Extrusion, twin-screw

Continuous extrasion of various energetic materials has been proposed in the 1980s [15-17]. Muller has proposed processing MTV via twin screw extrusion (TSE) for the first time in 1992 [18]. Ataboutthesame time, a TSE process for MTH using Hycar was developed in the United States [7,19] but was halted. In the late 

TSE of MTV was picked up again [20] and transferred into production at Crane [21]. 

MTV/MTH Both MTV and MTH can be processed via TSE with high reproducibility. The clear advantage of TSE is the absence of dead spots in the homogenization process and the low solvent level necessary to run the process. 

A MTH production-process developed in the United States, although using the same Werner and Pfleiderer TSE, used a different approach and consisted of a solid feedstream of Mg and a slurry feedstream of PTEE, Hycar and acetone. It used a weight ratio of 11.5 88.5 Hycar acetone for the second feedstream, which allowed stirring, pumping and pouring of the slurry [7]. 

As a Viton/acetone solution at the same solvent level was too viscous to be transported, adaptation of that process to MTV was achieved by feeding all solids and acetone separately. It was found that a solvent level of 16.5-19wt% acetone is satisfactory both to solvate Viton and disperse the composite. The viscosity r] of an MTV with 19wt% acetone feeding stream at 27°C was found to relate with shear rate, y, (s ) in the following manner  

For large-scale preparation of polymer-carbon nanotube composites, continuously working extruders are most suitable. However, to obtain appropriate mixing results the process 

In most cases polymer carbon-nanotube composites have to be further processed after their preparation either to obtain samples or the shape of desired components or semifinished products. During the forming process the materials are usually exposed to heat and forced to flow. In dependence on the applied forming technique as well as the corresponding processing parameters, the materials morphology can be affected significantly. 

Further, TEM investigations have been carried out to obtain information about nanotube alignment and distribution with high spatial resolution. The evaluation of the orientation factor at r = 16 nm exhibits no differences of nanotube orientation for 

---

J. L. White, Twin Screw Extrusion Technology and Principles, Hansei Publisheis, Munich, Germany, 1991. 

Janssen, L. P. B- M. Twin Screw Extrusion (Elsevier, Amsterdam, 1978). 

Our group has used twin-screw extrusion to produce many texturized whey-fortified puffed snacks. Whey protein has been blended with barley flour, com meal, rice flour, and wheat starch prior to extrusion, leading to corn puffs with a protein content of 20% instead of the usual 2% (Onwulata et al., 2001a). 

XRD was used to investigate the spacings of silicate layers of montmorillonite (from 1.9 to 4nm) in PP/montmorillonite (MMT) nanocomposites prepared by in situ graft-intercalation in the presence of acrylamide [331]. Similarly, XRD and TEM were used to study the dispersibility of PP/MMT nanocomposites prepared by melt intercalation using organo-montmorillonite and conventional twin screw extrusion [332]. Various delaminated and intercalated polymer (PA6, PA 12, PS,... 

White, J. L., Twin Screw Extrusion. Hanser, Munich, 1990. 

As the screw turns, it conveys the pellets from the feed zone towards the melting zone. A combination of external heating and mechanical work melts the polymer as it is transported towards the metering zone. The metering zone pumps a uniform stream of molten polymer to a forming device, such as a profile die. Other types of extruders that employ two or more screws are commonly used for compounding polymer blends. The principles of twin screw extrusion will be discussed in Chapter 12. 

White, J. L., Kim, E. K., Keum, ]. M., and Jung, H. C., Modeling Heat Transfer in Screw Extrusion with Special Application to Modular Self-Wiping Co-Rotating Twin-Screw Extrusion, Polym. Eng. Set, 41, 1448 (2001)... 

Keum, J. and White, J. L., Heat Transfer Coefficients and Screw Temperature Profiles in Modular Twin Screw Extrusion Machines, SPE ANTEC Tech. Papers, 50,108 (2004)... 

Nabar, Y., Narayan, R., Schindler, M. (2006). Twin-screw extrusion production and characterizatin of starch foam products for use in cushioning and insulation applications. Polymer Engineering and Science, 46,438 51. 

Fig. 31. Integrated twin-screw extrusion compounding technology for the preparation ol polymer composites filled with fibrous recyclate additives...

White, J.L. (1990) Twin-screw extrusion - technology and principles. Hanser, Munich... 

Agur EE. Extruder scale-up in a corotating twin-screw extrusion compounding process. Adv Polym Technol 1986 6(2) 225-232. 

Figure 7.9 Schematic diagram of twin screw extrusion...

The twin-screw extrusion (TSE) technology is utilized extensively in the plastics and food industries to complement continuous manufacturing of products. Ghebre-Sellassie et al. [37] and Keleb et al. [36] have cited the application of this technology in the continuous production of pharmaceutical products. Commercially available TSE provide the great Lexibility required for effective continuous mode of operation. The schematic of such a system is shown in Figure 23.6. The twin-screw extruder... 

A. C. Y. Wong, F. Zhu, and T. Liu, Qualitative Study on Intermeshing Co-rotating Twin Screw Extrusion Using Novel Visual Technique, Plast. Rubber Comps. Proc. Appl., 26, 271 (1997). 

L. Zhu and X. Geng, Visual Research of Melting Mechanism of Polymer Pellets in Intermeshing Co-rotating Twin-screw Extrusion, SPE ANTEC Tech. Papers, 55, 3684 (1997). 

Fig. 10.12 Schematic representation of two melting mechanisms observed by Janssen (24) with PP processed in a double-flighted 47-mm counterrotating TSE operating at low rotational speeds, (a) Melting when the die pressure was set at the low value of 50 psi, where chamber-to-chamber leak pressure backflows are negligible, (b) Melting under the high die pressure of 2700 psi, which enables leak backflows, which result in chamber solid bed compaction and introduce the possibility of dissipative mix melting. [Reprinted by permission from L. P. B. M. Janssen, Twin Screw Extrusion, Elsevier Scientific, Amsterdam, 1978.]...

T. Sakai and N. Hashimoto, Application of Novel Counter-rotating Intermeshed Twin Extruder for Degassing Operation, SPE ANTEC Tech. Papers, 32, 860-863 (1986) also T. Sakai, N. Hashimoto, and N. Kobayashi, Experimental Comparison between Counterrotation and Co-rotation on the Twin Screw Extrusion Performance, SPE ANTEC Tech. Papers, 33, 146-151 (1987). 

D. S. Bang, M. H. Hong, and J. L. White, Modular Tangential Counterrotating Twin Screw Extrusion Determination of Screw Pumping Characteristics of Modules and Composite Machine Behavior, Polym. Eng. Sci., 38, 485-498 (1998). 

L. Zhu, K. A. Nahr, and X. Geng, Modeling of Particle-dispersed Melting Mechanism and Its Application in Corotating Twin Screw Extrusion, J. Polym. Sci. Part B Polym. Phys., 39, 2461-2468 (2001). 

H. Jung and J. L. White, Investigation of Melting Phenomena in Modular Co-rotating Twin Screw Extrusion, Int. Polym. Process., 18, 127-132 (2003). 

Rouilly A., Jorda J., Rigal L. Thermo-mechanical processing of sugar beet pulp. I. Twin-screw extrusion process. Carbohydrate Polymers <56 81-87 (2006). 

---