Thermal diffusivity of an epoxy system as a function of the hardener content

Abstract

ABSTRACT:The influence on the thermal diffusivity of the changes induced on the macromolecular network of an epoxy-amine system by different hardener/resin ratios was experimentally investigated. For each hardener/resin ratio, the open photoacoustic cell technique was used to measure the thermal diffusivity. The thermal diffusivity data was correlated with the evolution of the characteristic infrared absorption bands of the epoxy and amine components using a fast Fourier transform spectrometer. The results show a sharp transition in the thermal diffusivity values at the beginning of the amine-rich domain, corresponding to a transformation from a rigid network to an amine saturated deformable structure. It is concluded that the open photoacoustic cell technique can be a useful monitoring tool for structural characterization and molecular evolution during the curing of this kind of system.

Effect of the hardener to epoxy monomer ratio on the water absorption behavior of the DGEBA/TETA epoxy system

“…Besides the stoichiometric formulation, epoxy rich as well as hardener rich mixtures were analyzed. The results obtained were correlated with former proposed networks developed due to the change on the hardener/epoxy ratio [8] , and with the presence of unreacted sites. v 2.…”

“…Besides the chemical nature of the hardener, other variables like the time and temperature of cure [3,4] and the hardener to epoxy monomer ratio [5] could produce very different macromolecular structures. For the epoxy system formed by the difunctional epoxy monomer, diglycidyl ether of bisphenol-A (DGEBA), and the hexafunctional aliphatic amine, triethylenetetramine (TETA), the hardener to epoxy ratio was shown to strongly affect mechanical [6,7] and thermal properties [8] .…”

“…Also, thermo-gravimetric analysis showed that some off-stoichiometric mixtures could have a two phase like microstructure, where very crosslinked domains could be embedded on a less crosslinked matrix [8] . These structural characteristics can strongly affect the moisture up-take behavior and contribute to a faster decrease of the mechanical performance of the material.…”

Ageing of the DGEBA/TETA epoxy system with off-stoichiometric compositions

“…For the particular system made of the triethylene tetramine, TETA, hardener and the DGEBA monomer the variation of the hardener to monomer ratio promotes strong changes on the mechanical behavior [18][19][20][21] . Of particular interest with respect to these changes is the very sharp increase in the impact strength, when amine rich mixtures were used 21 .…”

“…The epoxy system based on the reaction of the difunctional epoxy monomer diglycidyl ether of bisphenol-A, DGEBA, with aliphatic amines is such an example. The properties of this and other epoxy systems can be varied as a function of the molecular weight of the hardener molecule [7][8][9][10] , by variations in processing conditions [11][12][13] or by the use of different hardener to monomer ratios 8,11,[13][14][15][16][17][18][19][20][21] . This last variable introduces boundary condition (i.e., when a variable like temperature or the amount of monomers is changed).…”