High Char Residual, Anti-Dripping, High Efficiency Intrinsic Flame Retardant Pa66 Via Combustion-Induced Crosslinking Strategy

Abstract

The flame-retardant modification of Polyamide66 (PA66) is an essential measure to broaden its application spectrum and enhance the safety classification. Owing to its low melt strength, PA66 is associated with serious melt dripping during combustion. Establishing high-temperature self-cross-linking is an effective approach to address this issue. Nevertheless, incorporating cross-linkable structures directly into PA66 inevitably impacts the material’s processability. Herein, we propose a novel combustion-induced cross-linking strategy that shields cross-linkable groups using weak covalent bonds, ensuring their ineffectiveness during processing. During combustion, efficient cross-linking groups are revealed through the preferential rupture of weak bonds, initiating cross-linking reactions to prevent melt dripping and enhance polymer carbonization. Following this strategy, we successfully designed and synthesized an intrinsically flame-retardant PA66. The optimized polymer attained a UL-94 V-0 rating with an LOI of 31.0%, while its pHRR and THR decreased by 41.7% and 25.9% respectively, attributable to combustion-induced cross-linking strategy, confirming its superior fire safety performance. We then investigated its flame-retardant mechanism in-depth, uncovering the synergistic flame-retardant effect of combustion-induced cross-linking. This work provides a novel and promising method for developing flame-retardant PA66 with desirable processing characteristics.

Keywords: Combustion-induced cross-linking, Flame retardancy, Intrinsic, Phosphorus-containing flame retardant, Polyamide 66