Viscoelastic changes of epoxy resin–acid anhydride system during curing

Abstract

synopsisThe changed viscoelastic properties of the epoxy resin-acid anhydride system, Epikote 834-HHPA, are followed to the gel point a t 130, 140, and 150°C with a dynamic viscoelastometer. The viscosity increases with curing time through two inflections designated A and B. The point A is interpreted (from the reference to the chemical changes reported in the previous paper) as the termination of the initial stage of this curing reaction, and point B coincides with the gel point determined by the torsion method. The resonance frequency remains constant value up to the point B, followed by a rapid increase. The extents of reaction for epoxide, anhydride, and initial OH are 15, 45.8, and 100% a t the point A; 27.8, 63.7, arid 100% a t the point B, respectively. The apparent activation energies for viscosity are 7.5 kcal/mole for the resin mixture before curing, 10.5 kcal/mole for point A, 48.8 kcal/mole for point B (gel point). The overall apparent activation energies of this curing reaction are obtained from the Arrhenius plots for the curing time required for the resin mixture to reach the state of the points A and B; these values were 8.9 kcal/mole for point A and 16.2 kcal/mole for point B.

Modeling of Chemorheology of an Amine-Epoxy System of the Type Used in Advanced Composites

“…The parameters D and C of Equation (16) were determined from the slope and intercept of Figure 11. The herein observed increase in the flow activation energy with higher degree of cure has also been reported by Kamal [26] and Shimazaki [44].…”

Thermoset characterization for moldability analysis

“…The kinetics of thermosetting reactions ha\re been studied with the help of swelling measurements ( 18,19), spectroscopic analysis (20,21), rheological measurenieiits (22)(23)(24) , torsional and flexural braid analysis (25)(26)(27), electrical conductivity measurements (20,28), and a variety of other techniques.…”

The effect of resin stoichiometry and nanoparticle addition on epoxy/silica nanodielectrics

“…Eventually, vitrification occurs, whereupon the rate of reaction drops drastically, such that the chemical kinetics become diffusion and/or mobility controlled [23,24]. Even in the absence of such diffusion limiting effects, topological constraints can lower the ultimate conversion, in that residual reactive groups cannot meet and react [25]. The final conversion is therefore usually lower than unity although, by heating to devitrify the partially cured resin, chemical control of cure can be re-established to drive the system towards complete curing.…”