Preparation Of Electrospun Fiber Mats Of Styrene-Butadiene-Styrene Block Copolymer And Their Properties

During the development of fiber industry, ultrafine fiber is an important goal. With the rapid development of nanoscience and technology, the preparation and applications of nanofibers become the hot field in research. In order to make fibers with diameters between submicrometer and nanometer, electrospinning is the most important and viable method, in which the ultrafine fibers are forming from polymer solutions or melts with the help of high voltage electric field. The outstanding characteristic of electrospinning fibers is that the diameter of as-spun fibers is very small. These electrospun fibers or mats have high surface area and porosity, as well as small diameters and pores. They have enormous potential applications to wound dressing, filtration, protective clothing, tissue scaffolds, drug delivery system, high-performance cells, catalysis, and sensors. Styrene-butadiene-styrene triblock copolymer(SBS) is the high-performance thermoplastic-elastomer material, which presents the perfect combination of the rubber properties and thermoplastic processability. It is reported that elastomer nanofibers poss a unique advantage in air-filtration. Therefore, it makes sense to carry out the electrospinning research of SBS and produce electrospun fiber mats(EFMs) with the hope of further application in air-filtration.In this thesis, The ultrafine fibers of styrene-butadiene-styrene copolymer (SBS) were prepared by gas-jet/electrospinning of its solutions in a mixture of 75% tetrahydrofuran (THF) and 25% N,N-dimethylformamide (DMF). The influence of the concentration, the applied voltage, the tip-collector distance (TCD) and the inner diameter of needle on the diameter and morphology of electrospun fibers was investigated by scanning electron microscopy (SEM). At the same time, optimal process parameters were obtained under which SBS EFMs with different thickness were assembled on polypropylene (PP) nonwoven mats which served as supportor. Furthermore, The thermal and mechanical properties of the electrospun SBS membranes were examined.It was found by the observation of SEM that the concentration had a very important and direct influence on diameter and morphology of as-spun fibers. As the concentration increased from 10% to 18%, the average diameter of the electrospun fibers had a linear increase and the diameter distribution became broader. The formation of beaded fibers were observed when the concentration was 10% .The shape of the beads changed from spherical to spindle-like with increasing the concentration and finally beads disappeared as the concentration mounted up to 14%. The experimental results also showed that the diameter of electrospun fibers was decreased firstly and then increase with increasing the applied voltage from 23.8kV to 33.8kV. The tip-collector distance (TCD) seemed to have little influence on the fibers diameter and its distribution. When TCD increased from 10 to 30cm, the average diameter of as-spun fibers were 433, 429 and 401nm, respectively, namely there was only a very slight decrease in diameter. However, the less TCD tended to produce wet fibers and beaded structures because of poor evaporation of solvent and the too long TCD would increase the instability of electrically charged jet. The inner diameter of needle exerted a remarkable influence on fibers diameter. The SBS ultrafibers with average diameter of about 429 nm could be prepared at the following optimal process parameters: the concentration of SBS was 14 wt %, the applied voltage 28.8 kV, the TCD 20 cm, the inner diameter of needle 0.27 mm.It was indicated by DSC studies that in comparison with SBS bulk sample the glass transition temperature(T_g) of polybutadiene(PB) phase in SBS electrospun fibers was shifted to lower temperature. The reason was expected that the rapid stretching and the fast solvent evaporation rate during the electrospinning process allowed the polymer blocks only a short time to segregate. Contrast to the T_g change of PB phase, the T_g of polystyrene(PS) domains shifted to higher temperature and increased with decreasing concentration. This change was the result of the rapid stretching with solvent which favored the orientation and segregation of the stiff PS segments. The decreasing of T_g in PB phase would contribute to better elasticity and the increasing of T_g in PS phase tended to obtain better tensile strength of SBS electrospun fibers.The primary mechanical tests indicated that SBS EFMs exhibited good tensile strength and elasticity. The maximal tensile force of the SBS-PP composite mats increase with increasing area density of SBS EFMs. Compared with net PP nonwoven mats, when the density of SBS EFMs were 0.79, 0.96, 1.6 g/m~2, respectively, the maximal tensile force of the SBS-PP composite mats had a increase 4.3%, 4.9%, 10%, respectively. Approximate calculation showed that the tensile strength of SBS EFMs was 2.6 times that of the net PP nonwoven mats. In addition, when the area density of SBS EFMs was 1.6 g/m~2, the tensile strain of SBS-PP composite mats was higher by 24% than that of net PP nonwoven mats.