Enhancing the UV resistance and flame retardancy of epoxy resin composites with fluorescent carbon dots

Carbon dots (CDs) are a novel class of carbon material which have gained widespread usages owing to their exceptional optical properties, low toxicity, and high biocompatibility. The nitrogen-doped carbon dots (N-CDs) using a normal curing agent of 4,4′-diaminodiphenylmethane as resource was expected to not only have good compatibility with epoxy resin (EP), but also bring luminescent property to EP composites. It was interesting that the N-CDs-EP composites with 12.5 wt% addition exhibited a limiting oxygen index value of 31.4% and reached UL-94 V-1 grade, indicating a good flame retardancy. Compared with pure EP, the incorporation of N-CDs formed more residual char and had extra smoke suppression effect. Besides, the N-CDs-EP composites exhibited a low transmittance less than 10% for the light wavelength below 490 nm. The N-CDs contributed to the light shielding capabilities of the N-CDs-EP composites, which could effectively shield purple, blue, and cyan light. Furthermore, the mechanical properties including bending strength and impact strength, the dielectric property, and hydrophobicity of N-CDs-EP composites were also improved. The simple but effective modification strategy might be expected to be applied in many polymer systems.