| PA66 fiber as the world's first synthetic industrialized fiber has been widely used in military and civilian clothing, furnishings, upholstered furniture due to its excellent properties including good mechanical properties, low cost, resistance to shrinkage and pleasant aesthetics and so forth. However, PA66 fabric is easy to burn because of its higher specific surface area. And the melting drip during the burning might cause another fire and harm people's life. Therefore, there is an urgent need to improve the flame retardancy of PA66 fabric. At present, most flame retardant finishing used for PA66 fabric involves to the semi-softening of the substrate, which cause the infiltration of flame retardant into the fabric and the treated fabric has the low durability and the bad mechanical properties. Meanwhile, study on the flame retardant finishing of PA66 fabric is rarely. Until now, none of those technologies has achieved any substantial commercial success. In this study, surface photografting technology has been used in the flame retardant finishing of PA66 fabric. Photografting is often used in fabric surface modification to improve the wettability, biocompatibility and dyeability since it is an economical, environmentally sustainable and effective method for surface modification of materials without altering bulk properties. However, its application in flame retardant finishing of the fabric has been rarely reported. It is suggested that this could be the first time to use photografting technology to enhance the flame retardancy of fabric.The one-step modificaiton and the two-step photografting modification have been used to improve the flame retardancy of PA66 fabric. In the one-step approach, acrylamide (AM) and 2-hydroxyethyl methacrylate phosphate (HEMAP) have been used as the monomers. Maleic anhydride (MAn) and triethanolamine system has been used in the two-step approach. And the flame retardant mechanism has been investigated in this study in order to guide the future research.Acrylamide has used as a grafting monomer with benzophenone (BP) as photoinitiator to modify the sample surface in order to improve flame retardancy of the PA66 fabric. The effects of monomer concentration, photoinitiator concentration, irradiation time and finishing process on photografting have been investigated in this study. Flame retardancy and the chemical structure of the PA66 fabric have been studied by ATR-FTIR, XRD, SEM photo, LOI testing, the vertical burning testing, thermal analysis and cone calorimetry. The results show that untreated PA66 fabric sample has a LOI value of 19.9 while AM-g-PA66 fabric sample with DP of 32.5% has a LOI value of 26.2, which is 32% higher than that of the untreated sample and the sample has the shorter after-flame time, the shorter char length and no melt dripping in the vertical burning test. AM-g-PA66 could keep 91.6% of the original LOI after 10 cycles of washings with 0.5% commercial grade detergent solution. Combined to TG-FTIR and SEM photo of the residue, it is proposed that the improved flame retardancy of AM-g-PA66 fabric may be due to the earlier thermal degradation of fabric which can cause a rapider shrinkage and an earlier decompositon of amide groups from the grafting chains to release NH3 which can prevent fire from spreading.2-hydroxyethyl methacrylate phosphate (HEMAP) as a grafting monomer and benzophenone (BP) as the photoinitiator has been used in the second system. The effects of monomer concentration, photoinitiator concentration, irradiation time and finishing process on photografting have been investigated. Flame retardancy and the chemical structure of the PA66 fabric have been studied by ATR-FTIR, LOI testing, the vertical burning testing, thermal analysis and cone calorimetry. The results show that P-g-PA66 fabric sample with P of 11% has a LOI value of 31.2 and has no melt dripping, no after-flame time, the shorter char length in the vertical burning test and the grafted sample could keep the LOI value of 26.1 after 50 cycles of washings with 0.5% commercial grade detergent solution. Combined to TG-FTIR, FTIR, XPS analysis and SEM photo of the residue, it is suggested that the improved flame retardancy of P-g-PA66 fabric may be due to the formation of phosphoric and polyphosphoric acids during the thernal oxidative degradation of the grafting chains, which as the dehydration agents drives the the formation of the heat resistant carbonaceous char by carbonisation. According to Kissinger and Flynn-Wall-Ozawa method, the activation energies have been calculated, indicating that the difference in the change of the activation energy could be attributed to the different flame retardant mechanism. However, compared to the ungrafted PA66 fabric, both AM-g-PA66 fabric and P-g-PA66 fabric have the higher activation energies.In the two step approach, surface photografting modification with maleic anhydride (MAn) under UV irradiation in association with a post reaction with triethanolamine has been used to improve the flame retardancy of polyamide66 (PA66) fabric. The effects of irradiation time and monomer concentration on the fabric surface grafting were investigated. Flame retardancy and thermal decomposition behaviour of the samples have been characterized by limiting oxygen index test (LOI), thermal analysis, cone calorimetry and it shows that flame retardancy of the treated PA66 fabric samples has been significantly improved. The chemical structures of the treated samples'surface were characterized by attenuated total reflection infrared spectroscopy (ATR-FTIR). The results show that MAn-g-PA fabric sample reacted with triethanolamine has the LOI value of 29.1 and the sample's LOI value of about 25.7 is still retained after 10 cycles of water rinsing. However, MAn-g-PA fabric sample reacted with triethanolamine loses its flame retardancy after 10 cycles of washings with 0.5% commercial grade detergent solution. It is suggested the grafted chain is easy to degrade in the commercial grade detergent solution because of the alkaline condition.
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