Double-screw extruder

Single-screw and double-screw extruders are normally used for polymer melts to accomplish the deaeration or devolatilization of residual volatiles. Devolatilization in an extruder is effected through formation of the venting zone inside the chamber by carefully designed upstream and downstream screw sections. 

On the other hand, economically advantageous routes by continuous baking process have also been described in recent years. The processes are carried out in self-cleaning mixing apparatus such as double screw extruders. More recent patent literature claims yields as high as 80%. 

Figure 4.34. Double screw extruder with two separated screws placed in series inside a common barrel (explanation of the numbers see text).

Fig. 6.7-14 Typical robust double-screw extruder with integrally mounted pug sealer for the processing of stiff materials (courtesy ).C. Steele, Statesville, NC, USA)...

Fig. 6.7-13 Diagram of maxima of properties, such as strength, that are dependent on both porosity decreases and grain size increasing as a function of firing temperature or time [B.80]. The dashed line suggests that maxima may change with different material and fabrication parameters Fig. 6.7-14 Typical robust double-screw extruder with integrally mounted pug sealer for the processing of stiff materials (courtesy J.C. Steele, Statesville, NC, USA)...

Determination of Properties. For all determinations, the PVC and the PS had molecular weights comparable to that of the homopolymer present in the crude reaction products. PVC was characterized under conditions described previously (15, 23). With PS, beads of product mixed with a specific antioxidant of the olefin elastomer (0.05%) and with a stearic acid derivative as lubricant (0.2%) were homogenized by extrusion in a double-screw extruder thus the material was obtained as granules. The test specimens were machined to proper size and shape from compression-molded sheets (190°C, 40 kg/cm2). 

The extruder is still dominant in structural ceramics and for the production of complex extruded profiles in technical ceramics. There have been appreciable developments in both fields in recent years. Depending on the application, you can find piston presses and single-screw and double-screw extruders in two or three-stage versions. 

As already suggested in point 3.3, in the case of very fine masses, the situation can arise whereby the internal friction of the mass is no longer sufficient to convey the greater peripheral forces on the hub diameter of the screw outwards to the cylinder casing. It has to be examined here whether modifications to the mass are possible or whether a different extrusion principle, e.g. double-screw extruder has to be selected with respect to the potential for modification. 

C. R. Martins, M.-A. De Paoli, Antistatic Thermoplastic Blend of Polyaniline and Polystyrene Prepared in a Double-Screw Extruder. Eur. Polym. J. 2005, 41,2867-2873. 

As far as processing of ICPs is concerned, various methods have been developed to prepare electrically conductive composites [139], among which melt processing is quite popular for thermoplastics [140, 141]. Martins and De Paoli [142] prepared polystyrene and polyaniline blends in a double-screw extruder, giving a conductive thermoplastic with electrical conductivity of 10 to 10 S cm . In most cases, conducting polymers are incompatible with thermoplastic, so a fimctional dopant is needed to improve compatibility. For example, dodecylbenzenosulfonic acid... 

Martins, C.R. and De Paoli, M.A. (2005) Antistatic thermoplastic blend of polyaniline and polystyrene prepared in a double-screw extruder. Eur. Polym. J., 41, 2867-2873. 

Double-screw extruder See extrudery twin-screw. 

Extruder, twin-screw (double-screw extruder) n. An extruder with a barrel consisting... 

Although in general both a single- and a double-screw extruder can be used for SFE experiments we choose a Schwabenthan single-screw (D = 30 mm) extruder, equipped with a hopper, a three zone screw (L = 35 D), an injection unit for the extraction fluid at 20 D from the hopper and a capillary spin opening (0 1.7 mm). 

Extrusion is an energy eflftcient system able to break down the starch granule structure through a combination of high shear, temperature and pressure and can successfully melt starch. T3 ical single or double screw extruders, in general form consists of a hopper, barrel, feed screw, thermocouples, and dies. 

In addition, single-screw and double-screw extruders affect the performance of composites filled by whiskers differently, as shown in Table 4.3. 

Double-Screw Extruder See Extruder, Twin-Screw. 

New bioactive POM/HAp nanocomposites for bone long-term implants have been obtained by Pielichowska using the double-screw extruder. The method ensures homogeneous distribution of the filler within the POM matrix in core-shell... 

Before blending, the light fraction films were ground to pieces of a few mm and the heavy fraction to particles of about 100 im size. The blends were prepared in a Krauss-Maffei double screw extruder at T = 180°C and a rotation speed of 20 rpm. The extrudates were injection molded with a Negri and Bossi nb 55 machine, at T = 220°C in a cold mold and specimens for mechanical tests were produced. 

Easily added to the PET resin in single or double screw extruders. 

Dimethylaminopyridine is an efficient catalyst. When the system consists of a,ce-dihydroxy-polyoxytetramethylene and 2,2 -bis[4,4 -dimethyl-5(4H)-oxa-zolinone], the conversion is 100% after 30 min ranges from 7800 to 19000. The reaction is particularly fast when carried out in a double-screw extruder. 

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