Twin-screw kneader

Most plastics e.g. polyolefins and polystyrenes and their derivatives such as ABS (acrylonitrile-butadiene-styrene) and SAN (styrene-acrylonitrile) are supplied by the manufacturers in ready-to-use form with most of the above-mentioned stabilizers or simply need to be additionally stabilized with other additives, e.g. antistatic agents and HALS stabilizers, as required. On the other hand, in the case of other materials (e.g. PVC) it is the end user who adds the additives, pigments or preparations. This is normally done on fluid or high-speed mixers, although in the past gravity mixers or tumble mixers were also used. The mixture is then homogenized on mixing rolls, kneaders, planetary extruders or twin-screw kneaders and further processed. 

The new concept for processing of bimodal polyolefins was first presented in 2004 at the Kunststoffmesse in Dtisseldorf. The system, known as the ZSK-NT, combines two corotating, twin-screw kneaders in a cascade arrangement. Figure 15.1 shows the setup of the two ZSKs operating as ZSK-NT. ... 

Inclusion complex powders can be prepared by kneading with a twin-screw kneader. Among many tested flavors are o-limonene, allyl isothiocyanate (AITC), and hinokitiol, which is an antibacterial compound. The release time-courses of these flavors complexed with 3-CD are shown in Figure 1.23 under various RH values at 70°C. The retention of flavors was calculated from the molar ratio of the residual... 

XMC extra-high-strength molding com- ZSK twin-screw kneader... 

Poly(lactic acid)/EB/PP-PO copolymer/E-GMA Twin-screw kneader/DSC/TEM/ mechanical properties/two-step vs. one-step mixing process/also used ethylene-octene copolymer in place of EB Shimano and Moritomi 2010... 

The alumina paste is prepared in a twin screw kneader designed by AOUSTIN, FRANCE, by introducing aluminium hydroxyde powder (Pural SB from CONDEA CHEMIE GmbH) at a regulated mass flowrate and nitric acid solution (flow control). The two products are fed in the first mixing zone of the machine and react instantaneously. 

Other common continuous mixers involve substantial modification of single and twin screw extruders, aimed at improving distributive mixing capability in particular, and leading to the development of continuous mixers such as the Transfermix (50) and the Buss Ko-Kneader (51). Another approach in continuous mixer development is to transform batch mixers into continuous ones. Thus, the roll-mill can be converted into a continuous mixer by feeding raw material on one side and continuously stripping product on the other side. In addition, the Banbury mixer was imaginatively transformed into the Farrel Continuous Mixer (FCM) by Ahlefeld et al. (52), and, later, two similar continuous mixers were developed by Okada et al. (53) at Japan Steel Works and by Inoue et al. (54) at Kobe Steel. 

Mixing operations can be performed in a number of static and dynamic devices, e. g., in static mixers, kneaders, or twin screw extruders [1]- Extruders belong to the group of continuous dynamic mixers. 

At times, low- or high-intensity blending alone can produce a suitable product for use by the fabricator. An example of this would be a polyvinyl chloride (PVC) blend used for several large-volume extrusion applications. More frequently, however, a compounding process is required to obtain the desired physical property. The five primary compounding processes used in the industry for controlling the above parameters are single-screw extrusion (SSE), twin-screw extrusion (TSE), continuous mixers, batch mixers, and kneaders. Table 18.1 summarizes key aspects of each process. 

Reactive processing is limited to polymerization or chemical reactions of polymers in conventional singlescrew or twin-screw extruders, excluding processes in oscillatory kneaders, Banbury-type continuous mixers, or Diskpack equipment. Emphasis is placed on continuous processes that have been implemented commercially or that can serve as models for commercial purposes. 

Machine Type single screw extruder, twin screw extruder (co-rotating), twin screw extruder (counter-rotating), multi screw extruder, buss co-kneader, internal mixer, static mixer. 

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. 

Initial tests of microwave-supported plastification run in a test kneader, the kneading chamber of which has the same geometry as the counter-rotating twin-screw extruder, showed very good microwave transmission to the PVC to be plasticized. These tests also demonstrated that plastification is possible even at a clearly reduced kneading chamber temperature and that this clearly reduces the plastification time. 

Twin screw compounders or Buss Kneaders are used for fully mixed and melted compounds for injection molding because heat history has less effect on otyect molding as long as the process temperatures and times are adjusted to accormt for the use of lower molecular weight resins in the formulations. For flexible compounds, Banbury mixers, continuous mixers, or compounding extruders preceded by static mixers can be employed successfully. 

Compounding involves the use of equipment such as kneaders, mixers, and extruders of single-and twin-screw type, as well as downstream equipment especially with cooling systems. This improves thermal conductivity of the melt, resulting in faster heating and cooling of polymer thereby providing ... 

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