Deeper insights into the thermal properties of epoxy thermoset resins using torsion measurements

Abstract

AbstractThe glass transition temperature (Tg) of epoxy thermosets is a critical material property that depends on the component chemistry, the final cross‐link density, and processing conditions. This study incorporates dynamic mechanical analysis (DMA) testing with a torsion clamp geometry on a TA Instruments DHR‐2 and differential scanning calorimetry (DSC) to characterize five different two‐component epoxy‐amine systems. Investigation of the Tg dependence on DMA frequency and heating shows that lowering the frequency from 1 to 0.01 Hz results in a Tg very similar to that measured using DSC, while a heating rate of 0.3°C/min using DMA gives a Tg comparable to the DSC measured value at 30°C/min. The DMA technique reveals secondary relaxation transitions and peak broadening in the tan(δ) plots of poorly mixed epoxy blends, quantified using full width at half maximum (FWHM) of tan(δ) peaks, and are indicative of a non‐homogeneous cross‐linked network and off‐ratio blending, respectively. The increase in the FWHM due to poor mixing ranges from 8% to 96%. These parameters are easily measurable and quantifiable in DMA, but are not observed in DSC. The additional DMA insights are valuable for process development and failure analysis, and can improve the understanding of epoxies.