Preparation And Properties Of Polypropylene Micro/Nanofiber Membranes

Micro/nanofiber membranes have good properties, such as large specific surface area, high porosity, low density, small apertures and good pore interconnectivity, for many applications. Moreover, the surface area and the proportion of polymer chains exposed on the surface can increase with decreasing fiber diameter, so that the micro/nanofiber membranes have potential for incorporation of active chemistry or functionality on a nanoscale.In this paper, the isotactic polypropylene （iPP）, maleic anhydride graft polypropylene （PP-g-MAH） micro/nanofibers, the polypropylene micro/nanofiber membranes and polypropylene nanofiber/nonwoven composite membranes were prepared.The properties of nanofiber membranes, including the morphology, surface areas, pore size distribution, contact-angle, porosity, apparent density and water flux were characterized.The isotactic polypropylene or maleic anhydride graft polypropylene in nanosized can be obtained via melt extrusion of immiscible blends of cellulose acetate butyrate （CAB） and subsequent removal of the CAB matrix due to the phase separation behavior. The fiber dispersion was discussed when the nanofibers were placed in different organic solvent and various dispersant solutions. Compared with the appearance and performance of the finally iPP nanofiber membranes, the water with fatty alcohol polyoxyethylene ether of weight ratio 0.03% was finalized to use as the dispersion solution in this study, and the beatting-membrane-forming route was confirmed to prepare the nanofiber membranes. The beatting-membrane-forming process is an affective and feasible technology to make nano-fiber membranes, moreover the slurry concentration and the shape of membrane-forming supports can be adjusted according to the actual requirement to obtain some appropriate membranes.In this study, the nanofibers inside membranes were arranged closer between each other, especially, the bigger fibers were tend to form frameworks serving as supports, and the smaller fibers were filled in the frameworks, which can bring a smaller pore structure. The pore diameter range of the iPP micro/nanofiber membranes was 0.2-2.8μm, surface area was 3.5-5.5 m².g^-1, the contact-angle was >140°, the porosity was generally >80%, the water flux of iPP micro/nanofiber membranes were 2852.99 L/m².h, which was higher than that of PP commercial microporous membranes. The rejection of TiO₂ solution was 40%-50%, and the TiO₂ with diameter d>458nm can be intercepted by iPP micro/nanofiber membranes.In this study, the diameter of under surface of PP-g-MAH micro/nanofiber membranes was lower than that of upper surface. The pore diameter range of the PP-g-MAH micro/nanofiber membranes was 0.2-2.0μm, the surface area was >9.0 m²·g^-1, the contact-angle was <130°, the porosities were belong to 70-76%. The water flux of PP-g-MAH micro/nanofiber membranes were 2304.34L/m²·h, which was also higher than that of PP commercial microporous membranes, the TiO₂ with diameter d>255nm can be intercepted by PP-g-MAH nanofiber membranes, the rejection for TiO₂ solution of PP-g-MAH micro/nanofiber membranes was >99%, for disperse dye solution was >75%.The nanofiber/nonwoven composite membranes were also prapared in this study. The pore size distribution of iPP nanofiber/microfiber composite membrane was 0.2-1.9μm, and the pore size of PP-g-MAH nanofiber/microfiber composite membrane was 0.1-0.8μm, which were significantly lower than that of PP microfiber membranes （7.3-34μm）. The rejection for disperse dye solution of PP-g-MAH nanofiber/microfiber composite membrane was >99%.