PTFE (polytetrafluoroethylene) is a synthetic polymer commonly used in membrane filtration applications due to its excellent chemical resistance and low surface energy. Two common methods to modify the properties of PTFE membranes are mechanical stretching and chemical phase separation.
Mechanical stretching involves stretching PTFE membranes in one or more directions to induce changes in the morphology and properties of the membrane. During stretching, the PTFE chains align and orient, resulting in anisotropic properties such as increased tensile strength, reduced pore size, and improved filtration performance. The degree of stretching and the direction of stretching can be controlled to obtain specific properties of the PTFE membrane.
PTFE membrane based on mechanical stretching process is used in the following industries
1. Packaging industry: PTFE mechanical stretch film is widely used in heat sealing applications in the packaging industry. These films are used as release liners to prevent the packaging material from sticking to the sealing jaws.
2. Aerospace industry: PTFE mechanically stretched film is used in the aerospace industry for its excellent thermal stability, chemical resistance and low friction properties. These films are used as release agents in the manufacture of composite parts as well as in thermal insulation applications.
3. Electrical industry: PTFE mechanically stretched film is used in the electrical industry for its excellent electrical insulation properties. These films are used as insulating materials for high temperature cables and as dielectric materials for capacitors.
4. Medical industry: PTFE mechanical stretch film is used in the medical industry because of its biocompatibility and non-stick properties. These films are used as release liners for medical devices and as barrier materials in surgical applications.
In contrast, chemical phase separation involves the addition of a non-solvent to a PTFE polymer solution to induce phase separation and the formation of a porous structure. The non-solvent causes PTFE to precipitate out of solution and form a network of interconnected pores. The size, shape and distribution of pores can be controlled by adjusting the concentration and type of non-solvent used, as well as processing conditions such as temperature and time.
Compared with mechanical stretching, chemical phase separation can produce PTFE membranes with a wider range of pore sizes and morphologies, including a bimodal pore size distribution with macropores and micropores. However, chemical phase separation also leads to a decrease in mechanical properties, such as tensile strength and elongation at break. Additionally, the use of non-solvents introduces impurities and increases production costs.
PTFE membrane produced by chemical phase separation process is used in the following industries
1. Chemical industry: PTFE chemical phase separation membrane is widely used in the chemical industry due to its excellent chemical resistance. These membranes are used in filtration and separation applications such as removing impurities from chemical solutions and separating different components of mixtures.
2. Biomedical industry: PTFE chemical phase separation membrane is used in biomedical industry due to its biocompatibility and non-stick properties. These membranes are used in medical devices, such as blood oxygenators, and in tissue culture applications.
3. Environmental industry: PTFE chemical phase separation membrane is used in the environmental industry for its high filtration efficiency and chemical resistance. These membranes are used in water and wastewater treatment applications such as the removal of suspended solids, bacteria and other contaminants from water.
4. Food and beverage industry: PTFE chemical phase separation membrane is used in food and beverage industry for its non-stick performance and high filtration efficiency. These membranes are used in filtration and separation applications such as removing impurities from food and beverage products.
From the above analysis, it can be seen that the two processes of PTFE membranes, mechanical stretching and chemical phase separation are effective methods to change the properties of PTFE membranes, and the choice of the method depends on the required performance and application requirements. In actual production, due to the higher and higher requirements for PTFE membranes, it is the best choice to produce by combining the two processes, which not only ensures the mechanical tensile properties of the membrane, but also has better chemical stability.
Citation
1. Y. Lu et al., "Mechanical stretching of polymer films: A review", Progress in Polymer Science, vol. 38, no. 3-4, pp. 445-486, 2013. doi: 10.1016/j.progpolymsci .2012.06.003
2. S. Kawaguchi et al., "In-plane mechanical properties of biaxially stretched PTFE films", Polymer, vol. 42, no. 10, pp. 4593-4600, 2001. doi: 10.1016/S0032-3861(00) 00816-8
3. S. Boudjema et al., "Preparation and characterization of PTFE membranes by phase separation: Effect of the nonsolvent nature", Journal of Applied Polymer Science, vol. 91, no. 5, pp. 3118-3124, 2004. doi : 10.1002/app.13587
4. M. Meireles et al., "Chemical phase separation of PTFE membranes for water treatment: A review", Journal of Membrane Science, vol. 476, pp. 348-364, 2015. doi: 10.1016/j.memsci.2014.10 .058
Mechanical stretching involves stretching 
In contrast, chemical phase separation involves the addition of a non-solvent to a PTFE polymer solution to induce phase separation and the formation of a porous structure. The non-solvent causes PTFE to precipitate out of solution and form a network of interconnected pores. The size, shape and distribution of pores can be controlled by adjusting the concentration and type of non-solvent used, as well as processing conditions such as temperature and time.