Fluid extrusion

Manoi, K. and Rizvi, S. S. H. (2008). Rheological characterizations of texturized whey protein concentrate-based powders produced by reactive supercritical fluid extrusion. Food Res. Int. 41, 786-796. 

Alavi, S. H., Rizvi, S. S. H., and Harriott, P. 2003a. Process-dynamics of starch-based microcellular foams produced by supercritical fluid extrusion. 11 Numerical simulation and experimental evaluation. FoodRes Int 36 3321-30. 

Ayoub A, Rizvi SSH. 2008. Properties of supercritical fluid extrusion-based crosslinked starch extrudates. J Appl Polym Sci 107 3663-3671. 

Chen K-H, Rizvi SSH. 2006b. Rheology and expansion of starch-water-COj mixtures with controlled gelatinization by supercritical fluid extrusion. Internat J Food Prop 9 863-876. 

Patel S, Venditti RA, Pawlsk JJ, Ayoub A, Rizvi SSH. 2009. Development of cross-linked starch microceUular foam by solvent exchange and reactive supercritical fluid extrusion. J Appl Polym Sd 111 2917-2929. 

Using this expression it is possible to make an approximation for the temperature rise of the fluid during extrusion through a die. If it is assumed that all the work is changed into shear heating and that all the heat is taken up evenly by the polymer, then the work done may be equated to the temperature rise in the polymer. 

Viscous forces within the fluid will always prevent a completely unhindered discharge, but in extrusion practice an additional die head resistance is used to generate backflow and mixing, so that a more uniform product is obtained. The flow profile along the channel is then of some intermediate form, such as that shown in Figure 8.18c. 

Liposomes — These are synthetic lipid vesicles consisting of one or more phospholipid bilayers they resemble cell membranes and can incorporate various active molecules. Liposomes are spherical, range in size from 0.1 to 500 pm, and are thermodynamically unstable. They are built from hydrated thin lipid films that become fluid and form spontaneously multilameUar vesicles (MLVs). Using soni-cation, freeze-thaw cycles, or mechanical energy (extrusion), MLVs are converted to small unilamellar vesicles (SUVs) with diameters in the range of 15 to 50 nm. ... 

Homopolymers and copolymers from amido-sulfonic acid or salt containing monomers can be prepared by reactive extrusion, preferably in a twin screw extruder [1660]. The process produces a solid polymer. Copolymers of acrylamide, N-vinyl-2-pyrrolidone, and sodium-2-acrylamido-2-methyl-propane sulfonate have been proposed to be active as fluid loss agents. Another component of the formulations is the sodium salt of naphthalene formaldehyde sulfonate [207]. The fluid loss additive is mixed with hydraulic cements in suitable amounts. 

Rizvi, S. S. H. and Mulvaney, S. (1992). Extrusion processing with supercritical fluids. Google Patents, Pat. No. 

Extrusion with the aid of a vacuum applied to the screw. The process is applied particularly in the preparation of extrudates to be vulcanised by either the liquid curing medium or fluid bed techniques. It assists in removing the volatiles from the compound and thus improves the quality of the extrudate. 

A laminar-flow reactor (LFR) is rarely used for kinetic studies, since it involves a flow pattern that is relatively difficult to attain experimentally. However, the model based on laminar flow, a type of tubular flow, may be useful in certain situations, both in the laboratory and on a large scale, in which flow approaches this extreme (at low Re). Such a situation would involve low fluid flow rate, small tube size, and high fluid viscosity, either separately or in combination, as, for example, in the extrusion of high-molecular-weight polymers. Nevertheless, we consider the general features of an LFR at this stage for comparison with features of the other models introduced above. We defer more detailed discussion, including applications of the material balance, to Chapter 16. 

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