Single screw extruders modified

Erwin, L. and Mokhtarian, F., Analysis of Mixing in Modified Single-Screw Extruders, Polym. Eng. Set, 23, 49 (1983)... 

Garcia-Leiner and Lesser (2004) have studied the use of SCCO2 in the processing of a variety of polymers (s-PS, PEP, and PIPE) using a modified single-screw extruder with a CO2 injection (Fig. 5). The present of CO2 significantly enhanced the processability of the polymer-C02 system by plasticization effect and the hydrostatic contribution. This presented an effective alternative to process intractable or high melt viscosity polymers. 

Couette flow n. Shear flow in the annulus between two concentric cylinders, one of which is usually stationary while the other turns. By measuring the relative rotational velocity and the torque required to maintain steady flow, one can infer the viscosity of the liquid. Flow in the metering section of a single-screw extruder resembles Couette flow, modified by the presence of the flight and, normally, by the pressure rise along the screw. 

Figure 3b shows that in the range of initiator and MA concentrations studied, the ratio initiator/MA determines the grafting efficiency. This result is in accordance with Borggreve [5] who produced modified rubbers with a single screw extruder. He observed that if the initiator/MA ratio is kept constant, the grafting efficiency is independent of the MA concentration. 

Common means of enhancing the mixing efficiency of single-screw extruders include use of modified screw forms containing special mixing devices, or static mixers, which are located between the extruder and die. The various forms of mixing screw design available may function in either a dispersive and/or distributive manner. 

This form of continuous compounding equipment may appear as a variation of a single screw extruder. But truly it is not and hence not included in the category of modified single screw extruders, because of the radically different mixing action in it [27,64]. 

Single-Screw Compounding Machines The normal single-screw extruder is generally inadequate to homogenize PVC dry blend in a single pass but modified versions are used for this purpose. 

Figure 7.1 Modified TS-45 single-screw extruder (without cutting device).

The preparation of TPS/PLA blends was based on the technique described by Rodriguez et al. for polyethylene/plasticized starch blends [5]. The blends are made on a Leistritz 34 mm co-rotating twin-screw extruder with a L/D ratio of 42, with a single-screw extruder as a side-feeder to the twin-screw line for the PLA feeding. The glycerol content in the TPS was 36 and 39 wt% on a dry-basis, and the mixing zone was set at 180°C, 200°C or 220°C, to study the effect of temperature. The TPS concentration in the blends was maintained at 27% on a water free basis. In the interface modified blends, the PLA-g-MA was either blended directly with the thermoplastic starch or used to substitute 20% of the unmodified PLA. 

---