Synthesis,Characterization And Application Of Post-chain Extended Flame-retardant Waterborne Polyurethane

Reactive-type halogen-free flame retardant is the development direction of flame retardant modified waterborne polyurethane.Among them,post-chain extension flame retardant modification not only can greatly improve the flame retardancy of waterborne polyurethane,but also has other advantages such as the simple operation,low energy and less solvent consumption,high mechanical properties and high solid contents.In order to meet the requirements of waterborne polyurethane that are high flame retardancy,high solid contents and high mechanical properties,we designed and synthesized four series of reactive-type halogen-free flame-retardant waterborne polyurethane,and discussed their structure,properties and applications in this paper.First,a series of post-chain extension flame retardant waterborne polyurethane(AWPUs)was prepared using a phosphorus-containing diamine bis(aminophenyl)phenyl phosphorous oxide(BPPO).Then soft segment and hard segment modified post-chain extension flame retardant waterborne polyurethanes(AOWPUs and AFWPUs)were respectively prepared by using an organophosphorus oligomer ExolitOP 550 and small molecule organic phosphorus Fyrol 6.Finally,soft and hard segment co-modified modified post-chain extension flame retardant waterborne polyurethane(AOFWPUs)was synthesized by using ExolitOP 550 and Fyrol 6 together.FTIR,NMR and SEM-EDS were utilized to characterize the molecular structures of the above four waterborne polyurethanes.The results show that the target product is obtained.Emulsion properties tests show that the post-chain extension of BPPO increased the particle size but reduced the stability and viscosity of four series of emulsions.Furthermore,under the same post-chain extension ratio,the order of the particle size of four series of post-chain extension flame retardant waterborne polyurethane emulsions is: AOFWPUs> AOWPUs> AFWPUs> AWPUs,however,the order of the emulsion stability and the emulsion viscosity is the opposite.AWPUs has an actual maximum post-chain extension ratio(ACER)and the actual maximum post-chain extension ratio is at about 80%,however,the ACER of the other three is all at aroud 60%.The relationships between the micro-phase structures and the post-chain extension,the modification of soft segments by ExolitOP 550,hard segments by Fyrol 6 and soft-hard segments by ExolitOP 550 and Fyrol 6 were studied by hydrogen bonding effect analysis,DSC and TEM.The effects of post-chain extension of BPPO and the above segment modification on the properties were discussed with respect to mechanical properties and water resistance.The results show that the micro-phase separation,glass transition temperature and mechanical properties and water resistance are more affected by different modification methods and post-chain extension ratio of modified waterborne polyurethane.TGA tests show that compared with unmodified and none post-chain extended waterborne polyurethane(AWPU-0),the thermal decomposition temperatures of four post-chain extension flame retardant waterborne polyurethanes were decreased,the flame retardant modification of ExolitOP 550 and / or Fyrol 6 and the post-chain extension of BPPO promoted the whole thermal degradation process and increased the residual char yields a lot.Oxygen index tests show that the LOI value of AWPU-100 in which the post-chain extension ratio of BPPO was 100% in AWPUs reaches 30.4% with UL-94 of V-0;the LOI value of AOWPU-80 in which the content of ExolitOP 550 was 10% and the post-chain extension ratio of BPPO was 80% in AOWPUs is 31.9% with UL-94 of V-0;the LOI value of AFWPU-80 in which the content of Fyrol 6 was 10% and the post-chain extension ratio of BPPO was 80% in AFWPUs is 30.9% with UL-94 of V-0;the LOI value of AOFWPU-80 in which the content of ExolitOP 550 was 10%,the content of Fyrol 6,and the post-chain extension ratio of BPPO was 60% in AOFWPUs is 32.5% with UL-94 of V-0.Cone calorimeter tests show that,the peak heat release rate(PHRR)and total heat release(THR)of four post-chain extension flame retardant waterborne polyurethanes reduced,while the average specific extinction area(ASEA),carbon residue rate and fire performance index(FPI)increased with the increase of BPPO.Moreover,the results show that four post-chain extension flame retardant waterborne polyurethanes have the condensed phase flame retardant effect,and Fyrol 6 modified post-chain extension flame retardant waterborne polyurethane(AFWPUs)and soft and hard segment co-modified modified post-chain extension flame retardant waterborne polyurethane(AOFWPUs)also have the gas phase flame retardant effect.The thermal decomposition behaviors,morphology of carbon layer and thermal degradation mechanism of the flame retardant of AWPUs,AOWPUs,AFWPUs and AOFWPUs were studied by SEM–EDS,TGA-FTIR and FTIR of solid phase degraded products.The results show that the decomposition mechanism of AWPUs,AOWPUs,AFWPUs and AOFWPUs were speculated to proceed in two steps.During the first step the degradation of hard segments occurred,mainly producing into carbon dioxide,isocynates and polyols.At this stage,organic phosphorus was degraded into phosphoric acid and phenyl phosphate first;the earlier degadation of organic phosphorus decreased the thermal stability of waterborne polyurethane,and then was further formed into polyphenyl phosphate and polyphosphate,thus promoting the formation of the carbon layer.During the second step,polyols began to decompose,mostly generating ethers,carboxide compounds and a few olefins.The organphosphonate are able to catalyze the dehydration of polyols to form dioxane and water.Four post-chain extension flame retardant waterborne polyurethanes AWPUs,AOWPUs,AFWPUs and AOFWPUs were applied on poly(ethylene terephthalate)(PET)fabric.The performances of the treated fabric were investigated,such as flame retardant,fabric handle,color change,stiffness,breaking strength,hydrostatic pressure and so on.The results show that after treated by four post-chain extension flame retardant waterborne polyurethanes,all the fabrics maintained the true color of fabric,the flame retardancy,stiffness and breaking strength were increased,however,the hydrostatic pressure and the washability performance was reduced.In addition,after washed,fabrics treated by AFWPU-80 and AOFWPU-60 could reach B1 level according to GB/T5455-1997 vertical combustion standard.