Preparation And Properties Of Superhydrophobic Cellulose-based Materials

Cellulose is the main component of plant cell wall and the most abundant natural polymer in nature.It has the advantages of being renewable,environmentally friendly,non-toxic and biodegradable.It has the potential to replace part of synthetic organic materials and prepare biodegradable and multifunctional materials.However,the cellulose structure is rich in hydroxyl groups and naturally hydrophilic,which limits its functional application.Therefore,it is of great significance to build superhydrophobic surface with cellulose as the substrate to broaden its application field.In this paper,a variety of cellulose superhydrophobic materials were prepared based on the design of cellulose superhydrophobic micro/nanostructures,and their hydrophobic mechanisms and applications were explored by means of in situ precipitation and chemical grafting.In order to further broaden its application scope,the functionalized superhydrophobic cellulose was modified,and the anti-icing and conductive functions of the functionalized superhydrophobic cellulose were investigated.The main research contents and conclusions are as follows:1.A simple in-situ reduction technology was used to grow hydrated alumina（γ-Al OOH）on the surface of cellulose fiber（CFs）in situ to construct micro/nanostructures,study the influence of micro/nanostructures on the superhydrophobic performance,and explore the separation performance of the prepared superhydrophobic cellulose on oil-water mixture.The results showed that the surface ofγ-Al OOH modified CFs showed petal-like micro/nano structure.The prepared superhydrophobic CFs showed excellent oil-water selectivity and good oil absorption ability.After 120 adsorption/desorption cycles,the water contact Angle（CA）was greater than 145°,and the adsorption capacity decreased by only 19%.Superhydrophobic CFs exhibit stable superhydrophobicity under different harsh conditions and are able to remove oil from complex water environments.In addition,superhydrophobic CFs connected to the vacuum filtration system can achieve rapid oil and water separation,and 20 m L of n-hexane solution can be continuously separated within 15 s at a vacuum pressure of 0.05 MPa.The excellent separation performance of superhydrophobic CFs is due to its high oil flux,which provides the main adsorption power source for the capillary interaction between fiber bundles.The petal-like micro/nano structure provides large specific surface area and high oil-water selectivity,and the synergistic effect of the two forms a continuous and efficient oil-water separation process.2.The micro/nano structure and low surface free energy are two necessary factors for the preparation of superhydrophobic surfaces.Therefore,using low free energy materials directly to construct micro/nano structures on the surface of cellulose can simplify the superhydrophobic modification process.Polydivinylbenzene（PDVB）modified cellulose was used to investigate the technical feasibility of preparing superhydrophobic cellulose modified by PDVB.The technical characteristics of PDVB deposited on cellulose surface by in situ growth and simple spraying were compared.The superhydrophobic coating of polydivinylbenzene/cellulose fiber was prepared,and its oil-water separation performance was explored.The results showed that PDVB was successfully grafted and coated on the surface of CFs by in situ generation method.The water contact Angle of the prepared PDVB@CFs coating was about 157.2°,and it had high mechanical durability and chemical stability.Simple spraying is a method for rapid and large-area preparation of poly（divinylbenzene）/cellulose,which has a wider application prospect.PDVB nanoparticles and microclusters with different particle sizes can be prepared by hydrothermal reaction and ultrasonic treatment.The micro/nanostructure and infiltrability of PDVB/cellulose can be regulated by changing the morphology and adding ratio of PDVB clusters.The superhydrophobic coating with size classification and prominent structure is successfully prepared,and the maximum water contact Angle is about 160°.PDVB micro/nano scale protruding provides a stable superhydrophobic structure.The superhydrophobic coating has excellent durability and excellent self-cleaning ability.After 50 oil-water separation cycles,the separation efficiency remained above 85%and the water contact Angle was greater than 145°.3.Using cellulose itself to design and construct micro/nano graded structure can improve the role of cellulose in superhydrophobic structure and reduce the use of synthetic materials in the process of cellulose modification.The cellulose nanocellulose unit was reconstructed into three-dimensional nanocellulose based particles with micro/nano graded structure in one step by using the heat aggregation effect of spray drying process.As an ideal superhydrophobic structure,the cellulose superhydrophobic coating was prepared by spraying and fixed on the surface of the substrate.The relationship between micro/nano structure and superhydrophobicity was investigated,and the effect of particle suspension concentration on the coating infiltration was studied.The results show that the diameter of cellulose particles is about 2μm,and its surface is interlaced and entangled by cellulose nanofibers,forming a nanoscale convex structure.When the concentration of cellulose particle suspension is 6%,the coating achieves the optimal hydrophobicity,and the water contact Angle is about 156.2°.After 120 cm of mechanical wear,100 cycles of bending and continuous trampling,the prepared coating remained superhydrophobic.4.In order to further improve the mechanical durability of superhydrophobic cellulose materials,a cross-linked/self-assembled TOC/Si O₂dispersion system was formed in water by the adsorption between Tempo-oxidized cellulose（TOC）and Si O₂.TOC/Si O₂composite particles with micro/nano-graded structure were prepared by spray drying technology.TOC/Si O₂/PDMS superhydrophobic coatings were prepared by impregnating isocyanate and polydimethylsiloxane（PDMS）.The relationship between TOC/Si O₂mass ratio and micro/nano structure and the effect of TOC/Si O₂concentration on mechanical durability of coating were investigated.The anti-icing performance of superhydrophobic coating was studied.The results show that the TOC-1Si O₂/PDMS coating has the best hydrophobicity,and the contact Angle is about 158.6°.When the amount of TOC-1Si O₂is 4%,the wear resistance of the coating is the best.In addition,the TOC-1Si O₂/PDMS coating has obvious anti-icing ability,which can effectively delay the freezing time of water.5.In order to expand the application of cellulose based superhydrophobic materials,the superhydrophobic cellulose materials were functionally modified.TEMPO oxidized cellulose was used as the substrate to prepare the highly transparent superhydrophobic cellulose film.On this basis,the connected metal silver network was deposited on the membrane surface by electrospinning and electroless plating technology to prepare the highly transparent superhydrophobic nanocellulose/Ag nanowire composite film.The relationship between micro/nano structure and superhydrophobicity,as well as between superhydrophobicity and functionalization modification were investigated.The wettability,optical properties and electrical properties of the films were investigated.The results show that the superhydrophobic passivation can selectively deposit metal Ag on the surface of the network formed by electrospinning during the process of chemical deposition,thus ensuring the high transmittance of the film.The membrane had high light transmittance（81.4%）,electrical conductivity（Rs=40.3Ω/sq）and superhydrophobicity（CA=153.2°,SA=4.1°）.