Dynamic-mechanical response of carbon fiber laminates with a reactive thermoplastic resin containing phase change microcapsules

Abstract

Dynamic-mechanical analysis (DMA) was performed to investigate the viscoelastic response of multifunctional laminates for thermal energy storage (TES). The laminates were constituted by a microencapsulated paraffinic phase change material (PCM), a carbon fiber fabric, and an innovative reactive acrylic resin (Elium®). In the Elium®/PCM systems, the PCM fraction affected neither the glass transition temperature ( $T _{\mathrm{g}}$ ) of the resin, found at 100–120 ∘C, nor the activation energy of the glass transition, determined with multifrequency scans from the position of the $\tan\delta $ peaks. On the other hand, the low-temperature (0–40 ∘C) transition detected on the neat resin was hidden by the PCM melting, evidenced by a step in $E'$ and peaks in $E''$ and $\tan \delta $ . In the laminates, the amplitude of the $E'$ step and the intensity of the $\tan \delta $ peak associated to the PCM melting presented a linear correlation with the PCM content and the melting enthalpy. Cyclic heating/cooling DMA tests showed that the decrease in $E'$ due to PCM melting was almost completely recovered (90–95%) upon crystallization. The difference between the $\tan \delta $ peak positions on heating and on cooling decreased from 30 to 12 ∘C when the heating/cooling rate changes from 3 to 1 ∘C/min. Multifrequency tests highlighted that the activation energy of the glass transition of the laminates was lower than that of the matrices, and it did not follow a trend with the PCM fraction. Interestingly, also the $E''$ and $\tan \delta $ peaks related to PCM melting depended on the testing frequency, and their asymmetric shape could be interpreted by considering a progressive melting of the PCM in the microcapsules during heating.