Additive Printing Of Cellulose Nanocrystals To Construct Functional Materials

In the past decades,the rapid development of the global economy has brought the environmental issues to the stage,of which includes the exhaustion of the petroleum resource and the overload of the greenhouse gases.Facing those problems,natural polymers with its abundant sources,renewability and substitutability have received more and more attention in the field of functional materials.Among them,cellulose nanocrystals(CNC),a type of crystalline polymer,has shown remarkable potentials in many fields such as polymer reinforcement,biomedicine,energy storage,smart sensing and food science.Approaches for constructing CNC composite materials varies from simply mixing to smart printing.At present,the construction of CNC composite materials by additive printing has been the most promising method aiming to obtain materials with light weight and high strength as well as the enhancement mechanism.However,only a few studies of the printed CNC materials have been involved with other useful functions such as water filtration and optical coding.Therefore,it is of great significance to fully revealed the inherent characteristics of CNC for constructing various CNC-based functional materials by means of additive printing.In this work,focusing on the hydrophilicity and liquid crystal optical property of CNC,we have chosen the appropriate printing method and ink state to fabricate two functional materials based on CNC.Their application ability in oil-water separation and optical anti-counterfeiting has also been examined.The main innovations of this work were as follows:(1)For the first time,an all-cellulose based membrane with high efficiency for oil-water separation has been developed by layer-by-layer inkjet printing.The CNC can be distributed more evenly on the substrate by printing compared with the previous membrane.(2)A solvent-free liquid crystal nanocellulose fluid was prepared by two-steps surface modification to enhanced its processability.The liquid crystal nanocellulose fluid was successfully constructed into different types of recyclable CNC optical anti-counterfeiting pattern by 3D printing.The tuneability of the shape and the color of final patterns has also been realized by adjusting the printing parameters.The main content of this thesis was divided into two parts and the specific contents were as follows.The CNC suspension prepared by the hydrolysis of cotton cellulose with sulfuric acid and directly used as the printing ink.The all-cellulose membrane was constructed by layer-by-layer inkjet printing on the commercial mixed cellulose ester membrane.The surface morphology,effective pore size,thickness,water flux and wettability of all-cellulose membrane has been flexibly controlled by printing conditions,such as the concentration of CNC ink and the number of printed cycles.By setting the concentration of CNC ink at 5 wt%and the number of printed cycles at 9,the resulting membrane performed a superhydrophilicity in air and a superoleophobicity under water,and its effective pore size was 76-91 nm.When this membrane was applied to separate various oil-in-water nanoemulsions,it showed high water flux(>1500 L m^-2 h^-1 bar^-1)and excellent oil rejection(>99%).Moreover,the all-cellulose membrane had an excellent reusability for long-term separation and good tolerance in harsh environment.The membrane we fabricated here is a green,sustainable and economically friendly material for oily water treatment.CNC with both liquid crystal optical property and printability has been obtained through two-steps surface modification,so as to prepare the patterned optical anti-counterfeiting materials by extrusion 3D printing.First,the flexible organic molecular layer has been successfully grafted on the surface of rigid CNC and characterized by FT-IR,XRD and TEM.Then,the results from POM,DSC and rheometer analysis have proved that the surface-modified CNC not only retained its liquid crystal properties,but also possessed the phase transition behavior at room temperature,which was endowed by the flexible shell.It could remain solid while standing but become fluid when under shearing.This has laid a good foundation as an ink to construct optical anti-counterfeiting materials through 3D printing.During the printing progress,patterns with different degrees of parallel orientation and arrangement of the modified CNC can be realized by adjusting various printing parameters(such as writing angle,nozzle diameter and filling width).Thereby,the filling textures and colors under polarized light of the obtained anti-counterfeiting patterns can be tuned purposely.In addition,the modified CNC had a good redispersion ability as it can be recovered after application and exhibited excellent recycling property.