Preparation Of Nanohybrid Modified Intumescent Flame Retardant And Study On Structure And Properties Of Flame Retardant Polypropylene Composites

Polypropylene?PP?is one of the fastest growing general thermoplastics.It has many advantages,such as good comprehensive properties,large output,wide application and low price.However,like most other materials,PP is extremely easy to burn,and has serious droplet phenomenon.It is also easy to cause secondary combustion in the fire site,which has a serious impact on people's lives and tenure.It also greatly limits its application in the fields of electronics,electrical appliances,transportation and so on.Therefore,it is urgent to study flame retardant PP materials with green environmental protection and excellent comprehensive performance.In recent years,intumescent flame retardant?IFR?has become a research hotspot of flame retardant materials because of its low smoke,environmental protection,anti-dropping,remarkable flame retardant effect and irreplaceable characteristics.Among them,expansible graphite?EG?stands out as a new type of IFR,but it has some problems,such as poor compatibility with polymer matrix,easy to produce"popcorn effect",which makes the amount of flame retardant more and the mechanical properties of PP material decrease.Therefore,the preparation of PP composites with excellent flame retardancy and mechanical properties has become a challenge for the further development of PP flame retardant composites.In order to solve the above problems,an environmental friendly flame retardant with simple preparation method and high flame retardant efficiency is prepared by hybrid modification of EG with SiO₂ nanoparticles,which greatly improves the flame retardant efficiency of composites and the interfacial compatibility between matrix and flame retardant.Furthermore,in order to further improve the impact toughness of the composites with excellent flame retardant effect,octene-ethylene?POE?is used as elastomer to toughen PP,so that the composites with excellent flame retardancy and good impact toughness are obtained.On the other hand,the introduction of PA6 as a macromolecular carbon-forming agent reduces the amount of flame retardant and further improves the flame retardant efficiency of the flame retardant composite.The main results are as follows:?1?SiO₂ nano hybrid expandable graphite?nHEG?is synthesized in situ by one-pot method.It is found that the structure and morphology of nHEG have changed greatly,especially the thermal stability of nHEG has been greatly improved,which has great advantages for the application of nHEG as flame retardant.?2?The obtained nHEG is used to flame retardant PP.The results showes that when20%nHEG is added,the vertical combustion?UL-94?level of the composites reaches V-0,and the limit oxygen index?LOI?of the composites increases to 25.4%.The flame retardant properties and smoke suppression effects of the composites are excellent by cone calorimeter?CCT?.The flame retardant mechanism of the flame retardant composites is further elaborated by studying the structure and morphology of the carbon layer.In addition,SiO₂nanoparticles on the surface of nHEG promotes heterogeneous nucleation of PP,which greatly reduces the degradation of mechanical properties by inorganic particles.?3?In order to further improve the impact toughness of PP/nHEG20 composites with excellent flame retardant properties,the flame retardant composites are toughened by POE,and the impact toughness is greatly improved and the flame retardant properties are well maintained.In addition,POE in composites has a"sea-island"structure and good dispersion.When a small amount of POE is added,the crystallinity of composites can be improved.The improvement of impact toughness of composites can be explained by the analysis of rheological properties and impact section morphology.?4?PP/PA6/nHEG flame retardant composites are prepared with PA6 as macromolecule charring agent.The results show that the LOI of PP/PA6 composites is only 19.1%.With the addition of nHEG,the flame retardancy of composites increases greatly.Especially when the content of nHEG is only 10%,the UL-94 of composites reaches V-1 level,while the UL-94of composites with unmodified EG can not reach any level.It can be seen that SiO₂nanoparticles and macromolecule charring agent PA6 have good synergistic flame retardant effect.PA6 has good synergistic flame retardant effect.CCT test results further show that PP/PA6/nHEG composites have been greatly improved in terms of heat release rate,smoke release rate and carbon residue.