Constrution Of Halloysite Nanotube-based Composite Flame Retardants And Their Flame Retardant Properties

Halloysite is a natural mineral with a unique tubular nanostructure,which can be used for the fortifier,flexibilizer and flame retardant of the polymer materials.However,halloysite nanotubes?HNT?have poor flame retardant efficiency and need a high loading due to its single flame retardant mechanism when it is used as a flame retardant for polymer materials.In response to these problems,we used HNT as a carrier and introduced a polymer carbon-forming agent and a metal oxide carbonizing agent on its surface,to construct two new types of HNT composite flame retardants,using synergistic strategies to improve the fire retardancy of HNT.First,under acidic conditions,the surface of HNT was functionalized by electrostatic adsorption of chitosan?CS?to obtain a new type of composite flame retardant HNT@CS,which help HNT increase charring and improve the stability of the char residue.Next,the HNT@CS@Fe₃O₄ nanocomposite flame retardant was prepared using synthesized ferroferric oxide?Fe₃O₄?with excellent catalytic carbonization properties to modify on the outer surface of HNT@CS,which can improve the flame retardancy and thermal stability of epoxy resin?EP?.However,EP is endowed with good flame retardancy under a high loaing--10 wt.% of HNT@CS@Fe₃O₄.In order to reduce the amount of the flame retardant,we synthesized ultra-fine metal compounds with smaller particle sizes using the coordination of CS and metal ions.The HNT@CSZFMOH is prepared by the active functional groups of CS?-OH and –NH2?which use coordination bonds to interact with metal ions?Fe?III?and Zn?II??on the surface of HNT.And using stearic acid to modify the HNT@CSZFMOH,a new type of fluorine-free multifunctional hydrophobic flame retardant was prepared.Superhydrophobic HNT@CSZFMOH flame retardant can effectively improve the flame retardancy and hydrophobic properties of EP polymer with the addition of 10 wt.%.The main research contents and results are as follows:1.Preparation and characterization of HNT@CS@Fe₃O₄ composite flame retardant and its fire retardancy in EP.HNT@CS@Fe₃O₄ composite flame retardant is prepared by precipitation method,and its structure is characterized by Fourier transform infrared spectroscopy?FT-IR?,X-ray powder diffractometer?XRD?,and Transmission electron microscope?TEM?and Field emission electron microscope?SEM?are used to characterize its morphology.Subsequently,the thermal stability,flame retardancy and mechanical properties of HNT@CS@Fe₃O₄ are evaluated in EP polymers.The results are as follows: FI-TR and XRD results show that the HNT@CS@Fe₃O₄ composite flame retardant is composed of HNT,CS and Fe₃O₄ three-phase.TEM and SEM tests show that the Fe₃O₄ nanoparticles and CS are uniformly modified on the skeleton of HNT.Limiting oxygen index?LOI?and cone calorimeter tests show that adding 10 wt.% of HNT@CS@Fe₃O₄ can increase the LOI of EP to 31.3%,reaching a flame retardant level;the peak heat release rate?PHRR?,CO peak output?PCOP?and peak smoke production rate?PSPR?of EP are reduced by 32%,44% and 33%,respectively.Thermal analysis results show that the thermal initial degradation temperature of EP/HNT@CS@Fe₃O₄ composites is ahead by 24 °C compared with pure EP polymers,and the residual carbon content is increased by 6.2 wt.%.This is because that the HNT@CS@Fe₃O₄ promotes the decomposition of EP at an early stage and enhances the carbonization behavior to form more protective carbon layers.The results of dynamic thermomechanical analysis?DMA?show that HNT@CS@Fe₃O₄ improves the storage modulus of EP without damaging the tensile strength.Through the digital photo,SEM and Raman spectrum analysis,the improvement of EP fire retardance is based on the condensed phase mechanism of HNT@CS@Fe₃O₄ nanocomposite flame retardant.Under the synergistic effect of HNT,CS and Fe₃O₄ three-phase,the residual carbon is anchored to the HNT framework in the combustion process,enhancing the stability of the HNT carbon framework,and forming a continuous,dense and highly graphitized residual carbon.In addition,the metal residues in the residual carbon enhance the strength of the residual carbon and the resistance of the carbon layer to heat and gas,thereby reducing the release of heat and toxic fumes.2.Preparation and characterization of HNT@CSZFMOH multifunctional nanocomposite and its flame retardant and superhydrophobic properties in EP.The HNT@CSZFMOH nanocomposite flame retardant is prepared by the coordination effect of HNT@CS and metal ions?Fe?III?and Zn?II??.Then,using stearic acid to modify HNT@CSZFMOH nanocomposite flame retardant,a kind of superhydrophobic HNT@CSZFMOH composite flame retardant is synthesized.XRD and TEM analysis showed that HNT@CSZFMOH nanocomposite material has a tubular structure,and the coordination of CS with Fe3+ and Zn2+ results in more uniform growth of ultrafine Zn OOH and Fe OOH nanoparticles.X-ray photoelectron spectroscopy experiment shows the stearic acid modified HNT@CSZFMOH nanocomposite flame retardant.Subsequently,the flame retardant performance and hydrophobic capacity of EP/HNT@CSZFMOH are investigated.The results show that the addition of 3 wt.% superhydrophobic HNT@CSZFMOH nanocomposite flame retardant can reduce the PHRR,PCOP,and PSPR of EP by 31%,22%,and 22%,respectively.At the same time,the LOI value of EP is 28.0%,reaching a flame retardant level.The SEM analysis of the EP/HNT@CSZFMOH composite residual carbon shows that the superhydrophobic HNT@CSZFMOH nanocomposite flame retardant is well dispersed,and effectively suppresses the "candle wick effect" caused by the addition of HNT alone.The possible flame retardant mechanism are as follows.The Zn OOH and Fe OOH in the superhydrophobic HNT@CSZFMOH nanocomposite flame retardant promote EP to produce more carbon atom compounds,further promoting its catalytic carbonization behavior.On the other hand,the residual carbon covering the HNT skeleton with a high degree of graphitization leads to the interconnection of the HNT and the adjacent HNT composite.The dense physical barrier layer can enhance the shielding effect,reduce the formation of the smoke and oxygen side the polymer.At the same time,the superhydrophobic HNT@CSZFMOH nanocomposite flame retardant can convert the EP polymer to superhydrophobic,increasing the water contact angle to 162 °.In addition,the EP composite material also has self-cleaning,corrosion resistance and ultraviolet resistance.SEM shows that the EP/HNT@CSZFMOH composite material has a micro/nano hierarchical structure,which can form an air cushion layer or a hydration layer in the structure gap and provides the necessary conditions for achieving superhydrophobic performance.