Preparation of ammonium ethylenediamine tetramethylenephosphonate and characterization of durable flame-retardant cotton

Flame-retardant cotton is of great importance in clothing, household goods and various industrial products. In this work, we report a synthesis of phosphorus-rich ammonium ethylenediamine tetramethylenephosphonate (AEDTMP) and its application to flame-retardant cotton fabrics. We synthesize AEDTMP in three step reactions using ethylenediamine, formaldehyde, phosphorous acid and ammonia and characterized through Fourier transform infrared (FTIR), nuclear magnetic resonance, and ultra-performance liquid chromatography-mass spectrometry analyses. The flame-retardant finishing of cotton is done by immerse-pressing fabrics in 5% AEDTMP and 5% trimethylol melamine (TMM) binder solution with increasing treating times to realize multilayer coating on the fabrics. Vertical flame tests show an enhancement of flame retardancy and durability of the treated cotton samples as increasing the treating times. Through FTIR, thermogravimetric, cone calorimetry, scanning electron microscopy image and energy-dispersive X-ray analyses, we reveal that the P–O–C and C–O–C bonds are newly formed by reactions between the fiber, AEDTMP flame retardant and TMM binder, and the multilayer coating enhances such binding reactions. We further performed  the tests of mechanical properties, verifying that the 5-times treated sample has less effect on the comfort and air permeability of the cotton fabrics than the single-treated sample. Our work highlights that the multilayer coating with lower density AEDTMP is superior in flame retardancy, durability and mechanical properties of treated cotton. Graphical abstract