| Poly(butylene terephthalate)(PBT), one of crystalline thermoplastic polyesters, had been rapidly developed since 1970s'. It not only possesses many advantages such as high crystalline rate, good mechanical properties, outstanding dimensional stability and electrical insulation, but also has extraordinary heat, acid, oil and chemical corrosion resistance. All these advantages draw vast attentions from industries and scientific researchers. Melt-blown generated PBT nonwoven fabrics usually have small fibril diameter, high flexibility, well heat and oil resistance. Therefore, they would have promising application such as vehicle filtering media. Right now, domestic vehicle filtering media are mostly filtering paper, which are poor in pollutant loading capacity and short life time. While high efficiency filtering media are generally imported, which would increase cost sharply. Therefore, to prepare a domestic high efficient composite filtering media is becoming a imminent task.In this study, thermal property, crystallization behavior and rheological behavior of PBT have been analyzed. Effects of fabricating parameters such as air pressure, die-collector distance and pump feed on structure and properties of nonwoven fabrics have been investigated. Finally, a preliminary study on the forming process of composite filtering media, followed by its characteri-zation have been conducted.The physical properties of PBT utilized in this study was as following:melting point= 224.7℃; decomposition temperature=382.3℃; melting index=154.0 g/10 min. It was found that Ozawa equation, rather than Jeziorny equation, could be applied to study PBT non-isothermal crystallization. The Avrami index, obtained by Ozawa equation, varied between 1.06-1.80 as a-function of temperature. Since PBT was a non-Newtonian fluid, at same sharing rate, the apparent viscosity of the system would decrease as increasing the temperature. The viscous flow activation energy changed between 47-53 KJ/mol at shearing rate around 500-4000 s-1. Besides, as temperature increasing, the non-Newtonian index of PBT increased, indicating polymer chains became more flexible.During melt-blown process, it turned out that PBT fibril diameter decreased as increasing air pressure. Also, the break force of nonwoven fabrics increased with the same trend. It was interesting to found that the vertical break force was always larger than the horizontal one. In addition, it was noticed that average and maximum pore size decreased at the same time. When increased die-collector distance, PBT fibril diameter decreased slightly, while its air permeability increased. Moreover, the vertical and horizontal break force of nonwoven fabrics nearly decreased to the same level. Furthermore, the increase of pump feed would increase the fibril diameter and break force. A strong trend of conglutination was also observed at this time. The PBT nonwoven fabrics prepared during this study had fibril diameters around 3-7μm; average pore size between 7-12μm; maximum pore size in the range of 18-27μm. The maximum vertical break force is 27.9 N, while the maximum horizontal break force is 20.9N.The composite filtering media was prepared using PBT nonwoven fabrics generated from this study. It showed that as molding pressure increasing, physical properties such as thickness, air permeability, maximum and average pore size of resulted composite material decreased gradually. No significant effects of the amount of adhesive on thickness of composite material had been observed during experiment. However, it was found that air permeability, maximum and average pore size of decreased upon addition of adhesive.The contact angle, with water as solvent, of PBT nonwoven fabrics was tested to be 142.3°, which can be considered as a hydrophobic material. The generated composite material is highly effective for separating solid impurities (diameter>5μm), with filtering efficiency up to 99%. The carrying capacity is 2.11 times higher as compared with traditional filter paper. Further work need to be done to improve filtering efficiency for water and solid impurities with diameter< 4μm. |
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