Studies On Boehmite/Nylon66 Composites And The Synergistic Flame Retardant Mechanism Of Boehmite

High performance and low cost of PA66 composites have always been a hot research area. Boehmite（BM）is a new lamellar inorganic functional filler with high whiteness, small oil absorption value, perfect crystal structure and other characteristics,which can be used to improve the properties of reinforcement,thermal conductivity, flame retardancy, smoke suppression in polymers. The study of BM filled polymers report rarely, and the properties of its nylon 66（PA66）composites needs researched systematically. In addition, the efficiency of AlPi（aluminium phosphinate） and MPP（melamine polyphosphate） synergistic flame retardant PA66 is not high enough. The addition of BM in the above PA66 composites can further improve the flame retardant properties. The flame retardant mechanism of BM/AlPi/MPP system in PA66 composites is studied. Specific works are as follow.（1） Boehmite/Nylon 66 composites with good comprehensive properties in mechanical, flame retardancy and thermal conductivity were prepared. Through multiple sets of comparative experiments, the results show that comprehensive properties of composite is the best when BM Particle size is 1.5μm and modified with 1.5wt% KH-550. With the increase of BM filling content,properties of composites are improved observably in mechanical properties, flame retardancy, thermal conductivity, heat resistance, thermal stability with only small degrade in flow ability. BM has played a role of heterogeneous nucleation in the melt cooling process, it makes PA66 began to crystallize at higher temperatures, crystallization rate increases, and the degree of crystallinity is reduced. The comprehensive properties of composite are the best when the content of BM is 50wt%. Its tensile strength is 93.48 MPa, flexural strength is 157.8MPa, impact strength is 5.36KJ/m2, flame retardant rating is UL94 V-0, thermal conductivity is 0.75 W/（m?K）, heat deflection temperature is 169.3℃ and its processability and forming properties are good.（2） The effect of BM/AlPi/MPP system synergistic flame retardant PA66 were investigated. The results showed when the mass ratio of AlPi and MPP among 3:2²:3 and total content was 15.0 wt%, the flame retardant property passes UL-94 V-0 level for 3.2mm samples only. When the mass ratio of BM、AlPi and MPP is 3.0:8.5:6.5 or 3.0:9.0:6.0, and the total content was 18 wt%, all samples（3.2mm and 1.6mm） passed UL-94 V-0 level, and with a small increase in mechanical properties. With further reduce the amount of flame retardants to total content of 15 wt%, when the mass ratio of BM、AlPi and MPP is 3.0:7.2:4.8, the flame retardant properties passes UL-94 V-0 level for 3.2mm samples, and the LOI reaches 29.7%, and the mechanical properties do not deteriorate, tensile strength is 80.68 MPa, flexural strength is 121.4MPa, impact strength is 4.21KJ/m2.（3） The flame retardant mechanism of BM/AlPi/MPP system and formation of barrier layer were studied. The results indicated that three constituents played an important role in both gas phase and condensed phase respectively.In gas phase,AlPi partly evaporate and partly form diethyl hypo phosphorous acid, which transform into PO ? radical under high temperature and combined with H ?, OH ? radicals in flame, that break the combustion chain and suppress the flame. On the other hand, non-combustible gas generating from MPP when heated and water vapor releasing from BM decomposition both can be dilute flammability concentration. In condensed phase, both polyphosphoric acid and partly melamine decomposited from MPP, diethyl hypo phosphorous acid decomposited from AlPi and Al₂O₃ decomposited from BM, which cooperated to form a tight and continuous intumescent layer on the surface of the composite matrix, resulted in good flame retardancy.