Phenylenediamine-Guanidine Phosphate Carbon Dots for Flame-Retardant and UV-Resistant Poly(vinyl alcohol) Composite Films

A kind of phosphorus-doped carbon dots with flame retardancy was made from biphenylamine and guanidine phosphate by a simple hydrothermal method. The surface chemical structure, morphology, and optical property of the as-synthesized MPD-GP-CQDs were characterized by Fourier transform infrared spectrometry, Field emission transmission electron microscopy, and fluorescence spectroscopy, respectively. And then the MPD-GP-CQDs were added to poly(vinyl alcohol) (PVA) to prepare functional PVA composite film. The effect of MPD-GP-CQDs with different additions on the thermal, optical, and mechanical properties as well as flame retardancy of PVA composite film were explored by thermogravimetric analysis, differential scanning calorimetry, UV–vis spectroscopy, universal tensile test, vertical combustion test (UL-94), limiting oxygen index (LOI), microcalorimeter, etc. It showed that the addition of MPD-GP-CQDs not only endowed PVA film with flame retardancy but also improved its UV shielding and mechanical properties. The phosphorus content played a key role in the modification. As the added MPD-GP-CQDs increased, the flame retardant performance gradually increased. When 12.5% MPD-GP-CQDs was added, the UL-94 vertical combustion test rating of the MPD-GP-CQDs-PVA composite film reached VTM-0, and the LOI value was 30.8%. In addition, the transmittance of the MPD-GP-CQDs-PVA composite film in the UV-A band decreased to 35.3%, showing good UV shielding effect. These results suggested that the phosphorus-doped composite carbon dots had potential application in the development of some polymer materials such as multifunctional PVA films.