Abstract
The synergistic charring, flame-retardant behavior of the macromolecular charring agents polyimide (PI) and melamine polyphosphate (MPP) were studied in glass fiber-reinforced polyamide 66 (PA66). This kind of synergistic charring effect is explained by the fact that PI performed better char-forming ability while working with phosphorus content. The research results showed that, compared with the incorporation of individual MPP, MPP/PI with an appropriate ratio exhibited better flame retardancy and better charring ability. A blend of 11.9%MPP/5.1%PI/PA66 possessed an increased LOI (limiting oxygen index) value of 33.9% and passed the UL94 V-0 rating, obtained a lower peak heat release rate value (pk-HRR), a lower total heat release (THR) value, a lower total smoke release (TSR) value, and a higher residue yield. The results verified the synergistic flame-retardant effect between MPP and PI in the PA66 composite. Melamine polyphosphate and PI jointly interacted with PA66 matrix and locked more carbonaceous compositions in residue and formed a more compact char layer, resulting in a reduced burning intensity and a reduction in the release of fuels. Therefore, the enhanced flame-retardant effect of the MPP/PI system is attributed to the higher charring ability and stronger barrier effect of the char layer in PA66 in the condensed phase.
Highlights
Polyamide 66 (PA66) is widely applied as an engineering plastic due to the fact of its excellent melt flowability, heat resistance, and mechanical properties
The results imply that the melamine polyphosphate (MPP)/PI mixture exhibited a better flame-retardant effect than MPP or PI when it was individually applied in the polyamide 66 (PA66) composites
5.1 wt % PI system increased the limiting oxygen index (LOI) value to 33.5%, passed the UL94 V-0 rating, suppressed the combustion intensity, reduced the total heat release, and increased the residue yields compared with combustion intensity, reduced the total heat release, and increased the residue yields compared with the composite containing only 17wt % MPP
Summary
Polyamide 66 (PA66) is widely applied as an engineering plastic due to the fact of its excellent melt flowability, heat resistance, and mechanical properties. Research and exploration on halogen-free flame-retardant systems for polyamide materials are important for the development of high-end manufacturing of glass fiber-reinforced PA materials [6,7]. Our team explored the synergistic flame-retardant effect of a phosphaphenanthrene derivative and AlPi in PA66 materials [19]. Chemically bonding different flame-retardant groups with traditional flame-retardant groups or preparing their novel derivatives are other ways to obtain flame-retardant compounds with high efficiency in polyamide. Designing and preparing new flame-retardant molecules with novel chemical structures or modifying the compounds which were not applied in flame-retardant fields before are main ways to explore novel flame-retardant systems in polyamide. Based on the above approaches, many researchers have conducted studies on finding high-efficiency flame-retardant systems for polyamide. The synergistic flame-retardant effect and mechanism of the MPP/PI system were investigated comprehensively
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