Design And Mechanism Of Flame Retardant And Multifunctional Systems For Cotton Fabrics

Cotton fabric is the most widely used natural fabric due to its softness,comfort,breathability,and reasonable price.Cotton fabrics play an important role in the development of human civilization and have always been an essential material in human life.Unfortunately,cotton fabrics are easily ignited and flames spread rapidly,which easily ignites surrounding combustibles and cause most fires.Therefore,it is necessary to endow cotton fabric with flame retardancy to meet fire safety requirements.This thesis has designed highly efficient flame retardant systems for cotton fabrics.The durable flame retardancy was improved by the construction of hydrophobic layers and the formation of covalent bonds with cotton fabrics.Within a limited weight gain（about 15%）and with a minimal effect on flame retardancy,multifunctionalities such as antibacterial and moisture wicking properties were imparted to cotton fabrics to increase their added value.The flame retardancy,thermal stability,and flame retardant mechanisms of the five systems were systematically analyzed.The durability and durable flame retardant mechanism of the latter three systems were also studied.The hydrophobicity,antibacterial properties,and moisture wicking properties of the relevant functional systems are characterized.The specific studies are as follows:1.An environmentally friendly and efficient flame retardant finishing system for cotton fabrics was designed by foam finishing of sodium polyborate（SPB）.SPB was obtained by hydrothermal heating of boric acid and borax.The foaming agent and foam stabilizer were added to the SPB solution and the flame retardant foam was obtained by stirring at high speed.Then the flame retardant foam was bladed coated on the surface of cotton fabrics.When the weight gain（WG）of SPB was 6.7%,the limiting oxygen index（LOI）of the cotton fabric increased from 18.5%to 32.6%,self-extinguished in the vertical burning test（VBT）with a damaged length of 55mm.The peak heat release rate（p HRR）and total heat release（THR）were reduced by 87.0%and 72.7%,respectively.The peak smoke release rate（p SPR）and total smoke release（TSP）were reduced by 78.0%and 22.2%,respectively.When the WG of SPB was 16.7%,the flame retardancy of the cotton fabric was further improved with an LOI of 46.7%;self-extinguishing in VBT with a damaged length of 33 mm.The p HRR and THR were reduced by 91.2%and 85.7%,respectively.The p SPR and TSP were reduced by 85.4%and 80.6%respectively.The flame retardant mechanism was derived based on the analysis of the pyrolysis products in the gas phase and the morphology and composition of residues in the condensed phase.Besides,foam finishing has the advantages of water saving,energy saving,and reduction of waste liquid discharge.2.A halogen-free,phosphorus-free and fluorine-free flame retardant and superhydrophobic coating for cotton fabrics was prepared.A superhydrophobic flame retardant coating without halogen,phosphorus,and fluorine elements was designed.A polyelectrolyte complex（PEC）aqueous solution consisting of SPB and chitosan（CH）was prepared and finished onto the surface of the cotton fabric by dip-padding.The cotton fabric was then impregnated in a polydimethylsiloxane（PDMS）tetrahydrofuran solution.Due to the water solubility and tetrahydrofuran insolubility of chitosan,a rough structure was precipitated on the surface of the cotton fabric during the dipping process.The rough structure was then covered by the low surface energy PDMS,which synergistically improved the hydrophobicity of the cotton fabric surface.The prepared cotton fabric shows self-cleaning,oil-water separation properties.With a WG of 15.1%of the superhydrophobic flame retardant coating,the LOI of the cotton fabric was increased to 40.0%,self-extinguishing in VBT with a damaged length of 38 mm,p HRR and THR values were reduced by 63.8%and 57.6%respectively in the CCT compared to that of the control cotton.In addition,the TSP value of Cotton-PEC₂/PDMS samples decreased to 0.15 m²from 0.48 m²of Cotton-PEC₂.The flame retardant mechanism showed that the PEC and PDMS coatings acted mainly in the condensed phase.The PEC coating significantly inhibited the heat release of the cotton fabric and the porous silica layer generated by pyrolyzed PDMS inhibited the release of smoke.3.Durable flame retardant cotton fabrics were prepared by covalent bonding of ammonium polyphosphate（APP）and polyethyleneimine（PEI）with cotton fabric,and interfacial polymerization between PEI and trimesoyl chloride（TMC）.The LOI of the treated cotton fabric with a WG of 19.9%was increased to 42.0%and the fabric was self-extinguished in VBT.Besides,the cotton fabric was not ignited in 50 k W/m²CCT and the p HRR and THR were reduced by 88.4%and 55.3%,respectively.The LOI of treated cotton fabric remained at 35.3%after 300 wash cycles and the fabric was still self-extinguished in the VBT.The flame retardant mechanism was derived based on the analysis of the pyrolysis products in the gas phase and the morphology and composition of residues in the condensed phase.The mechanism for durable flame retardancy was proposed based on the analysis of the surface chemical composition of the cotton fabric and the change in elemental content before and after washing.The stable PEI layer stabilized by interfacial polymerization reduced the substitution of ammonium phosphate groups by Na⁺during the washing of the cotton fabric,resulting in a significant increase in the washing durability of the prepared cotton fabric.4.Phosphorylated polyethyleneimine（PPEI）was synthesized by the Mannich reaction and covalently bonded to cotton fabric（Cot-PPEI）.Cot-PPEI was then modified by quaternization reaction to obtain Cot-PPEI-Q.Cotton fabric was endowed with durable flame retardancy and antibacterial properties.With a WG of 15.3%and 14.8%,the LOI of Cot-PPEI and Cot-PPEI-Q increased to 36.3%and 36.8%,respectively.After 30 standard washing cycles,the LOI value of Cot-PPEI decreased to 27.3%,while the LOI value of Cot-PPEI-Q decreased to 30.5%.The quaternization modification increased the quaternary ammonium and primary amine content on the surface of the cotton fabric,which could bind to unreacted ammonium phosphate and thus improving the durability of the flame retardancy.Compared to control cotton,the p HRR values of Cot-PPEI and Cot-PPEI-Q decreased by 87.1%and 81.9%respectively,and the THR decreased by 44.6%and 22.9%respectively.Cot-PPEI-Q had better char formation ability and generate lower smoke than Cot-PPEI.PPEI-Q and PPEI act in both the condensed and gas phases during the combustion of fabrics.They promoted the char formation of cellulose in the condensed phase and reduced the generation of flammable volatiles.In the gas phase,they released non-flammable gases such as NH₃,H₂O,and aromatic compounds,which diluted the flammable gases.5.A novel durable flame retardant has been designed and the wettability of both sides of the fabric has been regulated to endow the cotton fabric with durable flame retardancy and moisture wicking properties.Quaternized ammonium polyphosphate（AQAPPA）was synthesized by the esterification reactionbetweenpolyphosphoricacidandbis（2-hydroxyethyl）dimethylammonium chloride.AQAPPA was covalently bonded to cotton fabric to obtain Cotton-AQAPPA.The wettability of both sides of Cotton-AQAPPA was then regulated by spraying PDMS on one side.At a WG of 14.3%,the LOI of Cotton-AQAPPA was improved to 41.8%.The damaged length in VBT was 3.5 cm.After 30 washing cycles,the LOI value of Cottono-AQAPPA decreased to 28.3%.Flame retardant mechanism showed that quaternary ammonium polyphosphate altered the decomposition path of cellulose.AQAPPA promoted the charring process of cellulose.Cotton-AQAPPA released more CO₂and fewer types of flammable volatiles in the gas phase compared to Cotton-APPA.Besides,AQAPPA improved the washing durability by both the closed phosphate ester and the quaternary amine cation,which reduced the combination of the ammonium phosphate group with metal ions during the washing of cotton fabrics.When the spray volume of PDMS solution was 0.6 m L,the obtained Janus fabric had moisture-wicking properties.Water droplets transferred from the hydrophobic side of the Janus fabric to the hydrophilic side,while not from the hydrophilic side to the hydrophobic side.It is expected this work provides new ideas for flame retardant cotton fabrics that are used as the inner layer of protective clothing,children’s sleepwear,and other applications.