Poly- and cyclophosphazenes are excellent flame retardants but currently, are not used as textile finishing agents because water-soluble and permanent washing systems are missing. Here, we demonstrate for the first time, the successful usage of a water-soluble cyclotriphosphazene derivative for textile finishing for cotton, different cotton/polyester, and cotton/polyamide blend fabrics. A durable finish was achieved using a photoinduced grafting reaction. The flame retardant properties of the various fabrics were improved with a higher limiting oxygen index, a reduced heat release rate, and an exhibition of intumescent. Furthermore, the finished textiles passed several standardized flammability tests.

Phytic acid (PA), as a natural source of phosphorus, was immobilized on cotton (CO) in a layer-by-layer (LbL) approach with polyvinylamine (PVAm) as the oppositely charged electrolyte to create a partly bio-based flame-retardant finish. PVAm was employed as a synthetic nitrogen source with the highest density of amine groups of all polymers. Vertical flame tests revealed a flame-retardant behavior with no afterflame and afterglow time for a coating of 15 bilayers (BL) containing 2% phosphorus and 1.4% nitrogen. The coating achieved a molar P:N ratio of 3:5. Microscale combustion calorimetry (MCC) analyses affirmed the flame test findings by a decrease in peak heat release rate (pkHRR) by more than 60% relative to unfinished CO. Thermogravimetric analyses (TGA) and MCC measurements exhibited a shifted CO peak to lower temperatures indicating proceeding reactions to form an isolating char on the surface. Fourier transform infrared spectroscopy (FTIR) coupled online with a TGA system, allowed the identification of a decreased amount of acrolein, methanol, carbon monoxide and formaldehyde during sample pyrolysis and a higher amount of released water. Thereby the toxicity of released volatiles was reduced. Our results prove that PA enables a different reaction by catalyzing cellulosic dehydration, which results in the formation of a protective char on the surface of the burned fabric.

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).

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