Flame retardant polypropylene with a single molecule intumescent flame retardant based on chitosan

A single molecule intumescent flame retardant was synthesized through in-situ polymerization by chitosan-based ammonium polyphosphate microencapsulated by melamine-formaldehyde resin. The multiple reactive hydroxyl and amino groups in its molecular chain made it a positively charged polymer with excellent coordination. The decomposition of melamine-formaldehyde resin produced a large amount of incombustible gas, which reduced the heat absorption on the surface of the composite material and inhibited its decomposition. Through thermogravimetric analysis, it was found that its thermal stability was better at high temperatures. Due to the decomposition of melamine-formaldehyde resin, a large amount of incombustible gas was produced, which reduced the heat absorption on its surface and inhibited its decomposition, so that polypropylene composites containing the flame retardant had a smooth decomposition process. The burning results showed that the limiting oxygen index and vertical combustion grade of the polypropylene composites containing the flame retardant had been improved, which the vertical combustion rating was V-1, and the limiting oxygen index was 25.7%. At the same time, it was clearly observed that composites containing the single-molecule intumescent flame retardant had an excellent anti-dripping effect. The surface temperature of the composite material was greatly reduced during combustion, from 343.7 ℃ to 156.9 ℃. Raman spectra and SEM of the surface carbon layer of the burned spline revealed the composite containing the flame retardant with a lower ID/IG value, indicating that the carbon layer it formed had more excellent crystallinity. Therefore, its carbon layer had a better structure and stability. It could be borne out that our single-molecule intumescent flame retardant had a good flame retardant effect on PP.