Isothermal curing of epoxy resins as seen by direct current and rheological measurements

Abstract

Isothermal curing of epoxy resins as seen by direct current and rheological measurements Summary-The investigations of epoxy-amine systems' curing were carried out by direct-current (DC) measurements in order to get better understanding of the evolutions of ionic conductivity and viscosity in the reactive medium. This study extends our earlier DC and ion mobility investigations (Time-of-Flight method) on this subject. The additional rheological examinations (Dynamic Mechanical Analysis) have allowed to determine the correlations between evolution of electric and viscoelastic properties such as dynamic viscosity. The experiments have been carried out for the epoxy-amine reacting system that gelates and vitrifies: diglycidyl ether of bisphenol A with 4,4'-methylenebis(3-chloro-2,6-diethylaniline) (DGEBA-MCDA) and for the reacting system that gelates only: diglycidyl ether of 1,4-butanediol with 4,9-dioxa-1,12-dodecane diamine (DGEBD-4D). An inconsistency between the time dependence of ionic conductivity and viscosity was explained by the fact that the concentration of the mobile ion charge carriers is decreasing with the advancement of reaction. This observation lead to the conclusion of limited application of the electric techniques for the direct in situ monitoring of chemical reactions.

Effect of crosslinking on the secondary relaxation in polyvinylethylene

“…Crosslinking of polymers slows down the segmental dynamics, as reflected in an increased glass transition temperature 13–20. For the case of polyvinylethylene (PVE), the effect of crosslinking on the segmental dynamics is typical: crosslinks broaden the dispersion in the mechanical and dielectric loss spectra and make the segmental relaxation time, τ α , more sensitive to temperature (more “fragile”) 21.…”

Physicochemical changes in epoxy-amine systems studied by ionic conductivity and ionic carriers mobility measurements

“…The basics and the practical applications of AC [6][7][8][9]19], DC [10][11][12][13] and DMA [20] techniques for cure monitoring are very well known and frequently illustrated in the literature. The backgrounds, the references and the experimental conditions of the TOF measurements we have also described elsewhere [15,16].…”

“…The electrical techniques are also engaged because direct current conductivity as well as dielectric parameters of a sample vary during the chemical reactions. Among the in situ electrical methods (electric response depends on the nature, the mobility and the concentration of charges) we may recall dielectrometry (AC technique) [6][7][8][9], direct-current measurements (DC investigations) [10][11][12][13] or impedancometry [7,14]. The electrical parameters used for the cure monitoring are usually the permittivity, the loss factor, the loss tangent, the ionic conductivity and the relaxation time.…”

“…Using TOF and DC techniques we have shown in our earlier studies that in the epoxy resin systems: diglycidyl ether of 1,4-butanediol with 4,9-dioxa-1,12-dodecane diamine (DGEBD-4D) and diglycidyl ether of bisphenol A with 4,4'-methylenebis[3-chloro-2,6-diethylaniline] (DGEBA-MCDEA) the above mentioned assumption was not fulfilled [13]. The differences found between the time dependence of the ionic conductivity and of the ion mobility were explained by the decrease in the concentration of ion charge carriers during the reaction according to our results and other observations [13,17,18]. In our previous paper it was shown that except of the beginning of the curing the evolution of the ionic conductivity did not follow the evolution of the viscosity.…”

“…Also the empirical Walden's rule could be applied only in the limited range of the advancement of the reaction. This was due to the changes of the concentration of mobile ions during the reaction [13].…”