Electret Masterbatch for Melt Blown PP

Fibrous filter materials are a widely used technology for the removal of fine particulates at low pressure drops. A considerable amount of fibrous filters is used in medical applications (e.g., surgical face masks and masks for personal protection).

In their clean state, these materials have very low pressure drops relative to other similarly efficient collectors due to their very porous structure. Particulates are thus not collected by any form of sieving process.Collection is due to

 (1) the hydrodynamics of flow past a single fiber, where particles are collected by inertia or interception;

 (2) the stochastic motion of small particulates (0.5 m) caused by collisions with gas molecules;

 (3) electrostatic mechanisms due to the particles’ charge. Depending on the particles’ diameter, one of these mechanisms of collection dominates.

Previously, the effects of filter packing density, fiber diameter, loading aerosol particle size, and face velocity on the loading behavior of conventional fibrous materials have been investigated, and for conventional materials (fibrous filters which do not employ electrostatics), it has been found that the dust holding capacity is improved for filters of larger fiber diameter and more open structure. Fibers for filter applications can be produced using such promising technologies as melt-blowing processes. This process allows control of the fiber structure over a very wide range. For example, the effects of formation and cooling rate, as well as modifying additives, have been studied.

In the past few decades, fine-fiber filters with electret fibers have been widely used. The term electret is used here to describe a material that carries local electrostatic charges, but is essentially neutral as a whole. Electret fibrous materials are obtained by fiber treatment in a corona discharge or using low-current electron beams. The addition of an electrostatic charge to the fibers results in increased particle removal efficiency, while the pressure drop remains unchanged or even decreases. The increase in efficiency is primarily attributed to the charged fibers attracting particles having an opposite charge, and the attraction of neutral particles when a dipole is induced by the charges on the fibers. 

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