Fabrication And Functionalization Of Superhydrophobic Cotton Fabrics

Cotton fabric(CF)is one of the most widely used materials in our daily life owing to its lightweight,flexible,breathable and renewable characteristics.However,CF is hydrophilic,which restricts its practical application.In recent years,superhydrophobic materials have attracted much attention due to their unique wettability,and many researchers have prepared superhydrophobic CFs with water contact angles(WCAs)above 150^o by constructing roughness and decorating low-surface-energy substance.At present,superhydrophobic CFs have shown great application potential in the fields of waterproofs,self-cleaning,and oil-water separation.However,the ordinary superhydrophobic CFs are difficult to meet the requirements of the rising fields such as flexible sensor,electromagnetic shielding,photocatalytic degradation and photothermal conversion.In this work,superhydrophobic CFs were fabricated and endowed with other functions via simple and efficient methods,and the applications in self-cleaning,oil-water separation,photocatalytic degradation,flame retardancy and pressure sensor were studied.The main research contents and results are listed as follows:(1)silica nanoparticles(SiO₂ NPs)were modified with(3-mercaptopropyl)trimethoxysilane(MPTMS)to generate thiol-functionalized silica nanoparticles(SH-SiO₂ NPs).Then,acryloyloxy-terminated polydimethylsiloxane(A-PDMS-A)was synthesized via a two-step reaction with isophorone diisocyanate(IPDI),?,?-aminopropyl terminated polydimethylsiloxane(NH₂-PDMS-NH₂)and 2-hydroxyethyl acrylate(HEA)as raw materials.Finally,after being immersed in the mixture of SH-SiO₂ NPs and A-PDMS-A,the crosslinked network structure was formed through thiol-ene reaction between SH-SiO₂ NPs and A-PDMS-A on the surface of the CF under the irradiation of UV light,and a UV-curing superhydrophobic CF was prepared.Scanning electron microscopy(SEM)and contact angle meter were utilized to study the effects of mass ratio of SH-SiO₂ NPs to A-PDMS-A on the micromorphology and wettability of the as-fabricated CF.The results showed that with the increase of the amount of SH-SiO₂ NPs,the surface roughness of the CF increased,and the WCA increased and then changed little.When the mass ratio of SH-SiO₂ NPs to A-PDMS-A was 0.2,the WCA of the CF reached 155^o,exhibiting good surface stability and self-cleaning ability.Additionally,the CF was successfully applied for oil-water separation,demonstrating high separation efficiency and good reusability.(2)Graphene oxide(GO)and the mixture of dihydroxyl-terminated polydimethylsiloxane(OH-PDMS-OH)and tetrabutyl titanate[Ti(OBu)₄]were successively covered on the pristine CF via a dip-coating method.Then,in the presence of the vapor of hydroiodic acid(HI)and acetic acid(HAc),the covered GO on the surface was reduced into rGO,and the crosslinking structure between OH-PDMS-OH and the generated TiO₂ from Ti(OBu)₄.was simultaneously formed.Finally,a conductive and superhydrophobic PDMS/TiO₂@rGO coated CF was fabricated.SEM,energy dispersion spectroscopy(EDS)and X-ray photoelectron spectroscopy(XPS)were utilized to investigate the effects of the mass ratio of OH-PDMS-OH to Ti(OBu)₄and reaction time on the micromorphology and wettability of the as-fabricated CF.The results showed that when the OH-PDMS-OH/Ti(OBu)₄ mass ratio and reaction time were 3 and 20min,respectively,the PDMS/TiO₂@rGO coated CF achieved a high WCA of 159^o and a low resistance per centimeter of 0.76 k?cm^-1,showing superhydrophobicity and good conductive property.The CF possessed good self-cleaning ability and the ability of photocatalytic degradation for oil-soluble contaminations.Furthermore,the PDMS/TiO₂@rGO coated CF was utilized to prepare a five-layer piezoresistive pressure sensor.The sensor showed high sensitivity,good resistance stability,fast response speed and excellent repeatability,and was applied for detecting different human behaviors.(3)Halloysite nanotubes(HNTs)modified with branched polyethyleneimine(b-PEI)and phytic acid(PA)were alternately deposited on the surface of the pristine CF via layer-by-layer self-assembly.Then,the surface was coated with a layer of octadecylamine(ODA)modified carboxylated carbon nanotubes(CNTs-COOH)/PDMS hybrid coating.After thermal curing,a flame-retardant and superhydrophobic cotton fabric(FRS-CF)was prepared.SEM was performed to observe the effects of assembled cycles and the spraying CNTs-ODA/PDMS composite on the micromorphology of the as-fabricated CF,and contact angle meter was used to study the surface stability of the FRS-CF.The results showed that the fibers of the CF were evenly covered by HNTs after 6 cycles of self-assembly.The WCA of the FRS-CF reached 162^oafter CNTs-ODA/PDMS composite was sprayed,showing good thermal stability,chemical stability and washing resistance.Additionally,the flame-retardant performance and possible flame-retardant mechanism of the FRS-CF were explored by thermogravimetric analyzer(TG),vertical burning test,thermogravimetry-Fourier transform infrared spectrometry(TG-FTIR)and SEM.The fabricated CF possessed excellent flame-retardant property,which was mainly attributed to the formation of physical barrier layer by thegenerated CNTs/Si-C compounds after the pyrolysis of the outer CNTs-ODA/PDMS layer and the inner HNTs layer.Meanwhile,the intumescent char layer formed by the N-P synergy of b-PEI and PA also could efficiently isolate heat and oxygen.In addition,the piezoresistive pressure sensor based on single-layer FRS-CF had the advantages of stable resistance signal and good repeatability,for detecting different human behaviors under a wet environment.