Design And Study On The Flame-Retardant Rigid Polyurethane Foam With Mxene-Based Nanocomposite Coatings

Rigid polyurethane foam(RPUF)is a kind of thermal insulation material with excellent comprehensive performance,but its flammable and toxic smoke release characteristics have brought great fire risks.Its porous foam structure makes it difficult for traditional halogen-free flame-retardant methods to achieve high-efficiency flame retardancy,and it will also adversely affect its excellent inherent properties.Therefore,based on the fire protection requirements of RPUF,this paper designs and prepares a variety of flame-retardant coatings to enhance the flame-retardant performance of RPUF.It is intended to build a RPUF system(Coated RPUF)with highly effective flame retardancy,smoke suppression and toxicity reduction,green environmental protection and excellent comprehensive performance.Study on the internal relationship between the composition and structure of the flame-retardant coating and the performance of Coated RPUF,optimize the design of the flame-retardant coating and reveal its performance improvement mechanism.The main research work is as follows:(1)Based on the intumescent flame retardant(IFR)system,a halogen-free phosphorus-nitrogen flame-retardant monomer was synthesized,and an UV-curable IFR coating was prepared and then coated on the surface of RPUF to obtain a Coated RPUF composite material.The comprehensive combustion tests show that Coated RPUF with 25 ?m-thick IFR coating has high flame retardancy and exhibit rapid self-extinguishing behavior.The study found that the IFR coating has a high char-forming ability,and a dense expanded char layer can be quickly formed on the surface of the RPUF during combustion.The expanded char layer has a high thermal oxidation resistance and can play a critical role in slowing the heat and oxygen insulation.In addition,compared to pure RPUF,the compressed performance of Coated RPUF has been improved,and the thermal insulation performance can be maintained.(2)Considering the “negative effect” in large amounts of heat and toxic fumes released when the IFR coating burns,we have introduced modified MXene and prepared nanocomposite IFR coatings(IFR/MXene).When the amount of MXene added is 1.0%,the self-extinguishing time of Coated RPUF becomes shorter,while the heat release and smoke production decrease significantly.The study found that MXene accumulated on the surface during the combustion process to form a jammed network,which strengthened the expanded char layer.MXene also played the role of “barrier effect” and “catalytic effect”,effectively reducing the “negative effect” of IFR coating,showing better flame-retardant and smoke-suppression performance.(3)Based on the environmentally friendly design concept and the problem that the IFR coating is easily ignited,we proposed the MXene-based hydrogel coating to prepare the flame-retardant RPUF.The introduction of polyacrylamide(PAAm)and polydopamine(PDA)to prepare PAAm-MXene-PDA hydrogel coating.The study found that the ignition time of Coated RPUF increased from 5 s to 30 s,which will greatly delay the flames spread.The hydrogel coating can effectively absorb heat through water evaporation.At the same time,the PDA shows good free radical scavenging ability and char formation performance.The multiple flame-retardant mechanisms make the Coated RPUF exhibits excellent flame retardancy and smoke-suppression properties.Besides,the excellent mechanical properties and adhesion of the composite hydrogel coating make Coated RPUF resist external damage better.