Synergistic Effect Of Bicummyl In Phosphorus-Bromine Composite Flame Retardant Polypropylene

In recent years,studies have shown that bicummyl can be used as synergist of traditional flame retardants.Even a small dosage can produce a good flame retardant synergistic effect,which will undoubtedly help to improve the performance of traditional flame retardants and open up a new way for the development of green and efficient flame retardants.It is of great significance to have a study on the flame retardant rule,the combustion behavior and mechanism of flame retardant PP of the flame retardant system as there is not relative report currently.The flame retardancy of bicummyl/aluminium hypophosphite/melamine hydrobromide,bicummyl/Aluminum diethylhypophosphite/melamine hydrobromide and bicummyl/ammonium polyphosphate/melamine hydrobromide in homopolymer polypropylene(PPH)and copolymer polypropylene(PPB)was studied through limiting oxygen index(LOI)measurement,vertical burning test(UL94)and cone calorimetric analysis(CCT).The results showed that DMDPB/ALHP/MHB had a good synergistic effect on flame retardancy in PP.When the addition of DMDPB,ALHP and MHB were 0.25 %,1.00 % and 1.50 % respectively,the LOI of flame retardant Homopolymer PP(PPH)could reach 25.8 % and the vertical combustion level reached V-2;Meanwhile,when they were added 0.25 %,2.50 % and 2.50 % respectively,the LOI of flame retardant Copolymerized PP(PPB)could reach 23.4 % and the vertical combustion level reached V-2.It was clear that the maximum heat release rate(PHRR),total heat release(THR),average effective combustion heat(MEHC)and maximum effective combustion heat(PEHC)of PP were significantly decreased by adding ALHP and MHB,it prolonged the time required for complete combustion and made combustion slow,and the above parameters were further decreased by compounding DMDPB.Synergistic effect on flame retardancy in PP was also found in DMDPB/ADP/MHB.When the addition of DMDPB,ADP and MHB were 0.25 %,1.50 % and 1.00 % respectively,the LOI of flame retardant PPH reached 24.7 % and the vertical combustion level reached V-2;Meanwhile,when they were added 0.25 %,3.00 % and 2.00 % respectively,the LOI of flame retardant PPB could reach 22.5% and the vertical combustion level reached V-2.There was a decreasing tendency to the PHRR,THR,MEHC and PEHC of PP when ADP and MHB were added in,somehow,it prolonged the time required for complete combustion and made combustion slow,but the above parameters were decreased not too significantly by compounding DMDPB.Further,synergistic effect on flame retardancy in PP was found in DMDPB/APP/MHB,but the effect was worse than that of ALHP/MHB and ADP/MHB.When the addition of DMDPB,APP and MHB were 0.25 %,1.50 % and 1.00 % respectively,the LOI of flame retardant PPH reached 23.3 % and the vertical combustion level reached V-2;meanwhile,when they were added 0.25 %,4.00 % and 4.00 % respectively,the LOI of flame retardant.PPB reached 23.0 % and the vertical combustion level reached V-2.There was also a decreasing tendency to the PHRR,THR,MEHC and PEHC of PP when APP and MHB were added in,somehow,it prolonged the time required for complete combustion and made combustion slow,but the retardant effect of above compounding DMDPB was not significant.The effects of the above flame retardant systems on the thermal stability of PP were studied by thermogravimetric analysis(TGA).It was showed from the results that the thermal stability of PP was decreased by adding ALHP/MHB,and the thermal stability of PP was reduced further by adding ADP/MHB.The thermal stability of PPH was increased by adding ADP/MHB,while the thermal stability of PPB was decreased,but the effect was less than that of ALHP/MHB.The thermal stability of PP was decreased by adding bicummyl.The synergistic mechanism of bicummyl in phosphor-bromide flame retardant polypropylene was studied by cone calorimetric test(CCT)and pyrolysis gas chromatography-mass spectrometry analysis(PyGC-MS)analysis.The flame retardant effect of DMDPB/ALHP/MHB and DMDPB/ADP/MHB in PP was mainly produced through gas phase mechanism.The burning flame was extinguished due to the combustion inhabitation of the combination of the dimethylphenyl tertiary carbon free radicals cracked out from bicummyl and the active free radicals during the burning process.In addition,the pyrolysis products of ALHP/MHB or ADP/MHB promoted the carbonization of PP,and formed a small amount of non-combustible carbon,resulting in a weak condensed phase flame retardant effect.What'smore,there were some potential safety hazards as highly toxic phosphane was produced with a lot of CO and smoke during the PP/DMDPB/ALHP/MHB was burning.To the contrast,although some CO and smoke were produced in the combustion of PP/DMDPB/ADP/MHB and PP/DMDPB/APP/MHB,it was safer as no highly toxic phosphane was released.In fact,the smoke emission of PP/DMDPB/APP/MHB was decreased somehow.