Study On The Morphology And Properties Of Flame Retardant Polyolefin Composites With Modified Expandable Graphite

Polypropylene(PP)and Polyethlene(PE)are polymer materials which are widely used in various industries such as chemical plant,petroleum and building.However,they are flammable and will release CO,combustible gas and other toxic gases during combustion,which are very harmful to human health and the environment.Furthermore,the flammability is a disadvantage in some applications industries where high flame retardancy is required,for example,in electrical applications,transportation sectors and daily necessities.Therefore,seeking desirable flame retardant is quite necessary.At present,the main method is to mix flame retardant into the polymer matrix directly.Over the past two decades,with limitation of halogen-containing flame retardants and increasing requirements of high fire security for residential safety and environmental concerns,the main effort on flame retardants has shifted to the development of halogen-free flame retardants.In this article,some efficient and simple approaches for the preparation of organic-inorganic intumescent interfacial flame retardants,aiming at enhancing the flame-retardant efficiency and interfacial adhesion between matrix and flame retardants was presented.The expandable graphite(EG)is functionalized by using grafting process,resulting in the formation of organic-inorganic intumescent flame retardants.Based on the successful grafting reaction,a series of flame-retardant composites with different content of modified EG are prepared and evaluated.The interfacial grafting flame retardants provided a novel way to prepare organic-inorganic intumescent flame retardants and the as-prepared flame retardants exhibited excellent flame retardant efficiency.The main results of this thesis as follows:1.A novel organic-inorganic interfacial intumescent flame retardant mode(MEG)is prepared by using DOPO,KH-560 and EG.With the incorporation of 30 wt%of MEG into PP,the satisfied flame retardant grade(UL-94)and limiting oxygen index(LOI)are obtained.The residues of the PP/MEG composites are significantly increased with PP/EG and PP/EG/DOPO composites.Moreover,the residual char of PP/MEG composites is more compact and integrated.In addition,the formation of organic side chains on the MEG surface by the grafting reaction also contributed to an improvement in the interfacial compatibility,leading to an enhancement in mechanical properties of the composites compared with the PP composites filled with EG.2.The effects of MEG on the combustion and flame retardancy of HDPE/EVA system are investigated.When the adding amount of MEG is 20%,the flame retardant composite can reach the level of V-0,the oxygen index is 26.5%and the carbon residue at high temperature reaches to the level of 37.68%.Cone calorimeter test results show that MEG can greatly reduce the heat release rate and smoke density and improve the combustion behavior of composites.The crystallinity of the composites increased with the addition of MEG,because of the role of heterogeneous nucleation.3.The modified NEG is prepared by surface treatment of expandable graphite with N-FR and KH-560.NEG can be used as flame retardant for HDPE/EVA materials.Because of the synergistic flame retardant effect,when the NEG content is 20%,the flame retardant composites can reach the level of V-0.Since NEG can produce a large amount of incombustible gas at high temperature,the gas phase flame retardant mechanism can reduce the heat release rate of the composites and improve the combustion behavior of the composites.4.The surface modification is carried out by using P-FRB and silane coupling agent(ITPS).The surface modified PEG is prepared with excellent thermal stability and the residual carbon content is up to 86.9%at high temperature.The LDPE can reach the V-0 level of vertical combustion test when the PEG addition amount is 12%,and the oxygen index is about 25.1%.PEG has little effect on the melting temperature and crystallization temperature of the flame retardant composites,which greatly improves the crystallinity of the composites and maintains the mechanical properties of the composites.Fourier transform infrared test results show that the expandable graphite on the surface of P-FRB and ITPS at high temperature to form phosphoric ester compound and the surface to form a layer of high temperature resistant protective layer,the flame retardant composites exhibit excellent thermal stability at high temperature.