Research On Preparation And Wear Mechanism Of Nanocellulose-based Superhydrophobic Coatings

As traditional natural green renewable materials,wood materials play an important role in various fields.With the development of science and technology,it is an important way for expanding the application scope and value to make functional wood materials.In recent years,research of wood materials has gradually extended to micro from macro,especially for the preparation and functional use of wood nanocellulose,geting a certain development.And in recent years,superhydrophobicity is hotspot of scientific research because of its potential application in anti-fouling,waterproof,anti-icing,drag reduction,and other fields.Preparation of superhydrophobic coatings is easy to implement by diversiform methods,but still exists some problems,especially the poor mechanical strength that restricting further development of superhydrophobic coatings.Therefore,this dissertation mainly used different types of wood nanocellulose as the main materials to build a variety of superhydrophobic coatings requiring micro-nanometer hierarchical surface structure and made low-energy modification by gas phase or liquid phase method to fabricate superhydrophobic coatings;and researching mechanical strength of nanocellulose-based superhydrophobic coatings from the different type of nanocellulose,selection of adhesives,and building way of surface structure and other aspects,also do the preliminary testing for their wettability and durability.The obtained main research conclusions are as follow:?1?Making use of nanofibrillated cellulose?NFC?that has high length-diameter ratio and easily intertwine to build rough structure,NFC₁ superhydrophobic coating was successfully prepared.The process was that NFC ethanol suspension was sprayed onto the wood treated with adhesive in advance,and rapid solidification of adhesive and rapid evaporation of anhydrous ethanol avoid NFC completely immersing in the adhesive,followed by making hydrophobic modification by chemical vapor deposition?CVD?.In NFC concentration of 1.2wt%,the superhydrophobic coating had superior WCA?160°?and SA?8°?;the surface rough structure built from entanglement of NFC was uneven network and had good strength,being able to withstand 8 abrasion cycles?abrasion length of 160 cm?by sandpaper with 1500 grit under load of 100g;there was also good durability.This study used a simple way to the adhesion problem between NFC coating and the substrate and had guiding significance to improve strength of superhydrophobic coating.?2?Using NFC and cellulose nanocrystal?CNC?particles formed from reunion of NFC and CNC in liquid hydrophobic modification to make NFC₂ and CNC superhydrophobic coatings were made by spraying respectively them onto water-based adhesive on woods.In this study,WCAs of NFC and CNC coatings were respectively 157.5°and 158.8°respectively and both of SAs were less than 8°;their surface structure was made from stacking of the NFC₂ or CNC particles and had weaker strenghten than that of NFC1 due to no adhesion between particles,maximally withstanding 6 abrasion cycles?abrasion length of 120 cm?by sandpaper with 1500 grit under load of 100g.In addition,the CNC superhydrophobic mesh for oil-water separation could had excellent separation efficiency that were higher than 95%and could be repeated for more than 40 times.This study prepared superhydrophobic coatings only by simple spraying and provided reference to simplify process and large-area preparation.?3?Lignin-coated cellulose nanocrystals?L-CNC?particles with high strength as structural material were mixed with PVA to prepare L-CNC/PVA superhydrophobic coating.In this study,the L-CNC particles were of irregular shape and the particles themselves and their concave and convex surface structure built micro/nano hierarchical structure;in the same L-CNC concentration of 6 wt%,in 0-1.5 wt%PVA,all the coatings were superhydrophobic and their wear resistance improved with the increase of PVA concentration;and when the PVA concentration reached 2 wt%,formation of the wide PVA membrane coating led to roughness decrease causing by loss of superhydrophobicity.L-CNC/PVA superhydrophobic coating maximally only withstood 5 abrasion cycles?abrasion length of 120 cm?by sandpaper with1500 grit under load of 100g,becauce PVA cannot provide sufficient adhesion while meeting superhydrophobicity.This study avoided using any organic solvent in the process of preparation and provide reference for green preparation of superhydrophobic coatings.?4?Research on influence of different types of adhesives on wear resistance of nanocellulose-based superhydrophobic coatings.Using two different properties of adhesives?double-sided tape with high viscosity and fast curing epoxy resin?to adhere respectively modified L-CNC particles to the substrate surface for preparing superhydrophobic coatings.In this study,the wear resistance of coatings greatly improved,and L-CNC/double-sided tape coating?D coating?and L-CNC/epoxy coating?E coating?can be respectively up to 23?460cm?and 17?340 cm?abrasion cycles by sandpaper with 1500 grit under load of 100g,which benefited from high strength of L-CNC particles and high adhesion of double-sided adhesive and epoxy resin.D coating has better wear resistance as nonrigid adhesive surface can offset some force of sandpaper;E coating had beterr jet-water resistance and temperature resistance.This study mainly explored the influence of different properties of adhesive on the wear resistance of superhydrophobic coatings,providing guidance for the choice of adhesives in preparation of superhydrophobic coatings.?5?Research on influence of the different building way of surface structure on the nanocellulose-based wear resistance of superhydrophobic coating."like-pearls"CNC/SiO2 rod formed from compositing CNC with ethyl orthosilicate?TEOS?was used to build CNC/SiO₂superhydrophobic coating.CNC/SiO2 superhydrophobic coating could withstand more than100 abrasion cycles?greater than 2000 cm?by sandpaper with 1500 grit under load of 100g;compared to pure SiO₂ coating prepared in the same method,the CNC/SiO₂ superhydrophobic coating had better wear resistance,because CNC played a role in fixing SiO₂ particles and micro structure built by CNC/SiO₂ rod had higher strength than that built by stacking of individual SiO₂ particles.CNC/SiO₂ superhydrophobic coating also showed outstanding durability.Studying the different ways of building micro structure provides guidance for building superhydrophobic coatings with high strength.