| Cotton fabrics have been one of the most widely used and bio-based textiles over the world.They have been widely applied in both civilian and military fields,thanks to their excellent properties of air permeability,hydrophilicity,comfortableness and softness,et al.However,their flammability is a significant weakness and limits their use in the production of high performance fire retardant textile products.Therefore,increasing interest in improving the fire retardancy of cotton fabrics has been risen sharply both in academia and industry.Considering the research status of flame retardant about cotton fabrics,market demanding and green,energy-saving and environmental concept,some environmental and friendly substances were selected as flame retardants in this study,sodium phytate extracted from plant seeds and root blocks,carrageenan extracted from red algae,chitosan extracted from chitin and crab shell and the 3-aminopropyltriethoxysilane(APTES)which is comburent and easy to be bound to cotton fabrics.Flame retardant cotton fabrics were prepared through layer-by-layer assembly,and and chitosan and APTES were used as cations,sodium phytate and carrageenan were used as anions,respectively.The effect of the combination of these four kinds of anions and cations on the flame retardancy of cotton fabrics were investigated in detail.The structure,thermal stability,flame retardancy,combustion properties,tensile properties and water repellency were studied in detail by Fourier transform infrared analysis(FTIR),scanning electron microscopy(SEM),thermogravimetric analysis(TG),thermogravimetric analysis coupled with Fourier transform infrared analysis(TG-FTIR),vertical burning,limiting oxygen index(LOI),cone calorimeter,universal material testing machine,contact angle tester,respectively.The main results obtained in this study are as follows:(1)The hydrolysis conditions of APTES on cotton fabrics were investigated: pH value and the concentration of APTES solution,the temperature on hydrolysis,soaking time of cotton fabrics.The results showed that the optimum pH values of APTES hydrolysis were from 3 to 4.The weight increasing rate of cotton fabrics increased with the increasing soaking time,the concentration of APTES solution and hydrolysis temperature.Based on the principle of energy,the optimal hydrolysis condition was chosen to control the hydrolysis of APTES on cotton fabrics.Microstructure and thermal stability of coated cotton fabrics were studied by SEM and TG.SEM results showed that the hydrolysis products of APTES were successfully coated on the surface of cotton fabrics.The TG results indicated that the onset degradation temperature and the maximum-rate degradation temperature of coated cotton fabrics were lower than those of untreated cotton fabrics,while the residual amounts at higher temperature zone of coated cotton fabrics were higher than that of untreated cotton fabrics.(2)The flame retardant cotton fabrics based on APTES and sodium phytate were successfully prepared by layer-by-layer assembly.FTIR results showed that APTES and sodium phytate were successfully coated on the surface of cotton fabrics.SEM results indicated that the products of APTES hydrolysis and sodium phytate were dispersed uniformly on the surface of cotton fabrics.TG test results showed the addition of APTES and sodium phytate reduced the onset degradation temperature and the maximum-rate degradation temperature of the cotton fabrics,but significantly improved the thermal stability and the residual amount of the cotton fabrics at higher temperature zone.The LOI value of 15 BL cotton fabric is 26.0%,which is significantly higher than that of cotton fabrics,18.1%.In the vertical burning test,after removing the ignition source,the coated cotton fabric with 15 BL extinguished at once,while the uncoated cotton fabrics were burned out,remaining only a little ash.The improved fire retardancy was due to the formed thermally stable residual char on the surface of cotton fabrics,which prevented mass/heat transfer.It was noted from TG-FTIR results that coated cotton fabrics released more H2 O and CO2,and less inflammable gases than those of uncoated cotton fabrics.The mechanical properties and contact angle test results showed that the addition of APTES and sodium phytate improved the tensile strength,elongation at break and water repellency of coated cotton fabrics.However,the water resistance was not good,the LOI value of 15 BL cotton fabrics decreased from 26.0% to 21.8% after watering 15 times.(3)In order to improve the flame retardancy of coated cotton fabrics based on APTES and sodium phytate,coated cotton fabrics based on APTES,sodium phytate and carrageenan were successfully prepared by layer-by-layer assembly.Morphology,thermal stability,flame retardancy,mechanical properties and water repellency of coated cotton fabrics were investigated.The results showed that the weight increasing rate was lower than that of coated cotton fabrics based on APTES and sodium phytate,and the flame retardancy of this system was also worse than that of coated cotton fabrics based on APTES and sodium phytate.The LOI value of 15 BL coated cotton fabrics is only 22.8%.The TG test results showed that the addition of APTES/sodium phytate/carrageenan reduced the onset degradation temperature and the maximum-rate degradation temperature of coated cotton fabrics.(4)In order to further improve the flame retardancy of coated cotton fabrics based on APTES and sodium phytate,coated cotton fabrics based on APTES,sodium phytate and chitosan were successfully prepared by layer-by-layer assembly.The morphology,stability,flame retardant properties,mechanical properties and water repellency were studied in detail.The results showed that APTES,sodium phytate and chitosan were uniformly coated on the surface of cotton fabric.The introduction of chitosan did not affect the adsorption of APTES and sodium phytate on cotton fabric.However,the introduction of chitosan significantly improved the flame retardancy of coated cotton fabrics based on APTES and sodium phytate.The LOI value of 15 BL coated cotton fabrics is 29.0%,and this sample pass the vertical burning test.The results of cone test showed that the addition of chitosan for 15 BL coated cotton fabrics significantly reduced the PHRR,TSP,THR,increased TTI and char residual amount.The addition of APTES,sodium phytate and chitosan reduced the onset degradation temperature and maximum-rate degradation temperature of coated cotton fabrics;however,this increased the thermal stability and char residual amount at higher temperature zone.With the increase of coating number,the tensile strength,elongation at break and water repellency of coated cotton fabrics are improved.After coated cotton fabrics were washed for 15 times,the LOI value of 15 BL coated cotton fabrics decreased to 23.8%,indicating that the flame retardant cotton fabrics prepared by this method did not have permanent flame retardant properties.Flame retardant mechnism indicated that the addition of APTES,sodium phytate and chitosan increased the release of unflammable gases(water,carbon dioxide,etc.),and reduced the release of flammable gases(hydrocarbons,carbonyl compounds,ethers,carbon monoxide,etc.),improving the flame retardany of coated cotton fabrics. |
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