Computer simulation study on the compatibility of cyclotriphosphazene containing aminopropylsilicone functional group in flame retarded polypropylene/ammonium polyphosphate composites

The compatibilization of cyclotriphosphazene N3P3[NH(CH2)3Si(OCH2CH3)3]6 (APESP) in flame retarded polypropylene (PP)/ammonium polyphosphate (APP) composites was investigated by atomistic and mesoscale simulations. Molecular dynamics (MD) and dissipative particle dynamics (DPD) simulation method were used to study the binding energy (Ebinding), radius distribution function, hydrogen bond, Flory–Huggins parameter (χ) and mesoscopic morphology of the composites. It was found that the compatibility of APP in PP matrix significantly got better due to the loading of the cyclotriphosphazene derivative APESP, compared with the loading of γ-aminopropyltriethoxysilane (APES) or hexachlorocyclotriphosphazene. The Ebinding value of APP and PP increased to 161.45 kJ/mol in PP/APP/APESP, in contrast to 2.82 kJ/mol in PP/APP. Furthermore, the last frame of MD profiles indicated the presence of strong hydrogen bond between APP and APESP molecules. The DPD data showed that APESP made the dispersion and distribution of APP in PP matrix more homogeneous because of improved interfacial interaction. To verify the simulation results, the PP/APP, PP/APP/APES and PP/APP/APESP composites were prepared to analyze mechanical properties, morphologies and flame retardancy. Elongation at break of PP/APESP/APP was 334.79%, nearly four times as much as that of PP/APP. Scanning Electron Microscope (SEM) microphotographs indicated that the dispersion of APP in PP matrix was improved because of the loading of APESP. At the same time, LOI value of the composites with APESP levelled up from 21.7% to 26.5%, and UL 94 rating reached to V-2. The above experimental data demonstrated that the simulation strategy in this investigation is an effective path for molecular design and performance prediction of the flame retarded systems.