UV Grafting of a DOPO-Based Phosphoramidate Monomer onto Polyamide 66 Fabrics for Flame Retardant Treatment Chanchal Kumar Kundu, Bin Yu, Chandra Sekhar Reddy Gangireddy, Xiaowei Mu, Bibo Wang, Xin Wang,* Lei Song, and Yuan Hu* State Key Laboratory of Fire Science, University of Science and Technology of China, 96 Jinzhai Road, Hefei, Anhui 230026, P. R. China * S Supporting Information ABSTRACT: A novel DOPO-based phosphorus- and nitro- gen-containing monomer named DOPO-DAAM was synthe- sized and grafted onto the surface of polyamide 66 (PA 66) fabrics via UV grafting in order to improve the flame retardancy. To facilitate the grafting efficiency, the PA66 fabric surface was first modified through the HCl treatment. In the UL-94 vertical burning test, the PA66 fabrics treated with DOPO-DAAM could stop the melt-dripping. Cone calorim- etry results showed that a 22% reduction in peak heat release rate was achieved for PA66 fabrics grafted with 20 wt % DOPO-DAAM. Thermogravimetric analysis indicated that the presence of grafted monomer catalyzed the degradation pathway of virgin PA66 fabrics where the initial decomposition temperature was reduced and the char yield was enhanced for all treated fabric samples. Moreover, real time FTIR analysis confirmed that the DOPO-DAAM decomposed ahead of virgin PA66 and catalyzed the formation of char residue. 1. INTRODUCTION Polyamide 66 (PA 66) is a thermoplastic textile material widely used in many fields including apparel and industrial textiles due to its superior performances such as high mechanical strength, low cost, resistance to shrinkage, and pleasant aesthetics. Nevertheless, these materials are highly flammable and also have dripping problems which limit their use in a wide range of applications. 1,2 Polyamide fibers are relatively hydrophobic in nature and have a low surface energy which makes the processing of such materials quite difficult. Surface modifications or partial degradation of such fibers through the hydrolytic or oxidizing action of chemicals or biological catalysts might create additional reactive functional groups on the material’s surface that can ease the way for more effective grafting or adherence of coatings in imparting flame retardant or some other functional properties. 3 Grafting technology displays superiority over other ap- proaches, such as tunable density of grafting chains and unchanged bulk properties. 4 Over the past few decades, a variety of grafting polymerization techniques have been developed, which can be induced by chemical initiator, 5 ion radiation, 6 plasma, 7 and UV light. 8 Among these techniques, UV irradiation is regarded as the most reliable method because it has the lowest probability to weaken bulk properties due to the lower radiation energy. 9 The mechanism of photoinduced grafting polymerization involves radicals being generated while the macromolecule is irradiated by UV light in the presence of the photoinitiator, and then, photosensitive monomers can be grafted on the surface. 10 Previously, Liu et al. used acrylamide as a flame retardant for PA 66 fabric through photografting and were able to enhance the thermal stability of PA 66 fabrics and simultaneously stop the melt-dripping. They also modified PA66 with maleic anhydride by exposure to UV light in association with a post- reaction with triethanolamine to enhance the fire retardancy of PA66. 11 Grafting of some other monomers like 2-hydroxyethyl methacrylate (HEMA) and allylthiourea in enhancing flame retardant properties of polyamide 66 fabric through microwave- induced grafting polymerization was also reported recently. 12,13 Apart from photoinduced graft polymerization, polyallyl- amine (PAH), sodium polyphosphate (PSP), TiO 2 nano- particles, ammonium polyphosphate, melamine, pentaerythri- tol, and MMT were already used through various techniques previously by some other research groups for improving the fire retardancy and solving the dripping problems of polyamide fabrics. 2,14,15 In recent years, development of new halogen-free flame retardants, especially some new organophosphorus compounds and their novel derivatives, has received increasing interest concerning environmental sustainability issues. 16,17 Among Received: October 28, 2016 Revised: January 13, 2017 Accepted: January 23, 2017 Published: January 23, 2017 Article pubs.acs.org/IECR © 2017 American Chemical Society 1376 DOI: 10.1021/acs.iecr.6b04188 Ind. Eng. Chem. Res. 2017, 56, 1376-1384