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The following table summarizes the relative sizes of small particles
Filtration is a science that is constantly enriched with information, unique terminology, and proprietary knowledge. These basic concepts are defined within the industry, allowing us to communicate with you, our customers, on a common understanding of filtration fundamentals. We will introduce some basic elements related to filtering technology and their interrelationships. Filtration is the process of passing liquid, air, and gas samples through a permeable medium to remove particulates. There are many different characteristics of membrane materials that affect their performance in different applications, and the following are important characteristics that should be considered when choosing the best membrane for you.
1.Biosafety
These tests are conducted in compliance with ISO-10993 and USP Class Vl.Tests conducted are: Cytotoxicity, Sensitization, lrritation or lntracutanous Reactivity, Systemic Toxicity (Acute), Hemocompatibility (Hemolysis)
2.Filtration efficiency and membrane pore size
Filtering through a thin film means that the filtering material will prevent particles larger than the rated aperture. This allows the absolute pore size of the membrane to be clearly classified. The bacterial retention can be determined according to the pore size of the membrane. Apertures are usually measured in microns or microns (μm) and should be explicitly specified as nominal or absolute values.The nominal aperture refers to the retention efficiency of retaining the majority (60%-98%) of the particle of a specific size, and it also depends on process conditions such as concentration, operating pressure, etc.Rating parameters may vary from manufacturer to manufacturer. When the aperture or retention rate is "nominal value", it should be expressed in particle size and percentage, and when the rate is "nominal value", it should be expressed in particle size and percentage, that is, the retention rate of 0.3um particles is 99.97%. Filtration conditions such as working pressure and pollutant concentration have obvious effects on the retention efficiency of the nominal rated filter.Absolute aperture is the ability to retain 100% of a specific size particle under specified test conditions (particle size, challenge pressure, concentration, detection method).Pore size and challenge organism Challenge organism pore size0.1 micron Chlamydia leydii,Shortwave monas defective 0.2 microns Serratia marcescens 0.45 microns 0.8 micron lactobacillus species 1.2 microns Candida albicans The table above shows the suitable pore size of the hydrophilic membrane used to retain the corresponding bacteria.The hydrophobic membrane is ten times more effective at retaining bacteria in air than in a liquid with the same pore size.The DOP test is used to characterize the efficiency of the filter in removing particulates from the air and is based on the retention of aerosol droplets formed by 0.3um oily aerosol particles (DOP), usually expressed as a percentage. The high efficiency air (HEPA) filter has a retention efficiency of at least 99.97% for 0.3um DOP droplets (ASTM:D2986-95A) The 0.3um particle size was chosen to characterize because most air filters are difficult to trap particles of this size.Filtration efficiency is used to characterize the efficiency of the filter membrane in removing particles from the liquid. When filtering a liquid, the filtration efficiency is based on the filtered particles greater than or equal to a certain diameter. When filteing gases, filter efficiency is based on all particles removed, including the most easily permeable particle size (see DOP experiment above). Some filter manufacturers use the weight percentage of filtered particles to indicate filtration efficiency, but this cannot truly represent the number of particles that can be filtered through the filter membrane, which is the nominal accuracy of the filter. Hepa filters are often rated B, and the filtration efficiency can be calculated using the beta values shown below:
% Efficiency (η)= (β-1) /βx100
Filters with an accuracy of 1μm or less are often rated by titer drop or log value
3.Effective Filtration Area (EFA)
This is the actual filtered area of the device being filtered. For example, in tubular filters, frames made of plastic should be excluded from the calculation of the device EFA. In a mesh filter, you should eliminate only sealed areas.
4.Bubble point
Typically, the test is performed on a hydrophilic membrane, and its purpose is to verify the integrity of the membrane through the swimmer. The test is usually performed with water, however, it can be performed on a hydrophilic film, using a liquid other than water to wet the film. BP is an indicator of membrane pore size and is related to actual bacterial retention. Hydrophilic membrane - Hydrophilic membrane has the permeability of aqueous solution, once soaked, it can stop the gas. This means that the aqueous solution passes through the hydrophilic membrane, but the gas is stopped when the membrane is wet until the applied pressure exceeds the "bubble point", at which point the air will drain out of the hole, the liquid is expelled, and the gas will pass through. The dry hydrophilic membrane allows gas to pass through. Our polyether sulfone membrane is a hydrophilic membrane. The bubble point is also often used to test whether the membrane has a pore size of 0.2 or 1.2 microns The bubble point is the air pressure required for the liquid to pass through the maximum aperture of the wetting filter membrane, which can indirectly measure the aperture and evaluate the ability of the filter membrane to filter out particles. The bubble point depends on the liquid of the wetting filter membrane. For a particular pore size of the filter, liquids with higher surface tension (such as water) have higher bubble points than liquids with lower surface tension (such as isopropyl alcohol). Bubble point rating is usedto determine the maximum pore size when bubbles are generated. The larger the aperture, the lower the pressure required to produce bubbles, and the unit of the membrane bubble point is expressed in psi or bar [ASTMF316-03 Standard test method for aperture Characteristics]
5.Water Flow Rate (WFR)
Typically, the test is performed on a hydrophilic membrane The purpose of WFR is to measure the flow of liquid through a wetted hydrophilic membrane at a fixed test pressure and time. The test is usually performed with water; However, as long as the filtration process is compatible with the liquid, it can also be performed with other fluids
6.Water Breakthrough (WBT)
Hydrophobic membranes are permeable to gases but block aqueous solutions. In other words, they do the opposite when compared to hydrophilic membranes. This means that the gas will pass through these membranes, but the aqueous solution will be prevented.This test is performed on a hydrophobic membrane and is also related to the pore size of the membrane. WBT pressure (sometimes called water intrusion pressure) is the pressure required to force an aqueous solution through a hydrophobic membrane.
The water breakthrough pressure is the pressure required for water to pass through the maximum pore size of the dry hydrophobic filter membrane, which identifies the filter's ability to act as a liquid barrier. The larger the aperture, the less pressure is required to force water through the microhole. The filtration industry uses pounds per square foot (psi) or bar to indicate the water breakthrough pressure of a device.
7.Air flow (AF)
This is the flow rate normally associated with hydrophobic membranes. It is the amount of air that passes through a membrane to hold a surface at a specific pressure.
8.Depth vs Membrane Filtration
A Depth Media is a filter consisting of either multiple layers or a single layer of a medium having depth, which captures contaminants within its structure as opposed to on the surface. Advantages Lower cost High throughputs High dirt-holding capacity Final filter Removes variety of particle sizes Potential Disadvantages Media migration (shedding) Nominal pore size Particulate unloading at increased differential pressure A Membrane Filter typically traps contaminants larger than the pore size on the surface of the membrane. Contaminants smaller than the rated pore size may pass through the membrane or may be captured within the membrane by other mechanisms. Membrane filters are typically used for critical applications such as sterilizing and final filtration. Advantages Absolute sub-micron pore size ratings are possible Can be bacteria and particle retentive (pore size dependent) Generally lower extractables Generally integrity testable Potential Disadvantages Lower flow rates than depth media More costly than depth media
9.Pressure difference (AP)
The pressure difference is the difference between the pressure in the system before the liquid enters the filter (upstream pressure) and the pressure in the system after the liquid flows through the filter (downstream pressure). In constant current applications, the pressure difference gradually increases as the filter membrane begins to clog.
10.Thermal stability
Thermal stability refers to the filter's ability to maintain functionality and integrity under increasing temperature conditions. Thermal stability is important when products need to be sterilized, such as high temperature autoclave, and some filters cannot be autoclave because of thermal instability. It should be noted that there is a correlation between chemical compatibility and thermal stability. Many filters are compatible with chemicals at room temperature, but not at high temperatures. The thermal stability of the filter can be characterized by determining the maximum operating temperature under specific conditions
11.Porosity
Porosity (also called "open space" or "void volume") is a measure of all open space (micropores) within the filter. Typically, the filter membrane has 50-90% open space. The flow rate is proportional to the porosity of the filter membrane (for a specific pore size and thickness of the filter membrane, more pores = faster flow rate).
12.Flow velocity
The pore size of the filter not only indicates its particle retention performance, but also affects its performance, including flow rate and flux. For example, a filter membrane with a large aperture will have a faster flow rate and a higher flux. It is worth noting that the flow rate and flux of filters with the same pore size but made of different polymers and casting processes will also be different.
Similarly, the flow rate and flux performance of the filter membrane are also affected by the porosity. Porosity is used to characterize the number of openings or micropores in the filter membrane. Flow velocity and flux were positively correlated with the porosity of the filter membrane.
13.Airborne particulate retention efficiency
Zhenfu Air filters use globally recognized methods to determine particle retention efficiency
The following table is the international standard for HEPA and ULPA classification and rating
Filter categories and ratings
Rank Class Test the particle size Filtration efficiency %
EPA- Efficiency Particulate Air
HEPA-High Efficiency Particulate Air
ULPA - Ultra Low Particulate Air
14.Bacterial and Viral Testing
This is normally performed at an independent test facility which develops specific protocols to simulate the types of challenges that a filter may see in the clinical setting. A challenge particle is chosen to simulate the size of the commonly occurring bacteria and viruses. Generally these tests are not conducted using a “live” virus due to the cost and safety issues. ZHENFU has appointed Nelson Laboratories, Utah, USA as their indipendent test facility. Their bacterial test protocol uses Staphylococcus Aureus as a challenge organism which has an approximate size 0.6 μm and the viral test uses an X174 Bacteriophage which has a size of 0.027 μm. It is worth noting that the HIV virus is 0.08 μm and Hepatitis C is 0.03 μm so the test protocol does offer a clinically relevant reflection of their performance.In other words, the filtration efficiency for hepatitis C virus and HIV virus is higher than the virus filtration efficiency given by Nelson Laboratories
