Amine hardening systems

As indicated in the preceding section, amine hardeners will cross-link epoxide resins either by a catalytic mechanism or by bridging across epoxy molecules. In general the primary and secondary amines act as reactive hardeners whilst the tertiary amines are catalytic. 

Similar properties are exhibited by dimethylaminopropylamine and diethyl-aminopropylamine, which are sometimes preferred because they are slightly less reactive and allow a pot life (for a 500 g batch) of about 140 minutes. 

A number of modified amines have been marketed commercially. For example, reaction of the amine with a mono- or polyfunctional glycidyl material will give a larger molecule so that larger quantities are required for curing, thus helping to reduce errors in metering the hardener. 

These hardeners are extremely active. The pot life for a 500 g batch may be as little as 10 minutes. 

The glycidyl adducts are skin irritants similar in behaviour in this respect to the parent amines. The skin sensitisation effects in the primary aliphatic amine may be reduced by addition of groups at the nitrogen atom. The hydroxyethyl group and its alkyl and aryl derivatives are the most effective found so far. 

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P.Y.139 is sometimes used in conjunction with inorganic pigments for paints, especially to replace Chrome Yellow pigments. The systems are fast to overpainting (up to 160°C for 30 minutes), but they are not entirely fast to acids. The pigment performs very poorly in contact with alkali, therefore it is not suitable for use in amine hardening systems or in emulsion paints which are to be applied on alkaline substrates. 

Two types of epoxy coatings are formulated those cured at ambient temperature and those that are heat cured. The first type uses amine hardening systems, fatty acid polyamides, and polymercaptans as... 

Bisphenol-A-based epoxy with a poly(amido amine) hardener system cured Mesuaferrea L. seed oil-based hyperbranched polyurethane (HBPU)/ clay nanocomposites obtained by an ex situ solution technique, was also reported. The partially exfoliated nanocomposites showed a two-fold improvement in adhesive strength and scratch hardness, 10 MPa increments in tensile strength and thermostability at 112°C with little effect on impact resistance, bending and elongation at break compared to a pristine epoxy-modified HBPU system. However, similar epoxy-cured Mesua ferrea L. seed oil-based HBPU/clay nanocomposites exhibited a two-fold increase in tensile strength, a 6°C increase in melting point and thermostability at 111°C after nanocomposite formation using an in situ technique. An excellent shape recovery of about 96-99% was observed for the nanocomposites. The above observations confirm that the performance characteristics of nanocomposites are influenced by their preparation technique. 

For overall corrosion resistance the epoxy novolacs are somewhat superior to bisphenol A. However, for strictly atmospheric corrosion resistance bisphenol A is satisfactory. The filler most often used with epoxy concretes is silica along with an amine hardening system. This combination provides a polymer concrete with outstanding physical properties and moderate overall corrosion resistance. However, it is perfectly suitable to resist normal atmospheric corrosion (see Table 10.2). 

Amine hardening systems are used at room temperature giving a fast cure rate and a product having good chemical resistance. Care must be taken with this type of curing agent as many of them are skin sensitisers. 

An important appHcation is for filament-wound glass-reinforced pipe used in oil fields, chemical plants, water distribution, and as electrical conduits. Low viscosity Hquid systems having good mechanical properties (elongation at break) when cured are preferred. These are usually cured with Hquid anhydride or aromatic-amine hardeners. Similar systems are used for filament-win ding pressure botdes and rocket motor casings. 

For the high temperature systems, dicyandiamide and aromatic-amine hardeners are frequendy used. For room temperature systems, polyamide aminoamide, and aliphatic-amine hardeners are preferred. 

Progressive replacement of amine hardener by a low-viscosity flexibiliser will reduce mix viscosity, increase pot life and reduce the heat distortion temperature of the cured system. Higher impaet strengths are achieved using approximately equivalent amounts of hardener and flexibiliser. 

Aliphatic amine hardeners make it possible to formulate tough epoxide systems, but with limited resistance to high energy radiation. 

Among these hardeners, amines are the most versatile ones at room temperature as well as elevated curing temperature. The curing mechanisms with amines and the structures of the amine cured epoxy resins have been most sufficiently studied, and the systems of epoxy resins with amine hardeners are most extensively used in the practical industrial fields. 

The system can be formulated with fillers, pigments and auxiliaries. They cure with aminic hardeners at room temperature according to the two-pack process. Specific construction applications with the above development are as follows ... 

Another case confirms the suspected role of conducting nanoparticles in increased conductivity during and after the reaction in a similar epoxy system. Martin et al. (2005) dispersed CNTs into a bisphenol-A based epoxy resin and reacted it with an amine hardener at SO C. After about 600 s. 

Knifing, Spot and Spray Fillers for Metal and Marble (here also coatings). Knifing and spot fillers are especially suited for filling large areas of unevenness in just a few operations in quick succession. Knifing resins (hard to flexible) are mixed to a paste-like consistency with the extenders described. Benzoyl peroxide and tertiary aromatic amine are used as the hardener system (the latter is usually a component of the resin supply form). 

Epoxy composites cured with IPD offer resistance to a wide range of chemicals up to about 100-120°C. They offer better corrosion resistance in general than polyesters, but in many respects they are not quite as good as epoxy vinyl esters. This is due to the presence in the cured resins of the more sensitive amine hardeners. They nevertheless outperform other resins in their resistance to water at temperatures above about 80°C. Because of the excellent mechanical properties associated with epoxy resins, they are the system of choice when high pressure pipes are required. 

The main obstacle to wide employment of organic compositions for impregnation purposes lies in selective adsorption of certain components by the pores of the surface of the impregnated materials. If this happens, the components are separated, leading to disturbance of the system s stoichiometry and to lack of curing. For example, when concrete is impregnated with epoxy resin/amine hardener mixture, the upper part of the concrete becomes impregnated with epoxy resin only, and the deeper parts with hardener. 

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