The molding process of hollow fiber ultrafiltration membranes is a crucial step determining their microstructure, separation performance, and operational stability. Its core lies in transforming polymer materials into a fiber morphology with a regular hollow structure and controllable pore size. Current industrial mainstream employs a phase inversion method combined with precision spinning technology, achieving high-performance membrane preparation through multi-stage parameter coordination.
Molding begins with the preparation of the casting solution, requiring careful selection of polymer types and solvent systems to ensure solution homogeneity and a suitable viscosity range. Based on this, extrusion is performed through a two-component or multi-channel spinneret, simultaneously forming a hollow cavity and an outer polymer flow, obtaining the initial fiber prototype. During this process, the extrusion speed, core liquid composition, and temperature must be strictly matched to avoid uneven wall thickness or cavity collapse, directly affecting the fiber's mechanical strength and flux distribution.
The subsequent phase inversion process is the core of structural finalization. After the fibers enter the gel bath, the solvent and non-solvent in the bath undergo bidirectional diffusion, initiating polymer phase separation and gradually forming a microporous network. The gelation temperature, time, and bath composition determine the pore size, porosity, and connectivity, thus defining the membrane's retention accuracy and permeation performance. Low-temperature slow gelation facilitates the formation of finger-like pore structures, increasing flux; high-temperature fast gelation easily forms sponge-like pores, enhancing retention stability.
To further improve the membrane's antifouling and durability, surface modification treatments such as plasma etching, UV grafting, or hydrophilic coating can be performed after molding to optimize surface energy and water contact angle, reducing the likelihood of contaminant adhesion.
Module encapsulation is also incorporated into the molding system. A large number of single fibers are packed into a pressure-resistant shell according to a preset density and arrangement, with both ends sealed with resin to form flow channels, ensuring uniform hydraulic distribution and controllable pressure loss during operation. The overall process emphasizes the integrated design of materials, processes, and structure; deviations in any link will affect the consistency and reliability of the final membrane.
The precise hollow fiber ultrafiltration membrane molding process not only achieves accurate construction of the microstructure but also provides solid support for the large-scale application of membrane separation technology under complex operating conditions.
