Synthesis of Ammonium-Polyphosphate-Modified Layered Double Hydroxide Nanohybrid via a Siloxane Polycondensation Method and Its Use as an Environmentally Friendly Flame Retardant Nanofiller in Polypropylene

A multifunctional organic–inorganic nanohybrid flame retardant, ammonium-polyphosphate-modified layered double hydroxide (m-APP@LDH), was synthesized by grafting the LDH onto the surface of APP via a siloxane polycondensation reaction between 3-amino propyl triethoxysilane (APTES) and tetraethyl orthosilicate. The synthesized m-APP@LDH was then melt-processed with polypropylene (PP), which resulted in PP nanocomposites with significant improvements in flame retardancy, antidipping, smoke suppression, and mechanical properties. Compared with neat PP, the composite showed 54.2 and 44.6% decreases in the peak heat release and total heat release rates, respectively, and the UL-94 rating of the composite was V-0. Moreover, the addition of m-APP@LDH resulted in prominent flame retardancy and improved the mechanical properties of the PP composites compared to the PP composites processed with physical mixtures of APP, LDH, and APTES. A combined TG-FTIR analysis further confirmed that the composite reduced the evolution of flammable components and toxic gases, indicating that m-APP@LDH significantly decreased the fire hazards of PP. The attractive properties of the m-APP@LDH/PP composites are attributed to favorable interfacial interactions between the m-APP@LDH surfaces and the PP matrix. In summary, the findings of this work provide new insights into the design of a next-generation environmentally friendly flame retardant for the development of multifunctional advanced polymer composite materials for engineering applications.