Preparation And Properties Of Polysiloxane Flame Retardants Containing Phosphorus And Nitrogen Elements For Cotton Fabrics

With the innovation and development of modern textile technology and the requirementsof functional textiles increased, functional textiles and functional chemicals have increasinglybecome research hotspots. The researches of flame retardant textiles and novel flameretardants belong to the research fields of functional textile materials. Halogen-free flameretardants have gradually become the focus of attention. In recent years, polysiloxanes haveattracted people’s attention because of theirs good thermal stability and environmentalfriendliness. They were regarded as a class of flame retardants which have potential fordevelopment. Due to the high efficiency, good environmental compatibility and thermalstability at high temperatures, phosphorus-silicon flame retardant system was considered tohave a good application value. However, few research and application of functionalpolysiloxane flame retardants for cotton fabrics were involved.Preparation methods of two kinds of polysiloxane containing phosphorus and nitrogenelements were studied. Two polysiloxane micromolecules containing silicon, phosphorus andnitrogen elements were designed via intruducting flame retardant and antibacterial functionalgroups respectively in this paper. They were Iodine butyl-co-N-methoxy-3-(dimethoxydibenzyloxyphosphoiyl) propionamide polysiloxane [(IB-co-N-MDPA)PDMS)] andGPPDMS.Based on hydrosilylation and Williamson ether reaction, poly(4-iodobutoxylmethylsiloxane)(PIBMS) with high reaction activity was synthesized using poly(hydromethylsiloxane)(PHMS), methyl iodide (MeI) and tetrahydrofuran (THF) in the presence of a catalyticamount of PdCl2. Reactive Iodine butyl-co-N-methoxy-3-(dimethoxy dibenzyloxyphosphoiyl)propionamide polysiloxane [(IB-co-N-MDPA)PDMS)] with double functions of waterrepellency and flame retardancy was synthesized using N-methylol-3-(dimethoxydibenzyloxyphosphoiyl) acrylic amide (N-MDDPAA), sodium hydroxide and PIBMS. Thestructure of the intermediate PIBMS was characterized, the presence and reactivity of theiodide ion of PIBMS were verified and the structure of the desired product(IB-co-N-MDPA)PDMS was characterized by FT-IR and1H NMR spectra using nuclearmagnetic resonance spectra.Based on guanidinated reaction, dicyandiamide was used as guanidine reagent. Undercertain conditions, APES was hydrolyzed to the corresponding silanol and the silanol wascondensed into the corresponding amino polysiloxane. GPPDMS with double functions ofantibacterial properties and flame retardancy was synthesized using amino polysiloxane,dicyandiamide and esterifying agent of phosphoric acid which was made by hydrolyzingphosphorus pentoxide. The synthesis conditions of GPPDMS were studied using four factorsand three levels of orthogonal experimental design. The structures of GPPDMS werecharacterized by using infrared spectroscopy, ultraviolet spectroscopy, nuclear magneticresonance (1H NMR) spectroscopy.The effects of water repellency and flame retardancy caused by differences of finishingprocess conditions of the cotton fabrics treated with (IB-co-N-MDPA)PDMS were studied. The best finishing process was determined. The thermal properties were analyzed and themorphology of the residue carbon, composition and element content of the cotton fabrictreated with (IB-co-N-MDPA)PDMS after combustion were analyzed. The washingperformance, whiteness, strength and comfortable performance of the cotton fabrics treatedwith (IB-co-N-MDPA)PDMS were investigated. The results showed that: after treated with(IB-co-N-MDPA)PDMS, the contact angle of cotton fabric increased from88.370to124.970and the water repellent grade was90. The LOI of cotton fabric after burning increasedfrom18%to28.5%, smoldering time was0s, continued burning time was3.5s and damagelength was5.8cm. The flame retardant properties of treated cotton fabrics were excellent.After20times washing, the water repellent grade of treated cotton fabric was still as high as70and the limiting oxygen index value was26.2%. After treated with(IB-co-N-MDPA)PDMS, the Ganz whiteness of cotton fabric reduced to77.21from83.77,while the tear strength improved5.7%, radial fracture strength and zonal strength improved12.6%and10.3%, respectively. The permeability and moisture permeability of treated cottonfabrics decreased slightly.(IB-co-N-MDPA)PDMS plays more important roles on reducingthe initial cracking temperature of cotton fabric, heat release rate, maximum heat release rate,total heat released, and the average mass loss of the effective heat of combustion, extendingthe time of the ignition of cotton fabric and increasing fire index. The CO2/CO ratio wasdecreased, so that the cotton fabric was more difficult to be lit and the mass loss decreased alot.(IB-co-N-MDPA)PDMS can promote the formation of a carbonized layer of cotton fabric.The final amount of residual carbon increased from10.5%to42.4%. EDS analysis resultsshowed that the surface of residual carbon that P, Si and C elements with atomic masspercentage increase in the percentage largely and N elements decreased. This indicated that P,Si, N elements played a synergistic role in charring process. Polyphosphate decomposed fromphosphoryl of (IB-co-N-MDPA)PDMS had severe phosphorylation and catalytic dehydrationto the cellulose during the process of combustion, formed a viscous layer of a heat insulatingand isolated the cotton fabric from the air. Polysiloxane of (IB-co-N-MDPA)PDMS producedamorphous SiO2and glassy carbon during the thermal degradation. They also played a role ofpreventing thermal and mass transferring. The nitrogen compounds combined with phosphatein the combustion phase could inflat in flames, which resulted in the puffing of cellulosefibers. This improved the thermal stability, charring performance and flame retardancy ofcotton fabrics.The limiting oxygen index, damaged charcoal long, smoldering time and continuedburning time of cotton fabrics treated with different add-on of GPPDMS were researched.Thermal performance in air and nitrogen atmosphere of cotton fabric, GPPDMS and cottonfabric treated with GPPDMS were investigated. The morphology of the residue carbon,composition and element content of the cotton fabric treated with GPPDMS after combustionwere analyzed. Thermal oxidative degradation kinetics of cotton fabrics treated withGPPDMS was investigated via Flynn-Wall-Ozawa method. Then the flame retardantmechanism of GPPDMS was discussed. The antibacterial properties of Escherichia coli andStaphylococcus aureus were tested. The washing performance, whiteness and strength of thecotton fabrics treated with GPPDMS were investigated. The results showed that: As the add-on of GPPDMS in treated cotton fabrics increased, the flame retardant of cotton fabricsgrew accordingly. The cotton fabric treated with18.6%(add-on) of GPPDMS has a LOI valueof31.9%, which is15.9%higher than that of the untreated cotton fabric. The damaged lengthof treated cotton fabric was3.5cm, smoldering time and continued burning times were0s.Cotton fabric treated with GPPDMS, their antibacterial bandwidth of E. coli was1.9mm,antimicrobial percentage was97%, the degree of inhibition of Staphylococcus aureusbandwidth was1.6mm, antimicrobial percentage was96%. Their antibacterial properties wereexcellent. After20times washing, their antibacterial against E. coli was90%, LOI value was26.1%.They showed excellent washing performance, little changed of whiteness and tearstrength decreasing lightly. Whether in the air or nitrogen, GPPDMS also played moreimportant roles on reducing the initial cracking temperature of cotton fabrics, heat release rate,maximum heat release rate, total heat released, and the average mass loss of the effective heatof combustion, extending the time of the ignition of cotton fabric and increasing fire index.The CO2/CO ratio was decreased, so that the cotton fabric was more difficult to be lit and themass loss decreased a lot. GPPDMS can promote the formation of a carbonized layer ofcotton fabric. The final amount of residual carbon in nitrogen atmosphere increased from13.4%to42.7%and in air atmosphere increased from1.2%to34.5%. EDS analysis resultsshowed that the surface of residual carbon that P, Si and C elements with atomic masspercentage increase in the percentage largely and N elements decreased. This indicated that P,Si, N elements played a synergistic role in charring process. During the combustion process,the silicon component of GPPDMS could be changed to crosslinked structure of Si-O-Si. Thephosphorous component of it generated a viscous phosphoric acid derivative of the cellulose,and the nitrogen group generated gas. A compact exterior, interior loose intumescent layer ofresidue carbon was formed under the influence of heat, which could prevent materials fromenergy exchanging between the flame and the degradation of cellulose fibers. GPPDMSimproved the flame retardancy of cotton fabric by promoting insulation of the heat andoxygen. Thermal degradation kinetics studies showed: GPPDMS also improved the thermaloxidation degradation activation energy of cotton fabrics and thermal stability of cottonfabrics. It made the cotton fabrics more difficult to degrade and improved the flameretardancy performance of cotton fabrics.