Synergetic modification of graphitic carbon nitride by Zr-based metal-organic framework and tetraethoxysilane for improving fire performance in composite coatings

In this study, in an attempt to get an excellent flame retardant, herein, a new nanofiller (CNP@UiO-66@TEOS) with polyethyleneimine (PEI) as a crosslinker, Zr-based metal-organic framework (UiO-66) and tetraethoxysilane (TEOS) modified graphitic carbon nitride (CN) was synthesized. Different characterization tests confirmed the successful preparation of CNP@UiO-66@TEOS. Then, CNP@UiO-66@TEOS was doped into intumescent fire retardant (IFR) coating by solution blending method and the coating (CNP@UiO-66@TEOS/EP) was gained after curing. As expected, the CNP@UiO-66@TEOS significantly improved the fire performance of the IFR coating. The coating (CNP@UiO-66@TEOS/EP) with the addition of 2 wt% CNP@UiO-66@TEOS reduced the backside temperature by 102.9 °C over that of pure EP, proving enhanced flame retardancy. Meanwhile, CNP@UiO-66@TEOS/EP achieved the highest expansion height (21.5 mm) in the furnace experiment, contributing to a lower heat transfer ratio. In addition, the thermogravimetric analysis revealed an increase in residual char content to 31.84 wt%, which helped to resist external heat penetration. Cone calorimeter testing (CCT) showed that the peak heat release rate (PHRR), total heat release rate (THR), peak smoke production rate (PSPR), total smoke production (TSP), peak CO production rate (PCOPR), and peak CO2 production rate (PCO2PR) of CNP@UiO-66@TEOS/EP were reduced by 29 %, 19 %, 35 %, 37 %, 36 %, and 19 %, respectively, compared to pure EP, demonstrating the improved flame retardancy and smoke suppression properties. The results indicated that CN formed a thermal barrier at a high temperature and UiO-66 generated zirconium oxide (ZrO2) to catalyze the formation of residual char, thus producing a barrier effect. The TEOS on the UiO-66 surface further decomposed to form a silicon network to enhance the char layer strength of the composite. The synergistic outcome of CN, UiO-66, and TEOS offers potential avenues for the development of efficient IFR coating.