Construction And Performance Of Hydrophobic,Flame-Retardant And Self-Healing Multifunctional Coating Of Cotton Fabric

Textile is closely related to people’s daily life.Cotton fiber is one of the most common natural fibers.It is favored by people because of its natural comfort,renewability,environmental protection and softness.Cotton fabric is widely used in clothing and home decoration.At the same time,many industrial textiles,such as oilwater separation fabrics,industrial filter materials,also use cotton fabrics as the substrate.However,cotton fabric is a highly combustible fabric,of which the limiting oxygen index（LOI）value is only about 18%.And cotton fiber belongs to hydrophilic fiber,which limits its application in many fields,such as oil-water separation,indoor decoration,automobile interior,medical treatment,fire protection and so on.In order to broaden the application scope of cotton fabric,it is very essential to endow cotton fabric with hydrophobic and flame retardant properties.At present,the hydrophobic finishing of cotton fabric is mostly carried out by the combination of nano particles and low surface tension additives.However,nano particles on the cotton fabric substrate finished by this kind of simple method are easy to fall off,which lead to poor abrasion resistance and insuffiecient durability of the functional coating.As for the flame retardant finishing of cotton fabric,due to the fact that halogen flame retardant has been banned by relevant laws and regulations,flame retardant contained phosphorus,nitrogen,silicon and boron are considered to be the most likely to replace halogen in the new generation of environmentally friendly flame retardant system.However,by traditional physical blending method,cotton fabric still suffers from poor water resistance and durability.Different from physical blending,combining the cotton fabric with flame retardant through covalent bonds can effectively solve the problem of poor flame retardant durability of cotton fabrics.Moreover,endowing cotton fabric with hydrophobic property can improved its washing resistance and durability.In addition,functional cotton fabric is inevitably subject to external influences such as scuffing and abrasion in the course of practical application,resulting in different degrees of damage to the coating.Giving the coating self-healing function that can timely repair the external damage to the surface or structure will effectively improve the service life of the fabric coating.Therefore,it is of great significance to research and develop hydrophobic and flame retardant multifunctional cotton fabrics with selfhealing properties.In order to expand the application scope of cotton fabrics,this paper used a variety of ways to finish cotton fabrics,intending to improve the washability,durability and service life of functional coating.Specifically,（1）durable superhydrophobic cotton fabric was prepared by sol-gel method and UV curing method with green environmental protection and low energy consumption.It can be used in oil-water separation field.（2）Cotton fabrics with hydrophobic and flame retardant properties were prepared by using ferrocene and 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide（DOPO）.There was synergistic flame retardancy between ferrocene and DOPO,resulting in smoke emission reduction.（3）Based on the consideration of green environmental protection,by using tannic acid,borax and polydopamine as raw materials,cotton fabric with dual functions of superhydrophobicity and flame retardancy was prepared,which showed efficient separation efficiency and durability in oil-water separation tests.（4）In order to solve the durability of flame retardant and water repellent coating on cotton fabric,waterborne polyurethane with hydrophobic,flame retardant and self-healing triple functions was synthesized and used for functional coating finishing of cotton fabric.The specific contents and conclusions of this paper are listed below.（1）In order to endow the cotton fabric with superhydrophobic property,the UV curable fluorine-free superhydrophobic coating cotton fabric with good wear-resistant was prepared by a simple method and applied to the practical field of oil-water separation.Firstly,thiol silica nanoparticles（SiO₂-S-PIH@cotton fabric）were prepared on the surface of the fabric by St（?）ber reaction.Then,the hydroxyl terminated Polydimethylsiloxane（PDMS）reacted with isocyanate to form isocyanate terminated prepolymer.Hydroxyethyl methacrylate（HEMA）terminated prepolymer（vinyl terminated PDMS（PIH））was sprayed onto the fabric surface,and then the superhydrophobic coating（SiO₂-S-PIH@cotton fabric）was formed by UV curing.The structure of the modified fabric was characterized by a series of characterization methods.And the results indicated that sulfhydryl groups on the surface of SiO₂ particles had reacted with the double bonds indeed,and the sprayed PIH had covered the fabric surface by covalent bonds.Low surface energy provided by PIH in cooperation with micro nano rough surface constructed by SiO₂ particles formed superhydrophobic surface.The test showed that the thermal stability of the modified cotton fabric was obviously improved.When the spray weight gain of PIH reached 1.8wt%,the superhydrophobic effect of modified cotton fabric was the best（Water contact angle（WCA）= 153° and sliding angle（SA）= 7°）.The order of breaking strength: SiO₂-S-PIH@ cotton fabric >SiO₂-SH@cotton fabric > pristine cotton fabric,and the order of breaking elongation: pristine cotton fabric >SiO₂-SH@ cotton fabric >SiO₂-S-PIH@cotton fabric.With the increase of PIH spraying amount,the bending stiffness increased.In order to investigate the application of superhydrophobic fabric in complex environment,the durability of modified cotton fabric was tested.The ultrasonic durability,acid and alkali resistance,high temperature resistance and washing resistance of SiO₂-SH@ cotton fabric and SiO₂-S-PIH@cotton fabric were tested respectively.The results showed that the durability of SiO₂-S-PIH@ cotton fabric was significantly better than that of SiO₂-SH@cotton fabric in ultrasonic environment and washing resistance test.When tested under acidic or alkaline conditions（p H value: 1-13）and temperature resistance（0-200 ℃）,the change of WCA was not obvious.The result showed that the friction resistance of SiO₂-S-PIH@cotton fabric was better than that of SiO₂-SH@cotton fabric.In this paper,the self-cleaning performance of SiO₂-S-PIH@ cotton fabric was tested with simulated solid powder pollutants and liquid pollutants.The results showed that the fabric had good selfcleaning performance.Through the experiment of dropping oil and water into SiO₂-SPIH@cotton fabric,it was found that the fabric had good hydrophobic and lipophilic properties,and could be used in the field of oil-water separation.Through the test of simulated oil-water separation device,the separation efficiency of dichloromethane/water mixture reached 99.1%.For other five different kinds of oil products（n-hexane,bromobenzene,trichloromethane,petroleum ether and tetrahydrofuran）,the separation efficiency was higher than 98.5%.After 30 times of repeated use,the fabric separation efficiency was still higher than 97.8%.（2）In order to explore the finishing methods of cotton fabrics with dual functions of hydrophobic and flame retardant,ferrocene and 9,10-dihydro-9-oxa-10-phosphine-10 oxide（DOPO）were introduced into the flame retardant finishing of cotton fabrics at the same time.The synergistic flame retardant effect was studied,and the hydrophobicity of the fabrics surface was also evaluated.In this study,in purpose of having better adhesion on cotton fabrics,polyethylene imides graft-modified cotton fabrics（PEI-g cotton fabric）were prepared under appropriate conditions,and then PEI-g cotton fabric were reacted with ferrocene formaldehyde,after which DOPO was connected to the surface of the fabric.Ferrocene methylaldehyde was anchored to the surface of cotton fabric by the formation of Schiff base by the formation of-NH2 on PEI-g cotton fabric,and then the active hydrogen on DOPO was grafted on the surface of cotton fabric by addition reaction with C=N,and the chemical reaction process has been confirmed.The surface of cotton fabric was characterized by a hierarchical structure with micro nano structure.The thermal degradation rate of Fe@DOPO cotton fabric was obviously slow.In N2 atmosphere,the carbon residue of Fe@DOPO cotton fabric increased from 8.25 wt% to 46.8 wt%,and the maximum weight loss rate(R_max)was 8.1 wt%/min,which was 81.5% lower than that of original cotton fabric,indicating that the thermal degradation rate was obviously slower.In air atmosphere,the carbon residue increased from 7.8 wt% of pristine cotton to 36.6 wt% of Fe@DOPO cotton fabric,and R_max decreased from 47.6 wt% of pristine cotton fabric to 9 wt%/min of Fe@DOPO cotton fabric,which is reduced by 35%,demonstrating that the thermal degradation and oxidation rate was obviously slowed down.The amount of volatile gas released by Fe@DOPO cotton fabric during the thermal degradation of cotton fabric was significantly reduced.In an effort to compare the flame retardant properties of pristine cotton fabric and modified cotton fabric,cone calorimeter test（CCT）and LOI were tested.The results showed that compared with pristine cotton,peak of heat release（PHRR）and total heat release（THR）of Fe@DOPO otton fabrics decreased by 48.9% and 19.2%,respectively.Although ferrocene had obvious smoke inhibition effect,it had only a little flame retardant effect when used alone.After 4 times of washing,DOPO-g cotton fabric had no flame retardant,but after 12 washing tests,LOI value of Fe@DOPO cotton fabric was still24%.Fe@DOPO cotton fabric had good washing resistance because of chemical bonding and surface hydrophobicity.The combustion mechanism of Fe@DOPO cotton fabric mainly included condensed phase flame retardance mechanism and gas phase flame retardant mechanism.Specifically,ferrcene synergies with DOPO at low temperature to produce phosphates rapidly,which provides acid source,making cotton fiber dehydrate into charcoal that covers cotton fabric surface and block heat source and air.On the one hand,ferrocene can inhibit the formation of smog.On the other hand,DOPO produces non combustible gas,diluting the concentration of combustible gas,which plays a synergistic flame retardant effect.WCA of Fe@DOPO cotton fabric was 138°,belonging to hydrophobic cotton fabric.WCA did not change with time in5 minutes.（3）In order to make the preparation of superhydrophobic flame retardant cotton fabric more green and environmentally friendly,TA/B@PDA cotton fabric was prepared by simple dip coating method and layer by layer self-assembly method,using tannic acid（TA）extracted from plants,borax（B）and polydopamine（PDA）from mussel as raw materials.It is proved that PEI-g cotton fabric,TA-loaded cotton fabric,TA/B-loaded cotton fabric and TA/B@PDA cotton fabrics are firmly anchored on the surface of cotton fabrics by chemical bonds.Moreover,the micro nano hierarchical structure was formed on the surface of cotton fabric,and the surface roughness was significantly improved.The following conclusions were drawn from TGA and TG-IR test,in N2 atmosphere,R_max of TA/B@PDA cotton fabrics was 80% lower than that of the original cotton fabric,and the carbon residue increased from 10.1 wt% of the original cotton fabric to 48.9 wt% of TA/B@PDA cotton;in air atmosphere,R_max of TA/B@PDA cotton fabric was 61% lower than that of the original cotton fabric,and the carbon residue increased from 8.6 wt% of the original cotton fabric to 27.9 wt% of TA/B@PDA cotton.In the two atmospheres,the thermal degradation rate of TA/B@PDA cotton obviously slowed down.The amount of volatile gases released during the thermal degradation process decreased significantly.In order to compare the flame retardancy of pristine cotton fabric with modified cotton fabric,CCT and LOI were tested.The results showed that PHRR and THR of TA/B@PDA cotton fabric decreased by 50% and 32%,respectively.After 10 times of washing,LOI value of TA/B-loaded cotton fabric decreased from 27.5% to 17.5%.LOI value of TA/B@PDA cotton fabric decreased from 28.5% to 24%,indicating that the structure of PDA can improve the washing resistance of cotton fabric.Through the analysis of the flame retardant process and carbon residue of TA/B@PDA cotton fabric,the flame retardant mechanism generally included condensed phase flame retardant mechanism and gas phase flame retardant mechanism.On the one hand,with the increase of temperature,borax formed a glass layer on the surface of cotton fabric,which hinders the heat transfer and makes the local temperature less than the combustible temperature.At the same time,the boric acid is also the acid source,which makes the fiber surface carbonize rapidly and form a flame retardant.On the other hand,in the gas phase,non combustible gas is generated,diluting the volatile combustible gas or oxygen in the air,slowing down the combustion.WCA and SA of TA/B@PDA cotton fabric are 153.3°± 1.2° and 9° ± 0.8°,respectively,which belong to superhydrophobic cotton fabric.The results show that the contact area between the water droplet and the surface of the modified fabric is only 5.84%,which has super hydrophobicity and low adhesion.In addition,the fabric has strong oil absorption and hydrophobicity,which can be used in the field of oil-water separation.The separation efficiency was tested by using the simulated oil-water separation device.The results show that the separation efficiency reaches 99.1% originally,and it still reaches 95.3% after 30 times of use.After 40 times of washing and 200 times of sandpaper rubbing,WCA of the fabric is still more than 134° and the initial separation efficiency of six kinds of oils（dichloromethane,nhexane,bromobenzene,trichloromethane,petroleum ether and tetrahydrofuran）is also more than 98%.（4）Self-healing property of the coating is a good way to solve the flame retardant and hydrophobic durability of the coating.In this paper,biselenidiol monomer with thermal response was self-made,and then self-healing,flame retardant and hydrophobic waterborne polyurethane emulsion was prepared by using biselenidiol,isophorone diisocyanate（IPDI）,polytetrahydrofuran ether glycol（PTMEG）,dimethylolpropionic acid（DMPA）,N,N-bis（2-hydroxyethyl）aminomethyl phosphonate（FRC-6）and side chain reactive PDMS.The particle size and chemical structure of the multifunctional waterborne polyurethane emulsion were characterized.The structure of the biselenidiol monomer was characterized by nuclear magnetic resonance（1H-NMR）,and the structure of biselenidiol was characterized.The chemical structure of WPU film was tested by 1H-NMR,FT-IR and XPS.The WPU material containing biselenidiol,FRC-6 and reactive PDMS was successfully prepared.According to the particle size of emulsion resuilt,the particle size of emulsion ascended with the increase of PDMS dosage,and the PDI value of particle size distribution parameter increased.When the dosage of FRC-6 was less than 8 wt%,the particle size had little change.Transmission electron microscope（TEM）of WPU-3（PDMS 4 wt% and FRC-6 dosage 6 wt%）showed that the spherical micelle was 80-100 nm in diameter and the emulsion had good stability.Dynamic mechanical properties（DMA）test results showed that PDMS could increase the flexibility of molecular chain in WPU film structure,and T_g,soft of WPU film decreased;T_g,soft reduced by addition of 6 wt% FRC-6.TG test of WPU film showed that the decomposition of WPU film contained three different stages.With the increase of FRC-6 content,the carbon residue and thermal stability of WPU film increased.LOI and UL-94 were used to test the flame retardancy of WPU film.When the content of FRC-6 was 10 wt%,LOI value reached 26.2% and rating V-1 level,but there was still droplet phenomenon.CCT test showed that FRC-6 could greatly improve the flame retardancy and reduce THR and PHRR of WPU membrane.Through the analysis of the flame retardant mechanism of WPU-3 film,it was the synergistic flame retardant mechanism of phosphorus and nitrogen,which is consistent with the condensed phase and gas phase flame retardant mechanism.The introduction of reactive PDMS and FRC-6 flame retardant monomer can significantly improve the thermal stability,hydrophobicity and water resistance of WPU film（WCA up to 103.7 ° and water absorption 4.5 wt%）.The mechanical properties and self-healing properties of WPU membrane were studied.It was found that when the content of PDMS was less than 4wt%,the tensile strength and elongation at break of WPU membrane were improved.However,excessive PDMS resulted in serious phase separation and decreased mechanical properties.The change trend of self-healing efficiency of WPU membrane was similar.When the dosage of PDMS was 4 wt%,the self-healing efficiency of WPU membrane was the highest（78.5%）.With the increase of FRC-6 content,the tensile strength and elongation at break first increased and then decreased,and the change trend of self-healing efficiency was similar.When the FRC-6 content was 6 wt%,the repair efficiency was the highest.According to the self-healing mechanism of thermal response,in the self-healing process,the hydrogen bond of carbamate and urea group in the adhesive film contributed to the early repair effect,and the movement ability of WPU macromolecular chain at a certain temperature promoted the "cross exchange" reaction between the cross sections.The flame retardancy of coated cotton fabric was studied.The results showed that the flame retardant coating adhesive must be used to obtain the flame retardant coating samples of cotton fabric,because the flammability of the coating adhesive would directly lead to the loss of flame retardancy of the flame retardant cotton fabric.If the flame retardant finishing of pure cotton fabric is carried out directly by coating without pre flame retardant finishing,it is difficult to achieve complete flame retardancy.The double-sided flame-retardant coating is applied to the pre flame retardant finished cotton fabric,which can protect the fabric and improve its washing resistance.In addition,WPU coating adhesive containing single ended PDMS can give the surface WCA of cotton fabric about 130°,and improve the washing resistance of the fabric.In addition,the coating can improve the breaking strength and breaking elongation of the fabric,but the softness of the fabric decreases slightly.