Preparation Of High-performance Polypropylene Hollow Fiber Membrane

Polypropylene(PP) hollow fiber membranes were prepared by the melt-spinning and stretching(MS-S) method. The effect of spin-draw rate on structures and performances of the membrane were investigated based on the preparation technique process of PP hollow fiber membrane. Also, the effects of annealing conditions on structures and performances of the PP hollow fiber membrane were researched. Else, the effects of stretching process conditions on the structure and properties of PP hollow fiber membranes were also discussed. The microstructure and properties of the precursors and membranes were characterized by differential scanning calorimeter(DSC), two-dimensional small-angle X-ray scattering(2D-SAXS), elastic recovery, scanning electron microscope(SEM), the pure water flux, porosity, etc. In the end, the best process of preparing membranes was obtained.The results showed that with the spin-draw rate increasing, the elastic recovery of fiber, microstructure uniformity, pure water flux and porosity of membranes increased, and were the largest at the rate of 420m/min. However, the crystallinity of fibers gradually increased below the rate of 350m/min, and then slightly decreased with increasing the rates. And the membranes with the excellent properties can be obtained at a spin-draw rate of 420 m/min.Under a spin-draw rate of 420 m/min, the properties of fibers and membranes enhanced with the increase of annealing temperature, such as elastic recovery, pure water flux and porosity etc. The membranes with the excellent properties can be obtained at an annealing temperature of 140?.But the other properties except elastic recovery of membranes declined when the temperature increased to 150?. In addition, annealing stress field also had great effects on structures and performances of the PP hollow fiber membrane. It was indicated that stress acting on precursors influenced the development of shish-kebab crystal structure and rigid amorphous fraction(RAF) during the annealing process. The membranes with excellent properties were obtained under no stress.At last, when the spin-draw rate and annealing temperature with no stress were 420 m/min and 140?, respectively, it was found that the total stretching ratio, cold stretching ratio, stretching rate and stretching temperature could affect the formation of microfiber during the stretching process. The microfibers were fractured at high total stretching ratio and cold stretching ratio, micropores were closed, and some crystalline lamellae were not pulled out. The micropores were not uniformly distributed on the surface of membranes at extra high stretching rates. The membranes with the excellent microstructure and properties can be obtained at a total stretching ratio of 200%, cold stretching ratio of 20%, stretching rate of 12mm/min and stretching temperature of 140?.In order to improve the hydrophilicity of PP hollow fiber membrane, hydrophilic additive HL-560 was blended with polypropylene. It was indicated that the microstructure of PP hollow fiber membrane would be worse with increasing the content of hydrophilic additives because the crystalline behavior was limited. The membranes with better pure water flux(from 96L/m~2·h to 131L/m~2·h) can be obtained when the content of HL-560 was 5phr of polypropylene, but other properties all became worse. In addition, hydrophilic membranes were prepared through modifying the surface of microporous film. It was indicated that pure water flux and flux recovery became better and other properties had little influence. The pure water flux of membranes increased from 96L/m~2·h to 139L/m~2·h and the flux recovery increased from 55% to 90% using acetone as the solvent.