Synergistic Effects Of Aluminum Hydroxide On The Properties And Mechanism Of The Flame Retardant Polyamide 66 System

Polyamide(PA) is an important engineering plastic with excellent mechanical performance and stability of chemistry, which has been applied to automobile、building and electric field. However, polyamide has been limited to apply due to the flammability and a great deal of dripping during combustion. It can improve the flame retardant performance of the polyamide materials by adding the flame retardant. The polyamide could display effective flame retardancy when using the halogen-containing flame retardant. But their use has been curtailed in many countries because of toxic and corrosive fumes released during combustion. Hypophosphite has significant effect of flame retardancy for polyamide among phosphorus-containing flame retardants, which is added into the polyamide with a lager number in order to achieve flame retardant efficiency. And the machine performance of polyamide reduces with the quantity of hypophosphite increasing.In this work, two flame retardants, aluminum diethylphosphinate (AlPi) and aluminum hypophosphite(AlHP), had been chosen to impart the flame retardancy for polyamide 66(PA 66) with four kinds of synergists by melt blending. The synergists were Sepiolite(Sep), nano-SiO2(SiO2), Silicon resin(SI) and Bamboo charcoal(BPC), respectively. A widely known method to improve the machine performance is to add the synergist into the polyamide system, which could reduce the additive amount of fire retardants and enhance the flame retardancy.Flame retardancy of PA 66 systems were assayed by limiting oxygen index (LOI) and vertical burning test (UL-94). The results indicated that when the three kinds of synergists (Sep, SiO2 and SI) were incorporated into the PA 66/AlPi and PA 66/A1HP composites, the flame retardant efficiency were obviously improved when AlPi and AlHP synergistic systems were added into the PA 66 composites. And the LOI values were kept at higher level. AlPi was mixed with different sizes BPC and used as flame retardant for PA66, and it could be observed that the specimens were no rating in the vertical burning (UL-94) rating. Combining with the BPC (0.2μm and 5μm), the flame retardant efficiency of PA 66/AlHP/BPC system was dramatically increased. According with results of limiting oxygen index and vertical burning test, the three synergists had excellently synergy with the AlPi and AlHP. However, the negative effects of BPC on flame retardancy of AlPi.The results of cone tests revealed that AlPi combined with three synergists (Sep、SiO2 and SI) could efficiently reduce the combustion parameters, such as heat release rate (HRR), total heat release (THR) and so on. When the BPC was added into the PA 66/A1HP system, the combustion performance was enhanced remarkably.TGA results revealed that the synergists could enhance char yield of PA 66 materials and stability at high temperature, when the three synergists were incorporation into the PA 66/AlPi and PA 66/AlHP systems, respectively. And the degradation process had moved to high temperature area when containing the 0.2μm and 5μm BPC in the PA 66/AlHP material. The quantities of residue were 14.5 wt% and 23.9 wt%, which indicated the BPC was beneficial to the improvement of thermal stability for PA66/AlHP composite.Flame retardancy mechanism of PA66 system was discussed by TG-IR test, FTIR, SEM and XPS which could be deduced that the incorporation of three synergists changed the degradation process of the PA 66/AlPi system from gaseous phase to condense phase flame retardancy mechanism. And the AlHP in PA66 composites played an important role of action in the condense phase. three synergists could react with the diethylphosphinate which was produced by AlPi. The analysis of XPS’ indicated that three synergists promoted the formation of flame retardant elements rich char layer on the materials surface, which enhanced the flame retardancy of PA 66/AlPi materials. For the PA 66/AlHP composites, the introduction of synergists in PA66/AlHP system stimulate the catalytic degradation reaction of AlHP to form phosphoric acid and pyrophosphoric acid which could promote PA 66 material degradation to form a solid and tough residue layer. The residue layer could improve the flame retaradancy of PA66 composite by preventing the heat and oxygen passed into the PA66 material.The mechanical properties of PA 66/AlPi and PA66/AlHP systems were slightly declined by incorporating with the three synergists. Except the Izod impact strength, the tensile and flexural strength of PA 66/BPC system was improved obviously comparison with pure PA 66 material. When the PA 66/BPC combined with AlHP, the negative effects of AlHP on the Izod impact strength of PA66 were slight.