Synthesis Of Charring Agents Containing Phosphorus And Nitrogen And Investigation On Intumescent Flame Retardant Polypropylene Nanocomposite

Polypropylene(PP),as an important polyolefin,has been extensively used in various fieds owing to its superior mechanical capacity,easy processability and chemical stability.However,the application of PP is strongly restricted owing to its easy combustibility and dripping tendency.Recently years,intumescent flame retardant(IFR)systems have been extensively employed to improve the flame resistance of polyolefins as a sort of no-halogen flame retardant.Furthermore,the development of nano-composite technology also opens up a new direction for halogen-free flame retardant polypropylene.In this paper,research overview of flame retardant PP has been reviewed on the basis of a lot of literatures.The experimental scheme is optimized for the problems of flammability,mechanical properties and water resistance of polypropylene.Based on molecular design,a polymeric char-forming agent containing phosphorous and nitrogen were synthesized and well characterized.Meanwhile,the polymeric char-forming agent and APP were incorporated into polypropylene matrix to improve the flame retardancy.In summary,the main work of this paper is divided into three parts.1)A novel linear polymeric char-forming agent(PEPAPC)containing cyanuric chloride,PEP A and piperazine is synthesized via the nucleophilic substitution reaction and well characterized using elemental analysis,FTIR,NMR,and TGA.And it proved that PEPAPC has excellent thermal stability and char formation ability.Then,it is combined with APP to prepare various intumescent flame retardant PP samples.TGA results indicate that the combination of PEPAPC and APP could be beneficial to improve the thermal stability of the char residues of PP materials,especially PP6 with 3/1 weight ratio of APP to PEPAPC.IFR-PP system with 3/1 weight ratio of APP to PEPAPC at 20 wt%total amount could reach a LOI value of 28%and pass UL-94 V-0 rating.At this optimum ratio,pHRR is reduced by 81.27%via the cone calorimeter test.In addition,when the same amount of flame retardant is added,with the increase of PEPAPC and the decrease of APP,PP composites have better water-resistance performance.This result indicates PEPAPC has excellent water resistance.2)The combination of PEPAPC and APP as intumescent flame retardant(IFR)and organically modified montmorillonite(OMMT)are added in PP matrix,and prepare various intumescent flame retardant PP/OMMT nanocomposite through the melt blending.SEM,XRD and TEM results show that the OMMT were intercalative or/and exfoliated in the PP matrix,exhibiting high dispersion degree,especially after the compatibilizer is added.TGA results indicate that IFR with OMMT could improve carbon yield of PP matrix under high temperature.When the total loading of flame retardants is 20%,the addition of OMMT obviously increases LOI values of intumescent flame retardant PP.Among them,PP7 sample can pass UL-94 V-0 rating.Besides,compared with pure PP,its LOI value can improve to 32%,and pHRR goes down 90.5%through the cone calorimeter test.The results of SEM,FTIR confirm that the formation of highly expansive char layer and MMT could enhanced flame retardant performance of PP matrix.Besides,the mechanical properties study shows that the tensile strength and elongation at break of the intumescent flame retardant PP is effectively improved when the weight ratio of OMMT is 2%.3)A range of nanometer hybrid consisting of PEPAPC and Na-montmorillonite(Na-MMT)are prepared through in-situ polymerization,and are named by PEPAPC-2Na,PEPAPC-4Na and PEPAPC-8Na respectively.Then,they are combined with MPP to prepare various PP nanocomposites.SEM,XRD and TEM results indicate that the montmorillonite in PEPAPC-2Na and PEPAPC-4Na were intercalated or/and exfoliated well in the PP matrix when the compatibilizer is not added.The combination of PEPAPC/Na-MMT nanometer hybrid and MPP could increase LOI values of PP material.PP/MPP/PEPAPC-NaMMT system with 1/1 weight ratio of MPP to PEPAPC-4Na at 20 wt%total amount could achieve UL-94 V-0 rating and the pHRR is decreased by 77%in comparison with that of neat PP.SEM and FTIR results reveal that the interaction of IFR and MMT could form effective intumescent char layer to protect the internal substrate in the heating process,and improve the flame retardant efficiency of PP material.An outstanding water resistance is also obtained for PP nanocomposites,which could be attributed to the lower water solubility of MPP and PEPAPC-4Na compared with APP and Na-MMT.