**3.4. Meltblown nonwoven**

As mentioned before, the meltblown process belongs to the general category of polymer-laid nonwoven material. It has been defined as below:

"Meltblowing is a process in which, usually, a thermoplastic fiber forming polymer is extruded through a linear die containing several hundred small orifices. Convergent streams of hot air (exiting from the top and bottom sides of the die nosepiece) rapidly attenuate the extruded polymer streams to form extremely fine diameter fibers (1–5 mm). The attenuated fibers are subsequently blown by high-velocity air onto a collector conveyor, forming a fine fibered selfbonded nonwoven meltblown **web** [1,4]." Figure 6 shows the schematic illustration of meltblown process.

**Figure 6.** Meltblowing process; primary and secondary air flow and web formation

The main force that holds meltblown fibers together in a nonwoven structure is a combination of entanglement and cohesive sticking. Nonwoven produced by meltblown method have low to moderate strength. During the process, the fibers are drawn to their final diameters while still in the semi-molten state; there is no downstream method of drawing the fibers before they are deposited onto the collector, and this is the reason of moderate mechanical properties of meltblown nonwovens (Figure 7).

All the above-described processes are based on fibers and fibrous laps or webs. The charac‐ teristics of the web are determined by the mode of web formation which is related to web geometry. This web geometry takes into account fiber orientation (oriented or random), type of bonding, crimp, mass per unit area, and weight evenness and distribution.

The knowledge of the web geometry is very important because physical and mechanical properties are directly related to it. For instance, as far as geotextile properties are concerned, separation, reinforcement, stabilization, filtration, and drainage are related to the mass per unit area and the distribution of mass per unit area [5,23].

**Figure 7.** SEM photomicrograph of heat bonded meltblown nonwoven

The following paragraphs will present a theoretical approach of an ideal fiber web. This theoretical approach will simulate the real faults of the fiber-web forming-step during the industrial process, random irregularity, periodic irregularity, and compound irregularity.
