A flame-retardant DOPO-MgAl-LDH was prepared and applied in poly (methyl methacrylate) resin

A novel inorganic and organic composite flame retardant (9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide [DOPO]-layered double hydroxide [LDH]) was synthesized via grafting DOPO with organic-modified Mg/Al-LDH, which was introduced into poly (methyl methacrylate) (PMMA) resin to prepare the flame-retardant PMMA composites. Thermogravimetric analyzer (TGA) showed that the T-50% of DOPO-LDH/PMMA composites enhanced by about 20 degrees C, and with the 20% flame retardant, the residual char content can be increased by 39.8% in the air atmosphere compared with LDH/PMMA composites. In the UL-94 and the limiting oxygen index (LOI) tests, it can be found that compared with LDH/PMMA composites, the LOI value of DOPO-LDH/PMMA composites were raised evidently with the increased flame retardants, and the droplet combustion was greatly improved. These results could be ascribed to the action of DOPO free-radical, catalytic charring of polymer and the effect of LDH physical barrier. Moreover, the novel DOPO-LDH not only given PMMA a good flame-retardant property and thermal stability, but also have higher visible light transmittance, ultraviolet-shielding effect, and low loss of mechanical properties, which could further facilitate the wide application of inorganic environment-friendly flame retardants in general resins and engineering resins and broaden the application of polymers.