Fabricating A Wetting-partial Wetting Structure For High-efficiency Flame Retardancy And Toughness Of Polyolefins

Polyolefin is widely used in many fields because of its unique physical and chemical properties,easy processing and good mechanical properties.However,polyolefin is very easy to burn,which causes serious security risks.Although IFR can improve the flame retardancy of polyolefin,it has the disadvantage of low flame retardancy and poor compatibility with matrix,which leads to the decrease of toughness.In this paper,the wetting-partial wetting structure was constructed in IFR flame-retardant polyolefin blends by steps melting process to realize its high-efficiency flame retardancy and toughness in polyolefin.In the first step,IFR was melt-blended with polyolefin and nylon 6（PA6）to construct the wetting structure of PA6 coated IFR distributed on polyolefin matrix;in the second step,after the anhydrated elastomer melt-blend with the blends prepared in the first step,molding was carried out near the melting temperature of PA6,and the wetting-partial wetting structure was prepared.The wetting-partial wetting structure is spherical elastomer distributed on PA6 surface.For the polyethylene（PE）matrix（High Density Polyethylene:HDPE,Linear Low Density Polyethylene:LLDPE）,Scanning Electron Microscope（SEM）results showed that PA6 can spontaneously wet and coat IFR to form core-shell structure;Infrared Spectrum（FTIR）,Dynamic Mechanical Analysis（DMA）,Differential Scanning Calorimeter（DSC）and SEM test results displayed that LLDPE-g-MAH and HDPE/PA6/IFR melt-blended at slightly lower melting temperature than T_{m PA6},LLDPE-g-MAH can form partial wetting structure on the surface of PA6,and partial wetting structure can significantly improve the interface adhesion between PA6 and matrix.The results demonstrated that the impact strength and elongation at break of flame-retardant polyethylene can be increased by 270%and43%,respectively,when the content of LLDPE-g-MAH was 2wt%.Through the analysis of the impact fracture morphology,it was found that the toughening mechanism was the result of the combined action of matrix shear yield and PA6 shell failure.The flame retardancy of LLDPE was significantly improved by coating IFR with PA6 and forming wetting structure.Compared with the system without wetting structure,the oxygen index（LOI）and vertical combustion grade（UL-94）of LLDPE were increased from 24.0%,NG to 30.0%,V-0,respectively.The wetting structure significantly improved the water resistance of flame-retardant polyethylene,simultaneously.For polypropylene（PP）matrix,organic montmorillonite（OMMT）was used to cooperate with IFR,and PA6 coated IFR was constructed by step-by-step processing.Spherical maleic anhydride grafted polyethylene octene elastomer（POE-g-MAH）distributed on PA6 surface fabricating wetting-partial wetting structure,and OMMT distributed on PA6 phase and PP phase were regulated,respectively.The flame retardancy and mechanical properties of blends were studied.The results indicated that the IFR coated with PA6 can significantly improve the flame retardancy of the blends,compared with the blend system without PA6,and its oxygen index（LOI）and vertical combustion grade（UL-94）increased from 26.3%,NG to 31.4%,V-0,respectively.The distribution of OMMT and the wetting structure of POE-g-MAH had no obvious effect on the flame retardancy.The toughness of the blends was significantly improved when OMMT was distributed in PP phase and the content of POE-g-MAH was 9%.Compared with the systems without partial wetting structure,the impact strength and elongation at break of the systems were increased by 467.2%,723.3%,respectively.The toughening mechanism was the result of the shear yield of PP matrix and the failure of PA6 shell.