Dielectric and rheological study of the molecular dynamics during the cure of an epoxy resin

Abstract

Composite manufacturing is currently one of the most challenging processes for industrial lightweight applications. To date, the process conditions for polymer-based composite manufacturing are evaluated by laboratory measurements: usually, the flow behavior and the curing of the polymer matrix material are characterized by rheology and quality assurance is performed by thermo-physical analysis in postprocess measurements. In contrast a dielectric in-mold sensor offers the possibility to measure the real-time behavior of the polymer during processing. This study focuses on the correlation of simultaneous rheological and dielectric measurements on Hexcel RTM6 using a coupled setup of both techniques. For dielectric measurements a reusable in-mold sensor was used and a calibration, taking into account the cable response, was performed. The results show good agreement with respect to glass-transition temperature and the gel-point. This can be understood by the fluctuation-dissipation theorem that explicitly relates molecular dynamics to the macromolecular mechanical properties under dynamic time-dependent load. Furthermore, it was found that the dynamic viscosity can directly be related to the electrical conductivity. This proves the high potential of dielectric analysis as online-capable technique for material characterization during composite manufacturing. V C 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2018, 56, 907-913

In situ resin age assessment using dielectric analysis and resin cure map for efficient vacuum infusion

“…The resulting sinusoidal current and phase shift response yields dielectric properties, including complex permittivity (e à ) and ionic conductivity (r). The reciprocal of r is the ion viscosity and exhibits a strong correlation to mechanical dynamic viscosity (g) [26][27][28].…”

Synthesis and application of thermal latent initiators of epoxy resins: A review

“…The curing of epoxy resins with apparent curing agents is carried out through addition polymerization or ion polymerization. [15][16][17][18][19][20][21][22][23][24][25][26] A latent initiator mixed with epoxy resin at room temperature can be stored for an extended period of time. When exposed to external stimulation, such as heating and photo-irradiation, the latent initiators initiate the curing reactions of epoxy resins.…”

Dielectric analysis monitoring of thermoset curing with ionic liquids: From modeling to the prediction in the resin transfer molding process

“…One possibility is the in situ monitoring by DEA, a robust and economical method, which measures the dielectric properties and its changes of a resin system during cure. Consequently, in situ nondestructive monitoring and thus optimizing the cure cycle during processing is possible in order to create excellent physical and mechanical properties and simultaneously reduce manufacturing time . The success of DEA as an in situ monitoring technique depends mainly on a well‐defined correlation between the ion conductivity and the relevant material properties such as degree of cure, glass transition temperature or viscosity…”

“…Consequently, in situ nondestructive monitoring and thus optimizing the cure cycle during processing is possible in order to create excellent physical and mechanical properties and simultaneously reduce manufacturing time. [4] The success of DEA as an in situ monitoring technique depends mainly on a well-defined correlation between the ion conductivity and the relevant material properties such as degree of cure, glass transition temperature or viscosity. [5] Another focus lays on new materials for potential improvements where the ionic liquids (ILs) emerging as innovative curing agents.…”

“…These are characteristics required to satisfy the increasingly demanding safety and health regulations. [7][8][9] In contrast to established hardeners for aerospace applications, such as Dicyandiamide (DICY) or Diaminodiphenylsulfone (4,, which are solid at room temperature, ILs are miscible liquid curing agents, which avoid difficulties such as proper dispersion quality and inhomogeneous cure. This facilitates manufacturing and processing when used alone or in combination with other hardeners.…”