Curing agents, epoxy aliphatic amines

The reaction between the terminal mercaptan and epoxide group proceeds very slowly at ambient temperature. However, the introduction of a basic material such as a tertiary amine greatly accelerates the cure. Poly sulfides are typically used at ratios of 1 1 or less with epoxy resins, and can be used as co-curing agents with aliphatic amines. Stoichiometric quantities of aliphatic amine and 25 to 50 parts by weight of polysulfide will react with 100 parts by weight of epoxy resin. 

A great variety of aromatic diamines and aliphatic di- and poly-amines are used as epoxy resin curing agents, and tert-amines can act as catalysts for anionic epoxide homopolymerisation. 

Substrate- attach preform Nitrile-modified epoxy, glass-supported fabric, aromatic-substituted urea curing agent or aliphatic ether amine 10-15% Dicy catalyst 1-2% MEK solvent <5% Ablebond 550... 

A large group of curing agents comprises derivatives of ethylenediamine. Generally, aromatic amines such as 4,4 -diaminodiphenylmethane require higher curing temperatures than aliphatic amines such as the ethylenediamine derivatives, which cure the epoxy resin at room... 

Paints, varnishes and lacquers based on epoxy resins are used in various industrial applications because of their strength and durability. Two-component epoxy paints that cure at room temperature need a hardener added before their use. One-component epoxy paints that are heat-cured contain a hardener which can be activated only by heating. Polyfunctional aliphatic amines, aromatic amines, solid polyamides and anhydrides can be used as curing agents. Epoxy-ester-resin paints are formed by reacting epoxy resin with... 

Curing agents. In general, amine curing agents are much more hazardous to handle than the epoxy resins, particularly at elevated temperatures. Aliphatic amines and anhydrides are capable of serious skin or eye irritation, sensitization, and even burns. Other curing agents possess consideration... 

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. 

To cine an epoxy adhesive, the epoxy ring must first be opened before polymerization can occur. The epoxy ring may be opened by an acid anhydride or an amine. The four general types of curing agents are aliphatic polyamine, aromatic polyamine, aeid anhydride, and catalytic. 

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. 

A tertiary amino group formed in curing with aliphatic amines can sometimes catalyze the epoxy group polymerization. When aromatic amines are used as curing agents, such reactions do not take place at all. 

The mechanisms of radiation damage and effects of hardeners were studied recently by pulse radiolysis [89], The epoxy resins require a relatively large amount of curing agents (hardeners), most of them are aromatic and aliphatic amines such as diamino diphenyl methane or triethylene tetramine. On the basis of the emission spectra and kinetic behavior of excited states observed, the radiation resistance of aromatic and aliphatic amine curing epoxy resin was explained by internal radiation protection effects due to energy transfer. 

In adhesive formulations, aliphatic amines are most commonly used to cure the DGEBA type of epoxy resin. Aliphatic amines are not widely used with the non-glycidyl ether resins, since the amine-epoxy reaction is slow at low temperatures. The reaction usually requires heat and accelerators for an acceptable rate of cure. Aliphatic amines are primarily used with lower-viscosity DGEBA resins because of the difficulty in mixing such low-viscosity curing agents with the more viscous epoxy resins. 

There are several reasons why unmodified aliphatic amines, such as those described above, are less widely used than other curing agents in epoxy adhesive systems. These include... 

Two curing agents that have found their way into many epoxy adhesive formulations are the polyamides and amidoamines. These are commonly used in the hardware store variety two-part epoxy resins that cure at room temperature. Both are reaction products of aliphatic amines, such as diethylenetriamine, and should be included under the subclassification of modified amines. However, these products have such widespread and popular use, they are addressed here as a separate classification. 

Amidoamine or polyamidoamine curing agents have reactivity with DGEBA epoxy resins that is similar to the polyamides. However, they are lower-viscosity products and are also lower in color. Amidoamines are derivatives of monobasic fatty carboxylic acids and aliphatic polyamines. Since the amidoamines have only one amide group per molecule, they are lower in molecular weight, viscosity, and amine functionality than the polyamides. 

Table 11.8 presents a typical triethylenetetramine cured epoxy adhesive formulated with selected fillers. In this formulation the use of aluminum powder and alumina increases substantially the resistance of the adhesive to boiling water.7 This is also true when DETA is used as the curing agent.8 A typical room temperature cured aliphatic amine cured epoxy adhesive for general-purpose use is shown in Table 11.9. This shows the difference that is achieved in shear strength by curing at elevated temperatures versus room temperature.

Table 11.12 shows two rapid-setting, room temperature cure epoxy adhesives based on epoxy acrylate resins with aliphatic amine curing agents. These adhesives have gel times of less than 5 min for a 100-g mass. The bond strength development is rapid with handling strength occurring in about 1 h at room temperature. 

Whereas most room temperature curing epoxy adhesives are cured with aliphatic amines, polyamides, or amidoamines, most elevated-temperature curing epoxy adhesives are cured with aromatic amines, modified aliphatic amines, alcoholic and phenolic hydroxyls, acid anhydrides, Lewis acids, and a host of other curatives. Latent curing agents, such as dicyan-diamide and imidazoles, are typically used in one-component epoxy adhesives systems. 

Table 12.9 shows a formulation for an accelerated general-purpose one-component, dicyandiamide cured epoxy adhesive compared to one with a modified aliphatic amine curing agent. Notice that the dicyandiamide cured system provides a higher glass transition tem-... 

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