ABSTRACT:The important properties of cellulosic fibers in the conditioned state are mainly influenced by fine structure. In particular, the development of new methods of spinning regenerated cellulosic fibers made from a cellulose/N-methylmorpholine-Noxide (NMMO)/H 2 O system require a better understanding of their fine structures in order to explain their special physical properties. The regenerated cellulosic films were made from cellulose/NMMO/H 2 O according to the degree of polymerization and solution concentration (wt %) of cellulose and the concentration (wt %) of NMMO in the coagulation bath. The quantification of crystal content was carried out by the resolution of the wide angle X-ray diffraction intensity distribution on the assumption that all diffracted intensities take the form of a symmetrical Gaussian distribution centering at its Bragg angle. The X-ray diffraction patterns resolved into individual integral intensities showed that the polymorphic structure mixed with part cellulose III and II was obtained for only coagulated cellulose films. The degree of crystallinity and apparent crystalline size of regenerated cellulosic films depended on the degree of polymerization, the solution concentration of cellulose, and the concentration of NMMO. The diameter of the microfibril decreased with an increase in the concentration of NMMO.
ABSTRACT:The acrylate comonomer in polyacrylonitrile (PAN) precursor markedly influences the microstructure of PAN fiber and its resulting carbon fiber. In this study, the change occurring during the heat treatment of PAN copolymers (acrylonitrile-comethyl acrylate) in the presence of air up to 260ЊC has been examined using both physical and chemical techniques. Considering the effect of the methyl acrylate content of PAN copolymers on the cyclization mechanism and fine structural changes in polymer chains under various heat treatment conditions, the composition of acrylonitrile and methyl acrylate Å 98 : 2 to 97 : 3 mol % was suitable for the precursor preparation because the cyclization mechanism and fine structural changes in the boundary of this composition of copolymers were significantly different. With increasing MA content, the exothermic onset and peak in the thermogram was found to shift toward higher temperatures, and the aromaticity index decreased. This evidence indicates that MA was believed not to activate at all but to interfere with the cyclization. Additionally, by means of 13 C nuclear magnetic resonance ( 13 C-NMR) analysis, the tacticities of copolymers were nearly same, regardless of the copolymer composition, and the cyclization occurred nonstereospecifically during the initial heat treatment at 240ЊC for 1 h.
In this work, we studied the effects of electrochemical oxidation treatments of carbon fibers (CFs) on interfacial adhesion between CF and epoxy resin with various current densities. The surface morphologies and properties of the CFs before and after electrochemical-oxidation-treatment were characterized using field emission scanning electron microscopy, atomic force microscopy, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, and single-fiber contact angle. The mechanical interfacial shear strength of the CFs/ epoxy matrix composites was investigated by using a micro-bond method. From the results, electrochemical oxidation treatment introduced oxygen functional groups and increased roughness on the fiber surface. The mechanical interfacial adhesion strength also showed higher values than that of an untreated CF-reinforced composite.
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