The core of microporous membrane technology's breakthrough in overcoming the limitations of traditional filter cartridges is to upgrade filtration from "deep disordered interception" to "surface nanoscale precise sieving," advancing the precision from the micrometer level (≥1μm) to the sub-nanometer level (1–100nm), achieving highly efficient interception of bacteria, viruses, and even macromolecules.
I. The Limitations of Traditional Filter Cartridges: Traditional filter cartridges (PP melt-blown, wound, and ordinary fiber) are limited by materials and processes, resulting in three inherent bottlenecks:
1. Large and uneven pore size: Fiber filtration is typically 1–100μm, with a wide pore size distribution and irregular shape, allowing large particles to easily penetrate and small particles to easily clog.
2. Low efficiency in deep filtration: Relying on the random pores of the fiber layer for "labyrinthine" trapping, impurities become embedded inside, resulting in limited dirt holding capacity, rapid pressure drop, and short lifespan.
3. Instability and drift in filtration accuracy: Fibers are prone to loosening and deformation when exposed to water/fluids, leading to increased pore size and a continuous decrease in filtration efficiency during use.
II. Nanoscale Interception Principle of Microporous Membranes
Microporous membranes (microfiltration MF / ultrafiltration UF / nanofiltration NF) utilize an ultrathin, dense separation layer as their core to achieve "precise sieving, surface interception, and high flux": Precisely controllable nanoscale pore size
Microfiltration membranes: 0.1–10 μm; Ultrafiltration membranes: 10–100 nm; Nanofiltration membranes: 1–10 nm.
High pore size uniformity (CV value <6%), regular pore shape (cylindrical straight pores), like a "precision sieve," allowing only molecules smaller than the pore size to pass through.
Surface Filtration, High-Efficiency Interception
Impurities are trapped on the membrane surface, forming a thin filter cake layer that is easy to clean, has stable pressure drop, and a long lifespan.
Retention rate for 0.1μm bacteria > 99.99%, and for 20nm viruses > 99.9%, far exceeding traditional filter cartridges.
Material Revolution: High Strength, Fouling Resistance, and Modifiability
Mainstream Materials: PVDF, PES, PTFE, ceramics, carbon nanotubes, offering high strength, acid and alkali resistance, and high-temperature resistance.
Hydrophilic Modification: Grafting hydroxyl/sulfonic acid groups increases flux, reduces adsorption fouling, and extends lifespan.
Composite Structure: Ultra-thin separation layer (<1μm) + porous support layer, balancing high flux and high strength.
III. Key Technological Breakthroughs: From Micrometers to Nanometers
Membrane Fabrication Process Innovation
Phase Inversion Method (NIPS/VIPS/TIPS): Generates uniform nanopores in a single step through solvent-to-non-solvent exchange, eliminating the need for mechanical drilling.
Electrospinning/3D Printing: Fabricates gradient-pore membranes, with surface nanopores for interception and underlying macropores for support, balancing precision and flux.
Heavy Ion Bombardment: Creates uniform (0.01–15 μm) cylindrical straight pores on polycarbonate membranes with sub-nanometer precision.
Upgraded Filtration Mechanism
Size Screening: Pore size < particle size, physical interception (core mechanism).
Charge Repulsion: The membrane surface is charged, repelling impurities with the same charge (e.g., nanofiltration membranes are negatively charged, retaining anions).
Adsorption: Modified functional groups on the membrane surface adsorb specific impurities (e.g., heavy metals, organic matter).
IV. Application Scenarios: The Value of Nanofiltration
Biopharmaceuticals: Sterilization-grade filtration (0.22μm), virus removal (20nm), and protein purification ensure sterility and pyrogen-free drug solutions.
Semiconductors: Ultrapure water preparation (1–10nm) removes microparticles, bacteria, and ions to meet the stringent requirements of chip manufacturing.
Environmental Water Treatment: Deep wastewater treatment (25nm ultrafiltration membrane) removes colloids, bacteria, and some heavy metals, ensuring effluent meets standards for reuse.
Food and Beverages: Sterilization and clarification of milk/juice retains nutrients and extends shelf life.
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