Preparation And Properties Of PA12/LLDPE Co-Continuous Flame Retardant Composites

The dispersion of flame retardants in multiphase composites becomes more complex for the flame retardants in blends.It can be uniformly dispersed in the matrix or selectively dispersed in a phase.At the same time,morphology and structure are also the key factors affecting the performance of multiphase and multicomponent systems.In previous studies,the structure and properties of the two phase flame retardant composites were investigated,and it was proved that the flame retardant properties of the polymer alloys with co-continuous structure were better than those with island structure.Is there a threshold for adding flame retardants in a co-continuous system（keeping the continuous structure unchanged）?How does the content and distribution of flame retardants affect the overall flame retardancy of a material in a co-continuous structure?Can the flame retardancy of co-continuous alloy be improved by enhancing the flame retardancy of flame retardancy phase and adding synergists?In order to answer the above questions,this paper based on the structural advantages of polymer co-continuous alloy.The use of flame retardant phase combustion to generate continuous carbon layer to protect the flammable phase.Different flame-retardant phase systems were designed and prepared by changing the processing sequence,filler content,changing flame retardant and synergistic compounding.The effects of filler content,dispersion state and carbon formation protection of flame retardant phase on the whole flame retardant property of polymer co-continuous alloy were investigated.The main research contents and results of this paper are as follows:（1）PA12/LLDPE polymer alloys with stable co-continuous structure have been prepared by two-step blending method:The quality ratio of PA12/LLDPE/PE-g-MAH/PB-g-MAH has been found to be the best formula=40/48/9/3.（2）The co-continuous flame retardant polymer alloys with different contents and different dispersion conditions were prepared by master-batch method.Considering the effect of the addition of flame retardant on the viscosity of nylon phase will affect the two phase co-continuous structure,the addition of flame retardant should not exceed 40 phr.（3）Through combustion test,TG analysis and carbon layer analysis,it was found that APP complete distribution and PA12 co-continuous materials have better overall flame retardancy.When 25 phr APP was added（PA12/APP）/LLDPE LOI value increased by 5.1%compared with PA12/（LLDPE/APP）,and it has certain self-extinguishing ability.APP can form phosphate ester intermediates with PA12 at the early stage of reaction,promoted the early carbon formation of nylon phase,and obtained a more closely ordered carbon protection layer.（4）Piperazine pyrophosphate（PAPP）,which has lower initial decomposition temperature and higher carbon reaction rate with PA12,was selected as the main flame retardant in view of the poor droplet melting and self-extinguishing ability of APP system.When 25 phr PAPP was added,the LOI value of PA12/PAPP/LLDPE was increased by 13.8%compared with that of PA12/APP/LLDPE,and the self-extinguishing time of T₁was reduced by 80 s.（5）Compared with PAPP/APP composite system and carbon catalyst Ni（OH）₂as synergist system.It was found that Ni（OH）₂as synergist system on the flame retardant phase and the overall flame retardant properties of co-continuous alloy,the self-extinguishing and carbon forming ability of co-continuous materials improved more.When the PAPP/APP mass ratio was 25/5,the LOI value decreased by 15.1%compared with the 25 phr PAPP sample and began to produce droplet.When 2 phr Ni（OH）₂synergist was added,the total self-extinguishing time between two ignitations was reduced by 15 s compared with 25 phr PAPP sample.It was found that only when the carbon layer of flame retardant phase has a high degree of graphitization,and the carbon layer can it play a good role in carbon formation protection.