Polyester membrane filters

An Inertial Spectrometer (Inspec) with membrane filters can also be used to collect different particle sizes on different locations of a filter (Molhave et al. 2000). In a study for the characterization of the indoor environment in a dental office, workday (6-8 h) integrated PM2.5 samples were collected using a size-selective impactor (model 200"), and treated (hydrophobic) polyester membrane filters at a calibrated flow rate of 10 L min . Filters were weighed before and after sampling using an appropriate conditioned electrobalance (Godwin et al. 2003). 

Membrane filter type, such as polycarbonate, polyester, nitrocellulose, etc. ... 

Filters CM, diameter 30 mm, pore size 0.4 pm, Millicell-CM, Millipore Corporation, or Transwell, diameter 24 mm, polyester membrane, pore size 0.4 pm, Ref 3450, Costar, Corning Incorporated... 

First, samples are filtered over a black membrane filter (e.g. polyester or polycarbonate) with an appropriate pore size (i.e. 0.4 rm for bacteria and 0.8-2 (xm for eukaryotic cells). These screen filters are used because of their low background fluorescence and high contrast, which facilitates validation using the epifluorescence microscope (see below) (Brailsford 1996). Secondly, the retained cells are fluorescently stained using one or more physiological or taxonomic probes (see Section Fluorescent Stains for SPC). 

Sterile filtration of liquids and gases is now virtually always done using mem brane filters. The first U.S. patent for membrane filters was filed in 1922 and pertained to cellulose acetate membranes. A wide range of membrane filter media are now commercially available to suit various applications cellulose esters, polyvinylidinefluoride, polytetrafluoroethylene (PTFE), and polyhexam-ethyleneadipamide (nylon 66), separately or as laminates with polyethylene, polypropylene, and polyester for more robust phy.sicai characteristics. 

Membrane filters are used to remove particulates from samples and solvents prior to HPLC analysis and also for the preparation of liquid samples, where no solvent is used. Typical materials of construction for membrane filters are usually synthetic polymeric materials, although natural substances, such as cellulose, and inorganic materials, such as glass fibers, are also used acrylic copolymer, aluminum oxide, cellulose acetate, glass fiber, mixed cellulose esters, nitrocellulose, nylon, polycarbonate, polyester, polyether sulfone, polypropylene polysulfone, PTFE, PVC, etc. The compatibility of the polymeric material with the solvents used must be a great concern of their different chemical properties. 

Membrane filters are available in a large variety of sizes, configurations, and materials. Often used materials are polyvinylidene fluoride (PVDF), polyethersulfone (PES), nylon, cellulose esters, polytetrafluoroethylene (PTFE), polyester and polypropylene. The choice for a material determines, to a large extent ... 

A cumulative success of artificial ion-channel functions by simple molecules may disclose a wide gate for the design of ion channels and possible applications to ionics devices. Incorporation of these channels into bilayer lipid membrane systems may trigger the developments towards ionics devices. The conventional BLM system, however, is not very stable, one major drawback for the practical applications, and some stabilization methods, such as impregnating the material in micro-porous polycarbonate or polyester filters, are required. On the other hand,... 

Collection on porous filter media is perhaps the most efficient means of particle removal. Aerosol filtration is an effective means of air purification, while at the same time it has been widely used for sampling airborne material for mass and chemical composition determination. A wide variety of filter media is available, ranging from fibrous mats of relatively inert material to porous membranes. Fibrous mats and model filter arrays appear microscopically as stacks of overlaid cylinders, where the cylinders may be smooth or rough. In contrast, the membrane media are plastic films with microscopic holes of nearly uniform size nuclepore filters, for example, are produced of sheets of polyester, and the holes are introduced by neutron bombardment. 

Finally, track-etched MF membranes are made from polymers, such as polycarbonate and polyester, wherein electrons are bombarded onto the polymeric surface. This bombardment results in sensitized tracks, where chemical bonds in the polymeric backbone are broken. Subsequently, the irradiated film is placed in an etching bath (such as a basic solution), in which the damaged polymer in the tracks is preferentially etched from the film, thereby forming cylindrical pores. The residence time in the irradiator determines pore density, and residence time in the etching bath determines pore size. Membranes made by this process generally have cylindrical pores with very narrow pore-size distribution, albeit with low overall porosity. Furthermore, there always is the risk of a double hit, i.e., the etched pore becomes wider and could result in particulate penetration. Such filter membranes are often used in the electronic industry to filter high-purity water. 

Polymeric membranes are prepared from a variety of materials using several different production techniques. Table 5 summarizes a partial list of the various polymer materials used in the manufacture of cross-flow filters for both MF and UF applications. For microfiltration applications, typically symmetric membranes are used. Examples include polyethylene, polyvinylidene fluoride (PVDF) and polytetrafluoroethylene (PTFE) membrane. These can be produced by stretching, molding and sintering finegrained and partially crystalline polymers. Polyester and polycarbonate membranes are made using irradiation and etching processes and polymers such as polypropylene, polyamide, cellulose acetate and polysulfone membranes are produced by the phase inversion process.f Jf f ... 

A recent development of the secondary flow-enhanced membrane processes is the helical membrane module, which is characterized by a DNA helical-like spacer enveloped by polyester filter cloth with a pore size around 22 pm [31-33]. Figure 10.12 shows the schematics of the helical membrane spacers with different twisted helical angles. The main parameters of the helical membrane include the angles of twist of the spacer or membrane and the ratio of the membrane width to the length. 

Any porous substrate (filter paper, polyester textile) covered by the PP of hexa-methyldisilazane or the double layer of hexamethyldisilazane and n-hexane becomes the membrane selective for the water and hydrophobic liquids (Bankovic et al. 2004). 

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