Enhancing the mechanical and thermal properties of polypropylene composite by encapsulating styrene acrylonitrile with ammonium polyphosphate

BACKGROUNDS: In recent decades, incorporating polypropylene (PP) within flame retardants has proved to be an effective method of improving the thermal stabilities of PP, but too much adversely affects the mechanical properties of this polymer materials. Herein we report a novel multifunctional flame retardant, (styrene acrylonitrile)–(titanate-modified ammonium polyphosphate) (SAN–TAPP), to simultaneously improve the mechanical properties and thermal stability of PP composites. METHODS: SAN–TAPP was synthesized by encapsulating SAN resins with functional titanate-modified APP (TAPP) and subsequently was incorporated into PP by a melt-blending process. The phase characteristics and morphology of SAN–TAPP were investigated, and the mechanical properties and thermal stability of different content of PP/SAN–TAPP composites were studied. RESULTS: The results showed that the TAPP was almost entirely wrapped in the SAN resins and PP/SAN–TAPP composites exhibited the sea-island morphology. For the mechanical properties, the impact strength of PP/SAN–TAPP composite was significantly improved, especially 15 wt% SAN–TAPP filled PP/SAN–TAPP composite exhibiting 2.17 times higher than that of pure PP. And the tensile strength and modulus also increased by addition of SAN–TAPP. For the thermal stabilities, melting temperatures (T(m)) and residual char yield were improved. Furthermore, the LOI value of PP/SAN–TAPP composites increased from 19.8 to 27.5%; The 15 and 20 wt% SAN–TAPP filled in PP/SAN–TAPP composites passed the V-2 test of UL-94, and exerted the similar effect on the flame retardancy to TAPP with the same loading. CONCLUSIONS: These results revealed that a novel PP/SAN–TAPP composites with synthetically enhancement on the mechanical properties, thermal stabilities and flame retardancy, suggesting a strong correlation between the phase structure, mechanical and thermal properties.