Multifunctional fire-resistant and flame-triggered shape memory epoxy nanocomposites containing carbon dots

Carbon quantum dots (CDs) are widely used as semiconductor systems, due to their facile synthesis and optical characteristics. CDs have been employed to enhance the light emission, UV resistance, and anticorrosive performances of epoxy nanocomposites (ENCs). Herein, we investigated the use of CDs to prepare multifunctional cycloaliphatic ENCs showing shape recovery capability. Following a waste-to-wealth approach, CDs were obtained from humic acid by a hydrothermal route. ENCs containing CDs exhibited photoluminescence, while the simultaneous addition of CDs and hexadecyltrimethoxysilane accounted for heat/flame-triggered shape recovery capability and hydrophobicity (contact angles as high as 137°). The polar character of silane-functionalized CDs allowed for their segregation at the surface of ENCs, making them very fire resistant. In particular, the CDs exerted an outstanding thermal shielding effect on the surface of ENCs, lowering the heat transfer at the boundary layer and increasing the time to flaming combustion up to ∼ 76 %. Besides, the graphitic nature of CDs and their charring behavior led to a huge increase in the back temperature at the ignition point (up to ∼ 30 %) during burn-through tests. Notwithstanding the low loadings (not exceeding 0.3 wt%) of CDs, ENCs lost their structural integrity only after almost 1 min of blowpipe flame application to their surface, whereas the resin counterpart degraded in less than 20 s. Besides, cone calorimetry tests carried out on ENCs highlighted a significant reduction of total smoke release (up to ∼ 40 %) compared to unfilled epoxy. Finally, we demonstrated the possibility of using multifunctional ENCs containing CDs as unique identification technology for polypropylene packaging, opening new perspectives on the effective protection of genuine products from counterfeiting.