| Thermoplastic polyurethane(TPU)is a class of polymer materials with both plasticity and elasticity.It has been widely used in transportation equipment,aerospace,automotive parts,wires and cables.However,TPU is flammable with severe molten droplets and toxic dense smoke,so it is necessary to do flame retardant treatment to suppress smoke and molten droplets generation.In recent years,various flame retardants have been used to improve the flame retardancy of TPU.Among them,ammonium polyphosphate(APP)did well.However,the mechanical properties of TPU are severely lost with high addition of APP,so synergistic flame retardant was developed to used with APP together to control the whole amount of additives.Metal-organic framework materials(MOF)is a organic-inorganic hybrid molecules,it showed flame retardancy promotion and mechanical enhancement simultaneously in many polymers including epoxy resin,polystyrene and polylactic acid.In this paper,a cobalt-based MOF and two zeolitic imidazolate framework-67 derivatives are prepared by hydrothermal synthesis,after confirmation of their molecular compositon,they were used as synergistic flame retardant.By their help,the additive amount of APP was reduced but the flame retardancy was kept.The content is displayed as follows:(1)A cobalt-based metal organic framework(Co-MOF)was prepared by a two-step method,and Co-MOF was used to synergize the flame retardant TPU with APP.The results showed the TPU is flammable with a low LOI of 21.7%,and it cannot pass any UL-94 grade;at the present of 1.5wt.%Co-MOF/4.5wt.%APP,the LOI increased to 28.2%,TPU reached UL-94 V-0,indicating droplets werealmostly killed,and the heat release rate during combustion decreased from 1359kW/m2 to 257kW/m2.SEM show that Co-MOF acts as a compatibilizer between APP and TPU matrix,which improving the mechanical properties of TPU composites.(2)A zeolitic imidazolate framework-67@graphite oxide material(ZIF-67@GO)was prepared by deposition and autogrowth.Characterization documented self-loading of ZIF-67 onto the surface of stripped GO sheets.The combination of(6.5 wt%APP/0.5wt%ZIF-67@GO)help TPU reach UL-94 V-0 level,and the LOI of 27.4%;and the smoke release rate of TPU composites decreased from 0.113 m2/s to 0.058 m2/s,indicating half smoke release was suppressed.(3)Poly(cyclotriphosphazene-co-4,4’-dihydroxy diphenylsulfone)(PZS)was prepared by substitution reaction of 4,4’-dihydroxydiphenylsulfone(BPS)and hexachlorocyclotriphosphazene(HCCP),and it was coated on ZIF-67 to obtain PZS@ZIF-67.Similarly TPU/APP/PZS@ZIF-67 composites showed ameliorate flame retardancy.Tests showed that the composite reached UL-94 V-0 level and the LOI was as high as 30.1%with the adding PZS@ZIF-67 and APP at the mass ratio of 2:5.Both pHRR and pSPR of TPU composites decreased significantly,being 281KW/m2 and 5.4m2,respectively. |
