Epoxy cycloaliphatic amines

Banal L, Cano J, Lopez J, Lopez-Bueno I, Nogueira P, Abad Ml, et al. Blends of an epoxy/cycloaliphatic amine resin with polyfether imide). Polymer 2000 41 2657-66. 

The specific AC conductivity values show a generally decreasing value with decreasing substrate corrosion, with one exception the novolac epoxy cured with an aromatic/cycloaliphatic amine. This is one of the coatings that also did not fit into the trend for the corrosion potential values. 

The best performing coatings studied were a vinyl ester, a bisphe-nol A epoxy cured with an aliphatic amine, and a novolac epoxy cured with a mixed aromatic/cycloaliphatic amine. A saturated polyester, and a bisphenol A epoxy cured with a polyamide amine showed significant deterioration in the acid and corrosion of the underlying steel. Two types of novolac epoxies cured with aromatic amines showed intermediate performance. 

Curing agents account for much of the potential hazard associated with use of epoxy resins. There are several major types of curing agents aliphatic amines, aromatic amines, cycloaliphatic amines, acid anhydrides, polyamides, and catalytic curing agents. The latter two types are true catalysts, in that they do not participate in the curing process. 

Suitable curatives for the polysulfide-epoxy reaction include liquid aliphatic amines, liquid aliphatic amine adducts, solid amine adducts, liquid cycloaliphatic amines, liquid amide-amines, liquid aromatic amines, polyamides, and tertiary amines. Primary and secondary amines are preferred for thermal stability and low-temperature performance. Not all amines are completely compatible with polysulfide resins. The incompatible amines may require a three-part adhesive system. The liquid polysulfides are generally added to the liquid epoxy resin component because of possible compatibility problems. Optimum elevated-temperature performance is obtained with either an elevated-temperature cure or a postcure. 

Cycloaliphatic amines can also provide high heat resistance when cured with a liquid DGEB A epoxy at room temperature (although better high-temperature characteristics can be achieved with an elevated-temperature cure). A range of cure schedules and working... 

Two examples of the characterization of IP stiffness profiles using FMM are given in Fig. 8.6. In both cases mixtures of epoxy resin with aliphatic/cycloaliphatic amines were cured in the presence of a Cu component. The investigated surface was prepared either by a replica technique similar to that described in Fig. 8.4, or by sectioning of a bulk sample (see Fig. 8.6a, b and Fig. 8.6c,d, respectively). 

Cycloaliphatic polyamines are less reactive than aliphatic amines, and an accelerator must therefore be used for curing at room temperature (e.g., salicylic acid). Aromatic polyamines are even less reactive than cycloaliphatic amines. Therefore, accelerators must be used to cure aromatic amines with epoxy resins at room temperature [2.125]. 

The most widely used epoxy resins are reaction products of either bisphenol A or a novolac phenolic resin with epichlorhydrin. When used to manufacture corrosion-resistant structures for use in the chemical process industry, epoxy resins are generally hardened with either aromatic or cycloaliphatic amines. The hardeners for epoxy resins are, with few exceptions, added at levels varying from 20phr (parts per hundred resin) to lOOphr. This means that the hardener is actually quite a high proportion of the matrix resin and has quite a profound effect on the mechanical and corrosion properties of the cured resin. Thus the selection of the most suitable hardener is critical to the eventual success of the application. Epoxy resins have viscosities of several thousand mPas at room temperature, which makes it much more difficult to wet out glass fibre efficiently with them than with polyesters. Wet-out therefore involves heating the resin formulation to between 40°C and 60°C to reduce the viscosity to less than 1000 mPas. 

Chem. Descrip. Modified cycloaliphatic amine Uses Epoxy curing agent for high-solids and solventless coatings and floors... 

Chem. Descrip. Modified cycloaliphatic amine epoxy Uses Epoxy curing agent for high solids coatings accelerator for polyamide and amidoamine curing agents Features Good chem. resist, and low temp, cure (30-35 E) exc. blush resist. 

Chlorinated polyether Polysulphone Polytetrafluoroethylene Epoxy resin, amine-cured Epoxy resin, anhydride-cured The same filled with 65% of quartz flour The same filled with 65% of Al(OH)8 Epoxy resin, glass-laminated Epoxy resin, cycloaliphatic Expanded polystyrene Expanded polystyrene, flame-retardant Expanded polystyrene, extruded profile The same with flame-retardant Rigid polyurethane foam The same with flame-retardant Polysiocyanurate foam Flexible polyurethane foam Paraffin (candle)... 

FIGURE 3.32 Cycloaliphatic amines for cure of epoxy resins. 

Curing agents are used with epoxy resins, the most commonly used ones are aromatic amines, and two of the most common are 4,4-methylene-dianiline (MDA) and 4,4-sulfonyl-dianiline (DDS). Like the epoxies, these compounds have very low vapour pressures and in principle they should not present any airborne hazard, unless a mixture is sprayed or cured at high temperatures and certainly potential for dermal exposure is high. Several other types of curing agents to consider are aliphatic and cycloaliphatic amines, polyaminoamides, amides, and anhydrides. 

Cycloaliphatic amines, such as piperidine (6) cure slowly at room temperature with epoxies. However, a subsequent heat cure provides adhesives which have a good balance of tensile strength and elongation. Adding rubber tougheners to these systems provides excellent tough adhesives. 

Cycloaliphatic Amines. Cycloaliphatic amines were originally developed in Europe, where their use as epoxy curing agents is well established. Compared to aliphatic amines, cycloaliphatic amines produce cured resins having improved thermal resistance and toughness. Glass-transition temperatures (Tg) approach those of aromatic amines (>150°C), while percent elongation can be doubled. 

Aromatic Amines. Because of conjugation, aromatic amines have lower electron density on nitrogen than do the aliphatic and cycloaliphatic amines. Consequently, they are much less reactive toward aromatic epoxies. They have longer pot-lives and usually require elevated temperature cures. Aromatic amines are usually solid at room temperature. These hardeners are routinely melted at elevated temperatures and blended with warmed resins to improve solubility. Eutectic mixtures of meto-phenylenediamine (MPD) and methylenedianiline (MDA or DDM) exhibit a depressed melting point resulting in an aromatic hardener that remains a liquid over a short period of time. MDA or 4,4 -diaminodiphenylmethane (DDM), 4,4 -diaminodiphenyl sulfone (DDS or DADPS), and MPD are the principal commercial aromatic amines. A new aromatic amine, diethyltoluenediamine (DETDA) has gained more significant uses in recent years. 

The reactive groups attached to the molecules of an epoxy resin can react with several curing agents, such as amines, anhydrides, acids, mercaptans, imidazoles, phenols and isocyanates, to create covalent intermolecular bonds and thus to form a three-dimensional network. Among these compounds, due to the enhanced environmental stability of amine-cured epoxy resin (Dyakonov et al., 1996), primary and secondary amines are the curing agents most commonly used in particular aliphatic or cycloaliphatic amines for low-temperature epoxy systems as adhesives or coatings and aromatic amines to produce matrices for liber-reinforced composites (Pascault and Williams, 2010). In Fig. 5.14 the structures of both an aliphatic and an aromatic amine are shown. 

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