| Combined spinning is one of the important methods to preparing nano-fibers. The sea-island structure was obtained after the blend system was processed by the combined spinning means, and the dispersed phase was stretched into nano-fibers. In the system of cellulose acetate butyrate / isotactic polypropylene (CAB/iPP) binary hybrids, CAB was one of the environmentally benign and recyclable polymers and iPP was one of the commercial polyolefin that were widely used. So preparing iPP nano-fibers with uniform size and distributions by the method of melt-blending extrusion had extensive value in use. However in order to control the final morphology structures and size of iPP dispersed phase, it was important to be understood the process of morphology evolution and the influential factors of the phase development during the process of blending extrusion.In this paper, the process of morphology evolution especially the initial phase development during the melting zone was analyzed by using the method of scanning electron microscopy(SEM) and dynamic rheology. The influence of the interfacial properties, rheology properties and relaxation properties on the phase development was discussed. And the quantitative relation between these factors and morphology of dispersed phase was studied.Firstly the interfacial tension of CAB/iPP was estimated using harmonic meanmethod and the viscoelastic characteristics and characteristic relaxation time wasmeasured by dynamic rheology test. It was demonstrated that there were four stages inthe meting zone: (1) the crushing of macro-pellets; (2) the deformation of micro-drops;(3) the formation and disruption of the sheets structure; (4) the formation of nano-fibers. This process was comprehensive determined by interfacial properties, rheology properties and relaxation properties.During the blending process, the micro-drops deformed in two ways: (1) by extending sheets that break up into nano-fibers by forming holes; (2) by stretching into nano-fibers directly. The results show that the system with small specific surfacearea, small interfacial tension, low viscosity rate p (p =η_d/η_m), high elastic rate(G_d /G_m) and long relaxation time was easier to form sheet structure. The final phasedimensions were found to be largely determined by the sheet thickness. And shortfibers that formed by extending sheets were 1-2 order of magnitude fine than that formed by stretching directly at the same initial drop dimensions. The deformation way of the micro-drops was determined by the parameters of stress ratio(?) and the Deborah number De =λγ. The larger stress ratio and Deborahnumber could accelerate the formation of sheet structure, whereas the drops was easier to stretched into nano-fibers directlyThe dynamic rheology properties of CAB/iPP blending system were significantly affected by the incompatible morphology. The elastic response and frequency dependence increased because of the deformation of the interface. It was found that the elasticity of the CAB/iPP blending was mainly dependence with that of matrix. The elasticity deviate degree of the blend system and the matrix increased with the decrease of the shortfibers dimensions due to the larger specific surface area. The influence of the interfacial on the loss moduli was mainly reflected at high frequencies, however, it was not obvious.Finally the effects of process conditions on the phase dimensions was discussed. It was found that the morphology was significant affected by the composition proportion. And the change of drawing speed not only affected the size but also the radial distribution of the dispersed phase. |
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