Flame-retardant functionalized biobased carbon dots as nanoenhancers for flame retardant, transparent and UV-shielding properties of epoxy resin

The concurrent integration of high flame retardancy and optical transparency into epoxy resins (EP) presents a considerable challenge in 5G technology. In this study, the bio-carbon dots (CDs) were successfully synthesized by a one-step hydrothermal method using corncob, ethylenediamine (EDA), and 2-carboxyethyl(phenyl)phosphinic acid (CEPPA) as raw materials. The phosphorus modification CDs (PCDs) were further functionalized through a nucleophilic substitution reaction between CDs and diphenylphosphinic chloride (DPPC). Then PCD used as functional fillers incorporated into epoxy resin to prepare a series of EP/PCDs composites. Interestingly, apart from flame retardancy, the prepared PCDs demonstrated additional capabilities in UV protection, optical transparency, and mechanical reinforcement. When the PCDs addition reached 5 wt%, the EP composite achieved a UL-94 V-0 rating and an LOI value of 36.5%. Relative to pure EP, the EP/PCDs composite exhibited marked reductions in peak heat release rate (pHRR), total heat release (THR), and carbon dioxide production (CO 2 P) by 33.4%, 20.1%, and 26.4%, respectively. In addition, EP/5PCDs composites exhibited a 19.8% and 21.4% enhancement in tensile and impact strength, respectively, while retaining their fluorescent properties. Furthermore, the transmittance of EP/5PCDs composites was reduced to 2% at UV-A wavelengths, which indicated that PCDs enhanced UV shielding properties. Meanwhile, EP/5PCDs composites maintained outstanding transparency and also exhibited good the thermal decomposition stability. To conclude, the EP/PCDs composite achieved a balance between flame retardancy, transparency, mechanical properties, and additional functionalities, demonstrating significant potential for anti-counterfeiting and advanced technological applications. • Bio-based flame-retardant modified carbon dots were formulated. • EP/PCDs composites exhibited excellent transparency. • PCDs significantly enhanced the flame retardancy and UV-shielding properties of EP.