Effects of polymeric microcapsules on self-healing composites reinforced with carbon fibers: a comparative study

Abstract Three different microcapsules, namely dicyclopentadiene (DCPD)-urea formaldehyde (UF) based single-walled microcapsules, DCPD-UF-Siloxane (DCPD-UF-Si) based double-walled microcapsules and DCPD-Carbon nanotubes-UF based dual-core microcapsules were synthesized, and their corresponding self-healing composites were prepared. This paper mainly focuses on the synthesis procedure of various microcapsules and a comparative study on the effect of microcapsules over the final composite properties. The core content of the microcapsules was measured and compared with theoretical calculations. DSC & TGA analyses have shown that the novel microcapsules (DCPD-UF-Si, DCPD-CNT-UF) and their composites have better thermal stability compared to DCPD-UF microcapsules. Epoxy-carbon fiber (2 wt.%) composite specimens with three different microcapsules were tested for surface morphology, mechanical, thermal and electrical properties. SEM analysis has shown that the microcapsules have a rough outer surface and smooth inner surface. The average diameter and shell thickness of the microcapsules were measured for all types of microcapsules. Addition of double-walled and dual-core microcapsules has reduced the glass transition temperature of the composites by 10 °C. Also, SHC with DCPD-UF-Si and DCPD-CNT-UF microcapsules have shown better thermal stability (300 °C) compared to DCPD-UF microcapsules (220 °C). The incorporation of CNT based microcapsules inside the composite has also improved the electrical conductivity by 2.2 times, without compromising on self-healing efficiency (78 %). Therefore, these novel microcapsules can be potential candidates for making multifunctional polymer composites for aerospace, windmills and automotive applications.