Thermal cure of epoxy resins

Wei, J., DeMuse, M. and Hawley, M.C., Kinetics modelling and time-temperature-transformation diagram of microwave and thermal cure of epoxy-resins, Polym. Eng. Sci., 1995, 35, 461. 

The crosslinking reactions are illustrated in Reaction 1.8, and they demonstrate that, in principle, only a trace of curing agent is necessary to bring about cure of epoxy resins. Selection of curing agent depends on various considerations, such as cost, ease of handling, pot life, cure rates, and the mechanical, electrical, or thermal properties required in the final resin. 

Tertiary amines are used to accelerate both amine and anhydride cures of epoxy resins (B-67MI11501). Certain heterocyclic amines have been used for this purpose, including pyridine and piperidine. In the case of anhydride cures, the use of an amine catalyst not only accelerates the cure, but also improves the thermal stability of the cured resin. 

Y. Chekanov, etal., Frontal curing of epoxy resins comparison of mechanical and thermal properties to batch-cured materials. J. Appl. Polym. Sci. 1997, 66(6), 1209-1216. 

The kinetics of copolymerization or curing of epoxy resins with cyclic anhydrides initiated by tertiary amines was investigated by chemical analysis 52,65,73,74,90) differential scanning calorimetry isothermal methods electric methods , dynamic differential thermal analysis , IR spectroscopy dilatometry or viscometry Results of kinetic measurements and their interpretation differ most authors agree, however, that the copolymerization is of first order with respect to the tertiary amine. 

Thermal cationic cures of epoxy resins can be achieved using Lewis acids based on amine-BF3 complexes. 

An epoxy resin made by thermal curing of an araldite prepolymer with the 3,5-diaminophenylester of a peripherically modified vitamin as hardener on carbon... 

Considering both the chemistry of epoxy resins and the reactants required to produce it, impurities, unreacted raw materials, catalyst and other monomeric species can be expected to be present in the resin in low levels (i.e. <100 ppm). Under the mechanical, thermal and chemical stress levels acting at the interface both during curing and after curing, concentration of these species at the interface could be quite high giving rise to an interface structure unrelated to the bulk. 

Pure epoxy resins, so-called basic resins, are unsuited to building applications because of their high viscosity. Modifications are necessary to achieve the required viscosity, wettability, carbonate resistance, curing rate, cost reduction and numerous other properties. However, the modifiers must be chosen so as not to impair the other valuable attributes of the epoxy resins. For example volatile solvents are unsuitable for thick coatings, because any solvent retained in the cured system will reduce the mechanical and thermal properties and the corrosion resistance. The specific property needs for a particular application may be tailored to each system to maximise the remarkable potential of epoxy resins (Dow Chemical Company, undated c). 

Figure 10.16 Examining the curing status of epoxy resins. The first scan reveals the curing process and the second scan shows a completion of curing. (Reproduced with kind permission of Springer Science and Business Media from M. Brown, Introduction to Thermal Analysis, Kluwer Academic Publishers, Dordrecht. 2001 Springer Science.)...

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