Compounding Twin-screw Extruder

Fig. 5 Schematic diagram of a twin-screw compounding extruder. (From Ref. f)...

Miyagawa, Y. Sato, H. Okabe, T. Nishiyama, T. Miyajima, M. Sunada, H. In vivo performance of wax matrix granules prepared by a twin-screw compounding extruder. Drug Dev. Ind. Pharm. 1999, 25, 429-435. 

The ILC/D-LFT process starts with continuous glass rovings, PP, and other additives and feeds them Into a twin-screw compounding extruder. The glass becomes cut during processing... 

In 1957 W P introduced the first high speed, co-rotating, twin screw compounding extruder and has been a major player in the twin screw extruder industry ever since. W P offers a wide range of sizes from as small as 25 mm to as large as 380 mm. Data on the various W P extruders is shown in Table 10.3. 

Generally, the anti-blocks are dry blended with other additives and stabilizers in a carrier resin. The concentration of anti-block may range from 5 to 10% for synthetic silica to 30-50% for DE or talc. The other additives will be in concentrations that yield the proper final additive levels when let down. To achieve the most thorough mixing, the blended materials are then fed into a mixer/compounder which may be batch equipment, such as a Banbury or Henschel or into a twin-screw compounding extruder and melt compounded. The pelletized concentrate will be blended with barefoot pellets and let down to the desired final concentration. 

The attraction forces between particles require tensile forces sufficiently high to separate them and cause break up of the agglomerates and also promote wetting by the polymer of the newly exposed particle surfaces. To achieve this, the surrounding polymer or polymer/wax matrix needs a flow field which will provide the necessary force. The turning rotors of internal mixers and co-rotating twin screw compounding extruders will usually provide the required shear forces. 

An advantage of this process is that a number of small single screw extruders which are of relatively low cost, can economically produce small orders for specialised colours. They can he easily cleaned between batches or maybe dedicated to a single colour. The attraction of this approach has probably declined over more recent years following the introduction of very small twin screw compounding extruders. 

In the extrusion of PA6/nanoclay composite films, a 4% nanoclay masterbatch prepared in a twin screw compounding extruder was combined in a 50 50 blend with the natural PA6 using the chaotic mixer. Permeability calculations indicated that closing pathways around platelets resulted in values approaching zero [38]. 

Figure 16-27 Classical formats of twin-screw compounding extruders.

---