Fabrication And Properties Of Superhydrophobic And Flame-retardant Coatings On Cotton Fabric And Polyurethane Sponge

Fabrics and polyurethane sponge?PUS?are widely used in daily life.However,the intrinsic inflammability of these combustible materials has caused not only massive damage to human lives and properties,but also severe destructions to the surrounding environment.Constructing flame-retardant coating on the surface is one of the most convenient and effective strategies to endow the materials with flame retardancy.However,most of the flame-retardant ingredients used in this method are hydrophilic and vulnerable to fouling and water.This may result in the release of flame retardants and the destruction of flame retardancy after repeated laundering processes.Using adhesives such as polyurethane and epoxy resin to improve the adhesion of flame retardants to the substrates is a traditional approach to improve the water-resistance and reduce the loss of flame retardants.However,these combustible adhesives will probably damage the flame-retardant properties.Nowadays,halogen-free flame retardant was reported as one of the most common non-toxic and environment-friendly flame retardants.Silicone with low-surface-energy and high thermal stability is not only used to prepare superhydrophobic coatings,but also utilized with nonflammable ingredients to achieve some synergetic flame-retardant effects.In this study,simple and efficient methods are proposed to construct superhydrophobic and flame-retardant coatings on cotton fabric and PUS,and the synergetic effect of flame retardants and hydrophobic components was also studied.The main contents and results are listed as follow:Fluorinated silica?F-SiO₂?was synthesized via the sol-gel reaction between the perfluorinated octyl triethoxy silane?FAS?and tetraethoxysilane.A superhydrophobic and flame-retardant?SFR?coating was fabricated by sequentially depositing branched poly?ethylenimine??b-PEI?,ammonium polyphosphate?APP?,fluorinated silica@polydimethylsiloxane composite?F-SiO₂@PDMS?on cotton fabrics via facile dip-coating and layer-by-layer assembly.The SFR cotton fabric with a water contact angle?WCA?of 158^o showed excellent self-cleaning and antifouling properties.Interestingly,after plasma treatment,the SFR cotton fabric showed a WCA of 0^o,and it could gradually recover the superhydrophobicity after heating at 100 ^oC for 2 h.Moreover,under the synergistic effect of APP and F-SiO₂@PDMS,a dense intumescent char layer was generated on the fiber surface to isolate heat and oxygen,providing outstanding flame-retardant properties to cotton fabric.The peak heat release rate?PHRR?decreased from 401 W/g of the pristine fabric to 58 W/g of the SFR cotton fabric,and the total heat release?THR?decreased from 13.1 kJ/g to 8.0 kJ/g.When suffering to vertical flame test,the SFR coating could rapidly generate intumescent char layers and extinguish the fire.A facile one-pot sol-gel approach was developed to construct SFR coatings on cotton fabrics.Under the catalysis of ammonia,the in situ sol-gel reaction of tetraethoxysilane?TEOS?and hydroxyl-terminated polydimethylsiloxane?HPDMS?was initiated to generate polydimethylsiloxane-silica hybrid?PDMS-silica?.The micro-nano structured composite coating on cotton fabric was successfully fabricated by the PDMS-silica and APP.The SFR cotton fabric possessed excellent superhydrophobicity and stable micro-nano structures on its surface when the amount of HPDMS was 2.4wt%of ethanol solvent,and the mass ratio of TEOS to HPDMS was 2.0 and the reaction time was 60 min.The SFR cotton fabric showed outstanding durability and self-cleaning ability with a WCA above 160^o.The physical barrier effect of PDMS-silica could work synergistically with the intumescent flame-retardant effect of APP to further promote the flame retardancy of cotton fabric.When exposed to fire,the SFR cotton fabric rapidly generated a dense intumescent barrier layer,and meanwhile released nonflammable gases to extinguish the fire.The PHRR decreased from 278 W/g of the pristine fabric to 80.6 W/g of the SFR cotton fabric,and the THR decreased from 9.5 kJ/g to 3.1 kJ/g.The graphene oxide?GO?was reduced by thiourea to produce the reduced graphene oxide?RGO?.The in situ polymerization of opamine?DPA?was initiated on the surface of PUS to genrate polydopamine?PDA?,and then stable micro-nano rough structures were constructed by the PDA and RGO to obtain the PDA/RGO coated PUS?PDA/RGO@PUS?.FAS was grafted onto the surface of PDA/RGO@PUS via the hydrolysis-condensation reaction between FAS and the hydroxy of PDA/RGO@PUS surface to improve the hydrophobicity,and the superhydrophobic and flame-retardant PUS?SFR-PUS?was finally fabricated.The SFR-PUS showed excellent superhydrophobicity with a WCA above 160°.When the SFR-PUS was suffered to fire,no melt-dripping was observed,showing outstanding flame-retardant property.These results manifested the synergistic advantage of the PDA/RGO hybrid to promote the carbonization of PUS and meanwhile improve its thermal stability and flame retardancy.In addition,the SFR-PUS showed excellent electrical conductivity.Even after 1000 loading-unloading cycles under the pressure range of 2-50 kPa,the electrical resistance of SFR-PUS still remained stable,showing outstanding electrical stability.