Synthesis And Properties Of Silicone Synergistic Flame Retardant

Polymer foam is a kind of porous material with light weight and high specific strength.As a heat insulating material,it has characteristics of heat insulation,sound insulation,shockproof,electric insulation,weather resistance and solvent resistance.They are widely used in various fields.However,large specific surface area leads to extremely high flammability,it is of great significance for proper flame retardant treatment of such materials.Rigid Polyurethane Foam(RPUF)has typical combustion characteristics of polymer foam and is widely used.It is often treated with a halogenated phosphate flame retardant.However,it is very important to find a green,environmentally friendly and synergistic flame retardant due to the combustion of halogen-containing flame retardants produce toxic gases,or potential toxicity in use,which is a serious threat to human health and the environment.Additive flame retardant is currently the most common flame retardant strategy,but the excessive addition of flame retardant will adversely affect the mechanical properties of the material.Intrinsic flame retardant strategy is to bond the structure with flame retardant function to the chemical chain of the polymer in the form of chemical bonds,thereby obtaining the intrinsic flame retardant polymer.Although this strategy can obtain relatively stable flame retardancy,it has high cost and complicated process.The surface treatment flame retardant strategy is relatively inexpensive and efficient compared to the first two methods because it only treats the surface of the material accordingly,and is particularly suitable for the porous,high specific surface area special structure of polymer foam.Therefore,it is the preferred experimental route for the subject.Innovatively,the phosphorus-based and nitrogen-based flame retardants are introduced into the silicone resin system by sol-gel method.By controlling the reaction conditions of the co-hydrolysis system,a green and environmentally friendly silicon-phosphorus-nitrogen hybrid flame retardant sol was successfully prepared.The solvent used for the flame retardant sol is environmentally friendly and the sol system can be stored for a long period of time.According to the flame retardant mechanism,the Si-O-Si structure can form a silica barrier layer on the surface after combustion;phosphorus compounds can exert a gas phase free radical trapping mechanism and a catalytic coacervate phase to form a carbon layer;the nitrogen compound decomposes and absorbs heat to produce non-flammable gas to dilute the combustible gas.These three elements have good complementarity in the flame retardant mechanism,so it is reasonable to design the synergistic flame retardant structural unit.In this paper,the synergistic flame-retardant system is applied to the RPUF surface by using a simple surface impregnation treatment process,and an ideal halogen-free environmentally friendly,green and efficient flame retardant foam composite is obtained.The specific work and conclusions of this paper are as follows:(1)The silicon-phosphorus flame retardant precursor DOPO-VTMS was successfully synthesized from phosphorus-based flame retardant DOPO and vinyltrimethoxysilane(VTMS).This structure retains the alkoxy structure to ensure that a sol-gel reaction can occur.The successful synthesis of the structure was confirmed by Fourier transform infrared spectroscopy and 1H,31P NMR characterization.(2)The MEL-KH structure was successfully synthesized from melamine and KH560,and the successful synthesis of the structure was confirmed by Fourier transform infrared spectroscopy and 1H NMR characterization.(3)Synthesis of silicon-phosphorus hybrid flame retardant sol(SiR-DOPO)by sol-gel method using silicon-phosphorus flame retardant precursor DOPO-VTMS and alkyltrimethoxysilane as raw materials.The foam was treated with the sol by vacuum impregnation and high temperature curing to obtain a silicon-phosphorus hybrid flame retardant rigid polyurethane foam composite(SiP-RPUF)with good flame retardancy and high thermal stability.The immersion curing effect and the flame retardancy of the treated RPUF were analyzed by scanning electron microscopy,EDS spectroscopy,oxygen index test,UL94 vertical burning grade test,thermogravimetric analysis,cone flow thermal analysis and XPS test.The conclusion is that when the ratio of DOPO-VTMS to MTMS is 3:7,the obtained sample SiP-RPUF(7/3)has the best synergistic flame retardant effect of silicon-phosphorus.Thermogravimetric analysis found that SiP-RPUF(7/3)had the best thermal stability,with a T20 of 445 ? and a sample residual ratio of 62%.The limiting oxygen index(LOI)increased from 18.2%of pure foam to 29.0%,the UL94 vertical burning grade reached V-0 level,and the heat release rate peak(PHRR)decreased from pure foam 235 kW/m2 to 80.69 kW/m2,the smoke generation rate(SPR)is about 69%lower than that of pure foam.Finally,it is concluded that the rapid self-extinguishing capacity of foam composites results from the fact that the "silicon-phosphorus hybrid coating can be converted into a silica-enhanced phosphorus-rich carbon layer during combustion".Therefore,this simple strategy can greatly increase the fire safety of the RPUF.(4)Silicon-phosphorus-nitrogen hybrid flame retardant sol(SiR-DOPO-MEL)was synthesized by sol-gel method using silicon-nitrogen flame retardant precursors MEL-KH and DOPO-VTMS and methyltrimethoxysilane(MTMS)as raw materials.The foam was treated with the sol by vacuum impregnation and high temperature curing to obtain a silicon-phosphorus hybrid flame retardant rigid polyurethane foam composite(SiPN-RPUF)with acceptable flame retardancy and high thermal stability.The results show that the introduction of melamine can effectively increase the thermal decomposition initiation temperature of RPUF,but the process of thermal decomposition of melamine releases the gas,which will adversely affect the formation process of solid barrier.Therefore,MEL-KH needs to further explore its suitable application field.