Construction And Properties Of Boron Nitride And Reduced Graphene Oxide Fire-retardant Coatings On Polyurethane Foams

Flexible polyurethane foam(FPUF)has been widely used as a material for sound insulation,shockproof,heat insulation due to its good resilience,sound absorption and thermal insulation properties.However,FPUF is mostly open-celled with low density,large surface area and high flammability.It is very necessary to impart flame retardancy to FPUF before using it.The layer-by-layer assembly is a simple and versatile method for constructing functional coatings on various substrates.Compared with flame-retardant additives and chemical reaction-type flame-retardant technologies,the greatest advantage of this method is that it will hardly damage the mechanical properties of the substrate,and has broad application prospects.Therefore,in this paper,the hexagonal boron nitride and reduced graphene oxide nanosheets with excellent barrier effects were deposited on FPUF to construct a fireproof coating by layer-by-layer assembly method.The effects of assembly conditions on the coating microstructure as well as the coating microstructure on the flame-retardant properties were studied.The main research contents and conclusions are summarized as follows:1、Construction and flame-retardant performance of boron nitride composite coatings on flexible polyurethane foamsThe chemical exfoliation method is used to prepare h-BN nanosheets and then the h-BN nanosheets/sodium alginate and polyethyleneimine are deposited on the surfaces of Quartz slice and FPUF,respectively.Fourier transform infrared spectrometer(FTIR),X-ray powder diffractometer(XRD)and Field emission scanning electron microscope(SEM)test results show that the structure and composition of the coatings can be regulated by adjusting the number of assembled layers and the concentration of h-BN nanosheets.With the increase of h-BN nanosheets concentration,h-BN nanosheets assembled on the surface of FPUF continuously increase,which can form a dense protective layer.The maximum assembly concentration of h-BN nanosheets is 5 mg/mL and the coating increment of the corresponding sample(FPUF-5mg,10 layers)is up to 14.4%,which has the highest coating increment compared with other samples.Thermogravimetry and cone calorimetry tests show that the flame-retardant performance of FPUF-5mg sample is optimal,which not only can improve the thermal stability of the sample at high temperature and increase the amount of carbon residue(from 8.5% to 15.6%),but also reduce the peak release of heat and CO by 50.1% and 53.8%,respectively,with delaying and suppressing the secondary peak release of heat and CO.The flame-retardant mechanism of h-BN coating may be due to the fact that as the concentration of h-BN nanosheets increase,the relative content of non-flammable inorganic components in the coating increase,and the highly heat-stable h-BN nanosheets can form a continuous protective layer on the FPUF,which effectively blocks the transfer of heat,oxygen,and volatile combustible gases between the gas phase and the solidified phase and therefore delaying and hindering the combustion of the matrix foams.2、Construction and flame-retardant performance of reduced graphene oxide composite coatings on flexible polyurethane foamsAlthough h-BN coatings can improve the flame retardancy of FPUFs,those coatings promote the increase of smoke emission from FPUF.In this chapter,reduced graphene oxide(rGO)that has a large layer structure and good smoke suppression effect is selected as an alternative to h-BN nanosheets in order to reduce the amount of smoke release during the combustion of FPUF.Firstly,polydopamine-coated rGO(PDA-rGO)is prepared by the self-polymerization of dopamine hydrochloride in a weakly alkaline environment.TEM and SEM results demonstrate that polydopamine is uniformly encapsulated on the surface of rGO.Results of FTIR,Laser Raman microspectroscopy,X-ray photoelectron spectroscopy,and thermogravimetry indicate that some of the oxygen-containing functional groups on the surface of GO are removed after encapsulated by polydopamine,indicating that GO is partially reduced and result in an increase in thermal stability.Subsequently,it was found that the pH and concentration of PDA-rGO suspension are important parameters for the growth of coatings.PDA-rGO suspension has a pH of 3 and a concentration of 4 mg/mL is the best assembly condition for the growth of coating by the SEM images and coating increment data.Cone calorimetry test indicated that PDA-rGO coating is a highly effective fire-retardant coating under the optimal conditions of assembly.The sample with only three layers of PDA-rGO coating(15.1% coating increment)can effectively reduce the peak heat release rate of FPUF(reduced by 49.3%),total smoke release(reduced by 33.5%)and the peak of release for the production of toxic gas CO(reduced by 46.2%),suggesting that the PDA-rGO coating has better flame retardant effect than h-BN coating.The reason that PDA-rGO coating can possess such excellent flame retardant properties may be due to the following reasons: the large layer structure of rGO is very favorable for forming a protective layer on the surface of FPUF;GO is reduced by the polydopamine,which not only increase the thickness of the sheet but also enhance the thermal stability of the sheet;the carbon skeleton of PDA-rGO with good thermal stability can act as a carbon-forming template to promote the formation of a stable protective carbon layer on the surface of the FPUF during the combustion process,effectively protecting the bottom undegraded polymer.