Layer-by-Layer Assembled Brucite Flame Retardant And Its Applications In Ethylene-Vinyl Acetate Resin

Nowdays,the flame retardancy of polymers without halogen has received the widespread attention.Metal hydroxides comprise the most important segment in the market of halogen-free flame retardants.However,it requires a high loading to achieve the desired flame retardant efficiency,which would reduce the mechanical and processing properities of polymer composites,and this limits the applications.Brucite is a unique natural mineral containing more than 95 wt%of magnesium hydroxide.Brucite is a scarce resource,only a few countries have recoverable reserves,China is one of them.The application of brucite is simple and the added value of brucite production is very low,which waste the resource.The layer-by-layer?LbL?assembly has been develop as a simple,versatile and environmentally friendly method for the molecularly-controlled fabrication of surface-confined nanostructured mutifountional materials.But its application research in the field of flame retardant has many limitations.In allusion to these problems,some green efficient brucite flame retardant?M-FR?was fabricated via the LbL method,which had high flame retardant efficiency and smoke suppression efficiency.The flame retardant,smoke suppression mechanism and toughening mechanism had been studied.Besides,the graphitization of alginate in polymer had been research for the first time,which had supplied a new method for preparing metal nanoparticles/C composites and hollow graphene sphere.This work had completed the following parts:?1?The new brucite flame retardants?M-FR?had been fabricated via the LbL assembly method with brucite,silane coupling?APTES?,sodium alginate,and soluble metal salts.The morphology,structure,composition,thermal stability of M-FR and the driving forces had been studied.The driving forces were the dehydration condensation reaction between the hydroxyl and silicon hydroxyl;the hydrogen bonding,electrostatic interaction between APTES and alginate;the chelating reaction between metal cations and the carboxylic acid,hydroxyl groups in sodium alginate.The results obtained from scanning electron microscope?SEM?,transmission electron microscope?TEM?and laser diffraction apparatus had shown that M-FR surfaces were more smooth and the lamellar structures had been covered by flocculent alginate gel;the particle size d?90?was18.54-21.30?m.X-ray diffraction?XRD?tests showed that the assembly did not change the crystal structure of the brucite.The chemical composition,alginate and APTES contents of M-FR had been characterized by XPS and inductively coupled plasma mass spectrometry?ICP-MS?.The thermo-gravimetric analysis?TGA?tests had shown that among three M-FR,only Cu-FR reduced the residual carbon and changed the first stage of thermal degradation.?2?After adding in EVA28 resin,the combustion performance,thermal degradation behavior of the EVA composites and the flame retardant,smoke suppression mechanism of M-FR were studied.The LOI,UL 94 and cone calorimeter?CONE?tests displayed Ni-FR had a better flame retardant and smoke suppression efficiency,followed by Cu-FR and Zn-FR.When the loading was 130phr,the LOI of EVA28+Ni-FR was 32.4%and UL 94vertical burning test could obtain V-0,the peak heat release rate?PHRR?,smoke release rate?SPR?and total smoke release?TSP?of EVA28+Ni-FR were 152.5 kW/m²,0.013 m²/s and 1.92 m²/kg,respectively,compared with EVA28+B-A,PHRR,SPR and TSP decreased by 41.5%,66.7%and 71.0%,respectively.TGA,FTIR,TGA,FTIR,SEM and TEM were used to studied the thermal degradation behavior and flame retardant,smoke suppression mechanism of M-FR.TGA tests displayed that alginate can improve the initial decomposition temperature of the EVA28+M-FR.FTIR tests indicated that the peaks of-C-H and R-CH=CH-R groups still existed in EVA28+M-FR composites under 535 ^oC.TGA-FTIR tests showed that Nia and Cua could decrease the release of H₂O,CH₃COOH and aromatic compounds in the pyrolysis of EVA28,Zna increased the release of CO₂.Compared with EVA28+B-A,EVA28+Ni-FR and EVA28+Cu-FR char looked like sponge or bubble and cotained few holes and no cracks,which indicated the residual char layers were more protectable and effective.The metal Ni and Cu could catalyze the pyrolysis intermediate of EVA28 into more stable aromatic compounds and graphite.And these species could bind MgO together and form more protectable char layer with better thermal stability.?3?The mechanical properties,rheological properties of EVA composites,the disperation and toughening mechanism of M-FR had been studied.M-FR could improve the elongation at break of EVA composites.when the loading was 130phr,compared with EVA+130B-A,the elongation at break of EVA+130Ni-FR was 252.09%,increased by131.02%.SEM tests showed that the fracture surface of EVA composites was smooth,after etched by acid,there were many closed and semi-closed holes,which indicated M-FR dispersed evenly and had a good compatibility with substrate.Torque rheometer and capillary rheometer tests showed that Ni-FR didn't deteriorate processability and rheological properties of EVA composite.The balance torque of EVA28+Ni-FR was lower than EVA28+B-A;when the shear rate was higher than 0.2 s^-1,their shear viscosity showed little difference.The toughening mechanism of M-FR was summarized as follow:in the processing of EVA composites,nickel alginate and EVA molecular chains formed some interpenetrating network?IPN?strucitures on the Ni-FR surface.During tensile test,two network beared stretch at the same time,the brittle alginate network will break first and absorb large energy,the flexible EVA network had much hidden conformation and could continue to bear larger stretch and deformation.?4?Three kinds of EVA28+alginates composites had been prepared and their residual char had obtained from tube furnace at different temperature.The composition,morphology and the catalytic grahitization mechanism of alginate were studied.XPS results showed there were five kinds of C bond states:C,H and C-C/graphite,C-O,O-C=O,metal-C?Ni,Cu?.XRD tests showed EVA+Nia and EVA+Cua residual char comprosed of amorphous carbon,graphite and metal?Ni,Cu?,as for EVA+Zna residual char,only amorphous carbon and zinc oxide?ZnO?could be found.TEM tests showed the Ni nanoparticles in residual char were irregular,the particle size was less than 50 nm and there were many graphene layers on Ni surfaces.Cu nanoparticles were spherical and their diameter were 35-40 nm,only 1-2 grahene layer could been found on the Cu surfaces.ZnO particles were irregular and had a broad particle size distribution?<500 nm?,there were no graphene layer on ZnO.The catalytic graphitization mechanism was summarized as follow:The Ni₂O₃ and CuO nanoparticles producing from alginates could be reduced into metal Ni and Cu by CO,hydrocarbons and aromatic compounds,which were the pyrolysis productions of EVA28resin.For the unique atomic structures,Ni and Cu nanoparticles could catalyze these productions into graphene.The catalytic graphitization had been confirmed with EVA18resin.For instance,compared with EVA18+130B-A,the PHRR,SPR and TSP were reduced by 48.0%,61.2%and 75.7%,respectively.