Creeping film process

Creeping film process (CFP) is a liquid membrane technique for simultaneous removal and concentration of dissolved species from their diluted aqueous solutions. CFP contactor is presented schematically in Figure 13.9. Feed and strip solutions flow down the vertical hydrophilic porous membrane sheets. A mobile organic LM is interposed between two creeping aqueous films. CFP is a continuous mass transfer process in which eddy diffusion controls the mass fluxes in all three liquid films. 

Boyadzhiev L. Recovery of valuable metals from diluted aqueous solutions by creeping film pertraction. In Devis GA Ed. Separation Processes in Hydrometallurgy. London 1987 Pt. 3, Ch. 26 259-287. 

Chlorinated rubber is also used to promote the adhesion of solvent-borne CR adhesives to metals and plasticized PVC. Addition of a low molecular weight chlorinated rubber (containing about 65 wt% chlorine) improves the shear strength and creep resistance of polychloroprene adhesives [75] but a reduction in open time is also produced. A heat reactivation (process in which the surface of the adhesive film is raised to 90-100°C to destroy the crystallinity of the film and allowing diffusion to produce polymer chain interlocking more rapidly) restores tack to the polychloroprene adhesives. 

In polymer processing, we frequently encounter creeping viscous flow in slowly tapering, relatively narrow, gaps as did the ancient Egyptians so depicted in Fig. 2.5. These flows are usually solved by the well-known lubrication approximation, which originates with the famous work by Osborne Reynolds, in which he laid the foundations of hydrodynamic lubrication.14 The theoretical analysis of lubrication deals with the hydrodynamic behavior of thin films from a fraction of a mil (10 in) to a few mils thick. High pressures of the... 

Modifed PTFE can be used in practically all applications, where the conventional polymer is used. In addition to that, new applications are possible because of its improved flow and overall performance. In the chemical process industry, it is used for equipment linings, seals, gaskets, and other parts, where its improved resistance to creep is an asset. In semiconductor manufacturing, modified PTFE is used in fluid handling components and in wafer processing components. Typical applications in electrical and electronic industries are connectors and capacitor films. Other applications are in unlubricated bearings, laboratory equipment, seal rings for hydraulic systems, and antistick components.103... 

To improve the properties of the raw polymer (wear resistance, creep resistance, thermal and electrical conductivity), various fillers, such as glass fibers, powdered metals, and graphite, are combined with all three types of PTFE polymers, mostly by intimate mixing. Filled fine powders are produced mostly by adding fillers into a dispersion and then coagulating the mixture. Aqueous dispersions can also be modified by the addition of certain fillers, pigments, heat resistant dyes, carbon blacks, and powdered metals, especially when processed into films (see Chapter 6). 

Levyt" has described a process for orienting perfluoropolymer films. Tables 6.20 and 6.21 (see Table 6.22 for resin composition) present the properties of PFA and FEP as a function of stretch ratio. A stretch ratio of 0 was indicative of as-cast unstretched film. Note that in the absence of any stretch in the transverse direction, with an increase in the stretch ratio TD modulus increased significantly, while creep decreased and shrinkage reached a constant level. In effect, stretching the film makes it stronger in many ways. 

Vinylidene Fluoride Hexafluoropropylene Copolymer - Thermoplastic copolymer of vinylidene fluoride and hexafluoropropylene. Has better thermal stability, antistick, dielectric, and antifriction properties, and chemical resistance, but lower mechanical strength at room temperature and creep resistance, compared to incompletely fluorinated fluoropolymers. Processing by conventional thermoplastic techniques is difficult due to its high melt viscosity. Uses include chemical apparatus, containers, films, and coatings. Also called TAM... 

Critical requirements for PE are rapid processing, thinner yet stronger films, ease of direct printing or adherence of labels, rapid heat sealing, high strain rate at high strain for stretch wrap, plastic memory for shrink wrap, cross-linkability to resist creep and stress relaxation, cross-linking to resist elevated temperatures when the... 

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