Twin-screw extruder, blending equipment

Performance of EFM attached to a singe-screw extruder, SSE, was evaluated examining its suitability for 1. Dispersion of viscous polymer in low viscosity matrix (where X > 4) 2. Impact-modification of engineering resins 3. Elimination of gel particles from either R-TPO or EVAc reactor powders 4. Dissolution of UHMWPE in HDPE, etc. For comparison, the blends were also pr ared using a co-rotating, intermeshing twin-screw extruder, TSE, equipped with high dispersion screws [42, 43 ]. 

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. 

To a continuing process the pigment dispersions are added directly to the plasticising equipment by volumetric or gravimetric measuring units. Further blending can then be done on a single- or twin-screw extruder. 

Polyamide-6 (PA-6) and polypropylene (PP) are both semi-crystalline polymers and the combination of an engineering plastic (PA) and the best commodity product (PP) could lead to new blends with Interesting Intermediate properties. We tested systems containing 50 wt% of each product and the ones obtained by addition of 3% of the reactive PP-g-AM resulting from previous continuous grafting in the extruder. The blends were prepared by simple mixing in the ZSK 30 twin-screw extruder and the samples for mechanical testing were molded by injection in a BILLION equipment. 

Although commercial twin-screw extruders can be as large as 300 mm size, capable of compounding up to 40 ton/hr, the acmal type and size of the equipment used depends on the type of the polymer blend and the production volume. Normally, for engineering polymer blends, twin-screw extmders of about D = 90 mm size (L/D = 30 to 40) and capable of compounding at 700 to 1000 kg/hr, are used. For blending PVC or elastomer blends other types of compounding equipment are used, e.g. Farrell continuous mixer (FCM), Buss co-kneader, or a batch mixer, such as Banbury. 

Figure 26.9 Equipment employed in the production of the blends (a) twin-screw extruder (b) hot-plates press.

Thiele (18) stressed the utility of continuous-single and twin-screw extruders compared with Banbury batch type mixers on the basis of the working volume, that is, small working mass in the extruder channels in continuous process equipment versus a large amount of blended material per cycle in batch type mixers. With a relatively smaller working volume in an extruder, there is more enhanced intimate mixing on the microscopic scale in a shorter period of residence time. 

Nanocomposites were prepared by melt-blending PET polymer with organically modified MMT. A variety of processing equipment was used, typically operated at 280 °C a Braben-der plasticorder twin-head kneader (7 min at 280 °C and 60 rpm) for PET/quinolinium-MMT, a Prism TSE 16TC extruder with an L/D ratio of 16 (280 °C at a screw speed of 280-330 rpm) for large-scale PET/imidazolium-MMT (10-30 Ib/h), and a laboratory-scale Haake counter-rotating twin screw extruder with an L/D ratio of20 (280 °C at a screw speed... 

Blends prepared in different mixing equipment showed some slight differences in blend morphology. The blends prepared with the Buss Co-Kneader-type extruder exhibited the finest dispersion of LCP phases. In contrast, the channeling effect and phase separation were most pronounced for the counterrotating twin-screw extruder, in particular for blends whose components had totally different melt viscosities. 

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