Flame-retarding nanoparticles as the compatibilizers for immiscible polymer blends: simultaneously enhanced mechanical performance and flame retardancy

Surface modified boehmite nanorods have been synthesized by binary grafting of reactive epoxide groups and long poly(methyl methacrylate) (PMMA) tails. The prepared nanoparticles have been incorporated into the immiscible poly(vinylidene fluoride)/poly(l-lactide) (PVDF/PLLA) blends. Unlike the traditional metal hydroxide flame retardants, a small amount of surface modified boehmite nanorods (5 wt%) can simultaneously enhance both the flame retardancy (with the LOI increasing 33%) and mechanical performance (with elongation at break increasing more than 10 times) of the PVDF/PLLA (70/30) blends. It is found that the boehmite nanorods are dominantly located at the interface between PVDF and PLLA phases. The reactive boehmite nanorods improve the compatibility of PVDF/PLLA blends by physical entanglement and in situ chemical reaction during melt blending. At the same time, the nanorods at the interface reduce the surface temperature and form a dense metal oxide layer which isolates the flame and oxygen through their thermal decomposition during combustion. Therefore, simultaneous enhancements in both mechanical properties and flame retardancy using flame-retarding metal hydroxides have been achieved for the first time.