Closely intermeshing twin-screw

These two-phase polymers are generated in an optimized single-stage process using a corotating, close-intermeshing, twin-screw extruder. 

K. J. Gadzenveld and L. P. B. M. Janssen, Scale-up of Counter-rotating Closely Intermeshing Twin Screw Extruders without and with Reactions, Polym. Eng. Sci., 30, 1529-1536 (1990). 

The first closely intermeshing twin screw extruders were built by Bayer using their own design (Section 2.1) and featured a vertical arrangement of the screws. Figures 1.2 and 1.3 show such a screw arrangement built by Bayer for chemical reactions. 

Screw Elements for Co-rotating, Closely Intermeshing, Twin-Screw Extruders... 

From the time they were first developed, co-rotating, closely intermeshing twin-screw extruders have proven to be highly effective for the continuous treatment of viscous products and they have successfully replaced many discontinuous technologies. They will certainly continue to be successful in other markets in the future, facilitating new production processes. 

The machines mainly used for compounding plastics, chemicals and food are co-rotating, closely intermeshing twin-screw extruders. Some 30 000 such extruders are in use worldwide, about 1/3 are ZSK from Coperion Werner Pfleiderer, Stuttgart. In the chemical industry increasingly more and more batch mixers are being replaced by continuous twin-screw knea-ders. 

A new process has been developed for the production of PLA using reactive extrusion polymerization based on a new catalytic system, which not only enhances the ROP kinetics of L-lactide but also suppresses side and degradation reactions such as intermole-cular transesterification reactions. Co-rotating closely intermeshing twin-screw extruders have often been used for polymerization reactions, but in any case, the reaction time was sufficiently smaller than the residence time in the extruder. In the case of ROP of lactide, the extraordinary effect of triphenylphosphine on the efficiency of Sn[Oct)2 as a catalyst was the key point to ensure further enhancement of the polymerization reaction. Thus, it was feasible... 

The closely intermeshing twin-screw extruders, both counterrotating (e) and corotating (f), can best be modeled as series of C-shaped chambers. Due to the rotation of the screws these chambers transport the material from hopper to die, while... 

If the chambers of a closely intermeshing twin-screw extruder are fully filled with material, the maximal throughput of a zone, Q,/, can be written as the number of C-shaped chambers (Fig. 2.7) that is transported per unit of time, multiplied by the volume of one such chamber ... 

Figure 2.8 Leakage gaps in a counterrotating, closely intermeshing twin-screw extruder (from Ref. 4).

An interaction diagram, as given in Section II, can be convenient to study the various interactions in reactive extrusion. A numerical model for closely intermeshing twin screw extruders, based on this diagram gives good results, except for the influence of the rotational speed on the final conversion, which is probably due to a retardation of the onset of the reaction connected to heat transfer problems. 

After determination of the kinetics, experiments were performed in a counterrotating closely intermeshing twin screw extruder (3). The screw... 

In this case study, a urethane prepolymer based on polyalkylene etherglycol and an aliphatic diisocyanate group (methylene-bis, 4-cyclohexyl isocyanate), Adiprene LW-520, reacted with 1,4-butane diol in a counter-rotating closely intermeshing twin screw extruder with dibutyltin dilaurate as a catalyst (5). 

For the reactive extrusion the Adiprene was heated to 50°C and subsequently fed to the extruder. The 1,4-butane diol was mixed with the catalyst di-butyltin dilaurate (0.03 weight percentage based on the amount of prepolymer). The mixture was fed to the extruder in a quantity ratio of 1 18 compared to the Adiprene. A 40 mm counterrotating closely intermeshing twin screw extruder was used with a L/D of 15. The screw rotation rate, the throughput and the die resistance were varied. The barrel temperature ranged from 80 to 110°C and the output varied between 2.1 and 4.1 kg/h. 

Thanks to their residence time distributions, co-rotating, closely intermeshing twin-screw extruders have assumed a dominant market position. Other machines, such as single-screw and counter-rotating extruders are used only for special tasks. Fig. 4.7 [35]. 

Self-wiping operation when closely-intermeshed twin screw and reciprocating single screw extruders are used. 

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