Summary of "J. Membr. Sci." by Professor Huang Qinglin from Tianjin University of Technology: Latest Research Progress in PTFE Porous Membrane Technology

updatetime：2023-03-24 09:19:25

Membrane separation technology has developed rapidly in the past few decades due to its advantages such as high separation efficiency, low energy consumption, and good environmental benefits. It has become one of the key common technologies to solve the current global energy crisis, water resource crisis, air pollution, and other major issues. Membrane materials are the core of membrane technology, and polymer membrane materials with excellent processing performance and high cost performance still dominate. However, increasingly complex processing environments require higher performance membrane materials, especially the development of membrane materials suitable for harsh environments such as high temperatures, strong acids/bases, and organic solvents. Due to the high electronegativity of fluorine atoms, low polarizability, and stable C-F bonds, polytetrafluoroethylene (PTFE) exhibits excellent temperature resistance, weather resistance, and chemical stability. As one of the ideal membrane materials, PTFE has been widely concerned and has shown great application potential in the fields of membrane contactors, air purification, biomedical, and new energy.

Recently, Professor Huang Qinglin from Tianjin University of Technology published a review entitled "PTFE porous membrane technology: A comprehensive review" in the authoritative journal "Journal of Membrane Science" in the field of separation membranes, which systematically summarized the preparation methods and latest research progress of PTFE porous membranes, The control strategies and functionalization methods for the pore structure of PTFE porous membranes are classified and described in detail. The typical applications of PTFE porous membranes in the fields of membrane contactors, air purification, water and moisture permeability are shown. The main challenges currently faced in the field of PTFE porous membranes are proposed, and the future development trends are prospected. The co first authors of this paper are Guo Qiang, a postgraduate student from Tianjin University of Technology, and Dr. Huang Yan from Yantai University. The corresponding authors are Professor Huang Qinglin from Tianjin University of Technology and Dr. Huang Yan from Yantai University. Professor Xiao Changfa from Shanghai University of Engineering and Technology are the co authors.

（1） PTFE material

In 1938, DuPont chemist Roy Plunkett accidentally discovered PTFE during refrigerant research, opening the field of perfluoropolymers and their commercialization. The basic properties of PTFE stem from its special chemical structure, where fluorine atoms form a shell around the carbon backbone, providing it with good chemical stability and inertia, low surface energy, low friction coefficient, and non adhesion. Nowadays, PTFE has been widely used in chemical, medical, environmental, aerospace and other fields. The second part of this article introduces the polymerization process, structure and properties, processing, recycling, disposal, and application of PTFE materials.

（2） Preparation of PTFE porous membrane

PTFE is almost insoluble in any organic solvent. Due to its unbranched molecular chains, high molecular weight, and high crystallinity, PTFE has a high melting point (327 ℃) and extremely high melt viscosity. Its processing performance is restricted by its "insoluble and non fusible" characteristics. Therefore, conventional non solvent induced phase separation (NIPS), thermal induced phase separation (TIPS), or melt spinning methods cannot obtain PTFE porous membranes. The preparation of PTFE porous films mainly began in the early 1960s, and the biaxial stretching process technology was patented by Gore in 1973. So far, the preparation methods of PTFE porous membrane (including flat membrane, hollow fiber membrane and tubular membrane) mainly include paste extrusion stretching method, pore forming agent assisted sintering method, lotion electrospinning method, near-field electrostatic direct writing method and wrapping method. In the third part of this article, the preparation techniques of PTFE porous membranes in recent years are introduced in detail, and the methods for controlling the pore structure of PTFE porous membranes are described.

（3） Modification of PTFE film

This article summarizes and discusses the latest progress in the modification of PTFE films from the perspectives of membrane surface wettability and functionalization. Hydrophilic modification mainly includes methods such as opening hydrophilic groups on molecular linkage branches, depositing hydrophilic inorganic substances on atomic layers, and surface coating. Hydrophobic and bi hydrophobic modifications are mainly achieved by improving membrane surface roughness and reducing surface energy. The functionalization of membranes is mainly aimed at meeting the needs of gradually expanding membrane applications by introducing functional substances to endow PTFE membranes with functions such as photoheating, photocatalysis, joule heating, and electrocatalysis.

（4） PTFE membrane application

This article shows the applications of PTFE membranes in membrane contactors (such as membrane distillation, membrane emulsification, membrane absorption, air dehumidification, etc.), air purification, oil water separation, and water and moisture resistance and permeability, and summarizes the practical performance of PTFE membranes obtained by different modification methods in membrane distillation. PTFE porous membranes also have great potential in new membrane processes such as nanofiltration, reverse osmosis, pervaporation, proton exchange membrane substrates, and battery separators.

Summary and outlook

At present, the preparation of PTFE porous membranes by paste extrusion stretching method is still the mainstream, but the controllability of membrane structure still needs to be improved. Fully fibrous PTFE nanofiber membranes have greater structural regulation and modification space, and can be used as an effective supplement to stretching membranes. The stability and economy of PTFE membrane modification methods should be further considered. Without weakening the temperature and solvent resistance of PTFE, achieving high throughput and precision separation, making full use of its solvent resistance, and developing substrates for nanofiltration, pervaporation, or reverse osmosis processes may be the focus of future research. PTFE films have been widely used in membrane contactors, but the problems of membrane wetting and membrane fouling still require more cost-effective and environmentally friendly solutions. Double hydrophobic PTFE films with self-cleaning properties, resistance to organic solvent wetting, and immunity from the influence of surfactants will receive increasing attention. In addition, the application of PTFE films in nano energy and intelligent wear, as well as as as as catalyst carriers, will be a research hotspot in the future.

Huang Qinglin, Professor of Tianjin University of Technology, has been engaged in the research on the formation mechanism, preparation technology, and product development of PTFE porous membranes for a long time. He has done a lot of representative work in the structural regulation, performance optimization, and functional modification of PTFE porous membranes. The fully fibrous, nodeless PTFE nanofiber membrane developed by the team has comprehensive advantages such as uniform pore structure, high porosity, high modulus, and strong self-supporting properties (Figure 5). It can be used as an effective supplement to PTFE biaxially stretched membrane, expanding its application in fields such as waterproof, breathable, and acoustic permeability, and new energy. Compared with the "fiber node" pore structure of PTFE biaxially stretched membrane (Figure 6), the developed homogeneous, circular pore structure PTFE porous membrane has a narrower pore size distribution and higher separation accuracy, demonstrating good application prospects in fields such as liquid separation under harsh conditions and membrane contactors.