Epoxy resin Cycloaliphatic amine

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)... 

Adhesion studies Rattana and co-workers [231] and Watts and co-workers [232] have studied the adhesion of aluminium and epoxy resins nsing amine and organosilane primers. Leadly and co-workers [261] give details of coating delamination in a hot, humid environment for a cationic radiation-cured coating of cycloaliphatic epoxy resin. XPS and ToF mass spectroscopy of the delaminated snrface showed that the phosphorus hexafluoride anion of the photoinitiator segregates to the interface. The durability of the coating was improved by reformulation with a rednced concentration of photoinitiator. 

The hardeners for cold-setting systems include aliphatic and cycloaliphatic amines and polyamines, adducts of polyamines and epoxy resins, phenol-amine combinations, and condensates of polyamines and dimerized fatty acids (polyaminoamides). Whereas amine hardeners must be used in a stoichiometric ratio to the reactive epoxy groups, polyaminoamides may be overdosed to a certain extent and thus used to elasticize the adhesive resin. 

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. 

Nonetheless, for the more than 50 years since the first publication in this field, NIPUs still do not have sufficiently broad application. This can be explained by certain features of these materials. Cyclic carbonate (CC) groups interact with aliphatic and cycloaliphatic polyamines at ambient temperatures more slowly than isocyanates with hydroxyl groups. The rate of this reaction is comparable to the rate of curing epoxy resins (ER) with amines. At the same time, the CCs react only with primary amino groups, in contrast to the ERs, which react with primary and with secondary amino groups. This results in a decrease in cross-linking density of the polymer network. 

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. 

Acid anhydrides are more effective curing agents for cycloaliphatic epoxy resins than are the amines. In addition, the amines might also react with ester groups that are present in some of these materials and form undesirable byproducts. 

A linear-chained epoxy resin was formulated from phenyl glycidyl ether and nadic methyl anhydride, catalysed by benzyldimethylamine (248). An IR fibre-optic probe was used to follow the conversion of a thermosetting tetrafunctional epoxy resin in which the hardener was an aromatic diamine and a carboxylic dianhydride. A polymerisation system consisting of a cycloaliphatic diepoxide, epoxidised natural rubber (ENR), glycidyl methacrylate (GMA) and a cationic photoinitiator, triphenylsulfonium hexafluoro-antimonate, was studied (75). Multifunctional epoxy/ amine formulations (Epon 825 plus 4,4 -methylene-... 

Underfill adhesive (snap cure) Epoxy resins (high purity Bisphenol-A and cycloaliphatic resins) 45-60% Resin modifier 1—5% Curing agents (amine) 3-5% Filler (amorphous silica) 50-80% Loctite 3563, Ablebond 7811... 

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. 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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