Research On Synthesis Of Triazine Charring-Foaming Agents And Their Flame Retardant Mechanism In Polypropylene

Polypropylene(PP) is widely used in many fields such as industrial construction, automotive industry,household appliances,electronics,furniture,packaging and building materials,etc.However PP has only a limiting oxygen index(LOI) value of 17%～19%,and is flammable.Therefore,the flame retardancy of PP is very important in order to widen its application areas.Therefor,the new IFR systems have been worked out continuously and used as the flame retardant in polypropylene.The research and application of PP-IFR systems have been paid a great attention.In this paper,a novel triazine Charring-Foaming Agents(CFAs) have been deviced and synthesized,and the reaction mechanisms also have been analyzed,and the structures of all the synthesized products have been characterized via Fourier transform infrared(FTIR) spectroscopy,elemental analysis(ELA),nuclear magnetic resonance spectroscopy(¹³C solid NMR) and thermogravimetry analysis(TGA).The result of TGA shows that CFA have good thermo-stability and high char residue,especially,CFA1 exhibited the most outstanding,its initial decomposition temperature was 300.2℃,and the char residue was 32.2%at 800℃.A new IFR system mainly consisted of charing-foaming agent(CFA),ammonium polyphosphate(APP) and Zeolite 4A,was used for flame-retardant PP.Some important factors affecting the flame retardancy and mechanical properties were studied,such as the ratio of APP to CFA,different loading of IFR and so on.Based on the results of experimental tests,an excellent CFA1 and formulation with best flame retardancy were obtained:when the weight ratio of APP/CFA is 4/1,and the IFR(Zeolite 4A) loading is only 18%in PP,the flame retardancy of IFR1-PP composites still passes UL-94 V0 rating,and its LOI value reached 34.3%.Thermal degradation and combustion behavior of IFR1/PP and IFR1/PP/Zeolite 4A were tested by TGA and CONE.The results proved that the thermal degradation behavior and combustion behavior of PP had been changed due to the addition of IFR1,and could make HRR,THR,MLR,COP and SPR of IFR1-PP composites decreased largely.The research also found that the Zeolite 4A could accelerate the degradation of the systems,enhance the char formation in high temperature,furthermore,which make HRR,THR,MLR,COP and SPR of IFR1-PP composites certain go down,thereby a better flame retardancy is obtained.The structure of char layer after burning and the fire-retarding mechanism of intumescent flame retardant PP have been investigated by means of SEM,FTIR and EDS methods. Combination of the results of TGA and CONE,the experimental results demonstrated that an effective foam char laver,can form while burning for IFR1/PP and IFR1/PP/Zeolite 4A,and the IFR1/PP/Zeolite 4A after burning can form more compact and stabile char layer,which is reticular formation.We also analyzed the inner and outside of char layer,it was found that they showed different structures of char layer:the inner char layer formed the early intumescent char layer;and the outside char layer formed crosslinked char layer by P-O-C,P-O-P primarily,which was more compact and stabile.