Macromolecular Intumescent Flame Retardant With Free-radical Quenching Capability Decorated Zirconium Phosphate And Its Synergism In Flame-retarding Polypropylene

Intumescent flame retardant(IFR)is one of the most promising halogen-free flame retardants in recent years.However,the existing IFR still has some disadvantages,such as large amount of addition and low efficiency,which limits its further promotion and application.Zirconium phosphate(Zr P)is a kind of layered nanomaterial with strong solid acid catalytic effect and barrier effect.It can catalyze the cross-linking of polymers into char at high temperature,and has unique advantages in flame-retarding polymers.N-alkoxy hindered amine(NOR),as an efficient free-radical quenching agent,can generate nitroxyl free-radicals when thermal decomposed,and capture macromolecular radicals generated by polymer decomposition,thus inhibits the degradation and combustion of polymers.Therefore,coupling the catalyzing carbonization of Zr P and free-radical quenching effect of NOR,and synergizing with IFR,high-efficiency halogen-free flame retardant polypropylene(PP)can be prepared.Based on this,in this thesis,zirconium phosphate(RQZr P)nanosheet with free-radical quenching capability was synthesized by modifying Zr P nanosheet with amine-terminated macromolecular N-alkoxy hindered amines,and combined with IFR to flame-retard PP.On this basis,macromolecular intumescent flame retardant with free-radical quenching capability(RQMIFR)was synthesized,and then used to decorate Zr P nanosheet to prepare RQMIFR-Zr P.The effects of RQMIFR and RQMIFR-Zr P on the flame retardancy,thermal stability and rheological performance of PP were studied,and flame-retardant mechanism was further revealed.The main research content and results include:(1)Amine-terminated macromolecular N-alkoxy hindered amine(MNOR)was firstly synthesized via nucleophilic substitution reaction by using hydroxyl-containing NOR(T152),cyanuric choride and ethylenediamine,and used to decorate Zr P nanosheet to prepare zirconium phosphate nanosheet with free-radical quenching capability(RQZr P).Subsequently,RQZr P was combined with a novel IFR composed of bicyclic cage phosphate/ ammonium polyphosphate(PEPA/APP)to flame-retard PP.The effects of RQZr P on the flame retardancy,thermal stability,mechanical properties and rheological performance of PP/IFR were studied.The synergistic flame-retardant mechanism of RQZr P and IFR in PP was investigated and revealed by thermogravimetry-Fourier transform infrared(TG-FTIR),scanning electron microscopy(SEM),pyrolysis gas chromatography-mass spectrometry(Py-GCMS)and X-ray photoelectron spectroscopy(XPS).It was found that when the amount of IFR was 23wt% and RQZr P was 2wt%,the limiting oxygen index(LOI)of PP increased from 19.0% to 33.0%,and reached the UL-94 V-0 rating.Compared with PP,the peak heat release rate(PHRR)and carbon monoxide production(COP)of PP/IFR/RQZr P-3 decreased by 75.1% and 69.7%,respectively.The mechanism research found that when being burned,the nitroxyl free-radicals(NO·)generated by RQZr P quenched the free-radicals produced by PP,thus inhibited the degradation and combustion of PP.Some of macromolecular free-radicals were captured by RQZr P nanosheet and catalyzed to form graphite char in an orderly structure.Besides,Zr P nanosheet acted as supporting skeleton to further improve the strength and compactness of the intumescent char,which effectively blocked the transfer of heat,combustible gases and oxygen,thus realized the high flame-retardant efficiency.(2)A novel macromolecular intumescent flame retardant with free-radical quenching capability(RQMIFR)was synthesized via nucleophilic substitution reaction by using cyanuric chloride,1-oxo-4-hydroxymethyl-1-phospha-2,6,7-trioxabicyclo [2.2.2] octane(PEPA),T152 and ethylenediamine,and combined with APP to flame-retard PP.The effects of the molar ratio of PEPA and T152 structure in RQMIFR,as well as the amount and ratio of RQMIFR and APP on the flame retardancy and thermal stability of PP were studied.The synergistic flame-retardant mechanism of RQMIFR and APP in PP was investigated and revealed by TG-FTIR,Py-GCMS,laser Raman spectroscopy(LRS)and XPS.The results showed that when the molar ratio of PEPA and T152 structure in RQMIFR was 1:0.005,the mass ratio of RQMIFR to APP was 1:2,and the addition of RQMIFR/APP was 25wt%,the LOI of PP increased from 19.0% to 39.5%,and reached the UL-94 V-0 rating.The PHRR of PP/RQMIFR/APP-3 decreased by 91.7% compared with PP,and the residue after the cone calorimeter test(CCT)was as high as 38.5wt%.The mechanism research revealed that during combustion,the nitroxyl radicals produced by RQMIFR could capture the free-radicals generated by the degradation of PP and inhibited the combustion of PP.Meanwhile,RQMIFR and APP worked synergistically to form a dense intumescent char through esterification,crosslinking,cyclization,and foaming reactions,thus effectively improving the flame retardancy of PP.(3)RQMIFR-Zr P with both free-radical quenching and catalyzing carbonation capability was prepared by decorating Zr P nanosheet with the synthesized RQMIFR,and combined with APP to flame-retard PP.The effects of the amount and ratio of RQMIFR-Zr P and APP on the flame retardancy and thermal stability of PP were studied.The synergistic flame-retardant mechanism of RQMIFR-Zr P and APP was investigated.The results showed that when the mass ratio of RQMIFR-Zr P to APP was 1:3 and the addition was 25wt%,the LOI of PP increased from 19.0% to 39.5%,and achieved the UL-94 V-0 rating.Compared with PP,the PHRR and total heat release(THR)of PP/RQMIFR/APP-3 decreased by 94.0% and 83.2%,respectively,and the residue after CCT was as high as 40.5wt%.The mechanism research revealed that during combustion,the nitroxyl free-radicals generated by RQMIFR-Zr P could inhibit the degradation and combustion of PP.Zr P nanosheet catalyzed RQMIFR into char on its surface,and formed countless sealed micro-nano confined space,where the nitroxyl free-radicals could more effectively capture the macromolecular radicals generated by PP.At the same time,under the strong solid acid catalyzing of Zr P,they cooperated with RQMIFR and APP to form a strong and dense intumescent char,thus inhibited the degradation and combustion of PP.