Preparation And Application Of Nanocellulose-based Superhydrophobic Coatings

The mystery of superhydrophobicity has been emerged by the mysterious phenomenon of lotus effect.After many years of research by scholars in various countries,two elements of superhydrophobicity have been found.One is micro-nano surface structure and another is low surface energy modification.Superhydrophobic materials have become research hotspot in recent years because of the wide application,and nanocellulose is suitable for preparation of superhydrophobic materials due to its own characteristics.This paper mainly takes advantage of nanocellulose as raw material to design and construct new superhydrophobic coatings through different methods,which is of great value to extend the industrial application of nanocellulose-based coatings.(1)Spray drying was used to prepare the nanocellulose-based micro-particles with hierarchical surface structure.The surface structure of particles can be regulated by changing the size of nanocellulose.The prepared particles were modified with methyltrimethoxysilane(MTMS)by chemical vapor deposition(CVD),and then the modified particles mixed with polydimethylsiloxane(PDMS)proportionally are formulated a new coating,which can be sprayed on filter papers or glass to obtain superhydrophobic surface.The new finding is that the length of nanofiber had great influence on surface structure of formed particles from spray,and the shorter nano-fiber was easier to derive micro-particles with more compact,more even rough surface structure and better superhydrophobicity of final coated materials compared with the longer nanofiber.The superhydrophobic property of the coating can be controlled simply by changing the cellulose nano-fiber length,which is of great significance on hierarchical structure design of the nanocellulose-based superhydrophobic materials.(2)Because of the characteristics of nanocellulose,the ability of stabilizing the interface is excellent.Therefore,TEMPO-oxidized cellulose nanofibrils(TOCN)and cellulose nanocrystal(CNC)was used as stabilizer particles to prepare composite microspheres with rough surface structure by Pickering emulsification method.The results showed that the particle size of composite microspheres decreased with the increase of fibers content,and smaller particle size was easier to prepare composite microspheres with complex structure.When washed with absolute ethanol,the nanoparticles formed by secondary nucleation would be adsorbed on the surface of the microspheres to form micro/nano double-size structure.The hydrophobicity of the coatings was better than that of the coatings prepared by the microspheres washed with deionized water.What's more,when CNC was added into the aqueous phase,nanocellulose interweaved with nanoparticles to form more complex micro-nano rough structure and the WCA of the coating was up to 172.2°.(3)Because of the large aspect ratio and specific surface area,nanocellulose can be entangled with each other,and a large number of hydroxyl groups can also enable nanocellulose to bond through hydrogen bonds.Here only using modified TOCN(mTOCN)as raw material to form superhydrophobic coatings.The results showed that the content of mTOCN and PDMS had a great influence on the hydrophobicity of the coating.Suitable amount of mTOCN can form a double-size structure on the surface of the substrate,which performed superhydrophobicity.The WCA was up to 153.6°.Excessive PDMS would cover the fine structure of the fiber aggregates,resulting in a reduction of hydrophobicity.Solid-liquid separation during spray-coating resulted in the formation of many particles with irregular shapes attached to the surface of the substrate to form superhydrophobic coatings,which can achieve better hydrophobicity than dip-coating.