The water purifier industry is one where ultrafiltration applications are particularly widespread. In household ultrafiltration water purifiers, the core component is the ultrafiltration membrane.

　　A ultrafiltration membrane is a microporous filter with uniformly sized pores, featuring a nominal pore size range of 0.001 to 0.02 microns. The membrane filtration process that utilizes this type of membrane, driven by a pressure difference, is known as ultrafiltration. Most ultrafiltration membranes are made from cellulose acetate fibers or other high-polymer materials with similar performance characteristics. Ultrafiltration is particularly well-suited for separating and concentrating solutes in solutions, and it’s also commonly employed to tackle colloidal suspensions—processes that often prove challenging with conventional separation techniques. As a result, its applications continue to expand across various industries. Membrane filtration driven by a pressure difference can be categorized into three main types: ultrafiltration, microfiltration, and reverse osmosis. These categories are distinguished based on the smallest particle size or molecular weight that the membrane layer can effectively retain. Specifically, microfiltration membranes (MF) have a nominal pore size range of 0.02 to 10 μm; ultrafiltration membranes (UF), 0.001 to 0.02 μm; and reverse osmosis membranes (RO), 0.0001 to 0.001 μm. This classification highlights that ultrafiltration membranes are ideally suited for tasks such as separating and concentrating solutes in solutions—or even isolating colloidal suspensions that are difficult to handle using other separation methods. Importantly, the technology used to manufacture ultrafiltration membranes, specifically achieving the desired pore size with a narrow distribution, plays a critical role in their effectiveness. Several factors influence pore control, including variations in the type and concentration of the solution during membrane formation, as well as differences in evaporation and coagulation conditions. These variables ultimately determine the resulting pore size and pore-size distribution of the membrane. Ultrafiltration membranes are typically classified as polymeric separation membranes, with common polymer materials used in their production including cellulose derivatives, polysulfones, polyacrylonitrile, polyamides, and polycarbonates. These membranes come in various forms, such as flat-sheet, spiral-wound, tubular, or hollow-fiber configurations, making them highly versatile for applications in fields like pharmaceuticals, food processing, and environmental engineering. To put it simply, a sieve is a tool designed to separate materials by size—allowing smaller particles to pass through while trapping larger ones. But have you ever heard of a "sieve" capable of sorting molecules? Enter the ultrafiltration membrane—a remarkable "super-sieve" that can precisely separate molecules of varying sizes! So, what exactly is an ultrafiltration membrane? It’s a specialized porous membrane endowed with exceptional "sieve-like" separation capabilities. With pore sizes ranging from just a few nanometers to tens of nanometers—roughly one-thousandth the width of a human hair—an ultrafiltration membrane can selectively retain larger solute molecules while allowing smaller ones to pass through. This makes it ideal for separating particles with molecular weights greater than 500 Daltons and diameters between 2 and 20 nanometers. Ultrafiltration membranes can exhibit either symmetrical or asymmetrical structures. Symmetrical membranes are isotropic, meaning they lack a distinct surface layer and feature uniform porosity in all directions, making them suitable for deep-bed filtration. In contrast, asymmetrical membranes boast a denser outer layer combined with a finger-like inner structure. The surface layer, typically less than 0.1 micrometer thick, contains orderly arranged micropores, while the underlying layer, measuring around 200–250 micrometers in thickness, serves as a support framework for the filtration process.

　　Industrial-grade ultrafiltration membranes are typically asymmetric membranes. The primary membrane materials for ultrafiltration membranes include cellulose and its derivatives, polycarbonate, polyvinyl chloride, and polyvinylidene fluoride.