Preparation And Properties Of Nanocellulose/Layered Double Hydroxide Composite Materials

Cellulose is one kind of biomass materials in nature,with many advantages including low-cost,degradability and environment-friendly.Nanocellulose,obtained from natural lignocellulose materials,has been attracting a great deal of interest in both academia and industry because of their appealing intrinsic properties,such as low density,high surface area and superior mechanical strength.However,nanocellulose was strongly restrained as membrane materials because of the hydrophilicity.To slove this problem,We introduced Layered Double Hydroxides（LDHs）,which owns hydrophobic and barrier properties,as the filler of nanocellulose film.In this work,LDHs was prepared via hydrothermal method.Then,the LDHs was implemented as nanofillers in the nanocellulose matrix,to prepare the funtional nanocomposites.This study will provide a new way for preparing high-value nanocellulose materials.CNCs、CNFs and POCNs were prepared from bleaching kraft eucalyptus pulp by means of acid hydrolysis,TEMPO oxidation/homogenization and ammonium persulfate oxidation.The morphological structure,crystallinity and thermal stability of nanocellulose were fully characterized.Result showed that,under defined conditions,there were some morphological differences among nanocelulloses.These three kinds of nanocellulose owns the same chemical and crystalline structure of cellulose,while compared with origin pulps,the crystallinity and thermal stability of nanocellulose decreased at different levels.MgAl-NO₃-LDHs could be exfoliated in formamide solvent to yeild a transparent positively charged colloidal suspension.Graphene Oxide（GO）suspension was ultrasonicated for 1 h to yeild a negatively charged colloidal suspension.On the basis of electronic among assembly units,（MgAl-LDH/CNC）_n and（GO/MgAl-LDH/CNC）_n nanocomposite film was prepared via layer-by-layer on the quart glass.We studied the process of assembly,the morphology and struture of nanocomposite films.Result showed that the process of assembly is controllable and the film surfaces are smooth and continuous,the thickness of single-deck MgAl-LDH/CNC and GO/MgAl-LDH/CNC was 11.2 and 42 nm,respectively.Due to the diversity of constitute and function of LDHs,this method offer an way to construct functional composites.Incorporation of MgAl-CO₃-LDHs into CNF via a filtering/evaporation technique endowed the nanocomposites with barrier and strengthen properties.It was found that MgAl-CO₃-LDHs could disperse very well in CNF matrix with an improved reciprocal adhesion.With the addition of LDHs,the Yong’s modules and tensile strength of composite were significantly enhanced with low level loadings of LDHs,which were 19% and 39% higher than CNF films,respectively.Meanwhile,the water vapour permission was significantly decreased with 5% loadings of LDHs,which was 50% lower than pure CNF films.When the content of LDHs was surpass 10%,the mechanical and barrier properties of MgAl-CO₃-LDHs/CNF composite begun to get worse,and the composite film would appeared obvious separate phase with the 25% loading of LDHs.Two organic UV absorber 2-pHenylbenimidazole-5-Sulfonic Acid（PBSA）,and Sodium 2,3-dihydroxynaphthalene-6-sulfonate（DNSA）has been intercalated into LDHs host by ion-exchange method using ZnA-NO₃-LDHs as precursor.After intercalation of UV absorber,the interlayer distance in LDHs increase from 0.89 to 1.78 nm for ZnAl-PBSA-LDHs,1.34 nm for ZnAl-DNSA-LDHs.FTIR and TG-DTG curves reveals the presence of a complex system of supramolecular host-guest interactions.The UV absorption capability of ZnAl-PBSA-LDHs and ZnAl-DNSA-LDHs was dramatically enhance,especially in UVB and part of UVA bonds.This shows the CNF/ZnAl-PBSA-LDHs and CNF/ZnAl-DNSA-LDHs has potential applications as UV absorber.CNF/ZnAl-PBSA-LDHs and CNF/ZnAl-DNSA-LDHs composite materials not only exhibit excellent UV photostability,but also have high transmittance at visible light region.