Superposition of dynamic mechanical properties in the glassy state

Abstract

Superposition of the loss tangent curves could be achieved for the β‐transition of a series of homologous epoxy resins. It was found that both a vertical and horizontal shift were necessary to achieve superposition when the curves were plotted as the logarithm of the loss tangent versus reciprocal absolute temperature. Resins from the diglycidyl ether of bisphenol A (DGEBA) were prepared with five different curing agents and their loss tangent curves measured on a free‐oscillation torsion pendulum (ca. 1 cps). The β transition is caused by DGEBA, which was found via molecular models to contain a mobile group. The intensity of the loss for three of the resins was found to be proportional to the concentration of DGEBA, molecular models revealing that no additional mobile groups were introduced by these curatives. The remaining two curing agents introduced mobile groups into their systems and for these two, no separate transitions were identified but the intensity of the DGEBA β transition was increased. This may be caused by a coupling of the DGEBA mobile groups through the flexibility of the curative‐introduced mobile groups.

The influence of the amount of hardener on the tensile mechanical behavior of an epoxy system

“…The TETA hardener is a hexafunctional compound and if all its functional points are used, a rigid macromolecular network is expected to be developed [31]. This is indeed in agreement with the experimental results obtained.…”

“…The epoxyrich, or amine avid mixtures, display a very limited deformation capacity as shown in Table 2. However, if, on average, some of the reactivity points at the hardener molecule remain unreacted, new mobile segments would be expected to be present in the macromolecular network formed [31,32]. Since aliphatic primary amine groups are highly reactive [4], the presence of nonreacted points at the TETA molecule has to be associated with the exhaustion of the epoxide rings, which is a possibility for amine-rich mixtures [33,34].…”

A study by Raman, near-infrared and dynamic-mechanical spectroscopies on the curing behaviour, molecular structure and viscoelastic properties of epoxy/anhydride networks

“…10B) is usually denoted as the b transition and is associated with isolated motions of small units of the network. In the case of epoxy/anhydride networks, the b transition has been attributed to the anhydride moiety incorporated into the network through diester linkages [26,27]. The elastic modulus, E 0 (Fig.…”

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

“…This versatility is a consequence of the many epoxy systems that can be fabricated by using different chemical compounds to open the epoxy ring and set the epoxy monomers. Therefore, by the use of anhydrides and aromatic or aliphatic amines as hardeners, different epoxy systems with a large range of chemical and physical properties can be obtained [3][4][5][6] . Among the most widely used epoxy systems, those that can be cured at room temperature are largely applied 3 .…”