Melt blowing schematic

Figure 8.41 Schematic diagram of horizontal and vertical melt blowing processes. ...

Figure 13.6. Schematic of the melt blowing process. For simplicity, only a single nozzle is shown. In actual production, multiple nozzles are used simultaneously.

In this method, the aqueous, concentrated solution is also atomised into fine droplets, but they are rapidly frozen by blowing them into a low-temperature bath, such as ice-acetone, liquid C6H14 or liquid Nj. The droplets are then dried in vacuum, by sublimation of the ice without melting. This means that the temperature must remain below the eutectic in the salt-H20 system. The anhydrous salts (nitrates, sulphates, chlorides, etc.) are calcined to produce powders which are 0.1 pm in size. A schematic freeze-drying process is shown in Fig. 3.5. 

This method can be used as an alternative to melt extrusion method. The polymer powder is fed into a screw extruder, which heats up the polymer. The molten polymer from screw extruder is forced through an annular die. An inert gas is then passed through the tube, so that due to gas pressure, the tube blows into a cylindrical bubble. The bubble is then flattened by a series of rollers to form a continuous film that can be wound up by specially designed rollers. This process is shown schematically in Figure 1.35. 

In particular the NMMO technology has inspired new developments, recognizing that the cellulose/NMMO/water solution can be considered in many aspects as a melt. As an example, cellulose has been shaped by a blown-film process similar to conventional thermoplastics [33,34]. A schematic of the blow-extrusion process is shown in Figure 3.8. 

The most commonly used of these techniques is extrusion blow molding, where the parison is a hollow, thick-wallcd tube of melt that is extruded vertically from a crosshead die. (A schematic diagram is shown in Fig. 19.39.) The parison then is surrounded by a split, cooled mold of the desired shape. One end of the parison is damped around a blow pin, which incorporates an inlet for compressed air that expands the parison to make it contact the mold wall. The molded object is ejected when solidified, and excess material is trimmed from the ends and recycled. Containers in the range of 0.25 to 5000 liters are made this way, and integral handles as well as special shapes can easily be designed in. 

---