Numerous types of fluid filtration systems, e.g. such as those used for home water filtration and as gas filtration respirators, are commercially available. Nonwoven fibrous webs are frequently used as a filtration medium in such fluid filtration systems. Such nonwoven fibrous webs may include two or more kinds of fibers, for example, two different populations of microfibers, each having a different average diameter, so that the nonwoven fibrous web can filter particulates of a broad range of sizes. Generally the different populations of fibers are intermixed within a single-layer web.
Nonwoven fibrous webs can be formed by a variety of techniques including carding, garneting, air-laying, wet-laying, melt blowing, spunbonding, and stitch bonding. Further processing of a nonwoven may be necessary to add properties such as strength, durability, and texture. Examples of further processing include calendering, hydroentangling, needle tacking, resin bonding, thermo-bonding, ultrasonic welding, embossing, and laminating. In some nonwoven fibrous webs useful as a filtration medium, it has been found to be advantageous to incorporate sorbent particulates, such as activated carbon, within the web. It is also known to bind sorbent particulates to the fibers of a nonwoven fibrous web by use of a separate binder material, thereby providing particulate-loaded articles suitable for use in some fluid filtration applications.