| In the recent decades, natural polymers are gaining fast and fruitful developments because that they are hopeful to reduce the use of petroleum-based polymers. Cellulose is one of the most abundant and widely used biopolymers, and shows attracting properties such as renewability, biodegradability, inertness and so on. Cuprammonium solution (Schweizer’s reagent) is one of the oldest cellulose solvents and usually used to prepare Cupra rayon, hollow fiber, non-woven cloth etc. However, cellulose-cuprammonium solution is rarely applied in the field of novel multifunctional composite materials. The Schweizer’s reagent contains large amount of copper, and shows advantages in constructing nanocomposites and inorganic materials with delicate structures with its low cost and practicality. Now, the application of cellulose in nanocomposites and template synthesis become hot fields of research directions. In this work, in situ synthesis and cellulose-cuprammonium solution has been applied in fabricating cellulose/inorganic nanocomposites and template synthesis of helical and hollow inorganic fibers. Moreover, the structure, morphology, properties and applications of the products have been carefully studied.The novel creations of this work are as follows.1) In situ synthesis has been carried out to fabricate multicomponent and multifunctional cellulose magnetic nanocomposite film and core-shell structure within the micropores of cellulose matrix.2) The identities of cellulose-cuprammonium solution and regenerated cellulose (RC) products from cuprammonium process are used to prepare the antibacterial and single-side conductive RC/Cu nanocomposite films without adding any copper-based additives.3) Continuous helical RC fibers are produced based on the "liquid coiling effect" of the viscous fluids; and inorganic helical fibers are obtained through making use of the helical regenerated cellulose fibers.4) Metal oxides hollow microfibers have been prepared by sintering the corresponding cellulose nanocomposite fibers as a result of the multi-layer heterogeneous structure of cuprammonium rayon; and the process and mechanism of the formation of the hollow structure have been investigated.The main content and conclusions in this thesis are divided into the following parts. RC/γ-Fe2O3/CuO nanocomposite films were prepared by a two-step in situ synthesis method. Structure and morphology of the nanocomposite film before and after sintering were characterized with XRD, XPS, TG, SEM and TEM. The nanoparticles inside the nanocomposite film had core-shell structure of CuO@γ-Fe2O3with size of10～15nm. After sintering, γ-Fe2O3reacted with CuO and formed CuFe2O4(104±39nm). The concentration of Cu2+showed a significant influence over the composition of sintered nanocomposite films. When the Cu2+concentration was0.35or0.5M, all γ-Fe2O3reacted with CuO and formed CuFe2O4. However, if the Cu2+concentration was too low or too high, some of γ-Fe2O3would transform into α-Fe2O3during sintering. The nanocomposite films showed superparamagnetism, but the magnetic behavior became distinctly different after sintering and presented strong ferromagnetism due to the formation of CuFe2O4and sharp increase in size.To avoid adding copper-based fillers, RC/Cu nanocomposite films were prepared from cellulose-cuprammonium solution through coagulation in aq. NaOH and subsequent one-step reduction in aq. NaBH4. Structure and morphology of the nanocomposite films were characterized with XRD, XPS, TG, SEM, TEM and AFM. The results indicated that Cu2+was successfully reduced to Cu and an ion migration from the inner to the surface of the RC films occurred during the reduction process. Cu nanoparticles were found to be embedded on the surface of the RC films. The nanocomposite film showed efficient antibacterial activity against S. aureus and E. coli. The dramatic reduction of viable bacteria could be observed within0.5h of exposure, and all of the bacteria were killed within1h. The RC/Cu nanocomposite film shows potential application in packaging, medical care products etc.Single-side conductive RC/Cu nanocomposite films were prepared using in situ coating. Structure and morphology of the films were investigated by XRD, ATR-FTIR, XPS, TG, SEM, TEM and AFM analysis. Mechanical properties and conductive performance of the films were also examined. The copper of cellulose-cuprammonium solution was employed as the coating source as opposed to addition of other conductive substances. The single-side coating of Cu nanocomposite film was achieved by a one-step reduction based on the asymmetric surface structure of RC film. Because the porous surface provided with channels for the ion migration during reduction, a layer of Cu nanopartilces with the thickness of-1(im was coated on the porous coagulant-contacting surface, while there were no copper nanoparticles on dense mold-contacting surface. The nanocomposite films displayed good mechanical performance, flexibility and high single-side conductivity. It was noted that the resistance could be tuned by changing the bending curvature. This study provides potential applications in areas such as electronic substrates, wearable electronics and sensors.A simple method for large-scale production of helical fibers from cellulose solution was proposed based on "liquid rope coiling" of viscous fluid. In the spinning process, cellulose-cuprammonium solution was extruded from a certain height above a mobile coagulating bath. Helical structure turned out to form spontaneously at the surface of the coagulating bath as a result of buckling instability, and the helical cellulose fiber was coagulated rapidly. RC helical fiber was obtained after treatment with acid and air-drying. Spinning parameters, such as spinning height, flow rate and moving speed of the coagulating bath were examined in relation to the size and morphology of the helical fiber. The results indicated that the size and shape of the helical fibers were determined by spinning height and affected by other spinning parameters. The diameters of the fiber and helix were found in the range of100～400and300～700μm, respectively. The helical fibers demonstrated high elongation at break and elasticity within certain range of strain, which were attributed to the coiling structure. The microporous feature of the RC helical fiber shows potential as helical scaffold and template for the preparation of inorganic materials.A facile process for preparing metal oxides hollow microfiber was described. CuO microfibers (outer diameter:5～36μm, shell thickness:0.4～5μm) with hollow structure were obtained by directly sintering the cellulose nanocomposite fibers containing copper compound nanoparticles derived from the cuprammonium process. XRD, XPS, TG, SEM and TEM were performed to study the structure and morphology of the coagulated composite fiber and CuO hollow fiber. The results suggested the hollow structure was formed based on the non-uniform distribution of CuO particles in the coagulated nanocomposite fibers. There were less CuO particles in the outer than the central part. The outer layer of cellulose had higher crystallinity and crystalline orientation, whereas the central part of cellulose was in an amorphous state. Therefore, the central part was first decomposed due to its lower pyrolysis temperature and finally hollow structure was formed. Moreover, CuO, Fe2O3, TiO2and SiO2hollow microfibers were also obtained successfully by sintering the cellulose nanocomposite fibers containing Cu, CuO, Fe2O3, TiO2and SiO2by in situ synthesis. The approach is considered as a generic one to prepare different kinds of inorganic oxide hollow microfibers. Since cuprammonium is commercialized, this method is appropriate for large-scale preparation of metal oxides hollow microfibers.This thesis combines cellulose and inorganic nano-materials and makes use of the identities of regenerated cellulose products and cellulose-cuprammonium solution to prepare several kinds of cellulose nanocomposites and inorganic materials with special structures via simple and green methods. Structure, morphology and properties of the products have been investigated, and the involved process and mechanism were carefully studied and discussed. Furthermore, this work provides novel approaches and thoughts for the preparation of cellulose nanocomposites and special inorganic materials, which is important for the developments of cellulose and materials science. Therefore, this work proves to be scientific, innovative and practical. |
