Reaserch On Strategy And Mechanism Of Highly Efficient Flame Retardant Rigid Polyurethane Foam

Rigid polyurethane foam（RPUF）has many advantages,such as light weight,high specific strength,low thermal conductivity and low cost.It is mainly used in refrigeration equipment,wall insulation,thermal insulation board and other fields,especially building insulation materials.However,because RPUF is rich in C-H segments,its limited oxygen index（LOI）is only 19%,which is a flammable material and the flame spreads rapidly after ignition,which greatly harms people’s lives and property safety.In recent years,fires caused by RPUF combustion are not uncommon.For example,in Jing’an District of Shanghai in 2010,a fire broke out in a high-rise residential building after RPUF insulation layer was ignited,resulting in 58 deaths.Based on this,it is of great theoretical value and application significance to study RPUF with high flame retardancy.Starting from additive flame retardant method,reactive flame retardant method and post-treatment flame retardant method,this paper uses three flame retardant methods to treat RPUF,and discusses the influence of different structures on the flame retardant mechanism of RPUF.The specific research contents and results are as follows:（1）In order to solve the problem of poor compatibility between solid additive flame retardant and RPUF,the ionic liquid flame retardant（DOPO-AZ）was obtained by using the oxides of 2-aminothiazole（AZ）and 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide（DOPO）through salt-forming reaction,and its ionic liquid characteristics made it have good compatibility with foaming materials.The successful synthesis of DOPO-AZ was verified by Fourier transform infrared（FTIR）and 1HNMR.Due to the change of cell structure after adding flame retardant,the density and compressive strength of RPUF composites increased,but the thermal conductivity remained basically unchanged.According to the test results of flame retardancy,when adding 17 wt%DOPO-AZ,RPUF/DOPO-AZ₁₇can pass the UL-94 V-0 grade,the LOI increases by 4.5%,and the peak heat release rate（PHRR）decreases by 32.3%.Combined with the flame retardant mechanism test,it can be analyzed that DOPO-AZ in RPUF can dilute the concentration of oxygen and combustible gas mainly by producing a large number of nonflammable gases,and at the same time,it can generate a dense carbon layer to isolate the spread of heat and flame,thus achieving the flame retardant effect.（2）In order to achieve the long-lasting flame retardant purpose,three kinds of P-N flame retardant polyols were obtained by the reaction of phenylphosphoric acid（BP）and diphenyl phosphoric acid（DP）with aminoglycerol（ADP）and dopamine（DA）respectively,and the intrinsic flame retardant RPUF was prepared by the reaction of them in polyurethane molecular segments.The effects of different structures on the flame retardancy,mechanical properties and thermal conductivity of RPUF were systematically discussed.The experimental results showed that BP-ADP,DP-DA and DP-ADP were successfully synthesized by means of FTIR and ¹HNMR.At present,the addition of 20 wt%of flame retardants of the two products can pass UL-94 V-0 grade,and the addition of 15 wt%of DP-ADP can pass UL-94 V-0 grade,and their PHRR decreased by 27.8%compared with RPUF.According to the test of flame retardant mechanism,it can be concluded that BP can produce more carbon layer on the surface of RPUF to play the role of heat insulation and oxygen isolation,while DP will dilute the concentration of combustible gas by releasing non-combustible gas.However,DP-ADP can flame retardant RPUF more efficiently,at the same time,it can improve its compressive strength and basically maintain the original thermal insulation of RPUF.（3）In order to simplify the preparation process and improve the LOI of RPUF,PVA-ATP sol with light weight and low thermal conductivity was coated on the surface of RPUF,and the effects of different concentrations of ATP on the flame retardancy,mechanical properties and thermal conductivity of RPUF/PVA-ATP composites were explored by adjusting the concentration of ATP.The results of FTIR,XRD and SEM-EDS show that PVA-ATP sol is successfully coated on the surface of RPUF.When the ATP concentration is increased to 7 wt%,RPUF composite can pass the UL-94 V-0grade,the LOI can reach 36.5%,and the PHRR decreases by 40.7%.In addition,the compressive strength of RPUF is increased by 74.2%and its thermal conductivity is decreased by 41.1%due to the support of the network structure of PVA-ATP aerogel.Combined with the flame-retardant mechanism,it can be analyzed that PVA-ATP aerogel decomposes on the surface of RPUF in advance after heating,resulting in a dense and high-strength carbon layer,which prevents the flame from reaching the inside of RPUF,thus achieving the purpose of protecting the substrate.