Preparation Of Graphitic Carbon Nitride Hybrid Phosphide Flame Retardant And Its Flame Retardant Application In Epoxy Resin

As one of the three major thermosetting resins,epoxy resin?EP?is widely used in semiconductor devices,automotive industry,engineering,sports goods and other fields that are closely related to people's life,due to its excellent electrical insulation,mechanical properties,and chemical corrosion resistance properties.EP is composed of C,O and H elements,and its essence is easy to burn.Moreover,EP releases a lot of heat,smoke and harmful substances in the combustion,which not only limits the application of EP,but also causes great threat to the environment,life and health.Therefore,to improve the fire resistance of EP has become the focus of scientific researchers.Studies have found that:flame retardant could improve the flame retardancy of EP effectively and the flame retardant mechanism mainly includes gas phase,condensed phase,free radical quenching and interrupted heat exchange mechanism.In this paper,combined with the synergistic effect of various flame retardant mechanisms to prepare graphitic carbon nitride?g-C₃N₄?,core-shell g-C₃N₄/zinc phytate hybrid materials?g-C₃N₄/PAZn?and silkworm like g-C₃N₄/hydrated nickel ammonium phosphate hybrid materials?g-C₃N₄/NiNH₄PO₄·H₂O?were applied to EP.The flame retardancy and smoke suppression of EP composites were studied by limit oxygen index?LOI?and cone calorimeter test?CCT?.The mechanisms of flame retardants were studied.At the same time,the influence of flame retardant on the mechanical properties of EP composite was explored by tensile test and pendulum impact test.The research content is as follows:The first part:the synthesis of g-C₃N₄ and its flame retardant properties in EP.In this chapter,g-C₃N₄ was prepared using melamine by calcination.The morphology,chemical structure and thermal stability of g-C₃N₄ were characterized by scanning electron microscopy?SEM?,transmission electron microscopy?TEM?,atomic force microscope,X-ray diffraction?XRD?,Fourier infrared spectrometer?FT-IR?and thermogravimetric analyzer?TGA?.The results showed that g-C₃N₄ is a two-dimensional nanosheet with an average thickness of 9.7 nm containing-NH₂ and-NH functional groups on the surface which can exert physical isolation of the two-dimensional sheet during the flame retardant EP effect.The flame retardancy and mechanical properties of EP composites with different content of g-C₃N₄ were characterized by LOI,tensile test and pendulum impact test.The results showed that when the content of g-C₃N₄ is 5 wt%,the EP composites reached nonflammable level with LOI of 27.4%,and g-C₃N₄ with 5 wt%had almost no effect on the mechanical properties of EP.The second part:synthesis of core-shell g-C₃N₄/PAZn and its flame retardant properties in EP.In this chapter,with the aid of the-NH₂ on the surface of g-C₃N₄ which can react with-OH of phytic acid?PA?and the chelation effect of PA,core-shell g-C₃N₄/PAZn hybrid material was prepared.The morphology,chemical structure and thermal stability of g-C₃N₄/PAZn were characterized by SEM,elemental analysis,TEM,XRD,FT-IR and TGA.The results showed that there was an obvious cladding layer containing C,N,O,P and Zn elements on the surface of g-C₃N₄.Meanwhile,new chemical bond was formed between g-C₃N₄ and PAZn and the residual char?R-mass?of g-C₃N₄/PAZn was significantly improved at 800^oC.g-C₃N₄/PAZn hybrid materials was applied into EP to study the flame retardant property.The results showed that core-shell g-C₃N₄/PAZn hybrid material had excellent flame retardancy and smoke suppression properties.The LOI is 28.3%reaching the flame-retardant level.Compared with pure EP,the peak heat release rate?PHRR?and the peak smoke release rate?PSPR?of g-C₃N₄/PAZn-EP decreased by 71.4%and 25.0%.And the fire growth index of g-C₃N₄/PAZn-EP was decreased.The flame retardant mechanism was further discussed by TGA,SEM and Raman spectroscopy analysis of char residue.In the third part:synthesis of silkworm like g-C₃N₄/NiNH₄PO₄·H₂O and its flame retardant properties in EP.In this chapter,NiNH₄PO₄·H₂O with different morphologies?nanowires,nanofilaments,micro flowers?were prepared by mix solvothermal method with changing the apparent tension of water in solution,and the silkworm like g-C₃N₄/NiNH₄PO₄·H₂O hybrid material was synthesized by hybridization of NiNH₄PO₄·H₂O nanowires with g-C₃N₄.The morphology,crystalline structure and thermal stability of g-C₃N₄/NiNH₄PO₄·H₂O hybrid material were characterized by SEM,XRD and TGA.The results showed that g-C₃N₄/NiNH₄PO₄·H₂O hybrid material is silkworm like structure with g-C₃N₄ as core coated with NiNH₄PO₄·H₂O nanowires,and its decomposition temperature could well match the decomposition temperature of EP.When it was applied into EP,g-C₃N₄/NiNH₄PO₄·H₂O-EP had excellent flame retardant.The LOI level reach the flame-retardant level.Compared with pure EP,the PHRR and PSPR of g-C₃N₄/NiNH₄PO₄·H₂O-EP decreased by 70.4%and 35.4%,respectively resulting from the synergistic flame retardant effect between g-C₃N₄ and NiNH₄PO₄·H₂O.The flame retardancy mechanism was studied by TGA,SEM of char residue and TGA-FT-IR.The results showed that g-C₃N₄/NiNH₄PO₄·H₂O could release nonflammable gases such as N₂ and NH₃,and promote EP to form stable and dense char layer,improving the flame retardant performance of EP.