Dependence of dynamic mechanical behavior of DGEBA/DDM stoichiometric epoxy systems on the conditions of curing process

Abstract

SYNOPSISDynamic viscoelastic properties of diglycidyl ether of bisphenol A (DGEBA) cured with diaminodiphenylmethane (DDM) have been studied. The relaxation spectra of stoichiometric mixtures have been investigated as a function of the casting procedure and the thermal history during curing. Variations on the temperatures of the loss peaks and also on their magnitude have been observed when a solvent was employed to cast the mixtures. These variations have been attributed to the existence of high crosslinked regions formed at the earlier stage of curing inside the overall matrix. The results obtained from mixtures cured with different thermal histories underline the importance of adequate selection of curing conditions in order to obtain the optimum properties for these materials. Differences in crosslink density amongst the mixtures cured at different conditions have been correlated to the extent of reaction obtained by infrared measurements. 0 1995 John Wiley & Sons, Inc.

Nanoindentation study of interphases in epoxy/amine thermosetting systems modified with thermoplastics

“…For all values of applied load the trend was similar: a minimum of stiffness in the proximity of value r = 1, with an increase more pronounced for stoichiometric ratio values lower than unity than those for r > 1. These results correspond qualitatively well with the results obtained by several authors [39][40][41][42][43][44][45][46][47][48] for the change in elastic modulus with the stoichiometric ratio in epoxy systems cured with aromatic amines, which points out network topology and the corresponding packing density of elastically active bonds as responsible for the maximum value of the elastic modulus in epoxy rich mixtures. The highest stiffness value then corresponds with the lower specific volume and therefore higher density.…”

On the nodular morphology and mechanical behavior of a syntactic foam cured in thermal and microwave fields

“…Indeed when the T gv values are comparable it may be assumed that also the density nodules [22,23], which act as supporting sites of the framework, are fairly comparable. In the present investigation the fulfillment of the cited requirement has been assessed by carrying out DSC analyses on different microwave (MCS) or thermally cured (TCS) samples taken from selected areas (see Table 1 and Furthermore, it may be observed that the DT gv values reported in Table 1 for both microwave (MCS) and thermally-cured (TCS) samples are rather negligible.…”

Résines époxy réticulées par des polyamines : structure et propriétés

“…La taille des nodules serait comprise entre 5 et 100 nm et dŽpendrait des conditions de polymŽrisation telles que la concentration en durcisseur [24] et 26], la cuisson [24] et [26], ou lÕagitation lors du mŽlange [27]. Les techniques ayant ŽtŽ utilisŽes pour mettre en Žvidence cette morphologie sont les suivantes : la microscopie Žlectronique ˆ transmission et b alayage, la diffraction des rayons X aux petits angles, la rŽsonance paramagnŽtique Žlectronique, la rŽsonance magnŽtique nuclŽaire et la spectromŽtrie mŽcanique [28] et [29].…”