Research On Flame Retardancy Of Multi-component Composite System To Rigid Polyurethane Foams

In recent years,under the background of the development concept of green environmental protection implemented by country,rigid polyurethane foams(RPUFs)have been widely used in various fields due to their excellent thermal insulation performance,among which building exterior wall thermal insulation material is one of their main applications.However,RPUFs themselves are very easy to burn,which would generate a serious threat to social safety.Therefore,it is necessary to carry out flame retardant modification on them.In this paper,the RPUFs were modified by the multi-component flame retardant system,attempting to give them higher flame retardancy and reduce their fire risk.The specific research contents of this paper are as follows:(1)Continuous flame retardant actions of quaternary composite system was constructed with expandable graphite(EG),dimethyl methyl phosphonate(DMMP),aluminum hydroxide(ATH)and 10-(2,5-dihydroxyphenyl)-10-hydro-9-oxa-10-phosphoryl-phenanthroline-10-oxide(DOPO-HQ),which played a role of flame retardancy in the whole combustion process of RPUFs.6 phr EG,8 phr DMMP,12 phr ATH,and 4 phr DOPO-HQ increased the limiting oxygen index(LOI)of flame retardant RPUFs from 18.6%to 30.8%,decreased the peak heat release rate(PHRR)by 54.4%,and increased the residue yield to 32.6%.It was found in the thermogravimetric curve that DMMP preferentially decomposed in the quaternary system at the initial stage of combustion to play a flame retardant role,and EG,ATH and DOPO-HQ promoted formation of residue foam at the middle stage of combustion,playing a barrier effect flame retardant role in condensed phase.In this process,especially after adding DOPO-HQ,the amount of residue foam increased significantly.Therefore,the quaternary composite system had flame retardant effect in each combustion stage of RPUFs.(2)To reduce the influence of flame retardants on the foaming performance,the intercalated flame retardant(DT-MEG)was prepared by intercalating phenanthroline small molecule flame retardant DT into microexpanded graphite(MEG)sheets,which was compounded with DMMP and flame retardant RPUFs.6 phr DT,8 phr MEG and 16 phr DMMP was able to give RPUFs a high flame retardancy,with LOI value reaching 30.3%,PHRR decreasing by 70.4%,and total heat release(THR)was only 14.9 MJ/m~2.On the one hand,DT continued to play the role of quenching effect after DMMP in gas phase;on the other hand,the"worm-like"structure of the graphite covered the surface of foam,while the phosphoric acid-based substances from the decomposition of the two phosphorus compounds DT and DMMP contributed to the dehydration of foam into charring,increasing the denseness of the charring layer and reducing the exchange of heat and oxygen.(3)In contrast to the high addition of ATH,zinc borate(ZB)was added at a lower dosage and had a better smoke suppression effect than ATH.A quaternary high residue formation composite system of EG,DMMP,ZB and DT was constructed and applied to RPUFs,and the LOI value of RPUFs increased from 18.4%to 30.6%,the PHRR decreased by 59.2%and the residual yield increased to 39.6%when EG,DMMP,ZB and DT were added in the ratio of6:8:10:2.The introduction of high residue formation composite system effectively suppressed the combustion intensity and heat release behavior of the foams matrix.In addition,the high residue formation composite system also played a significant role in smoke suppression performance,and the total smoke release(TSR)decreased by 44.1%.In the composite system,the residual yield increased significantly and TSR decreased significantly by retaining large fragmented solid particles generated by cracking in condensed phase.The composite system revealed the smoke suppression behavior and high residue formation of EG/DMMP/ZB/DT flame retardant RPUFs,and to reveal the correlation between the two.(4)The effect of DDBA,a reactive phosphoramidite derivative containing a phenolic structure,on the flame retardancy and charring formation properties of EG/DMMP/RPUF was investigated.In terms of flame retardancy,8 phr EG,12 phr DMMP and 9 phr DDBA increased the LOI value of RPUFs to 29.0%and decreased the PHRR by 58.9%,which effectively inhibited the release of heat during combustion of foam and imparted high flame retardancy to RPUFs.In terms of charring formation performance,DDBA in nitrogen promoted the charring formation of RPUFs,resulting in a significant increase in the residual yield of RPUFs at 700°C.In the cone calorimeter test,DDBA in air had minimal improvement in the residual yield of RPUFs,which was due to the fact that oxygen maked the combustion process of combustible materials exceptionally complicated and the flame retardant did not contribute significantly in the respect.