Polyvinylidene fluoride hollow fiber membrane and preparation method thereof

Abstract

The invention provides a large-scale production process for preparing a beta-crystal form polyvinylidene fluoride hollow fiber membrane by an improved TIPS method and the polyvinylidene fluoride hollow fiber membrane prepared by the preparation method. According to the method, an existing high-speed mixer is used for mixing and stirring materials, a twin-screw extruder is used for heating, melting, meshing and modifying the materials, and the materials are extruded by a granulation die head, cooled, formed, granulated, bagged and stored into a semi-finished product; similarly, the twin-screw extruder is additionally provided with a melt metering pump for metering and pressurizing, a spinning die head is replaced, the process is adjusted, and hollow fiber nascent filaments can be produced by using the granules; by carrying out stretching and annealing shaping combined post-treatment on the obtained hollow fiber membrane filaments, on the premise of ensuring high strength, hydrophilicityand high flux of the beta-crystal structured polyvinylidene fluoride product, the process is simpler, the production efficiency is higher, the membrane filament quality is more stable, and the product is particularly suitable for membrane bioreactors with higher requirements on the membrane filament strength and the membrane flux.

Description

technical field [0001] The invention relates to the technical field of microporous membranes, in particular to a polyvinylidene fluoride hollow fiber membrane and a preparation method thereof. Background technique [0002] Polyvinylidene fluoride (PVDF) has excellent thermal stability and corrosion resistance, and its good chemical resistance is excellently used by the water treatment membrane industry. Therefore, it has attracted more and more attention in the field of membrane separation in recent years. and promotion. Thermally induced phase separation (TIPS) method is an emerging ultra-microfiltration membrane preparation technology. This method uses polymers and additives with the polymer's hot solvent (solvent that can dissolve PVDF polymers when heated to a certain temperature, but precipitates when cooled). , such as phthalates, benzophenone, r-butyrolactone, etc.) are melted at high temperature, and then cooled to cause phase separation to form a three-dimensional ...

AI Technical Summary

Problems solved by technology

However, due to the use of a high-temperature stirred tank to heat up and stir, and then adopt a method similar to the NIPS method for static defoaming, the production cycle is too long, the output is low, and the molten spinning solution with high viscosity has a poor static defoaming effect , so that there are more pore defects in the membrane filament during spinning, and because of the limitation that the greater the viscosity, the worse the defoaming effect, the increase in the proportion of high polymer content is limited, and the proportion of organic liquid is relatively high. The comprehensive influence of various factors results in its product The tensile strength is low, and its embodiment introduction is only about 3MPa; at the same time, because it wants to obtain a higher β-crystal content under the lower tensile strength, it has to adopt a multi-stage high-temperature annealing process, so that During the annealing process, the mold holes that have been formed are deformed and collapsed, resulting in a decrease in the porosity of the membrane filaments and a decrease in water flux

For PVDF membranes, the stretching method is a simple and effective way to prepare β-crystal form. The traditional thermotropic phase membrane method has a low polymer concentration and a relatively high high-temperature solvent content, which is high when the polymer solution is extruded. The entanglement between molecules is limited, so that the tensile properties of the membrane filaments are not good before and after molding, so the ratio of the β-crystal form of the prepared membrane filament product is not high, and post-treatment processes such as annealing are required to further improve the β-crystal form. Ratio, but it also causes a decrease in porosity and deformation of the membrane pore diameter, which cannot give full play to the advantages of the β-crystalline PVDF membrane, and it is difficult to improve the performance of membrane filament strength and water flux.