Preparation Of Piperazine Pyrophosphate And Its Application In The Flame-retardant Polypropylene

Polypropylene(PP)is an important general-purpose high polymer material that can be used in a wide range of applications due to its excellent overall performance.However,its poor fire resistance and low limiting oxygen index make it extremely flammable.During its violent burning process,it not only releases a huge amount of heat,but also produces a large number of molten droplets attached to the flame,making it difficult to control the spread of fire,which can,seriously threaten the safety of life and property.As such,it is important to improve the flame retardant properties of PP for its application and development.In recent years,as people pay more attention to environmental protection,the research and development of halogen-free flame retardants has been developed day by day.The development of phosphorus and nitrogen-based flame retardants has become popular in the area of the halogen-free flame retardants.In this paper,the research on the preparation of a phosphorusnitrogen flame retardant,namely piperazine pyrophosphate(PAPP),was carried out.Based on the study of its preparation,the compound flame retardant system was developed and applied in PP with the aim of improving the flame retardant properties of PP.The main aim of this thesis was mainly on two aspects:(1)Study on the preparation process of phosphorus-nitrogen flame retardant PAPP.Using anhydrous piperazine and phosphoric acid as raw materials,piperazine diphosphate was synthesised,and PAPP was prepared by the new pulverisation-calcination process.The influence of calcination temperature,calcination time and the times of pulverisationcalcination process on the thermal stability of PAPP was studied to determine the best PAPP preparation process.The thermal decomposition behaviour of the prepared PAPP was studied using the thermogravimetric analysis(TGA)method,the structure of the PAPP was studied using infrared spectroscope(FT-IR)and the elemental composition of the PAPP was studied using energy-dispersive X-ray spectrometer(EDS).The results showed that the decomposition of the prepared PAPP at around 250℃ disappeared when the calcination temperature was 270℃ to 280℃ and the calcination time was greater than 1 h,indicating that the prepared PAPP at these condition was completely dehydrated.When the pulverisation-calcination process was repeated for 2 to 3 times,the carbon residue of the prepared PAPP at 700℃ is more than 40%.At this point,the prepared PAPP has a high decomposition temperature and good char formation.The IR structure study of the prepared PAPP showed that the characteristic absorption peaks of P-O,P=O,N-H and-CH2-in PAPP appeared at 974 cm-1,1086 cm-1,1635 cm-1 and 1456 cm-1.The EDS results showed that the PAPP contains about 25%phosphorus and 10%carbon.As a result,high performance PAPP was prepared by the new pulverisation-calcination process.(2)Flame retardant PP based on PAPP compounded flame retardant system.PAPP was compounded with melamine cyanurate(MCA)and ammonium polyphosphate(APP)flame retardants to investigate the effect of the ratio of each component on the flame retardant properties of PP.The combustion properties,mechanical properties and thermal stability of the prepared flame retardant PP materials were investigated using the limiting oxygen index test(LOI),vertical combustion test(UL-94),cone calorimetry test and tensile strength test.The results showed that,when PAPP was used in combination with MCA,the LOI showed a gradual decrease when the mass ratio of the two was changed from 4:1 to 1:4.When the amount of compounded flame retardant added is 20%and the mass ratio of PAPP to MCA is 4:1,the LOI value can reach a maximum of 28.6%.To further improve the flame retardant properties of PP,PAPP/MCA was compounded with APP to study the effect of the ratio of APP on the simultaneous use of the three flame retardants.The results showed that when the mass ratio of PAPP/MCA to APP was changed from 4:1 to 1:4,the LOI showed a trend of first increase and then decrease.When the addition of the three-component compounded flame retardant was at 20%,the LOI value can reach a maximum of 33.6%.The UL-94 test also proveed that the flame-retardant PP prepared at this ratio can reach the V-0 rating.