Water-Soluble Cyclophosphazenes as Durable Flame-Retardant Finishes for Nylon/Cotton Blend Fabrics

Nylon-cotton textile blends (Nyco) are known to be challenging substrates regarding their flame-retardant functionalization and its durability. In this study, two different water-soluble flame retardants based on cyclophosphazene together with glycerol (GlyCPZ) and thioglycerol (ThioGlyCPZ) were synthesized enabling a waterborne finishing for Nyco. An extensive investigation of the flame-retardant performance and mechanism as well as the washing fastness was conducted. Thermogravimetric analysis (TGA) indicated changed degradation mechanisms for treated samples, which resulted in a reduced heat release capacity in microscale combustion calorimetry (MCC) measurements and an increased char yield. As a consequence, the limiting oxygen index (LOI) was enhanced from 20% for pure Nyco to 23% and 27.5% for GlyCPZ and ThioGlyCPZ, respectively. Also, the standardized flammability test according to ISO 15025 was passed. In addition, self-extinguishing characteristics were observed even after 10 washing cycles at 80 °C confirming the durability of the finishing. Sulfur was found to be gas phase active, as recombined sulfur compounds were identified in pyrolysis gas chromatography mass spectrometry (Py-GC/MS). Phosphorus was mainly active in the condensed phase, which was verified by analyses of digested burned textile samples using inductively coupled optical emission spectroscopy (ICP-OES).