Synthesis of intrinsically flame-retardant copolyamides and their employment in PA6-fibers

Abstract

Flame-retarded polyamide 6.6 (FR-PA6.6) was prepared by the cocondensation of hexamethylene diammonium adipate (AH-salt) with the corresponding salts of hexamethylene diamine and two different organophosphorus compounds, namely, 3-hydroxyphenylphosphinylpropanoic acid (3-HPP, 1) and 9,10-dihydro-10-[2,3-di (hydroxycarbonylpropyl]-10-phosphaphenanthrene-10-oxide (DDP, 2). The incorporation of the phosphorus comonomers and the thermal and physical properties of the resulting copolyamides have been studied. The phosphorus-modified FR-PA6.6 possesses high relative viscosities of 2.0 to 2.4, good thermal stability, and was used for the production of polyamide blends by merging FR-PA6.6 with commercial PA6. This offered access to flame-retarded PA6 multifilaments, which possess tensile strengths up to 0.7 GPa and elastic moduli up to 6.2 GPa. Knitted fabrics of FR-PA6 exhibit high limiting oxygen index (LOI) values between 36 and 38 and executed burning tests demonstrate that the incorporation of phosphorus-based comonomers improve flame retardancy significantly. The approach presented here offers a straightforward access to effective flame retardancy in nylon 6.