

The exceptionally fast rate of anionic polymerization of cyanoacrylates in the presence of a base, including water, made this class of monomers unique among all acrylic and vinyl monomers. Of the alkyl cyanoacrylate family of monomers, fhe mefhyl- and ethyl-esters are used extensively in industrial and consumer-type adhesives. Meanwhile, the isobutyl, fi-butyl, and n-octyl cyanoacrylate esters are used clinically as blocking agents, sealants, and/or tissue adhesives in different parts of the world due to their much lower toxicity as compared to their more reactive methyl coxmterpart. 

The letter R is used in organic chemistry to represent a part of a molecule that differs within a family of compounds. In the cyanoacrylate family, the R group is the alcohol that forms the ester with the acyhc add portion of the molecule. The type of alcohol used gives the cyanoacrylate adhesive its name. Thus methyl cyanoacrylate is the ester formed between methyl alcohol and cyanoacrylic acid. Figure 2 shows the configuration of some of the commerdally available cyanoacrylate adhesives. 

With cyanoacrylate adhesives, the reactor used to convert the liquid monomer to the hard solid is the space between the parts being bonded. When conditions vary in this space, the performance of the adhesive will vary. Such parameters as temperature, humidity, space between the parts, and the type of surface being bonded can vary considerably in a given application. 

The types of adhesives commonly considered to be in the acrylic class are anaerobic, cyanoacrylate, and reactive acrylics. The differences in the types of acrylic adhesives that lead to their suitability for different end-uses lies in the initiation and the mechanism of polymerization. All but the cyanoacrylates polymerize by a free-radical mechanism (2). 

Adhesives based on higher homologs than the methyl form have been in use for a number of years. These include the ethyl, propyl, and butyl esters of cyanoacrylic acid. Moisture resistance of the methyl-2-cyanoacrylate is only fair. Ethyl cyanoacrylate has been shown to form stronger bonds than the methyl form between several different types of plastic surfaces. The higher homologs, however, generally do not form bonds as strongly as the methyl form. ... 

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