Study On Preparation And Flame-retardant Performance Of C-N-P Intumescent Fireproofing Materials

Fire is a significant hazard that threatens human lives and property safety.To minimize the damages caused by fires,new fire prevention methods,technologies,and materials are constantly being developed and applied.Among various fire-resistant materials,CNP-based fire-resistant materials have attracted considerable attention due to their remarkable fire performance,halogen-free and environmentally friendly nature,and easy installation.However,there is still room for improvement in terms of component stability,thermal insulation performance,and oxidation resistance Therefore,in this study,a novel intumescent fire retardant（IFR）and intumescent coating with the inorganic layered materials doping were prepared.A new method for calculating the relative thermal resistance of the intumescent char layer generated after the combustion of ultra-thin fire-resistant coatings was proposed,and the porosity of the intumescent char layer was determined.In addition,we conducted a comprehensive investigation on the thermal degradation performance,thermal insulation performance,and oxidation resistance of CNP-based intumescent fire-resistant materials.Based on the research findings,the following main works and conclusions can be summarized:（1）In this study,a CNP intumescent flame retardant IFR was prepared using ammonium polyphosphate,pentaerythritol,and melamine.This IFR combines the functions of acid source,carbon source,and gas source.Through solid-state nuclear magnetic resonance and X-ray photoelectron spectroscopy analysis,we investigate the gas-phase and condensed-phase flame retardant mechanisms of CNP IFR.The synthesized flame retardant was deposited on the surface of the fabric.The dual-action of gas-phase and condensed-phase of the IFR exhibited excellent flame-retardant effects on the fabric fibers.For the treated fabric,a char layer was formed on the surface of the straight fibers during combustion,altering the oxidation process of the fabric and reducing the heat release rate during fabric burning.（2）Ca Al CO₃-LDH was synthesized using the constant p H method,which involved salt solutions containing Ca（NO₃）₂·4H₂O and Al（NO₃）₃·9H₂O,as well as alkaline solutions containing Na₂CO₃ and Na OH.Ca Al CO₃-LDH and MMT were separately added as inorganic fillers to binders（amino resin and acrylic resin）containing CNP IFR,resulting in the preparation of a novel CNP-based nanocomposite fire-resistant coating doped with inorganic layered materials.The optimal doping amounts of the two inorganic layered materials in the CNP-based IFR coating were determined（e.g.,4.8 wt%Ca Al CO₃-LDH and 7.0 wt%MMT）.The use of an appropriate amount of inorganic filler can enhance smoke suppression,improve the mass of residual char,and create a porous honeycomb char layer,thereby enhancing the fireproof performance of the coatings.However,excessive addition amounts of inorganic layered materials（e.g.,7.0 wt%Ca Al CO₃-LDH and 9.1 wt%MMT）markedly inhibit the expansion of the fireproof coating and reduce the thermal insulation capabilities of the coating,although it increases the mass of the residual char layer.（3）A new method for calculating the relative thermal resistance of the intumescent char layer generated after the combustion of ultra-thin fire-resistant coatings was proposed.During steady-state heat transfer,a linear correlation was observed between the relative thermal resistance of the char layer and the surface temperature at the back of the coated steel plate.By utilizing a three-dimensional closed model encompassing the flame,steel plate,and wall,radiative heat exchange calculations were performed to determine the radiant heat flux in vertical burning experiments.By combining scanning electron microscopy（SEM）images with the digital image processing techniques,the porosity of the expandable char layer was calculated.It was found that the addition of Layered Double Hydroxide（LDH）improved the pore structure and internal morphology of the intumescent char layer,thereby enhancing its thermal insulation performance.（4）Through experimental results,characterization analysis,and density functional theory calculations,the synergistic effect between CNP intumescent flame-retardant materials and inorganic layered materials（such as Ca Al CO₃-LDH and MMT）was systematically investigated.It was found that amorphous carbon species of the intumescent char layer played a crucial role in the condensed-phase flame retardant mechanism.The research results demonstrate that the enhanced flame-retardant properties,particularly the oxidative resistance,depend on two fundamental factors:the chemical stability of metal-doped nitrogenated graphene（M-N-G）structure and the alteration of lattice curvature in the M-N-G structure,thereby affecting the morphology of the char layer.When excessive amounts of inorganic layered materials are doped,an excess of metallic elements is introduced,leading to an increased lattice curvature of the char layer,which inhibits its expansion and results in an excessively dense intumescent char layer.Consequently,the flame-retardant properties of the intumescent char layer are diminished.In summary,IFR coatings with an appropriate MMT doping exhibit the most promising char layer structure due to the significant Si doping of MMT,which enhances the thermal stability and porous morphology of the char layer.