The principle of microporous filtration membrane sterilization, what are the membrane materials used

Microporous filtration membranes can be used to remove bacteria from solutions. The working principle is very simple. The pore size of the membrane is smaller than the size of the bacteria, preventing them from passing through. Although this filtration method can effectively remove bacteria in the filtered liquid, it does not kill it. Dead bacteria have not caused damage to the tissue and structure of the bacteria. The filtered bacteria are still alive on the filter membrane. Unless further measures are taken to inactivate them, such as using disinfectants or incineration of the used filter membrane, it is considered sterilized. , So, strictly speaking, filtration with microporous membranes is not sterilization, but filtering out bacteria is a rigorous statement.

Bacteria come in many sizes, but the diameter of most particles is between 0.2 and 2.0 microns. The common pore size of sterilization grade filter membrane is 0.2 microns, which can be said to be small enough. It can remove a variety of bacteria. For example, the particle size is E. coli 0.5 to 1.0 microns in diameter and 2.0 to 6.0 microns long, Staphylococcus aureus 0.5 to 1.0 microns in diameter, Pseudomonas aeruginosa 0.5 to 1.0 microns in diameter and 1.5 to 5.0 microns long, 0.25 to 5.0 microns in diameter 1.0 microns, Bacillus subtilis 3.0 to 10.0 microns long, etc.

Some microporous filtration membranes we know can remove smaller microorganisms such as viruses in addition to the above functions of filtering bacteria. However, it is important to know that a standard microporous membrane with a pore size of 0.2 microns is usually not sufficient to remove viruses, because many viruses are significantly smaller than this size. Therefore, if the purpose of filtration requires the removal of viruses, you need to choose a special ultrafiltration membrane with a smaller pore size. Or nanofiltration membrane can be achieved.

The size of a typical viral particle can vary greatly depending on the specific virus. Viruses are extremely small infectious agents, ranging in size from approximately 0.02 microns to 0.4 microns. For example, the diameter of influenza virus is about 0.08-0.120 microns, the diameter of human immunodeficiency virus (HIV) is about 0.1-0.15 microns, the diameter of herpes simplex virus is about 0.15-0.2 microns, the diameter of adenovirus is about 0.07-0.09 microns, hepatitis B Viruses are approximately 0.042 microns in diameter, poliovirus is approximately 0.022-0.03 microns in diameter, and SARS-CoV-2 (the virus that causes COVID-19) is approximately 0.06-0.14 microns in diameter. These size ranges are also approximate and may vary depending on the specific situation. It varies depending on the strain and stage of the virus life cycle, but from these data we can see that ordinary microporous filter membranes are not sufficient to filter viral particles.

Membrane materials commonly used to filter bacteria include cellulose acetate (CA), polyethersulfone (PES), polytetrafluoroethylene (PTFE) and nylon (polyamide). Their pore sizes, flow rates and chemical compatibility vary. There are also some differences in the function of filtering bacteria, here is a brief summary:

1. Cellulose acetate (CA) membrane,

Pore Size: 0.1 to 10 microns, suitable for filtering larger bacteria.

Flow rate: Due to the small pore size, the flow rate is moderate.

Chemical Compatibility: CA membranes are generally compatible with many aqueous solutions but may not be suitable for organic solvents or strong acids and bases.

2. Polyethersulfone (PES) membrane,

Pore Size: 0.1 to 0.45 microns, suitable for effective filtration of bacteria.

Flow rate: PES membrane provides a good balance between filtration efficiency and flow rate, providing a relatively high flow rate.

Chemical compatibility: PES film has excellent chemical compatibility and is resistant to acids, alkalis and organic solvents.

3. Polytetrafluoroethylene (PTFE) membrane,

Pore Size: 0.1 to 10 microns, suitable for filtering larger bacteria.

Flow Rate: PTFE membranes generally have lower flow rates due to their hydrophobic nature.

Chemical compatibility: PTFE membrane has excellent chemical compatibility and is resistant to many chemicals, including acids, alkalis and organic solvents.

4. Nylon (polyamide) membrane,

Pore Size: 0.1 to 10 microns, suitable for filtering larger bacteria.

Flow rate: Nylon membranes have a relatively high flow rate due to their large pore size.

Chemical Compatibility: Nylon membranes have good chemical compatibility, but may not be suitable for strong acids and alkalis or certain organic solvents.

These differences in pore size, flow rate and chemical compatibility make each membrane material suitable for different applications. It is recommended that selection criteria be used in practical applications. It is important to consider the specific requirements of the filtration process, in conjunction with the membrane manufacturer or supplier of the membrane. performance and other factors to select the membrane material that best suits our needs.

Citation

1. Centers for Disease Control and Prevention (CDC) website: www.cdc.gov

2. World Health Organization (WHO) website: www.who.int

3. Scientific journals and research papers: PubMed (www.ncbi.nlm.nih.gov/pubmed)