Twin-screw extruders mixing

J. P. Christiano and M. Lindenfelzer, Investigation of Mixing Patterns in Co-rotating Fully Intermeshing Twin Screw Extruders Mixing Elements Using Dynamic Pressure Distributions, SPEANTEC Tech. Papers, 43, 78-83 (1997). 

HDPE-CaC03 nanocomposites were prepared by mixing (melting) the individual components in a twin-screw extruder. Mixing was performed at a temperature of 210-220 °C with a screw speed of 15-25 rpm over 5 min. Test samples were obtained using a casting under pressure method on casting machine at 200°C and a pressure of 8 MPa. 

Twin-screw extruder mixing plant schematic (a typical TPV-compounding line)... 

Several commercial products of PVC/TPU blends are available. The BF Goodrich Chemical Group has a PVC/ TPU blend based on their Estane series TPUs. For example, their Estane 54620, a polyester-based TPU with a °ShA 85 hardness, shows excellent compatibility with flexible PVC. The blends are produced by mixing PVC, TPU, plasticizer, stabilizer, and lubricant in a twin-screw extruder. These polymeric blends show intermediate mechanical properties between PVC and TPU. 

In another case where the twin-screw extruder was used, the rubber and plastic were melt mixed with all ingredients in a similar manner as described in blend compositions for static vulcanizations. The product was then dumped, cooled, and granulated. The premixed granules were then fed into a twin-screw extruder where a very narrow temperature profile was maintained with a relative high compression (2 1), and the screw speed was adjusted depending on the final torque and the flow behavior of the extruded stock. The stock was cured by shear force and temperature enforced by the twin-screw extruder. The dynamically crosslinked blend was taken out in the form of a strip or solid rod to determine the... 

Homopolymers and copolymers from amido-sulfonic acid or salt containing monomers can be prepared by reactive extrusion, preferably in a twin screw extruder [1660]. The process produces a solid polymer. Copolymers of acrylamide, N-vinyl-2-pyrrolidone, and sodium-2-acrylamido-2-methyl-propane sulfonate have been proposed to be active as fluid loss agents. Another component of the formulations is the sodium salt of naphthalene formaldehyde sulfonate [207]. The fluid loss additive is mixed with hydraulic cements in suitable amounts. 

Twin screw extruders introduce the necessary shear to thoroughly compound the dry blend into a polymer melt. They achieve this by utilizing aggressive mixing and kneading elements on the screw. Unfortunately, processing speeds are limited by the requirement that temperatures must be kept low to prevent excessive degradation. 

PC PC/15% MWNT masterbatch 2 wt.% 105 2-cm Melt mixing in intermeshing co-rotating twin screw extruder... 

Fig. 26. Typical mixing elements for a co-rotating intermeshing twin-screw extruder...

Bigio D, Wang K. Scale-up rules for mixing in a non-intermeshing twin-screw extruder. Polym Eng Sci 1996 36(23) 2832-2839. 

A mixture consisting of powdered polypropylene (59.91 g) and the step 1 product (90 mg) were tumble-mixed in a glass container for 24 hours. Thereafter the mixture (4.5 g) was compounded at 239°C using a small co-rotating twin-screw extruder. The sample required 4 minutes at a screw speed of 40rpm to be prepared. The extruded material only had a slight haze content. 

For gel processing, the components, UHMWPE, optionally filler, processing oil, and lubricant are mixed. The components are preferably mixed in a continuous fashion, e.g., in a twin-screw extruder or a Brabender extruder, or a screw extruder with a blown film die. After mixing, the mixture is shaped. Shaping will depend upon the... 

The aliphatic-aromatic poly(ester)s discussed above are prepared from butanediol and a mixture of adipic acid and terephthalic acid. Blending can be performed on twin-screw extruder equipped with a medium shear mixing screw. 

---