Preparation Of Intumescent Flame Retardant And The Study Of Combustion Performance On Flame Retardant Polypropylene

As one of the five general-purpose plastics,polypropylene(PP)has a broader development prospect,while its flammability and molten drop limit the scope of application greatly.Intumescent flame retardant(IFR)has become a hotspot in flame retardant PP because of its low toxicity and smoke,good thermal stability,high efficiency and environmental protection.Traditional IFR is mainly consisted of ammonium polyphosphate(acid source),melamine(gas source)and pentaerythritol(carbon source).But both ammonium polyphosphate and pentaerythritol have serious hygroscopicity and poor thermal stability.In order to overcome these problems and improve the flame retardancy of PP the surface treatment of the flame retardant is used to improve the water resistance and thermal stability.Different types of carbon sources and synergists are also used with flame retardants to improve the combustion performance and expand the application range of PP.In this work,both the flame retardant which encapsulated ammonium polyphosphate into melamine formaldehyde resin-sodium silicate and the single chitosan-based ammonium polyphosphate IFR were prepared by in-situ polymerization.The two IFRs were all added into PP to study the thermal stability and the flame retardant property.The specific work was showned as follows:(1)The melamine formaldehyde resin was encapsulated on the surface of ammonium polyphosphate by in-situ polymerization.In this process,sodium silicate was reacted into the melamine formaldehyde resin as a flame retardant synergist.So far,a micro-envelope core-shell structure flame retardant(MCSF)containing sodium silicate with melamine formaldehyde resin-sodium silicate as the outer shell and ammonium polyphosphate as the core was successfully obtained.The thermogravimetric analysis of MCSF showed that the thermal stability of MCSF had been greatly improved.It was particularly obvious that the degradation rate of ammonium polyphosphate slowed down a lot after 400℃,which proved the better heat resistance.At the same time,the limiting oxygen index of PP improved to 28.6%when 30wt.%of MCSF and carbon source(Polyamide 6)were added into PP.The vertical combustion grade was also reached V-0.Moreover,the total heat release(33k J/g) and heat release rate(378.4W/g)of the PP composites dropped significantly.It was reduced by 50.15%and 18.7%compared with PP,respectively.The carbon layer after burning was also analyzed.The results showed that the carbon layer formed by PP/MCSF/polyamide 6 had a stable and dense structure,which could inhibit the combustion of PP materials and improve the flame retardant efficiency of IFR better.(2)The chitosan-based ammonium polyphosphate(CSAPP)was synthesized by high- temperature reaction between ammonium polyphosphate and chitosan.Then the CSAPP was encapsulated by melamine formaldehyde resin through in-situ polymerization to obtain a single core-shell IFR(CSAPP@MF),which was“three sources in one”.Through thermogravimetric analysis,it was found that it had better thermal stability at high temperature after 30wt.%of CSAPP@MF was added into PP.The flame retardant results showed that its limiting oxygen index and vertical combustion grade had been significantly improved,which the vertical combustion rating was V-1,and the limiting oxygen index was 25.7%.At the same time,it was clearly observed that PP/CSAPP@MF had a excellent anti- dripping effect.Through the heat release performance tests of the PP composites,it drew a conclusion that CSAPP@MF could inhibit the heat release of PP well and reduce the surface temperature of the composites during combustion.