Multiple synergistic effects of copper salicylaldehyde-modified P-N inorganic-organic hybrid in enhancing flame retardancy, smoke suppression, and anti-dripping properties of TPU

Abstract

In recent years, significant progress has been made in the research of flame-retardant thermoplastic polyurethane (TPU) elastomers. However, challenges persist in balancing the enhancement of flame retardancy, smoke suppression, and anti-dripping properties with the preservation of mechanical properties. To address this challenge, a copper salicylaldehyde-modified P-N inorganic-organic hybrid flame retardant (P-N@CuSA) has been prepared and used to improve both the fire safety and mechanical property of TPU in this work. The experimental results showed that the incorporation of 4 wt% P-N@CuSA leads to a 65.1 % reduction in peak heat release rate, a 31.9 % decline in total smoke production, and a 31.3 % decrease in total carbon monoxide production for TPU/4 %P-N@CuSA compared with pure TPU (TPU/0). Notably, 4 wt% P-N@CuSA endowed TPU with a UL-94 V-0 rating without melt dripping. Further analysis of the thermal degradation behavior of TPU composites, combined with an examination of the char residue structure after the cone calorimeter test (CCT), reveals that P-N@CuSA acts through both gas-phase and condensed-phase flame retardant mechanisms during combustion. It subtly alters the thermal cracking trajectory of TPU composites and promotes the formation of a high-quality char residue layer, which serves as a formidable barrier against heat transfer and gas emission. As a result, this innovative approach significantly enhances the overall fire safety performance of TPU materials. This work presents a new strategy for the chemical modification of phosphorus-nitrogen-based flame retardants (P-N FRs) by metal chelates, offering a fresh perspective for the development of fire-safe composites.