Compounding with Single Screw Extruders

Six examples are described next which indicate the diversity of single screw compormding applications which have been evaluated, including several comparisons with twin screw extruders. In some cases, there is an inference that the single screw extruder machine s attribute of being easier and cheaper to maintain, is a consideration. This applies to compounding materials which are not extruder friendly e.g., abrasives. 

2) Comparisons were made by Utracki and Sepehr [6] between single and twin screw extruders for compounding nano-clays into polyamide-6 and PP, in which the elongational flow mixer (EFM) described in Chapter 15, was used. The combination of single screw extruder plus EFM produced better dispersions than were achieved with a twin screw extruder with or without an EFM. 

A situation that often exists, which may be particularly relevant to waste recycling, is that deficiencies may appear with larger continuously running production extruders which were not apparent in the laboratory. 

Black in Plastics Compounding Equipment and Processing, Ed., D.B. Todd, Hauser Publishers, Munich, Germany, 1998, Chapter 2. 

Sigl and H-G. Fritz in Proceedings of the Annual SPE Conference -ANTEC, New York, NY, USA, 1999, Volume 2, p.2709. 

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Gale, M., Compounding with Single-Screw Extruders, Adv. Polym. TechnoL, 16, 251 (1997)... 

Mixing of compound with single-screw extruders is economic and attractive. 

Compounding with single-screw extruders is better with respect to the cost of raw materials, scrap disposal and above all environmental aspects. 

Mirel P(3HB-4HB) can be extruded into sheets with single screw extruders and compounded with additives in a twin screw extruder. Tianan P(3HB-4HB) and Tianan PVHB can be compounded with additives in a twin screw extruder. Currently, Tianan P(3HB-4HB) and Tianan PVHB do not provide an extrusion grade plastic and thus are not typically extruded, blow molded, or thermoformed. 

Many compounding processes are configured with a twin-rotor mixer or twin-screw extruder to perform the compounding followed by a single-screw extruder to pressurize the material for pelletization. A typical process is shown in Fig. 13.8. In... 

Figure 4.4 compares the independent setting parameters of the compounding process with the process values. Other than with a single screw extruder, the throughput rate can be chosen independently of screw speed. 

Although there are very few twin-screw (TS) extruders in comparison to the many more single-screw extruders, they are used also to produce products such as window and custom profile systems. Their major use is in compounding applications. The popular common twin-screw extruders (in the family of multi-screw extruders) include tapered screws or parallel cylindrical screws with at least one feed port through a hopper, a discharge port to which a die is attached, and process controls such as temperature, pressure, screw rotation (rpm), melt output rate, etc.143... 

Single-screw extruders for compounding have relatively long L/D ratios (from 32 1 to 40 1), usually with several barrier sections Venting is almost always employed to remove the molten polymer of unwanted vapors (Chapter 3). 

The Concentrate is a high level of pigment mixed with pulverized polyethylene. This preblend is then extruded on a twin-screw. The concentrate is letdown at end use levels and compounded on a single screw extruder. The compound is then injection molded to make displays. 

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