Smart blenders

The amount of melt structuring in the smart blender is specified through selection on a process control computer (Fig. 19.2) of the number N of time-periodic speed changes of the stir rods. For example, small N yields a multilayer blend morphology whereas larger N and further stretching and folding by chaotic advection can lead to layer... 

Chaotic advection in the smart blender is shown in the inset of Fig. 19.2. Results were obtained through finite element modeling with a procedure analogous to those employed in chaotic mixing studies [27] where numerous particles are located initially within... 

Figure 19.4 Industrial smart blender for manufacture of blown film and other tubular extrusions. Because the smart blender substitutes for conventional dies and allows on-line control of structure in an extrusion, it is also referred to as a smart die. ...

Figure 19.5 Example of a blend morphology map that can be compiled to guide machine operation. Databases can be developed in terms of pertinent melt properties to reduce trial-and-error used typically in polymer processing. Chaotic advection blending machines are thereby referred to also as smart blenders or smart dies.

To illustrate the dynamic operation of a smart blender and use of the morphology map, the designated value of N on the process control computer can be changed to restore State 4 from State 5 in Fig. 19.5 if desired. Additionally, screw extruder flow rates can be changed to increase to 30% and reach state 6. Multilayers at State 7 can be attained by reducing N, as shown. Such dynamic operation facilitates cost and property optimization of extruded plastics and can lead to more rapid research and development for new products. 

Whereas examples in Fig. 19.6A,B pertain to immiscible polymer melts. Fig. 19.6C pertains to a miscible polymer pair [31]. Submicron layers were formed in a blend of 30% by volume EVOH and polyamide (PA). To improve phase contrast in the scanning electron image, samples were etched in a solvent so that some or portions of EVOH layers were removed. Thicknesses of layers were determined by separate transmission electron examinations to be less than 0.5 pm. The potential amount of layer refinement obtained with a smart blender is demonstrated for a blend consisting of 15% by volume LDPE and high density polyethylene (HDPE) [5]. Because interfacial tension was very low due to... 

Droplet dispersions in a polymer blend are obtained differenhy in smart blenders than in convenhonal mixing machines. The general sequence... 

Dispersions are obtained by specifying to the smart blender large values of the parameter N (Section 19.2). Even so, a variety of structural types are formed in the smart blender prior to the extrusion point due to progressive structure development. An extrusion with droplets such as Fig. 19.1 lA can be transformed to one having other blend morphologies such as depicted in the morphology map of Fig. 19.5. Similarly, extrusions with the platelet dispersion of Fig. 19.1 IB can be changed to extrusions have platelets localized within many layers such as the example in Fig. 19.10. 

The ability to produce an infinite variety of simulated wood patterns is done via online control with no physical changes to the smart blender. Similar opportunities are available to form simulated rocks and abstract patterns in plastics or in ceramic materials processable as slurries. Due to pattern uniqueness and their chaotic advection basis, counterfeit-proofing of products may also be achievable using these approaches. Many patterns that appear in extrusions have fingerprints of the chaotic motions used to create them. 

Zumbrunnen DA, Zumbrunnen ML. Realistic appearance of wood grains formed with smart blenders on surfaces and inside extruded plastics. In Proceedings of the 67th Annual Technical Conference 2009, Society of Plastics Engineers, p. 1078-80. 

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