Kinetic research on low-temperature cure of epoxy adhesive

Abstract

Low-temperature cure of epoxy adhesives was investigated by means of differential scanning calorimetry analysis (DSC) on both isothermal and dynamic curing process and isothermal and dynamic curing phenomenological autocatalytic models were established. For dynamic curing section, an advanced isoconversional method was taken into account for computing the minimum apparent activation energy Ea value for each value of α lying between 0.05 and 0.95 with a step of 0.01. The correlation of invariant apparent activation energy and pre-exponential factor was expressed by “compensation parameters” equation. The isothermal experimental results showed that curing at low-temperatures of 10–15°C did take place but it was difficult to reach complete reaction over a reasonable experiment time period because the curing process was significantly decelerated owing to the effects of material vitrification and diffusion control in the late curing stages. In order to match the calculated and measured data better and describe the cure in the later stages of reaction, a heating rate-dependent pre-exponential factor and diffusion control were taking into account. The modified modeling with the heating rate-dependent pre-exponential factor and diffusion control agreed well with experimental data. Moreover, analysis of nonlinear regression was carried out on the isothermal modeling, results showed that the nonlinear least squares fitting had a satisfactory effect.