The Construction And Mechanism Study Of Flame Retardancy And Smoke Suppression For Flexible Polyurethane Foam

Flexible polyurethane foam（FPUF）,as a high resilience flexible material,is widely used in furniture,decorations,and other fields.However,due to its unique open cell porous structure and chemical composition,it is easy to burn and burn rapidly,which is more difficult to fire retardant than closed cell rigid polyurethane foam;In addition,the presence of isocyanate groups in FPUF leads to the production of a large amount of toxic smoke during combustion,posing a serious threat to people’s lives and health.Improving the flame retardancy and smoke suppression of FPUF is still industry focus and difficulty.The flame retardant methods of FPUF are divided into two categories:surface coating and addition of flame retardants.The former mainly adopts layer by layer self-assembly method,which shows some problems such as long period,poor durability,and solution pollution;The latter for flame retardants shows problems such as easy migration,large addition amount,and significant reduction in the inherent performance of FPUF.This research focuses on the flammability and smoke toxicity of FPUF,attempting to solve the current problems of surface coating treatment and flame retardant addition.Durable flame retardant and smoke suppression coatings were constructed on the surface of FPUF using different treatment methods（Chapters 2-4）,and hyperbranched flame retardants were designed and added to FPUF to achieve long-lasting and efficient flame retardant and smoke suppression（Chapters 5,6）;From the perspectives of the diversity of char layer structure and the formation of carbon precursor,the essence of heat transfer and smoke release was analyzed,and the flame retardant and smoke suppression mechanisms of various coatings in FPUF were deeply explored;Based on different branching units,the influence of flame retardants with different structures on the flame retardancy and smoke suppression effect of FPUF was investigated.The structure-activity relationship between the molecular structure of different added flame retardants and their effects was established,and simulation analysis and verification were carried out using molecular dynamics.This work aims to provide new ideas and theoretical support for the preparation of durable,environmentally friendly,flame retardant,and low smoke FPUF.The main research results are as follows:1.An efficient environmental protection and fatigue resistant coating(PEI/APP-r GO₁₅₀)was constructed on the surface of FPUF through polyelectrolyte composite composed of polyethylene imine（PEI）and ammonium polyphosphate（APP）,combined with graphene oxide（GO）nano sheets,which improved the flame retardant and smoke suppression performance of FPUF.The results showed that the limiting oxygen index（LOI）of the coated FPUF is 25.7%,and it was self-extinguished immediately after removing the external ignition source.The total heat release（THR）of FPUF samples treated with coating was decreased by 23.2%,and the peak of smoke density was decreased by 33.3%.Characterization analysis proved that the coating formed cross-linked molten char during thermal decomposition,this char layer formed a dense outer surface and a complex internal expansion char layer under the action of inert gases and GO support,effectively improving the flame retardancy and smoke suppression of the sample.In addition,the PEI/APP-r GO₁₅₀ coating effectively improved the compressive strength of FPUF（+175.0%）,and the compressive strength of the sample still recovered to 99.0%of the initial value after 200 compression cycles at ambient temperature,demonstrating its excellent self-healing ability.2.Preparation of flame retardant and smoke suppression FPUF through co deposition and in-situ growth methods.Firstly,polydopamine（PDA）and sodium alginate oxide（OSA）were deposited on the surface of FPUF,and thenβ-Fe OOH nanorods were grown in situ on its surface to construct coatings with micro/nano multi-level structures,which improved the durability of flame retardant and smoke suppression coatings on the surface of FPUF.The LOI of FPUF samples treated with coating reached 25.5%,THR was decreased by39.7%,TSP was decreased by 15.2%,and peak of smoke density was decreased by 72.2%.It was indicated by the research on smoke suppression mechanism that the Fe₂O₃ generated by the decomposition ofβ-Fe OOH in coatings adsorbed small molecules and increased the density of carbon precursor,thereby causing the smoke particles to quickly settle and form char.The coating exhibited excellent water resistance and durability,and the LOI value of the sample remained above 23.5%after being soaked in water for 24 h or subjected to 100 cycles of friction.In addition,the micro/nano multi-level structure of the coating exhibited significant resistance to Escherichia coli or Staphylococcus aureus in humid environments.3.The one-step co deposition of bio-based PDA and nucleotide（GMP）on the surface of FPUF simplified the sample preparation process and further improved the flame retardant and smoke suppression efficiency of bio-based green coatings on FPUF.It was indicated that the LOI value of FPUF samples treated with PDA-GMP reached 24.5%,which was self-extinguished in the horizontal burning test.The THR and TSP were reduced by 42.0%and 63.8%,respectively,and the release of CO,CO₂,and HCN was also significantly reduced.This was because the PDA-GMP coating formed a dense and stiff char layer during thermal decomposition,which prevented the foam from collapsing during combustion,and the maintained internal porous structure providing the"curvature effect"of smoke and heat transfer.In addition,after soaking in water for 24 h or undergoing 100 cycles of friction,the LOI value of the sample remained above 23.0%.4.A highly efficient hyperbranched flame retardant（DTEAA）was designed and synthesized by the ester exchange reaction between dimethyl methylphosphonate and triethanolamine,which formed a biomimetic structure of tree roots and soil with FPUF.This effectively solved the problem of easy migration and large addition of the added flame retardants and balanced the flame retardancy with the inherent performance of FPUF.It was indicated that DTEAA exhibited excellent flame retardancy and smoke suppression performance in FPUF:after adding only 8 wt.%DTEAA,the LOI of FPUF samples increased to 26.3%;THR and TSP were decreased by 63.5%and 74.7%,respectively.In addition,after being placed at 100^oC for 216 h,the LOI of FPUF-DTEAA8 samples was still remained at 26.1%.Hydrogen bond analysis and molecular dynamics simulations proved that the high affinity between FPUF and DTEAA effectively prevented the migration of flame retardants,thereby achieving durable flame retardant and smoke suppression effects.5.The hyperbranched flame retardants（DHTST and DHEIC）with hyperbranched center structures containing N hexagonal rings and N hexagonal ring derivatives were designed and synthesized,respectively.By comparing and analyzing with DTEAA flame retardants,the influence and mechanism of the structure of hyperbranched flame retardants on the combustion and smoke release of FPUF was further investigated.FPUF samples containing different hyperbranched flame retardant structures exhibit different combustion performance,with the order of LOI values being FPUF-DTEAA8>FPUF-DHEIC8>FPUF-DHTST8,the order of THR being FPUF-DHEIC8<FPUF-DTEAA8<FPUF-DHTST8,and the order of TSP being FPUF-DHTST8<FPUF-DHEIC8<FPUF-DTEAA8.This was because three different flame retardants play different roles in the second stage of FPUF degradation:the acyclic N-containing structure（DTEAA）was more prone to decomposition,producing amino and other free radicals to terminate gas-phase chain reactions;The N-containing six membered ring structure（DHTST）tended to form triazine rings and reduce char precursor;The structure of N-containing six membered ring derivatives（DHEIC）was most conducive to promoting the formation of dense char layers.