Lyotropic Liquid Crystal Behavior Of Carboxylated Cellulose And Preparation Of The Composites Of Tunicate Cellulose

Nanomaterials based on renewable resources are attracting great interest because of its broad application prospects.Natural nanomaterials offer ecological advantages,extraordinary mechanical performance and photonic crystal character,and which are meaningful for the development of multifunctional nanomaterials.As a sustainable material with extensive sources,nanocellulose can be used for the preparation of various new materials.2,2,6,6-tetramethylpiperidine-1-oxyl radical(TEMPO)-NaBr-NaClO catalytic oxidation system is an effective method to prepare cellulose nanocrystals(CNCs)by oxidative modification.Significant amounts of C6 carboxylate groups are selectively formed on the surface of CNCs under mild condition.In this thesis,TEMPO-oxidized cotton cellulose nanocrystals(c-TOCNs)and lyotropic chiral nematic liquid crystals(N*-LCs)are prepared by hydrochloric acid hydrolysis and TEMPO-mediated oxidation system of cotton cellulose.Different concentration of c-TOCNs suspensions are prepared to investigate the critical concentration of liquid crystals(LCs)formation.It turns out that the critical concentration of LCs formation for c-TOCNs suspension was 4.1 wt%.Furthermore,fingerprint texture is clearly observed for the first time when the concentration is 9.0 wt% under a polarizing optical microscope(POM).We have made a comparision about lyotropic LCs behavior of CNCs prepared from TEMPO-mediated oxidation system and sulfuric acid hydrolysis system,respectively.Influences of size and surface charge density of CNCs on the critical concentration of LCs formation and helical pitch(P)are also discussed.The influence of ionic strength on lyotropic N*-LCs behavior of c-TOCNs has been studied.The ionic strength of c-TOCNs suspension is adjusted by the addition of NaCl solution with different concentration.The results show that there is decreased ordered domains size in the anisotropic phase and smaller P with the increase of NaCl concentration.This is attributed to the surface charge screening of NaCl,which lead to the decrease of electrical double layer thickness.The effective diameter and apparent volume of the charged nanorods are decreased,making electrostatic repulsion weakened and P decreased.Polyaniline has excellent conductivity,and it can be used to prepare conductive nanocomposites with cellulose.In this thesis,cellulose is abstracted from the tunicate and TEMPO-oxidized tunicate cellulose nanocrystals(t-TOCNs)are prepared by TEMPO-mediated oxidation system.Using t-TOCNs as template,PANI/t-TOCNs nanocomposites are prepared successfully via in situ oxidative chemical polymerization.The introduction of carboxylate radical improve the dispersion of t-TOCNs and provide more hydrogen bonding sites that attract aniline monomer to form the conductive coating.PANI and t-TOCNs are bound together mainly through hydrogen bonding and the processability of PANI is improved.Moreover,PANI/t-TOCNs nanocomposites have electrical conductivity(0.26 S·cm-1),showing the property of semiconductors.The conductivity increased with the ratio of An and OH increased.With those good properties,it may find broad applications such as super capacitor,sensors and so on.