| Poly(trimethylene terephthalate)(PTT) is a new member of linear saturated polyester family. It combines high mechanical strength and good heat resistance of poly(ethylene terephthalate)(PET) with good flexibility and processing features of poly(butylene terephthalate)(PBT), and hence, is a promising candidate in the field of engineering thermoplastics, especially in the field of fibers. Moreover, the monomer of PTT, namely propanediol, can be derived from corn sugar, a renewable resource, and hence PTT has also drawn considerable attention as a new generation of green material for its biobased origin.With the development of science, the nano-technology becomes more and more important in the field of fibers. In this case, preparing superfine fibers is the one of the significant research areas. Electrospinning is one of the simple and effective methods of preparing superfine fibers. Therefore, it has been widely investigated. Using this technology, many polymer based superfine fibers has been successfully prepared. But the electrospinning of PTT has not yet been reported in detail till now, which is necessary for the extended applications of PTT fibers.Thus, in this work, the electrospinning of PTT was studied firstly in terms of solution concentrations, voltage and distance. Then the effects of those aspects on the PTT electrospinning were discussed and the best experimental conditions were finally determined. The electrospinning of PTT/CNT composites was also studied. The dispersion of CNTs with different surface structures in the PTT matrix and the fibers was stressed, aiming at exploring the aspects controlling the formation of PTT based nano-wire and their mechanisms. In addition, the membrane sample was fabricated using electrospinning technology for the observation of PTT banded spherulite. The preliminary results are as follows.(1) At lower solution concentrations, the micro-drops are easy to form instead of continuous fibers during electrospinning, while at higher solution concentrations, it is hard to perform spinning continuously. The ratio of compound solvents also affects the morphology of fibers:in the lower content of trifluoroacetic acid, PTT is hard to be fully dissolved, while in the higher content of trifluoroacetic acid, the obtained fibers show the conglutination structure with one another. With the increasing voltage, the average diameter of fibers reduces accompanied by the lowered uniform level of fibers. Furthermore, the average diameter of fibers is more or less dependent on the distance between the tip and collect plate. The best experimental conditions for the electrospinning of PTT are finally determined:the ratio of compound solvents is1:2(v/v) between trifluoroacetic acid and methylene chloride; the solution concentration0.200g/ml; the voltage16kV and the distance between tip and collect plate15cm. Under these conditions, uniform PTT fibers without beads or micro-drops are formed, and the average diameter is317nm with the distribution of between285and345nm.(2) The influence of solution concentration and other experimental conditions on the electrospinning of PTT/CNT composites show almost same trends with those on the neat PTT despite the higher average diameter of composite fibers than that of the neat PTT. In addition, the surface modification and the aspect ratio of CNT affect the dispersion of CNT in fibers and the fiber morphology strongly. The hydroxy CNTs show poorer dispersion in the matrix due to their lower affinity to PTT than that of carboxylic CNTs. Compared with those with lower aspect ratio, the carboxylic CNTs with higher aspect ratio are far more flexible and hence dispersed in the PTT matrix mainly as flocs with large hydrodynamic radius and high volume fraction but not individuals or small bundles. Therefore, the fibers with hydroxy CNTs show beaded and misshaped morphology while only the beaded and uncontinuous fibers are formed with high aspect ratio CNTs. Under the same experimental conditions, only the carboxylic CNTs with low aspect ratio are embedded well in the fibers with bead-free and uniform morphology, which forms nano-wire structure.(3) The thin film samples prepared by electrospinning can be well used for banded spherulite observations. After crystallization at the temperatures ranged in regime Ⅱ, both the neat PTT and the composites show banded spherulites, which is attributed to lamellar twisting followed by interlamellar or intralamellar origins. The presence of CNTs, not only increases spherulite growth rate but also reduces spacing and peak-to-valley height of band structure. Although the folding surface free energy is reduced in this case, the narrowed lamellae size and the accelerated growth can cause enhanced level of fold staggering to the opposite fold surfaces, forming the spherulite structure with reduced band spacing and twist period in the composite. |
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