Meltblown polypropylene is charged by corona discharge or by forcing water through it (hydrocharging), and needled felts of polypropylene blended with acrylic pick up charge by friction during carding. The charge captures fine particles that would slip past the fiber network mechanically, giving high efficiency at low pressure drop. Heat, oily aerosols, alcohol and time can drain the charge, which is why respirator media is tested after conditioning.
Electret media is reading five points low on efficiency off the line, so check the charging bar before we blame the meltblown.
Keep alcohol and solvent wipes away from charged media samples unless the method calls for them; they strip the charge.
Also heard as
- electret filter
- charged media
Related terms
Meltblown
Web of very fine fibers made by blasting molten polymer from a row of tiny die holes with hot, high-speed air.
BFE
Bacterial filtration efficiency: the percentage of a bacteria-laden aerosol that a mask or filter fabric stops.
Air permeability
Rate of air flow through a fabric at a fixed pressure difference, reported per unit area.