Do You Really Know the Classifications of Filter Membranes?

1.Classifications of filter membranes

The filter membrane is used for the separation and concentration of the solute in the solution, and it is also commonly used for the separation of the colloidal suspension. As the selective passage between two phases, the membrane can allow one or more components of the two phases to pass through the membrane and retain other components, so as to realize the separation between different components and achieve separation, concentration and purification. It mainly uses the fluid pressure difference as the driving force for the screening and separation process.

Filtration membranes are classified according to the size of the raw water particles retained, and the membrane pores are divided into microfiltration membrane (MF), ultrafiltration membrane (UF), nanofiltration membrane (NF) and RO membrane.

The MF membrane has a pore size of 0.05um or more, or a molecular weight of 1000 or more, and is aimed at removing colloids and macromolecular organics. The pore size of the NF membrane is 100-1000 molecular weight. The substances it removes are between UF and RO to remove trihalomethanes, odor, color, pesticides, soluble organics, Ca, Mg, etc. The RO separation particle size is several tens of molecular weight, and the object is to remove table salts and inorganic salts. The pressure of RO permeate water is 1-2 times higher than its permeation pressure.


2. Classifications of microfiltration membrane

PVDF, polyvinylidene fluoride mainly refers to vinylidene fluoride homopolymer or copolymer of vinylidene fluoride and a small amount of other fluorine-containing vinyl monomers. In addition to its chemical resistance, high temperature resistance, oxidation resistance, weather resistance, and radiation resistance, it also has special properties such as piezoelectricity, dielectricity, and pyroelectricity. It ranks second in the output of fluorine-containing plastics big product. The chemical structure is bonded by fluorine-carbon bonds, and this structure with short bond properties forms a stable and firm bond with hydrogen ions. Therefore, fluorocarbon coatings have specific physical and chemical properties, not only strong wear resistance and impact resistance, but also high fading resistance and UV resistance in harsh and harsh environments.

PVDF membrane filters is a solid support commonly used in Western blotting. PVDF is essentially a hydrophobic polymer that does not wet out in aqueous solutions. In order to use PVDF membranes in aqueous buffers and systems, they must first be soaked in 50% or higher alcohol solutions. The PVDF membrane needs to be pretreated before use. Complete wetting is evident as the membrane’s appearance went from opaque to translucent. After repeated rinsing with water to remove alcohol, the pretreated membrane can be equilibrated directly in transfer buffer.
PVDF membrane soaking steps:

Wet turn:
(1) Immerse the membrane in methanol for 30 seconds. The film should be uniform from opaque to translucent.
(2) Carefully place the membrane in double distilled water and soak for 2 minutes.
(3) Carefully place the membrane in transfer buffer and equilibrate for at least 5 minutes.

Semi-dry turn:
First, it only takes 15 seconds to soak in methanol, and the other steps are the same as above.
Once the membrane is wetted, protein binding can be achieved by contact of the protein with the membrane. Since the binding of proteins to the membrane extends through the entire thickness (depth) of the membrane, the binding capacity is determined by the internal surface area of the pore. The internal surface area of the 0.2um PVDF membrane is approximately three times that of the 0.45um PVDF membrane, making its adsorption capacity higher. PVDF membrane is hydrophobic. Generally, proteins larger than 20kD can use a 0.45μm membrane, and proteins less than 20kD can use a 0.2μm membrane.

The PVDF filter membrane has chemical stability and inertia, and is suitable for chemically aggressive organic solvents, acid-base solutions, and sample preparation for liquid chromatography analysis. The polyvinylidene fluoride film is laminated on the support mesh, which has strong strength and mobility, and can withstand high temperature of 130 degrees.