Study On The Flame-retardant And Multifunctional Finishing Of Cotton Fabrics With Biological Phytic Acid

Cotton is a kind of popular textile material owing to its softness,comfort,good moisture absorption,and breathability.However,cotton has the lowest limiting oxygen index(LOI,18%)among all natural fibers,making it can easily catch fire.Therefore,flame-retardant finishing of cotton fabric is essential.With people’s increasing attention to material functions,cotton fabric is well-developed for multi-functionality,which is the focus of current research and development on textile products.When flame-retardant cotton fabric is endowed with various functions such as electrical conductivity and antibacterial capability,it can meet several needs of the market.Among several types of flame retardant for cotton,phytic acid(PA),a bio-based flame retardant,gets a lot of attention due to its high phosphorus and ionized proton content,biocompatibility,and superior chelation.Attributed to the negative charges in PA,a layer-by-layer assembly method can be typically used to achieve a flame-retardant finish on cotton fabrics.The method is energy saving with less emission;however,it requires multiple cycles and seems to be cumbersome,with poor washability of the finished product.In order to improve the washing ability and introduce multi-functional property to flame-retardant cotton fabrics,two-step process in flame-retardant finishing with bio-phytic acid was investigated in this paper.Based on the proton-providing property of PA,aniline was in situ polymerized on flame-retardant cotton to acquire fabrics with flame retardancy and conductivity.Owing to the superior complexing property of PA,in situ reduction of Ag nanoparticles on the surface of the flame-retardant fabrics imparted anti-bacterial property.The process and mechanism of phytic acid finishing,the control structural property of finishing products,the compatibility in phytic acid multifunctional finishing were systematically studied,which provide a theoretical and applicable basis for the ecological flame retardant and multifunctional finishing of cotton fabrics with biological phytic acid.The main research work and conclusions are as follows.(1)A two-step method was used to impart flame-retardant function to cotton fabrics.Polyethyleneimine(PEI)was grafted on cotton fabrics via the crosslinker EH(both concentrations 10%),and then,the crosslinker EH was used to graft PA(concentration=0.4 mol/L,pH=2)for improving the flame retardancy and washing ability of the fabric.The structure,physical property,thermal property and flame retarding mechanism of flame retardant fabric was studied,as well as the molecular dynamics model of adsorption of PA or PEI on the surface of cotton fiber.Flame retardant cotton fabric with self-extinguishing effect after 30 times of mild water washing could be obtained.While,the strength retention value of the fabric was 75%.PEI and PA in flame retardant fabric form intumescent flame retardant system.The flame-retardant fabric degraded easily in the initial stage of pyrolysis,while the degradation was slow in the middle and later stage,due to dense carbon layer.The total heat release,average heat release rate and average effective combustion heat were reduced by 17.8%,36.9%and 33.3%respectively.In the same pyrolysis system,for the flame-retardant fabric,the ratio of the combustible and noncombustible gas intensities was significantly lower than the untreated one.Compared with untreated(i.e.,non-flame-retardant fabric),the barrier and charring effect of the flame-retardant fabric increased by 84.94%and 11.35%,respectively,while the flame-retardant effect increased by 33.08%.The probability of amino group in PEI molecule existed on the fiber surface was greater than that of hydroxyl group in PA molecule,though the adsorption rate of PA molecule on the modified fiber surface was greater than that of the unmodified fabric.(2)Complex conductive finishing of flame-retardant cotton fabric with phytic acid was studied.Using the proton-donating property of PA,pH responsive,flame-retardant conductive textile was prepared by in situ polymerizing PA doped aniline on flame-retardant fabric,marked as PPC-44(the mass concentration of phytic acid and aniline was 0.4 mol/L).The preparation process,doping/de-impurity characteristics,structure and thermal property of flame-retardant conductive fabric were studied.Results showed that the flame-retardancy and conductive properties of textile prepared from flame-retardant cotton fabric increase with increasing aniline mass concentration.The colors,flame retardancy,and electrical conductivity of PPC-44 and C-44(controlled cotton fabric as substrate)changed with increasing number of doping/de cycles.In the de-doped state,both fabrics were dark purple,C-44 was not electrically conductive and flame-retardant,while PPC-44 was flame-retardant and non-conductive.For C-44,there was discrepant due to different dopants(phytic acid or hydrochloric acid).And PPC-44 was also flame-retardant and electrically conductive when treated with HCl.The binding energies of phosphorus in the PPC-44 and C-44,visual morphology after combustion,and thermal parameters(Initial decomposition temperature(Ti),extrapolated initial temperature(Te),maximum weight loss rate temperature(Tmax))also varied with the de/doping cycles.In the same pyrolysis system,for PPC-44,the ratio of combustible to non-combustible gas intensities was lower than that of the untreated fabric while slightly higher than that of the flame-retardant fabric.Thus,through PA-doping of polyaniline,reversible flame retardancy and electrical conductivity can be achieved,which provides a new idea for preparing pH-responsive flame-retardant and electrically conductive fabrics.(3)Complex antibacterial finishing of flame-retardant cotton fabric with phytic acid was investigated.Owing to the superior complexing property of PA(six phosphate groups),PA in the flame-retardant fabric was used as a soft film substrate,then Ag nanoparticles were in situ reduced on its surface to obtain flame-retardant antibacterial fabric.The relationship between phosphorus content,pH and LOI was analyzed,the structure and thermal property of flame-retardant antibacterial fabric were studied.Results showed that in the same pH solution,with increasing PA concentration,the LOI of the fabric increased.The binding energy of phosphorus on the fabric surface changed slightly only.When the number of moles of phosphorus in the solution was unchanged,the LOI value and binding energy of phosphorus increased gradually with decreasing pH,while flame retardancy of the fabric was rather good.To the flame-retardant antibacterial fabric,the thermal parameters(Ti,Te and Tmax)were higher than those of the flame-retardant fabric,but the LOI was lower,while still keeping good flame retardant effect.Flame-retardant antibacterial fabric has obvious antibacterial effect against E.Coli and S.Aureus,and the antibacterial effect on E.Coli was better than S.Aureus.Ag nanoparticles were evenly distributed on the surface of the flame-retardant antibacterial fabric,the particle size of Ag nanoparticles was～20 nm,and the lattice fringes were obvious with a fringe spacing of d=0.238 nm.(4)The thermal stability of cotton fabric,flame-retardant fabric,flame-retardant conductive fabric and flame-retardant antibacterial fabric were evaluated based on two model,i.e.,free dynamic differential method Kissinger and integral method F-W-O.For different kinds of fabrics,the pyrolysis stage of fabrics varied,the value of pyrolysis parameter decreased with increase in flame retardancy.For the same fabric,different heating rates only slightly influenced the quality of the fabric,while influenced the pyrolysis interval at different extent.The pyrolysis temperature increased as the heating rate increased.Apparent activation energy of the four fabrics was calculated according to the F-W-O integration method,results showed that the apparent activation energy of the three finished fabrics was higher than that of the untreated fabric,the pyrolysis rate was reduced while the thermal stability was improved.The Kissinger differentiation method was used to determine the apparent activation energy of the three fabrics and indicated an irregular zigzag increase with increasing conversion rate.In the conversion rate interval of 0.2～0.6,and the apparent activation energy was stable.However,in cases of excessively low and excessively high conversion rates,the apparent activation energy fluctuated greatly.For each fabric,the apparent activation energy obtained by the Kissinger differentiation method was generally higher than that from F-W-O integration method.For all the four fabrics,the variation of activation energy obtained by the two methods were similar,and the consistency of the fabrics in the pyrolysis process was further demonstrated to provide a theoretical basis for the behavior of fabric pyrolysis.