Polymer mixing flows

For a free-radical polymerization and a condensation polymerization process, explain why the molar mass distribution of the polymer product will be different depending on whether a mixed-flow or a plug-flow reactor is used. What will be the difference in the distribution of molar mass ... 

The fundamental processes and mechanisms that control single-screw extrusion are presented in Chapters 5 through 8. These processes include solids conveying, melting, polymer fluid flow, and mixing. The analyses presented in these chapters focus on easily utilized functions needed to assess the operation of the single-screw extruder. The derivation of these relationships will be presented in detail in the appendices for those who desire to explore the theory of extrusion in more detail. 

One of the significant limitations of the use of first- and second-generation superplasticizers in ready-mixed flowing concrete is the rapid decrease in the initially achieved high workability and this constitutes one of the chief constraints to their wider acceptance. Therefore, a number of major producers of admixtures have sponsored active research to improve the workability retention characteristics of their superplasticizers. Some recent developments [48] have shown promise, among these are materials based on acrylate polymers (AP). The AP-based materials are reported to be more effective than SNF- or SMF-based surplasticizers in terms of water reduction, slump increase and slump retention. Figure 7.19 shows the remarkable improvement in the retention of workability produced by the AP type superplasticizer compared to an SNF type. 

Surface tension plays a significant role in the deformation of polymers during flow, especially in dispersive mixing of polymer blends. Surface tension, as, between two materials appears as a result of different intermolecular interactions. In a liquid-liquid system, surface tension manifests itself as a force that tends to maintain the surface between the two materials to a minimum. Thus, the equilibrium shape of a droplet inside a matrix, which is at rest, is a sphere. When three phases touch, such as liquid, gas, and solid, we get different contact angles depending on the surface tension between the three phases. 

B.A. Davis. Investigation of non-linear flows in polymer mixing using the boundary integral method. PhD thesis, University of Wisconsin-Madison, Madison, 1995. 

It is important to note that similar beneficial mixing flows and solid polymer particulate charge deformations to those discussed earlier also occur in the multilobal variants of the counterrotating, intermeshing TSEs, as well as in CMs. We used the co-rotating, fully intermeshing twin screw kneading element pairs, because the relentless expansion/ contraction cycles can best be demonstrated with them. 

Fig. 11.33 Dispersed PS 685 streaks of ligaments and droplets in the equiviscous Blend 2. PS is flowing/deforming in an affine fashion in the expected stretching and folding pattern. Experiments were conducted at 180°C and 120rpm. [Reprinted with permission from Proceedings of the Tenth Semiannual Meeting of the Polymer Mixing Study, Polymer Processing Institute, Hoboken, NJ (1995).]...

Chaotic mixing flows have recently been used for rapid development of morphology of immiscible polymers. Three morphological forms have been identifled -lamella, flbrils, and droplets (Figure 8.12) [200-205]. 

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