5 Main Technical Parameters and 6 Main Types of Filter Membranes

5 main technical parameters of the filter membrane

1. Absolute pore size: The pore size refers to the pore size that can be distinguished by 100% interception of challenge bacteria of a certain size under very strict test conditions. Among the conditions that must be specified are test organism (or molecule) size and concentration, test pressure, and detection method.

2. Air flux: the flow of air flowing through under different pressures, different porosity, and different filter areas.

3. Bubble point: Use a specific liquid to infiltrate the filter membrane, and at a specific temperature, the minimum pressure to expel the liquid in the filter membrane hole.

4. Hydrophilicity: Hydrophilic membranes usually have a special chemical layer that allows the membrane to be wetted by water; Hydrophobicity is a reference to the repulsion of water. Hydrophobic filters are rarely completely free of water. If small water droplets stay on the filter membrane surface, they will not be adsorbed and diffuse into the water surface. The size of the hydrophobicity depends on the pore size of the filter material and the characteristics of the membrane material.

5. Flow rate and flow flux: The flow rate is the total amount of filtrate passing through the membrane per unit of time at a specific temperature and pressure. The flow flux is closely related to the membrane surface properties. Flow rate and flux are two important parameters for the performance of microporous membranes. The following aspects can decide the performance.
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1) Viscosity: Viscosity determines the ease with which the liquid flows. Under certain temperature and pressure conditions, the higher liquid viscosity of the liquid, the lower the flow rate. A higher pressure is required to achieve the same flow rate.
2) Pressure difference: the pressure difference between the inlet and the outlet during filtration, when the filter is fully loaded, the filtration pressure difference increases.
3) Porosity: refers to the proportion of the volume of all pores on the membrane to the volume of the entire membrane. It has a direct relation to membrane porosity.

6 main types of filter membranes

1. Nylon membrane (Nylon)
Features: good temperature resistance, can withstand 121 ℃ saturated steam autoclave for 30 minutes, maximum working temperature 60 ℃, good chemical stability, can withstand dilute acids, dilute alkalis, alcohols, esters, and many inorganic and organic compounds, like the organic oxides and halogenated hydrocarbons.
Applications: it’s often used in microelectronics, electronics, and semiconductor industry water filtration, organic mobile phases and aqueous filtration, beverage filtration, and high-purity chemical filtration.

2. Polyvinylidene fluoride membrane (PVDF)
Features: It can be hydrophobic and hydrophilic, with high mechanical and tensile strength, excellent heat resistance and chemical stability, and a low protein adsorption rate. But not resistant to acetone, DMSO, THF, DMF, dichloromethane, chloroform, etc.
Uses: Hydrophobic polyvinylidene fluoride membrane is mainly used in gas and vapor filtration, and high-temperature liquid filtration; hydrophilic polyvinylidene fluoride membrane is mainly used in tissue culture medium, additives sterilization, and purification filtration.

3. Mixed Cellulose Esters(MCE)
Features: With a thin texture, high porosity, uniform pore size, and without medium shedding, it has low resistance, fast filtration, minimal adsorption, and more importantly, it is cost-effective. But please note it isn’t resistant to strong acid or alkali solutions and organic solutions.
Uses: The pharmaceutical industry needs autoclaved water injection, and large infusions to filter out particles. For the sterilization of heat-sensitive drugs (insulin ATP, coenzyme A, and other biochemical preparations), use a 0.45-micron filter membrane (or 0.22) to analyze and determine the particles and oil insoluble in the solution, and determine the water pollution index. It is used in scientific research departments such as somatic cell hybridization and mitochondrial complementation prediction of heterosis research.

4. Polypropylene (PP)
Features: without any adhesive, stable chemical properties, flexible, not easy to break, high-temperature resistance, can withstand high-pressure sterilization. Non-toxic, tasteless, acid, and alkali-resistant.
Uses: It can be applied to make all kinds of coarse and fine filters and pleated filter elements in medical and beverage industries and so on. Also, it can be used to pretreat the ultrafiltration and reverse osmosis membrane. Polypropylene membrane is non-toxic and can be widely used in medicine, the chemical industry, food, beverage, and other fields; it is hydrophobic, especially for gas filtration.

5. Polyethersulfone (PES)
Features: The microporous filter membrane made of ether sulfone is a hydrophilic filter membrane with a high flow rate, low extractability, good strength, no adsorption of protein and extracts, and no pollution to samples.
Application: it is often used to filter high-temperature liquids and filter aqueous samples, proteins, acids, alcohols, aliphatic hydrocarbons, and so on.

6. Polytetrafluoroethylene (PTFE)
Features: it has the widest chemical compatibility, which is resistant to strong solvents.
Application: it’s mainly used for filtration of strong chemical corrosive organic solvents; filtration of strong acid solvents; gas filtration as well as steam filtration.