| Poly (butylene terephthalate)(PBT), a kind of crystalline thermoplastic polyester, possesses not only many advantages such as fast crystalline rate, good mechanical properties, outstanding size stability and electrical insulation, but also extraordinary heat, acid, oil and chemical resistance. PBT melt-blown nonwoven fabrics, fibers of which are fine and soft, are an ideal fuel filter material. In this thesis, proper dosage of flow modifier (FM) was blended in PBT resin to improve the flow capability of PBT melt during the melt-blown process. And modified PBT melt-blown non-woven filter with smaller fiber and pore diameter and better filtration precision was prepared prospecting good application in the field of automobile fuel filter.In this thesis modified PBT/FMs with different content of FM were blended by twin-screw extruder and then granulated. A series of characterizations were conducted to analyze their thermal property, crystallization performance and rheological behavior. Furthermore, modified melt-blown PBT nonwoven fabrics were prepared with different conditions. The effects of the content of FM, air pressure, die-collector distance, metering pump speed and weight on the structure and properties of modified melt-blown PBT nonwoven fabrics were studied according to the orthogonal analysis,.Study on thermal property showed that melting temperature of PBT wouldn’t change and remained at225℃after modification. The difference in thermal decomposition temperature was not so much that the initial degradation temperature (T5%) was not influenced much by adding FM, remaining at about390℃. Non-isothermal crystallization kinetics studies showed that crystallization temperature of PBT/FM increased with sharper and narrower peak because of the addition of flow modifier. As the cooling rate increased, the crystallization temperature and the crystallization period decreased. In the blend system, small amount of flow modifier (2%FM) can promote crystallization as nucleating agent. In addition, capillary rheological behavior showed that the apparent viscosity decreased with the increase of shear rate in the PBT/FM system, a non- Newtonian fluid. With the content of flow modifier increased, the apparent viscosity went down obviously. Viscous flow activation energy (△Eη) of pure PBT declined with the increase of shear rate. And after modification,△Eη was stable in the wide range of shear rate of1000-5000s-1and much lower than pure PBT when the shear rate was below2000s-1. It was shown that the flow modifier could promote the flow capability of PBT melt obviously.According to SEM figures of melt-blown samples, statistics of fiber diameter showed that average fiber diameter decreased and the fiber diameter distribution was widened after modification. Especially PBT with4%flow modifier had great role in promoting the ratio of finer fibers. Moreover, the higher air pressure, the finer is fiber diameter and slightly wider is fiber diameter distribution. Die-collector distance had little effect on fiber diameter. When metering pump speed was higher, fiber was thicker but distribution was narrower. Aperture tests showed that flow modifier could effectively reduce and uniform the pore size of nonwoven fabrics. In addition, with water as solvent, the contact angles of modified PBT non-woven fabrics were between115°and135°, which showed that the flow modifier had little influence in hydrophilia of PBT nonwoven fabrics. The breaking strength tests showed that content of flow modifier had little influence on the breaking strength. Higher air pressure and weight would increase the breaking strength, while longer die-collector distance would decrease the breaking strength.In summary, flow modifier would not decrease heat resistance of PBT much, while could promote flow capability obviously. The fiber and pore diameter of modified PBT nonwoven fabrics were both smaller, and the distribution of pore diameter was uniform. Besides, the addition of flow modifier would not decrease the break strength.4%flow modifier in PBT was proper in consider of the properties and price of nonwoven fabrics. |
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