Study On The Flame Retardant Effect Of Piperazine Pyrophosphate-based Intumescent Flame Retardant In Polyolefin

Piperazine pyrophosphate-based intumescent flame retardant(IFR)is a new type of IFR.Compared with ammonium polyphosphate-based IFR,it has better flame retardant,heat resistance and water resistance,and has a wider range of applications.It is a halogen-free flame retardant with great development potential.However,the formulation of piperazine pyrophosphate-based IFR is still rare,the flame retardant mechanism has not been reported,and its application is not widespread.Therefore,it is of great significance to carry out this research.The flame retardant of IFR in polypropylene(PP)and polyethylene(PE)by limit oxygen index(LOI),vertical combustion test and cone calorimetry test(CCT).IFR was composed by piperazine pyrophosphate and two nitrogen flame retardants(nitrogen flame retardant-1 and nitrogen flame retardant-2)respectively.The synergistic effect of six synergists(synergist-1,synergist-2,synergist-3,synergist-4,synergist-5 and synergist-6)on IFR were also investigated.The results showed that IFR composed of piperazine pyrophosphate and nitrogen flame retardant-1 has good flame retardant effect in PP and PE.When the mass percent of nitrogen flame retardant-1 and piperazine pyrophosphate was 1:2.5(referred to as IFR-1 according to this mass ratio),the dosage of IFR-1 was 26 %,the LOI of PP can reach 35.2 %,and the vertical burning level can reach UL94 V-0 rating.Compared with pure PP,the peak of heat release rate(PHRR),total heat release(THR),peak of effective heat combustion(PEHC),mean of effective heat combustion(MEHC),peak of mass loss rate(PMLR)and mean of mass loss rate(MLR)of PP/IFR-1 were reduced by91.34 %,31.42 %,8.75 %,16.60 %,52.60 % and 33.33 % respectively;When themass percent of nitrogen flame retardant-1 and piperazine pyrophosphate was 1:2.5(referred to as IFR-3 according to this mass ratio),the dosage of IFR-3 was 30 %,the LOI of PE can reach 34.7 %,and the vertical combustion level can reach UL94V-0 rating.Compared with pure PE,PHRR,THR,PEHC,MEHC,PMLR and MLR of PE/IFR-3 were reduced by 68.72 %,27.51 %,1.20 %,44.56 %,58.54 % and74.39 % respectively.IFR composed of piperazine pyrophosphate and nitrogen flame retardant-2 also has good flame retardant effect in PP and PE.When the mass percent of nitrogen flame retardant-2 and piperazine pyrophosphate was 1:2(referred to as IFR-2 according to this mass ratio),the amount of IFR-2 is 26 %,the LOI of PP can reach 35.5 %,and the vertical burning level can reach UL94 V-0 rating.Compared with pure PP,the PHRR,THR,PEHC,MEHC,PMLR and MLR of PP/IFR-2 were reduced by 85.45 %,17.33 %,10.0 %,20.32 %,67.05% and 19.05%respectively;When the mass percent of nitrogen flame retardant-2 and piperazine pyrophosphate was 22:78(referred to as IFR-4 according to this mass ratio),the adding amount of IFR-4 is 30 %,the LOI of PE can reach 35.3 %,and the vertical combustion level can reach UL94 V-0 rating.Compared with pure PE,PHRR,THR,PEHC,MEHC,PMLR and MLR of PE/IFR-4 were reduced by 69.41 %,30.23 %,6.02 %,26.77 %,61.79 % and 74.39 % respectively.Synergist-3,synergist-5 and synergist-6 have synergistic effect with IFR-1 in PP,but synergist-1,synergist-2 and synergist-4 have no obvious synergistic effect with IFR-1 in PP.Synergist-1,synergist-3 and synergist-6 have synergistic effect with IFR-2 in PP,but synergist-2 and synergist-5 have no obvious synergistic effect with IFR-2 in PP.Compared with PP/IFR-2,PHRR,THR,PEHC,MEHC,PMLR and MLR of PP/IFR-2/synergist-3 were reduced by 21.28 %,10.95 %,2.78 %,4.05 %,5.26 % and 23.53 % respectively,the PHRR,THR,PEHC,MEHC,PMLR and MLR of PP/IFR-2/synergist-6 were reduced by 3.09 %,6.31 %,4.17 %,18.79 %,42.11 % and 52.94% respectively,the PHRR,THR,PEHC,MEHC,PMLR and MLR of PP/IFR-2/synergist-1 were reduced by 9.75 %,4.54 %,5.56 %,9.38 %,42.11 % and 17.65 % respectively.Synergist-3 and synergist-5 have synergistic effect with IFR-3 in PE,but synergist-1 and synergist-6 have no obvious synergistic effect with IFR-3 in PE.Synergist-6 has synergistic effect with IFR-4 in PE.Synergist-1,synergist-3 and synergist-5 have no obvious synergistic effect with IFR-4 in PE.Compared with PE/IFR-4,PHRR,THR,PEHC,MEHC,PMLR and MLR of PE/IFR-4/synergist-3were reduced by 78.42 %,14.56 %,5.13 %,6.73 %,80.85 % and 19.05 %respectively,PHRR,THR,PEHC,MEHC,PMLR and MLR of PE/IFR-4/synergist-6were reduced by 45.72 %,15.81 %,6.41 %,22.76 %,31.91 % and 23.81 %respectively,PHRR,THR,PEHC,MEHC,PMLR and MLR of PE/IFR-4/synergist-1 were reduced by 25.25 %,11.65 %,10.26 %,27.40 %,25.53 % and28.57 % respectively.The effect of piperazine pyrophosphate-based IFR on the thermal stability of PP and PE was studied by thermogravimetric test(TGA).The results showed that piperazine pyrophosphate-based IFR significantly improved the thermal stability of PP and PE,and the effect of IFR-2 on the thermal stability of PP was greater than that of IFR-1,and the effect of IFR-4 on the thermal stability of PE was greater than that of IFR-3.The addition of synergist further reduced the thermal stability of PP and PE.The flame retardant mechanism of piperazine pyrophosphate-based IFR in PP was discussed by analysing the residures in CCT and TGA.The results showed that piperazine pyrophosphate-based IFR is mainly flame retardant through condensed phase.Polyphosphoric acid and other phosphoric acid substances decomposed from piperazine pyrophosphate promote the dehydration of charring agent into char.Nitrogen that noble gas released from piperazine pyrophosphate at high temperature makes the system expand and foam.A dense inflammable expansive carbon layer is formed.The expansive carbon layer has flame retardant effect by heat insulation,oxygen insulation and preventing volatilization of polymer pyrolysis products.