Polymer cross-flow

Figure 8.19. Simplified description of polymer cross-flow in a two-layer reservoir (a) schematic diagram and (b) corresponding pressure profiles with and without cross-flow (Clifford and Sorbie, 1985).

Addition of fibers tends to balance the difference between inflow and cross-flow shrinkage usually found in crystalline polymers. When a particulate is used to reduce and balance shrinkage, some fiber is needed to offset degradation. 

The plug flow contacting of phases may be accomplished in many ways by countercurrent flow as in blast furnaces and cement kilns [Fig. 26. ( )], by cross-flow as in moving belt feeders for furnaces [Fig. 26.1(6)], or by cocurrent flow as in polymer driers [Fig. 26.1(c)]. 

It is necessary to discuss another chemical feature related to water-soluble polymers cross-cross-linking — the component that separates viscous systems from gel systems. Viscous systems flow, and it follows, therefore, that they do not possess the tensile properties of muscles. High-viscosity systems have structural integrity, gels provide the necessary combination of tensile strength and elongation or stretch. 

Figure Three (3) illustrates the mechanism of cross flow microfiltration. Microfiltration involves the removal of insoluble particulate materials ranging in size from 0.1 to 10.0 microns (1000 to 100,000 angstroms). Microfiltration membrane polymers include ...

UV exposure (at k < 300 nm) of the AZ resist prior to plasma etching causes polymer cross-linking (167, 168) or decomposition (169) of the resist photosensitizer near the surface. Thus, a hardened shell or case is formed that permits a higher bake temperature without resist flow and also reduces the etch rate due to plasma exposure. Exposure to inert plasma (e.g., N2) causes similar effects (170), possibly because of ion and electron, as well as UV, bombardment of the resist surface. When F-containing discharges are used, fluorination of the resist surface occurs that strengthens the resist (because of the formation of C-F bonds) and minimizes reactivity (171). 

Most data about the Ludwig-Soret effect of polymers in solution have been obtained from thermal field-flow fractionation (TFFF), developed by Giddings and coworkers [17,18]. TFFF is one member of the family of field-flow fractionation techniques, which are all characterized by a laminar flow of the polymer solution or colloidal suspension within a relatively narrow channel. An external field, which may be gravitation, cross-flow, or temperature as in TFFF, is applied... 

Cell test uses small, approx lOO-cm cut pieces, of sheet membrane mounted in a cell that exposes the membrane to the test solution by cross-flow mode. This test is effective for quick evaluation of a number of different membrane polymers to determine the degree of separation. However, it cannot determine the long-term chemical effect of a solution on the polymer and does not provide engineering scale-up data. 

Y. Matsumoto, S. Nakao and S. Kimura, Cross-flow filtration of solutions of polymers using ceramic microfiltration. Int. Chem. Eng., 28 (1988) 677. 

In cross-flow flltration, the wastewater flows under pressure at a fairly high velocity tangentially or across the filter medium. A thin layer of solids form on the surface of the medium, but the high liquid velocity keeps the layer from building up. At the same time, the liquid permeates the membrane producing a clear filtrate. Filter media may be ceramic, metal (e.g., sintered stainless steel or porous alumina), or a polymer membrane (cellulose acetate, polyamide, and polyacrylonitrile) with pores small enough to exclude most suspended particles. Examples of cross filtration are microfiltration with pore sizes ranging from 0.1 to 5 pm and ultrafiltration with pore sizes from 1 pm down to about 0,001 pm. 

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