High-shear internal mixer

Figure 4.10 Loading ingredients into the high-shear internal mixer in the PRL process. Reproduced with permission from Polymer Recyclers Ltd, Dordon, Tamworth, UK. 2014, Polymer Recyclers Ltd...

Urethanes are processed as mbber-like elastomers, cast systems, or thermoplastic elastomers. The elastomer form is mixed and processed on conventional mbber mills and internal mixers, and can be compression, transfer, or injection molded. The Hquid prepolymers are cast using automatic metered casting machines, and the thermoplastic peUets are processed like aU thermoplastic materials on traditional plastic equipment. The unique property of the urethanes is ultrahigh abrasion resistance in moderately high Shore A (75—95) durometers. In addition, tear, tensUe, and resistance to many oUs is very high. The main deficiencies of the urethanes are their resistance to heat over 100°C and that shear and sliding abrasion tend to make the polymers soft and gummy. 

Another difference between the extruders and continuous mixers, pointed out by Valsamis and Canedo, is that, in the former, channel solids and melt flow dominate, and flow over screw flights is a secondary effect (except for power calculations). In contrast, the circumferential flow in CMs (and internal mixers) over the wing tips is the major flow component. Thus, while wing tips and screw flights appear to be equivalent machine elements, their role and function are quite different. The wing tips provide high shear... 

Internal mixers, such as the Banbury mixer (Figure 11.5), contain two connecting chambers, in which blades rotate in opposite directions with a narrow clearance to the walls, resulting in local high rates of shear. The walls can be cooled or heated. After mixing, the pieces are removed from the chambers, milled into a sheet and cut into ribbons for storage or further processing. 

Internal batch mixers are batch systems that have both a lower-shear homogenizing region and a localized high-shearing section. Refer to the schematic disgram in Figure 6.20. 

Thoroughly disperse the bentonite and activated aluminium chlorhydrate in the isopropyl myristate and DC 344 fluid, using a high-shear mixer. Add the DC 1401 and the fragrance, mixing well. Fill into internally lacquered aluminium aerosols, as shown above. 

The behaviour of elastomers in internal mixers reflects consequently a combination of shear and extensional responses. Any model of the mixing process has to take account of both shear flow and transitory extensional flow, since for the latter the steady state cannot be achieved. Therefore the response of the elastomers in the earlier times of an elongational process gives information about the mixing behaviour. Using a high rate extensometer,... 

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