Improving The Flame Retardancy Of Nylon 66 Fabric By Introducing Natural Proteins During Finishing

Nylon 66(PA66)fabric is widely applied in military and civilian fields owning to its excellent mechanical property,shrinkage resistance,wear resistance,easy dyeing characteristics and so on.However,the low thermostability and high flammability has restricted its further application in many cases.In addition,the PA66 fabric is easy to burn and there are serious melt dripping generated during the combustion.The melt dripping can lead to secondary injuries,such as flame spreading and skin burning.Therefore,it is of great practical significance to improve the flame retardancy of PA66 fabric.In this paper,soybean protein or wheat proteins were introduced onto the surface of PA66 fabric by traditional diping-padding process or coating in order to develop an eco-friendly and non-toxic flame retardant finishing method for fabric.The flame retardant mechanism was also proposed.The modification technical is simple,low cost,which is suitable for industrial production.It is proposed that this might be the first time to use soybean protein/wheat proteins to improve the flame retardancy of synthetic fabrics.Firstly,the soybean protein isolate(SPI)and thiourea were introduced on to the surface of PA66 fabric by dip-padding finishing treatment.The flame retardancy and anti-dripping property of the modified fabric were evaluated by limited oxygen index(LOI)test,vertical burning test,morphology analysis(SEM),thermal stability analysis and so on.The effects of SPI concentration,thiourea concentration and temperature on the combustion properties of PA66 fabric were analyzed.The optimal finishing conditions and formulation were obtained:the temperature was 60℃,and the concentration of SPI and thiourea was 5%and 10%respectively.In this way,the LOI of the modified PA66 fabric was increased from 20.5 to 25.5,and the damaged length was reduced from 20 cm to 4.1 cm.It was proposed that SPI mainly took effect through gas phase.After heating,the soybean protein isolate(SPI)and thiourea could produce sulfur and nitrogen contained non-combustible gas.Therefore,the concentration of combustible gases and oxygen in the combustion zone could be diluted,resulting increase of the flame resistance.Secondly,the effects of water-borne polyurethane(WPU)on the durability of SPI/thiourea flame retardant modified PA66 fabric were investigated by three processes:diping-padding,single-sided coating and double-sided coating.By single-sided coating,PA66 samples with the weight gain of 28.6%WPU had the best water resistance and the minimal damaged char length.Before washing,the fabric has a LOI value of 23.1,the damage length of 4.5cm,showing only very few melt droplets during the vertical test.After washing,the fabric had a LOI value of 22.9,the damage length of 4.8 cm with very few droplets during the vertical test.The treatment of WPU could improve fabric’s thermal stability in the high temperature range.Moreover,the mechanical properties of WPU treated fabrics were promoted.Thirdly,wheat proteins with different molecular weight(WWP,molecular weight of 1000;YWP,molecular weight of 3000)in association with ammonium polyphosphate(APP)and Urea were introduced into the surface of PA66 fabric by dip-padding respectively.For WWP/APP/Urea(15%WWP/10%APP/10%Urea)treated sample,the LOI increased from 20.5 to 25.2 and the damage length was about 13 cm in vertical combustion test.There was no melt dripping during the combustion process.For the YWP/APP/Urea(15%YWP/10%APP/10%Urea)treated sample,the LOI increased from 20.5 to 25.6 and the damage length was about 16 cm.The modified PA66 fabric had no melt dripping during the combustion process and decomposed at lower temperature than pure PA66 fabric.But the thermal stability of treated fabric was improved at high temperature range and the content of residue char was significantly increased.It was proposed that wheat proteins/APP/Urea mainly took effect in the solid phase through promoting char formation.