Modification And Controllable Electrospinning Of Cellulose Acetate

With the development of nanotechnology, nano-fiber material exhibited many novelfeatures in the fields of electricity, magnetism, light, heat, for which received extensiveattention of the researchers. Electrospinning was a simple and effective method to preparefibers with nano-and micro-diameter distribution. Cellulose acetate was first prepared in1865, and it was stable in light, soluble in organic solvents, and had good compatibility. CAis commonly used as the substrate material in the electrospinning. However, CA had lowoxidation and chemical affinity which limited its further applications. Therefore,modification of CA have become a commercially viable approach to produce new materialswith improved properties.In this dissertation, CA was modified by polyethyleneimine (PEI), polyaniline (PANI),and poly (lactic acid)(PLLA) respectively through electrospinning. CA composite fiberswere characterized by SEM, TEM, DSC, XPS, etc. In addition, the influences of the polymerconcentration, electrospinning condition and polymer properties on CA fibers were studiedsystematically. This thesis consisted of the following four parts:(1) CA/PEI electrospun nanofibers were successfully fabricated by electrospinning.Acetone and water was chosen as the co-solvent. SEM and TEM images showed thatelectrospun CA fibers after water-treated remained smooth surface and cylindrical shape,while eletrospun CA/PEI fibers had a large number of recesses and holes on the surface, andhollow structure in the interior. DSC, FTIR and XPS data proved the distribution of the twocontents. When PEI content was low, the enhanced interaction from the polar groups of CAand PEI led to even distribution of PEI in the CA/PEI system. And then hollow structure wasobtained after water treated. When PEI content increased gradually, the repulsive forcebetween the side group enhanced with the increasing of electric force. PEI content diffusedoutward to the surface of the composite fibers.(2) Based on the simulation of finite element and the analysis of the electrospun fibersorientation mechanism, the controllable CA/PANI nanofibers were fabricated successfully.The parallel copper wires on the insulated substrate were used as the collector. Theexperimental results were shown as followed. With the conductivity increased, the orderedarrangement of the electrospun fibers enhanced. Improving the distance between the two copper wires with a certain range, the order degree of the fibers increased. Whenconcentration of PANI increased, the conductivity of the fibers enhanced. And the fibersposited on the coppers had a better orientation. Besides, HCSA could increase the solubilityof the PANI in the CA/PANI solution effectively. Thus, fiber conductivity reinforced andordered orientation of the fibers raised.(3) Poly(L-lactic) acid (PLLA) nanofiber was prepared successfully by electrospinningusing chloroform and acetone as the solvent. Increasing the concentration of the PLLA couldeffectively reduce the beaded structure to obtain controllable diameter of the fibers.CA/PLLA mixtures of different compositions were successfully electrospun to obtaincomposite nanofibrous membranes. The microstructures of the membranes changed fromhomogeneous to heterogeneous with the addition of CA, which was observed by FE-SEM.The CA/PLLA fabric membranes were characterized by mechanical testing, DSC andcontact angle measurements. The tensile stress of the composite fibrous membranesincreased obviously with the increase of CA content. DSC results indicated that the CAcomponent was the main factor for the changes of enthalpies in the composite fibers. Contactangle measurements showed the hydrophilicity of the electrospun nanofiber membranes wasimproved with.(4) PLLA and CA/PLLA fiber membranes were prepared as biosensor substrate. Biotinwas added into PLLA and CA/PLLA fibers successfully. By using of the rapid and specificbinding between the biotin/streptavidin, the protein was immobilized on the surface of thefiber membrane and detected. SEM, XRD, colorimetric assay and enzyme linkedimmunosorbnent assay (ELISA) were used to characterize the capability of PLLA/biotin andCA/PLLA/biotin fibers binding streptavidin. The results showed that the introduction of CAcomponent enabled composite fibers to produce micro-porous structure, and furtherimproved the effect of the substrate material binding biotin, and finally improve thesensitivity and effectiveness of the biosensor.