Abstract:

Significance Surfaces with special wetting behavior, especially superhydrophobic surfaces with high water contact angles greater than 150° and low slide angles less than 10°, have attracted attention because they can be used in a variety of applications requiring special surface properties, such as anti-corrosion, self-cleaning, and drag reduction. Polyterafluoroethylene(PTFE) is a good material for preparing superhydrophobic membranes because of its good thermal stability, chemical resistance, low surface energy and low thermal conductivity. However, the surface of the membrane material prepared by PTFE resin cannot meet the requirements of superhydrophobic, so the superhydrophobic modification becomes the focus of research.

Progress In this paper, the preparation, modification and application of PTFE membranes were reviewed. The advantages and disadvantages of different processes for the preparation and modification of superhydrophobic PTFE membrane were summarized. According to the superhydrophobic modification principle of PTFE membrane and the molecular chemical structure of PTFE, two modification mechanisms of "not changing the molecular structure of PTFE" and "changing the molecular structure of PTFE" were analyzed. Based on practical cases, the early modification methods such as laser etching, ion irradiation and plasma etching are introduced one by one, and their shortcomings are analyzed. The super hydrophobic modification of PTFE further reduces the surface energy of the membrane, which can solve the problems of easy contamination, poor selective permeability and short service life. Finally, the application of super hydrophobic PTFE membrane in oil-water separation, membrane distillation, printing and dyeing wastewater treatment is introduced.

Conclusion and Prospect The preparation technology of superhydrophobic PTFE membrane was summarized into two types: "no change in the chemical structure of PTFE" and "change in the chemical structure of PTFE". The first method is relatively simple and economical, but because most of the bonding methods are physical bonding, its bonding strength is low, the superhydrophobicity cannot be maintained over time, and it is prone to secondary pollution. The second method is fast, easy to control the surface structure, and has good hydrophobicity retention, but the molecular structure of PTFE is destroyed, which will adversely affect the mechanical strength and chemical stability of the membrane. Subsequent development should be carried out from the following aspects. 1) The selection of environmentally friendly nanoparticles and the enhancement of partical bonding strength and uniformity should be extensively explored. Nanoparticles should be combined with the industrial production process of PTFE membrane, and the process of dual-directional stretching to prepare PTFE membrane should be added to form a superhydrophobic PTFE membrane in one step. 2) A mild and efficient surface construction method, which can reduce the damage to the PTFE membrane substrate as much as possible while obtaining super hydrophobicity should be developed to achieve the coexistence of functional performance and strength. 3) The density ratio between the crystalline state and the amorphous state of PTFE should be controlled during membrane making, and the surface energy of PTFE should be reduced by increasing the amorphous state density, so as to directly realize the super hydrophobic of PTFE membrane.

Key words: separation membrane material, polytetrafluoroethylene membrane, superhydrophobic, modification method, separation technique