Method film-casting

Fig. 8. Schematic of methods for MLC manufacturing (a) belt casting (b) carrier film casting using a doctor blade.

Extmsion technology is used to produce spunbond, meltblown, and porous-film nonwovens. Fabrics produced by these systems are referred to individually as spunbonded, meltblown, and textured- or apertured-film nonwovens, or genericaHy as polymer-laid nonwovens. These fabrics are produced with machinery associated with such polymer extmsion methods as melt-spinning, film casting, and extmsion coating. In polymer-laid systems, fiber stmctures are simultaneously formed and manipulated. 

The PIA-investigations were carried out under dynamic vacuum (p< 10 5 mbar) and at 77 K with films cast from toluene solution onto KBr substrates. For the dispersive method [29, 30] the globar, the KBr-prism premonochromator, and the grating monochromator of a Perkin Elmer 125 lR-spcctrometer were used in the spectral range of 0.25 to 1.24 eV. The pump beam was chopped mechanically... 

It must be kept in mind that the ( )-diastereomer is a mixture of enantiomers that were not separable by reverse phase HPLC. Since the method for separation of (+)- and meso-diastereomers (reverse phase HPLC, C-18 column) is based on the difference in conformation between isomers (related ultimately to their differential attraction to the column), it is unlikely that the two enantiomers of the (+ )-diastereomer have different conformations at the air-water interface. It is not known, however, how the energetics of compression and expansion will differ for films cast from either R,R or S,S enantiomer from those cast from the racemic mixture. 

In 1966, Cadotte developed a method for casting mlcroporous support film from polysulfone, polycarbonate, and polyphenylene oxide plastics ( ). Of these, polysulfone (Union Carbide Corporation, Udel P-3500) proved to have the best combination of compaction resistance and surface microporosity. Use of the mlcroporous sheet as a support for ultrathin cellulose acetate membranes produced fluxes of 10 to 15 gfd, an increase of about five-fold over that of the original mlcroporous asymmetric cellulose acetate support. Since that time, mlcroporous polysulfone has been widely adopted as the material of choice for the support film in composite membranes, while finding use itself in many ultrafiltration processes. 

Prepare the sample, if not readily available, in the form of a film approximately 1 mm thick or less for rigid polymers or 4 mm thick for flexible polymers. Film preparation methods include casting from solution, milling, or compression molding (Note 1). 

Materials and Methods. The isomeric compositions of the four polybutadienes used are listed in Table I. Samples were prepared for infrared measurement from solutions of the polymer without further purification. Most films were cast from carbon disulfide solutions on mercury or on glass plates, but a few films were cast from hexane solutions to determine whether or not the solvent affected the radiation-induced behavior. No difference was observed for films cast from the different solvents. The films were cured by exposure to x-rays in vacuum. (Doses were below the level producing detectable radiation effects.) They were then mounted on aluminum frames for infrared measurements. The thicknesses of the films were controlled for desirable absorbance ranges and varied from 0.61 X 10 s to 2 X 10 3 cm. After measuring the infrared spectrum with a Perkin-Elmer 221 infrared spectrophotometer, the mounted films were evacuated to 3 microns and sealed in glass or quartz tubes (quartz tubes only were used for reactor irradiations). 

Measurement of Practical Photosensitivity. The photosensitivity of the polymer was measured by a gray-scale method (15) as follows. The polymer solution (10%) in cyclohexanone was cast on a copper plate by using a rotary applicator and dried. The Kodak step tablet No. 2 (Eastman Kodak Co.) was placed upon the polymer film cast on the plate, exposed on a chemical lamp (15w x 7) from 3 cm for 1 min., and then the exposed film was developed by the solvent for 2 min. 

Two methods, annealing and film-casting by slow solvent evaporation, have been used effectively to develop maximum crystallinity in PVDF blends. The... 

Fig. 5. Use of the Mayer rod technique in film casting. Unit volume deposited = dV = — n/4)2fi d/ film thickness deposited = dV/dA. (Reprinted, with permission, from Methods in Enzymology, Vol. 137. San Diego, CA Academic, 1988.)...

Today the majority of polymeric porous flat membranes used in microfiltration, ultrafiltration, and dialysis are prepared from a homogenous polymer solution by the wet-phase inversion method [59-66]. This method involves casting of a polymer solution onto an inert support followed by immersion of the support with the cast film into a bath filled with a non-solvent for the polymer. The contact between the solvent and the non-solvent causes the solution to be phase separated. This process involves the use of organic solvents that must be expensively removed from the membrane with posttreatments, since residual solvents can cause potential problems for use in biomedical apphcations (i.e., dialysis). Moreover, long formation times and a limited versatihty (reduced possibUity to modulate cell size and membrane stmcture) characterize this process. 

The method of preparation also influences the properties of the film. Cast films of varying properties can be prepared by variation inter alia of the solvent power of the casting solution containing the polymer, although the complex processes involved in film formation are not yet fully understood. It is clear, however, that the conformation of the polymer chains in concentrated solution just prior to solvent evaporation will determine the density of the film, and the number and size of pores and voids. Dmg flux through dense (nonporous) polymer membranes is by diffusion flux through porous membranes will be by diffusion and by transport in solvent through pores in the film. With... 

Nanostructured metal oxide film deposition can also be prepared by hydrothermal decomposition, film casting method (sonication of nanoparticles in aqueous solution (H20) or preparation of aqueous suspension of nanoparticles for spread on conducting glass plate) and nanosized metal nanoparticles prepared by controlled hydrolysis [16,18,19,21,26],... 

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