Functional design of epoxy-based networks: tailoring advanced dielectrics for next-generation energy systems

Abstract

Epoxy resins are widely used as the primary insulation material in many demanding energyrelated applications. As such, the ability specifically to tailor the electrical performance of such systems to meet increasingly demanding insulation situations has considerable utility. This paper describes a new approach to this problem, which is based upon the controlled introduction of specific functional groups into the cured resin's network architecture. Here, two additives are considered, termed functional network modifiers (FNM), namely glycidyl hexadecyl ether and glycidyl 4-nonylphenyl ether; in all the investigated systems, the ideal stoichiometric ratio of epoxide groups to amine hydrogens is retained. In the case of both FNM, their inclusion resulted in a progressive reduction in the glass transition temperature T g of the system, a reduction in the real part of the permittivity and reduced dielectric losses wihin the accessible frequency range, increased DC conductivity and increased AC breakdown strength. The magnitude of the observed effects are found to be dependent upon the choice of functional modifier, which suggests that such changes are not related merely to the inclusion of an additive within the system, but are also influenced by the chemistry of the additive itself. Explanations for these effects are proposed. It is concluded that the use of such FNM at low concentrations (~4% in the work reported here) offers a novel alternative means of engineering advanced materials to meet the current and future needs in an adaptable and easily implemented manner.

The nature of the gamma dielectric relaxation in diglycidyl ether Bisphenol-A (DGEBA) based epoxies

“…As such, we suggest that the molecular structure of the FNM is also important; here, the alkyl chain in GHE contains sixteen carbon atoms while that in GNPE contains only nine. Consequently, additional free volume should be introduced by the GHE, which is consistent with published work on the effect on Tg of GHE [17] and of FNMs with long chain alkyl groups [39]. Secondly, the GNPE contains an aromatic ring within its chemical structure, which may interact physically with the aromatic rings within the backbone of the epoxy network, thereby restricting the mobility of the overall branching moiety.…”

“…A number of studies have considered such effects with respect to stoichiometric imbalances in anhydride-and amine-cured ERs: while a moderate (~20%) excess of epoxide groups reduces DC conductivity at temperatures below the glass transition temperature (Tg), an excess of amine groups was found to promote conduction [15]; elsewhere, a comparable excess of anhydrides resulted in a pronounced reduction in AC breakdown strength in both the base ER and a nano-filled equivalent [16]. In contrast, an increase in breakdown strength of 10% was seen on incorporating glycidyl 4-nonylphenyl ether into an epoxy network (constant, optimal epoxy/amine stoichiometry) [17], while an increase of twice this magnitude was observed on adding a glycidyl polyhedral oligomeric silsesquioxane into the same base epoxy system (again, constant, optimal epoxy/amine stoichiometry) [18].…”

On the Dielectric Behavior of Amine and Anhydride Cured Epoxy Resins Modified Using Multi-Terminal Epoxy Functional Network Modifier

“…The anhydride-hardened systems were cured, initially at 90 °C for 2 h, then at 150 °C for 4 h, as recommended by the manufacturer. Previously, we have reported on the effect of FNMs on thermal stability [17]; the above protocol does not approach the onset of decomposition for any of the systems. The different formulations are hereafter referred to as XTTE or XATTE, where X represents the molar percentage of epoxide groups in the system that was derived from the FNM, A signifies anhydride curing and TTE indicates the appropriate FNM.…”

Effects of cross‐linked networks on dielectric properties of epoxy resins based on molecular dynamics

“…Several studies have shown that the conductance loss was related to the density of states of special chemical groups, such as aromatic and aliphatic anhydrides. [10][11][12] Similarly, cross-linked networks of epoxy resins can be changed by subtle chemical group differences. 7,11 The length of alkyl chains of epoxy resins was considered to affect the free volume and mobility of cross-linked networks, thus affecting the relaxation polarization loss.…”

“…[10][11][12] Similarly, cross-linked networks of epoxy resins can be changed by subtle chemical group differences. 7,11 The length of alkyl chains of epoxy resins was considered to affect the free volume and mobility of cross-linked networks, thus affecting the relaxation polarization loss. 7 It was pointed out that the molecular volume of diester segments played an important role in dielectric polarization of anhydride-cured epoxy resins.…”