Preparation And Flame-retardant Properties Of Polypropylene Nanocomposites

In this paper,ZnO and MoO₃ nanowires(NWs)were prepared by hydrothermal method,and they were added into polypropylene resin(PP)by melt blending method to prepare ZnO NWs/PP composites and ZnO/MoO₃/PP composites,respectively.ZnO/MoO₃/ATH/PP composites were successfully prepared by compounding ZnO/MoO₃ NWs and nano-aluminum hydroxide(ATH)into PP.The effects of ZnO NWs,ZnO/MoO₃NWs and ZnO/MoO₃/ATH on the flame retardancy and mechanical properties of PP composites were studied.The morphology and structure of ZnO NWs and MoO₃ NWs were characterized by scanning electron microscopy(SEM)and X-ray diffraction(XRD).The thermal stability,flame retardancy and smoke suppression properties of ZnO NWs/PP,ZnO/MoO₃/PP and ZnO/MoO₃/ATH/PP composites were tested and analyzed by thermogravimetric analysis(TGA),limiting oxygen index testing(LOI),microcalorimeter(MCC),smoke density tester and cone calorimeter testing(CCT).The flame-retardant mechanism of the composites was analyzed by the thermal degradation kinetics study of the composites.The mechanical properties of the composites were tested by tensile testing and cantilever beam impact testing.The results showed that with the addition of ZnO NWs,the initial decomposition temperature(T_5%),maximum weight loss temperature(T_max),residual weight at 700?and LOI of ZnO NWs/PP composites were increased,while the peak heat release rate(PHRR)and total heat release(THR)of composites were decreased.The maximum smoke density(MSD)and smoke density rate(SDR)of composites were also decreased,which indicated that ZnO NWs improved the thermal stability and flame retardancy of the composites and reduced the smoke release of the composites.With the 30 wt%addition of ZnO NWs,T_5%and T_max of nanocomposite were increased by34.6?and 20.8?compared to pure PP.PHRR and THR of nanocomposite were decreased by 36.0%and 37.8%in comparison to pure PP.Moreover,MSD of nanocomposite was reduced by 53.9%compared to pure PP.The activation energy(E_a)of the composites was increased with the addition of ZnO NWs.Mechanical properties testing results revealed that the tensile strength,elongation at break and impact strength of the composites are larger than those of pure PP when the mass fraction of ZnO NWs is less than or equal to 30%.For ZnO/MoO₃/PP composites,T_5%,T_max and residual weight of the composites were increased,while PHRR,THR,smoke release rate(SPR)and total smoke release(TSR)of composites were decreased.When15 wt%ZnO NWs and 25 wt%MoO₃ NWs were added into PP,T_5%and T_max of ZnO/MoO₃/PP composite were increased by 22.4%and 8.1%compared with pure PP,respectively.The LOI value of composite was 24.8%.Compared with pure PP,PHRR and THR of the composite were reduced by 56.9%and 23.7%,respectively.And SPR and TSR of composite were reduced by 0.02 m²/s and 3.3 m²,respectively.Thermal degradation kinetics research found that the addition of ZnO/MoO₃ NWs could increase E_a of the composites,thereby enhancing the difficulty of thermal degradation of the composite.The mechanical properties testing results showed that the tensile strength and elongation at break of nanocomposites were larger than that of pure PP when the mass fraction of ZnO/MoO₃ NWs was less than or equal to 20%,indicating that ZnO/MoO₃ NWs could improve the strength and toughness of PP.When ZnO/MoO₃ NWs and ATH were compounded to PP,the flame retardancy of ZnO/MoO₃/ATH/PP composites was better than that of ZnO/MoO₃/PP and ATH/PP composites.When the content of ZnO NWs is 3.75 wt%,the content of MoO₃ NWs is3.25 wt%,and the content of nano ATH is 21 wt%,LOI value of the composite reached 25.3%,and the residual weight of ZnO/MoO₃/ATH/PP composite is 24.6%.PHRR of the composite decreased by 570.4 k W/m² and THR reduced by 34.1 MJ/m²compared with pure PP.The char layer after combustion in the compounding system was flat and compact.The comprehensive analysis showed that ZnO NWs and ZnO/MoO₃ NWs could significantly improve the thermal stability,flame retardancy and smoke suppression performance of PP.After compounding ZnO/MoO₃ NWs with nano-ATH,it has synergistic flame-retardant effect.