Construction And Property Studies Of Inorganic-Organic Modified Nanocellulose Superhydrophobic Coatings

Nanocellulose is the most widely sourced and abundant biomass coating material in nature and has excellent properties of non-toxic and high tensile strength,which attracted extensive attention of researchers.However,because the cellulose has strong hydrophilicity,it needs to be modified in order to be better applied to superhydrophobic coatings.In this paper,the superhydrophobic coatings were constructed by TiO2 and fluorosilane modified cellulose nanowhiskers(CNWs)and the influence rules of TiO2 modification,fluorosilane modification and preparation methods on the structure and properties of superhydrophobic coatings were obtained.The main contents are divided into the following parts:(1)Effect of TiO2-modified nanocellulose on composite coatingsTiO2 is selected as inorganic particles for constructing rough structure to modify CNWs to prepare composite coatings.The effects of additive amount and particle size of TiO2 on the surface microstructure and water contact angle(WCA)of the coatings were studied.The results show that the hydrophilicity of the TiO2/CNWs composite coating was affected by the surface roughness(Rq)of the coating,the distribution of TiO2 in the coating,integrity of the coating,as well as the forming the micro-nanoscale mastoid structures.When the particle size of TiO2 was 30nm and the additive amount of TiO2 was 0.2wt.%,the TiO2 particles were relatively evenly distributed in composite coating and formed the micro-nanoscale roughness structures,the Rq of the coating reached the maximum and was 135nm,as well as the WCA of the coating reached the maximum and was 82.1°.(2)Preparation of fluorosilane-modified TiO2/CNWs composite coatingWood-based TiO2/CNWs composite coatings were constructed by fluorosilanemodified TiO2/CNWs composite coatings.The effects of fluorosilane modification conditions and PVA pretreatment of the wood substrates on the hydrophobic properties and stability of TiO2/CNWs composite coatings were investigated.Researches show that PVA pretreatment of wood substrates is beneficial to improve the stability of TiO2/CNWs composite coatings and fluorosilane modified TiO2/CNWs composite coating can improve the hydrophobicity of TiO2/CNWs composite coating.When the concentration of fluorosilane is 5%and the modification temperature is 70℃,the hydrophobicity of coating is the highest,and the WCA can reach 123.4°.(3)Preparation and formation mechanism of fluorosilane/TiO2/CNWs superhydrophobic composite coatingFluorosilane/TiO2/CNWs composite coatings were prepared by simultaneous modification of TiO2 and fluorosilane in CNWs emulsion.The preparation conditions on the influence of superhydrophobic properties of fluorosilane/TiO2/CNWs composite coating were studied,and the formation mechanism of fluorosilane/TiO2/CNWs superhydrophobic composite coating was explored.The research results show that the better conditions for the preparation of superhydrophobic coatings are as follows:2%of fluorosilane ethanol solution,2 days of the deposition days,9 of the reaction pH,10℃ of the reaction temperature,and 0.5wt.%of the additive amount of TiO2.Under this condition,the WCA of the fluorosilane/TiO2/CNWs composite coating is 158.2°and the water sliding angle(WSA)is 4°.Fluorosilane is chemically bonding with TiO2 and CNWs to forming an interpenetrating polymer network structure in which TiO2 is embedded,and the coating surface is concave-convex and rich in fluorine,which realizied the superhydrophobicity of the coating.(4)Properties of fluorosilane/TiO2/CNWs superhydrophobic composite coatingsThe environmental durability,mechanical stability,self-cleaning performance,high and low temperature resistance and chemical corrosion resistance of fluorosilane/TiO2/CNWs superhydrophobic composite coatings were investigated.The results show that the fluorosilane/TiO2/CNWs superhydrophobic composite coating has good comprehensive properties:after the coating is placed indoors for 90 days,the WCA and the WSA are 156.4° and 5°,respectively;the WCA is still as high as 154.8°and the WSA is 6° after 25 cycles of water droplet impact,and the WCA remains at 135°after three cycles of sandpaper abrasion;the dust is easily absorbed and taken away by water droplets without leaving traces;after being placed in the temperature environment of-15℃～105℃ for 4 hours and soaked in an aqueous solution with the pH value of 1.5～11.5 for 1 hour,the WCA can still remain above 150°.