Impoving The Flame Retardancy Of Nylon 66 Fabric By Microwave Induced Surface Grafting

Nylon 66 (PA66) fabric has been widely used in civilian and military areas due to its low cost, shrinkage resistance, wear resistance, excellent mechanical property, good wearing characteristics and so on. However, PA66 fabric also has many disadvantages, such as easily burning, low limit oxygen index and low thermostability. Besides, its combustibility and serious melt dripping problems during burning will cause the spread of fire and burn the skin, causing secondary harm to people. So it is necessary to improve the flame retardancy and anti-dripping property of PA66 fabric.In this work, microwave induced grafting is used to graft the monomer into the surface of PA66 fabric by double bonds. The thermostability, char formation, flame retardancy and anti-dripping property of grafted fabric have been improved significantly. It is suggested that microwave induced surface grafting modification process has minimal effect on the handle feeling and mechanical property of the fabric.The content of this work is as follows:The first part is grafting the flame retardant monomer vinyltrimethoxysilane (VTMS) onto the surface of PA66 fabric by one step microwave induced grafting. In this way, the melt dripping during combusting has been eliminated, the char formation and flame retardancy have been improved. Potassium persulfate (KPS) is used as the catalyst and H2O is used as solvent during the reaction. Sodium dodecyl sulfate (SDS) is used as the emulsifier to form the emulsion system. VTMS can be fully dispersed in the emulsion. The optimal grafting conditions are obtained as follows:the monomer concentration is 40 wt.%; the reaction time is 75 min; the reaction temperature is 75 C, and the initiator concentration is 0.5 wt.%. The thermostability and char formation have been improved significantly, the melt dripping during combusting have been completely eliminated.The second part is grafting glycidyl methacrylate (GMA) and thiourea onto the surface of PA66 fabric by a two-step microwave induced grafting process. Potassium persulfate (KPS) is used as the catalyst in the first step and H2O is used as solvent during the reaction. The optimal grafting conditions are as follows:the concentration of GMA and thiourea is 5 wt.% and 20 wt.% respectively; the reaction time is 90 min; the microwave power is 500 W. After two-step modification, the thermostability increases obviously, LOI increases to 25, the melt dripping during combusting have been eliminated and char formation property has also been improved.The third part is introducing the synthesized copolymer onto the fabric by two dips and nips. In microwave circumstance, tetrakis (hydroxymethyl) phosphonium sulfate (THPS) reacts with thiourea and forms the copolymer, this copolymer is then coated onto the surface of PA66 fabric by two dips and nips, then cure process. After modification, the damaged length decreases from 20 cm to 10 cm in the vertical burning test, melt dripping in combustion has been eliminated thoroughly, and LOI increases to 25.6, the thermostability has been improved greatly. Cone calorimetry result indicates that:the time to ignite increases from 4 s to 11 s, the peak heat release rate (pHRR) decreases from 219.2 kW·m-2 to 140.7 kW·m-2, total heat release (THR) decreases from 6.1 MJ·m-2 to 4.7MJ·m-2.