Chemorheological and dielectric study of epoxy-amine for processing control

Abstract

The curing of an epoxy prepolymer based on diglycidyl ether of bisphenol A (DGEBA) with isophorone diamine (IPD) as a hardener was analysed using differential scanning calorimetry, rheological measurements, microdielectrometry, and insolubles in THF for gel point detection. The effects of the initial hydroxyl concentration of the DGEBA prepolymer, the molecular features of which are different, were determined on the cure kinetics of epoxy networks Chemical reaction kinetics of this DGEBA/IPD system during isothermal conditions was studied in the 60–120 °C temperature range and a kinetic model relation based on assumption of an autocatalytic mechanism has been proposed. Gelation and vitrification phenomena of this reactive mixture were studied and allowed us to establish the TTT diagram. Furthermore, dielectric data and viscosity measurements have been interpreted with respect to kinetics. Indeed, it was shown that the modified percolation law equation suggested by Macosko et al can be used to describe the chemoviscosity as a function of temperature and extent of reaction by using a temperature‐ and conversion‐dependent critical exponent. In other respects, dielectric properties such as ionic conductivity were related on one hand to viscosity through a Stokes‐based equation in the 0 to 0.5 conversion range, and on the other hand to conversion through an experimental equation. © 1999 Society of Chemical Industry

In situstudy of the epoxy cure process using a fibre-optic sensor

“…In this case, it is useful to carry out on-line curing process monitoring to provide the best cross-linking density. To date, numerous real-time, in situ techniques have been used to monitor thermoset resin curing (dielectric, ultrasonic sensors, etc [1,2]). Fibre-optic sensors are promising candidates for this process due to their immunity to electromagnetic interference, their short response time and their compatibility with the manufacturing process.…”

Determination of Gel Point of Epoxy Thermosets via Electric Resistance Measurements

“…The likelihood of the resistance changes during reaction is that at the very beginning of the cure process (equilibration time) an initial increase in electrical resistance is a result of the decrease in viscosity with the temperature raise and wetting of the NCG particles with nonconducting epoxy material. As the reaction proceeds, branched oligomeric molecules are created causing an increase in viscosity of the reaction mixture10 (see Figure 1) as well as increase in the thickness of the insulating layer11 around NCG particles. At the gel point the very first polymeric network is created and as the reaction proceeds the number of three‐dimensional bonds increases dramatically.…”

Chemorheological studies on a dicyanate resin modified with polyethersulfone

“…Dielectric analysis has been helpful in understanding the kinetic and rheological behaviours of thermoset resins during the curing process 23–25. Dielectric analysis measures the electrical characteristics of materials, such as orientation and alignment of dipoles on polymer chains.…”

“…Gelation and vitrification phenomena should be considered when analyzing the chemorheology of thermoset resins. Several researchers have investigated dielectrical property changes during curing to analyze their chemorheology 9–11…”