Preparation Of Zirconium Phosphate-decorated Macromolecular Charring Agent And Its Highly Efficient Catalyzing Carbonization In Flame Retardant Polypropylene

The char layer formed by intumescent flame retardant(IFR)can effectively restrain the combustion of polypropylene(PP),because it can not only protect the matrix from heat and oxygen,but also inhibit smoke and melt-dropping.However,the formation of the intumescent char layer of traditional IFR system is mainly dependent on IFR itself,and the strength and the thermostability of the formed char layer are always unsatisfactory.Therefore,a large amount of IFR(?25wt%)is needed to guarantee the protection performance of the char layer.In recent years,catalyzing carbonization of PP is considered to be one of the most effective ways to prepare high-performance halogen-free flame retardant PP,because the carbonization of PP can not only decrease the generation of combustible gases,but also act as a charring agent to improve the quality of the intumescent char layer.To investigate a new kind of IFR with the catalyzing carbonization function on PP,in this dissertation,a series of layered zirconium phosphate(Zr P)with different sizes were synthesized,and the relation between the ZrP size and its catalyzing carbonization capability on PP was studied.Subsequently,ZrP-decorated macromolecular charring agent(ZrP-MCA)was synthesized and combined with ammonium polyphosphate(APP)to flame-retard PP.The flame retardant mechanism of the system was also studied in depth.Moreover,N-alkoxy hindered amine(NOR)with free-radical quenching capability was used as a synergist of ZrP-MCA/APP and its synergistic mechanism was also studied.The contents and results of this study are mainly as follows:Firstly,a series of ZrP with different sizes were synthesized with zirconyl chloride octahydrate and phosphoric acid by hydrothermal method or reflux method,and were characterized with scanning electron microscopy(SEM),X-ray diffraction(XRD)and Fourier transform infrared spectrometry(FTIR).The effect of the size and content of ZrP on the flame retardancy and thermostablity of PP was studied,and the flame retardant mechanism of ZrP in PP was analyzed with thermogravimetry-Fourier transform infrared spectrometry(TG-FTIR),scanning electron microscopy and energy dispersive X-ray spectrometry(SEM-EDX)and X-ray photoelectron spectroscopy(XPS).The results showed that when 2wt% ZrP with the size of 1400 nm was added into PP,the limiting oxygen index(LOI)of PP was increased from 18.0% to 19.5%.Meanwhile,the peak heat release rate(PHRR),average heat release rate(AV-HRR),total heat release(THR),peak smoke production rate(PSPR)and total smoke production(TSP)were decreased by 27.0%,7.8%,5.3%,29.4% and 9.8%,respectively.The residue in cone calorimetric test(CCT)was increased from 0 to 4.6wt%.Besides,compared to PP,the maximum mass loss rate temperature(Tmax)of PP/ZrP was increased by 4? and the maximum mass loss rate(Rmax)was decreased by 12.8%.The residue at 800? was increased from 0 to 2.9wt%.The results revealed that ZrP could improve the flame retardancy of PP by its layer barrier effect and the catalyzing carbonization of PP.Secondly,ZrP-decorated macromolecular charring agent(ZrP-MCA)was synthesized with ZrP,cyanuric chloride,ethanediamine and 3-aminopropyltriethoxysilane(KH550)and characterized with SEM,FTIR,13C-nuclear magnetic resonance(13C-NMR)and XRD.ZrP-MCA was combined with APP to flame-retard PP and the flame retardant mechanism of the system was studied with FTIR,TG-FTIR,SEM-EDX,XPS,XRD and laser Raman spectroscopy(LRS).The results showed that ZrP-MCA/APP could significantly improve the flame retardancy and thermostablity of PP.When the content of ZrP-MCA/APP was 20wt% and the mass ratio of ZrP-MCA to APP was 1:3,PP/IFR could reach a LOI value of 32.5% and achieve a V-0 rating in the vertical burning(UL-94)test.Meanwhile,compared to PP,the PHRR,AV-HRR,THR and AV-MLR of PP/IFR were reduced by 81.3%,76.5%,56.1% and 50.0%,respectively,and the residue in CCT was increased from 0 to 28.3wt%.Besides,compared to PP,the Ti and Tmax of PP/IFR were increased by 13? and 22?,respectively,and the Rmax was decreased by 39.4%.The residue at 800? was increased from 0 to 13.9wt%.The mechanism study revealed that during combustion,ZrP could firstly catalyze the charring reactions of MCA on its surface,dividing the intumescent char layer into countless closed micro-nano char-cages,in which PP and its degradation products would be trapped and catalyzed into thermostable graphitization char.Finally,N-alkoxy hindered amine(NOR)was used as the synergist of IFR(i.e.,ZrP-MCA/APP)to further improve the flame retardancy and thermostablity of PP/IFR.The synergistic mechanism of NOR in PP/IFR was studied with SEM-EDX,XPS,XRD and LRS.The results showed that NOR could further improve the catalyzing carbonization capability of IFR on PP and therefore significantly improved the flame retardancy and thermostablity of PP/IFR.When employing 0.2wt% NOR to replace the same mass of IFR,the LOI of PP/IFR/NOR was increased from 32.5% to 36.0%,and a UL-94 V-0 rating was achieved.Meanwhile,the PHRR,AV-HRR,THR,PSPR and TSP of PP/IFR/NOR were decreased by 78.5%,70.9%,50.8%,71.1% and 51.7%,respectively,and the residue in CCT was increased from 23.3wt% to 37.9%.Besides,compared to PP/IFR,the Ti of PP/IFR/NOR was increased by 8? and the Rmax was decreased from 19.4wt%/min to 18.8wt%/min.The residue at 800? was increased from 13.9wt% to 21.2wt%.The mechanism study revealed that NOR could suppress the initial degradation of PP,and improve the catalytic efficiency of ZrP on the carbonization of the degradation products of PP by quenching its macromolecular free-radicals in the micro-nano char-cages.