Aliphatic polyamine hardeners

Table 2.5 summarises typical values of these bulk mechanical properties at around 20 °C for a range of epoxy adhesives. Of particular note is the low strength and stiffness of the epoxy polyamides and polysulphides as compared to those with aliphatic polyamine hardeners. For the design of bonded assemblies, joint tests are often used to determine the relevant mechanical properties. It must be remembered, however, that the results will be highly dependent on the specimen geometry and testing conditions and... 

Aliphatic polyamine hardeners These are used in adhesive systems capable of curing at normal or slightly elevated temperatures. The most important examples are diethylen-etriamine, triethylenetetramine, and diethylenepropylamine. 

In addition, contact urticaria can be caused by aliphatic polyamine hardeners (Rietschel and Fowler 1995) and possibly by other amines (Savonius et al. 

We have investigated the recovered glassfiber-resin powder for its properties as a filler for epoxy resin compounds which are used as paints or adhesives, and compared it to conventional fillers, such as talc and calcium carbonate. The epoxy resin compound, composed of bisphenol A type epoxy resin (50.0wt%), aliphatic polyamine type hardener (18.0wt%) and filler (32.0%), was prepared. Strength and thermal expansion properties were measured for the molded epoxy resin compound cured 23°C for 7 days. Viscosity was measured for the epoxy resin compound before adding the hardener. Adhesive strength was measured by tearing two ferric boards bonded with the epoxy resin compound which was composed of bisphenol A type epoxy resin (49.2wt%), polyaminoamide type hardener (18.0wt %), and filler (32.8wt%), and was cured at 23°C for 7 days. 

The most widely used epoxy systems are those which are based on pure epoxy resins, hardened with a curing agent. Curing of epoxy resins containing two epoxy groups per molecule can be readily accomplished by the addition of primary polyamines, such as ethylene diamine, diethylene triamine, triethylene tetramine, tetra-ethylene pentamine, etc. Aliphatic polyamines produce cured resins with the greatest chemical resistance. However, these systems have inadequate durability, weather resistance and film-forming properties. They are sensitive to humidity, errors in addition rates are quite possible, and the catalysts are relatively toxic. 

Stoichiometric ratios can be calculated similarly for hardeners. In principle, each active hydrogen will react with one epoxy group. Thus a low-molecular-weight aliphatic polyamine such as diethylene triamine (DETA) has a molecular weight of 103 and five active hydrogens. The hydrogen equivalent is thus 20.6. The stoichiometrically correct ratio with an epoxy resin of EEW 200 would thus be 100 parts resin to 10.3 parts of DETA. In practice there is always a percentage of homopolymerization, especially at the temperature... 

Chem. Descrip. Aliphatic polyamine adduct (80%) in water Uses Hardener for solid epoxy resin disps. or emulsified liq. resins for use in water-reducible coatings on metallic substrates, corrosion-protection primers (in combination with Beckopox EH 386w)... 

Irritative, low-MW degradation products may be produced in the tooling of epoxy products and in heating processes (Engstrom and Henriks-Eckerman 1988). Amine and anhydride hardeners and epi-chlorohydrin irritate the skin and conjunctivae. In addition to causing irritant contact dermatitis, epi-chlorohydrin, as a highly reactive compound, and aliphatic polyamines, as highly alkaline compounds (pH 13-14), can cause corrosive burns on the skin (Ippen and Mathies 1970 Adams 1983). Ippen and Mathies (1970) described protracted chemical burns minutes or several hours after the exposure of five patients to epichlorohydrin. 

Aromatic amines are solids at room temperature and are routinely melted at elevated temperatures and blended with warmed resin. Eutectic mixtures of metaphenylene and methylene dianiline exhibit a depressed melting point, producing an aromatic hardener that remains liquid over short periods of time. Pot life is considerably longer that that of aliphatic polyamines. Cure at elevated temperature is needed to develop optimum properties, which are maintained at up to 15()°C. Aromatic amines have better chemical and thermal resistance than aliphatic polyamines. 

Flexiblization. Aliphatic diepoxide reactive diluents enhance the flexibility or elongation by providing chain segments with greater free rotation between cross-links. Polyaminoamide hardeners, based on aliphatic polyamines and dimerized fatty acids, perform similarly. Liquid polysulfide polymers possessing terminal mercaptan functionality improve impact properties in conjimction with polyamine hardeners. 

Adducted aliphatic polyamines such as D. E. H. 52 (Dow) epoxy hardener and D. E. H. 58 (Dow) epoxy hardener offer the advantages of lower vapor pressure, reduced tendency to blush, and less critical mix ratios. 

A two-component epoxy system consists of a resin and a hardener, along with possible additives such as accelerators, reactive diluents, resin modifiers, plasticizers, and fillers. Typical hardeners include aliphatic polyamines, which cure at room temperature or at slightly elevated temperatures polyamides, which provide flexibility and are widely used aromatics, which are solid and anhydrides, which require elevated temperature cure and produce thermally stable but brittle adhesives. Low molecular weight epoxies are liquid and are usually cured by amines, carboxylic acid anhydrides, and Lewis acid and base catalyst. Higher molecular weight epoxies are cured through their hydroxyl groups. Cure of epoxies involves an exothermic reaction. 

Aromatic polyamine hardeners These mostly solid hardeners include metaphenylenediamine, diaminodiphenylmethane, and diaminodiphenyl siflfone. In general, these hardeners provide poorer bond strengths and are more sensitive to temperature cycling than the aliphatic amines. Shrinkage is also high... 

Commercial cement modifiers used were based on a bisphenol A-type epoxy resin, diglycidyl ether of bisphenol A (DGEBA), which was mixed with three types of hardeners, modified polyamide-amine (MPAA),modified aliphatic polyamine (MAPA).and modified amine (MA) at the hardener contents recommended by the respective manufacturers. The hardener content was expressed as follows ... 

In addition to primary polyamines, secondary and tertiary amines are also utilized. The tertiary amines, such as methylated aliphatic aromatic amines,are most commonly utilized. They can best be described as catalysts, rather than hardeners, since they speed up a reaction and contribute to cross-linking, rather than entering into the reaction itself. 

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. 

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