How does the phase inversion process shape the porous structure of Alloy PVDF Gradient Hollow Fiber UF Membrane Filter?

In the preparation process of alloy PVDF gradient hollow fiber UF membrane filter, the phase inversion process is a key link to determine its performance. This process is not only related to the formation of the microstructure of the membrane, but also has a profound impact on the application performance of the filter in different fields. From spinning to form hollow fibers to the final porous structure, how does the phase inversion process work, and how to shape a filter membrane that meets specific needs? ​
The core of Alloy PVDF gradient hollow fiber UF membrane filter lies in its unique membrane structure, and the phase inversion process is the cornerstone of building this structure. When the spinning process is completed and the hollow fiber is initially formed, it is immersed in a coagulation bath. At this time, the concentration difference and chemical potential difference become the driving force of the entire process. The solvent in the spinning solution begins to exchange with the non-solvent in the coagulation bath. In this process, the polymer gradually separates from the solution and finally forms a porous structure. This seemingly simple process actually contains complex physical and chemical changes, and every detail affects the final performance of the membrane.​
The composition of the coagulation bath plays a crucial role in the phase inversion process. Different coagulation bath solvents will change the speed and mechanism of phase separation. The selection of a certain coagulation bath solvent may make the phase inversion process faster, the polymer precipitates quickly, and forms a loose structure with relatively large pore size; while another solvent may make the phase inversion process slower, and the polymer has more time to arrange, thereby forming a membrane with uniform pore size and dense structure. In addition, various additives added to the coagulation bath will also affect the structure of the membrane. Some additives can change the exchange rate between the solvent and the non-solvent, or affect the aggregation mode of polymer molecules, thereby obtaining membranes with different porosity and pore structure distribution. These different structural characteristics make the alloy PVDF gradient hollow fiber UF membrane filter suitable for different filtration scenarios, from removing large particle impurities to intercepting tiny microorganisms and organic molecules. ​
The temperature of the coagulation bath is also an important factor affecting the phase inversion process. A lower coagulation bath temperature will slow down the exchange rate between the solvent and the non-solvent, making the phase inversion process smoother. In this case, the polymer molecules have more time to arrange in order, which helps to form a uniform pore structure. Higher temperatures will accelerate the exchange process, and phase separation will occur rapidly, which may lead to uneven pore structures and even irregular large pores. By precisely controlling the coagulation bath temperature, the preparation personnel can adjust the structure of the membrane according to actual needs. For example, in scenarios where high-precision filtration is required, the coagulation bath temperature is lowered to obtain a membrane with a smaller pore size and uniform distribution to ensure efficient interception of tiny particles and impurities; while in applications that pursue high water flux, the temperature is appropriately increased to form a membrane structure with a larger pore size and higher porosity. ​
Coagulation time is also a factor that cannot be ignored. If the coagulation time is too short, the exchange of solvent and non-solvent is insufficient, and the polymer phase separation is incomplete, the membrane structure may be loose, the strength is insufficient, and the porosity is low, which cannot meet the actual filtration requirements. With the extension of the coagulation time, the phase separation process is more complete, the structure of the membrane gradually stabilizes, and the porosity and pore size will also change accordingly. However, too long a coagulation time is not beneficial, as it may change the performance of the membrane and even cause some undesirable phenomena, such as shrinkage and deformation of the membrane. Therefore, in actual production, it is necessary to find a suitable balance point of solidification time to ensure that the membrane has good structure and performance. ​
The porous structure formed by the phase inversion process directly determines the filtration performance of the alloy PVDF gradient hollow fiber UF membrane filter. The uniform and reasonable pore structure distribution can ensure that the membrane maintains a high water flux while efficiently intercepting pollutants. In the field of drinking water purification, this precisely controlled porous structure can effectively intercept bacteria, viruses, colloids and suspended solids in water, while allowing water molecules to pass smoothly to ensure the safety and purity of drinking water. In industrial wastewater treatment, for different types of pollutants, the structure of the membrane is adjusted through the phase inversion process, so that it can intercept heavy metal ions, organic pollutants, etc. in a targeted manner, and achieve wastewater purification and resource recovery. ​
Not only that, the porous structure formed by the phase inversion process also affects the anti-pollution performance of the membrane. Reasonable pore structure can reduce the adsorption and deposition of pollutants on the surface and inside of the membrane. When pollutants contact the membrane surface, the uniform pore structure can avoid local aggregation of pollutants and reduce the risk of membrane pollution. Even if there is a certain amount of pollutant accumulation on the membrane surface during long-term use, simple physical or chemical cleaning methods can easily restore the membrane flux, extend the service life of the membrane, and reduce the maintenance cost of the filter. ​
From the molecular arrangement at the microscopic level to the macroscopic filtration performance, the phase inversion process plays a decisive role in the preparation of alloy PVDF gradient hollow fiber UF membrane filters. Through the precise control of factors such as the coagulation bath composition, temperature and coagulation time, membranes with different porous structures are prepared to meet the filtration needs of different fields and scenarios. In the future, with the continuous improvement of the requirements for filtration technology, the phase inversion process will continue to develop and optimize, bringing better performance to the alloy PVDF gradient hollow fiber UF membrane filter, and playing a more important role in ensuring water quality safety and promoting the development of various industries.