Microfiltration polypropylene

Microfiltration membranes usually have a nominal pore diameter in the range of 0.1-10 pm. However, the membrane specification is not an absolute parameter. The membranes usually present a pore size distribution around the nominal value and the shape of the bioparticles can determine whether they are retained or pass through the membrane. The membranes are manufactured from polymers, such as Teflon, polyester, PVC (polyvinyl chloride), Nylon, polypropylene, polyethersulfone, and cellulose, or from inorganic materials, such as ceramic and sinterized stainless steel. 

In micro- and ultrafiltrations, the mode of separation is by sieving through line pores, where microfiltration membranes filter colloidal particles and bacteria from 0.1 to 10 mm, and ultrafiltration membranes filter dissolved macromolecules. Usually, a polymer membrane, for example, cellulose nitrate, polyacrilonytrile, polysulfone, polycarbonate, polyethylene, polypropylene, poly-tretrafhioroethylene, polyamide, and polyvinylchloride, permits the passage of specific constituents of a feed stream as a permeate flow through its pores, while other, usually larger components of the feed stream are rejected by the membrane from the permeate flow and incorporated in the retentate flow [10,148,149],... 

Microfiltration units can be configured as plate and frame flat sheet equipment, hollow fiber bundles, or spiral wound modules. The membranes are typically made of synthetic polymers such as Polyethersulfone (PES), Polyamide, Polypropylene, or cellulosic mats. Alternate materials include ceramics, stainless steel, and carbon. Each of these come with its own set of advantages and disadvantages. For instance, ceramic membranes are often recommended for the filtration of larger particles such as cells because of the wider lumen of the channels. However, it has been shown that spiral wound units can also be used for this purpose, provided appropriate spacers are used. 

Microfiltration membranes can be used as pretreatment for other membrane technologies and to remove microbes and total suspended sohds (TSS) including fibers and particles. Retention of salts and dissolved organics is negligible, if they are not bound to the suspended sohds. MF can be used for the recovery of coating color pigments. MBRs generally use UF or MF membranes. The materials used in microfiltration are polyvinylidenefluoride (PVDF), polypropylene, polyethylene, polysulfone, polyether suUbne, Teflon, and ceramic materials. 

Curved slit channel with 180° curve section Polypropylene microfiltration membrane... 

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 ... 

Johnson, J. N., Cross-flow Microfiltration Using Polypropylene Hollow Fibers, Fifth Annual Membrane Technology Planning Conference, Cambridge (Oct. 1987)... 

Meagher L., Klauber C., Pashley R.M. (1996), The influence of surface forces on the fouling of polypropylene microfiltration membranes. Colloids and Surfaces, A Phraicochemical and Eneineerine Aspects, 106, 63-81. 

During sintering, a powder of particles of a given size is pressurized at elevated temperatures in a preformed shape so that the interface between the particles disappears. Microfiltration membranes can thus be obtained from PTFE (polytetra-fluoroethylene), PE (polyethylene), PP (polypropylene), metals, ceramics, graphite and glass, with pore sizes depending on the particle size and the particle-size distribution. Porosities up to 80% for metals and 10-20% for polymeric membranes can be reached with pore sizes varying between 0.1 and 10 pm. Most of these materials have excellent solvent and thermal stability. 

Porous membranes can be made of polymers (polysulfones, polyacrylonitrile, polypropylene, silicones, perfluoropolymers, polyimides, polyamides, etc.), ceramics (alumina, silica, titania, zirconia, zeolites, etc.) or microporous carbons. Dense organic membranes are commonly used for molecular-scale separations involving gas and vapor mixtures, whereas the mean pore sizes of porous membranes is chosen considering the size of the species to be separated. Current membrane processes include microfiltration (MF), ultrafiltration (UF), nanofiltration (NF), gas and vapor separation (GS), and pervaporation (PV). Figure 1 indicates the types and sizes of species typically separated by these different separation processes. 

Pore-filling MIP composite membranes had been first prepared by Dzgoev and Haupt [100]. They casted the reaction mixture into the pores of a symmetric microfiltration membrane from polypropylene (cutoff pore size 0.2 pm) and performed a cross -linking copolymerization of a functional polyacrylate for imprinting protected tyrosine. Hattori et al. [101] had used a commercial cellulosic dialysis membrane (Cuprophan) as matrix and applied a two-step grafting procedure by, (i) activation of the cellulose by reaction with 3-methacryloxypropyl trimethoxysilane from toluene in order to introduce polymerizable groups into the outer surface layer, (ii) UV-initiation of an in situ copolymerization of a typical reaction mixture (MAA/EDMA, AIBN) for imprinting theophylline. 

Deng, H.-T., Xu, Z.-K., Dai, Z.-W., Wu, J. and Seta, P. 2005. Immobilization of Candida rugosa lipase on polypropylene microfiltration membrane modified by glycopolymer Hydrolysis of olive oil in biphasic bioreactor. 

We have used a polymer track membrane (PTM) [64, 65] as a support for reagent immobilization. Such membranes are used for microfiltration in medicine, electronics, biotechnology etc. PTM is made by irradiation of a polymer with high energy ions. The irradiated film is etched and in this way the tracks after passing ion beams are removed. Various polymers can be used as a base film for fabrication of PTM (e.g. polypropylene, polyamide, polycarbonate etc.). The diameter of the pores obtained depends on the type of ions used and on their energy. 

Membrane characterization by CSLM has been rather limited when compared with other microscopic techniques such as SEM and atomic force microscopy (AFM). The earliest work found in the literature [13] records how van den Berg et al. used a combination of AFM and CSLM to study qualitative differences in the pore geometry of different brands of polypropylene membranes. The first reported applications that used only CSLM for membrane characterization [14,15] were by Charcosset et al. who used CSLM to characterize microporous membrane morphologies and to obtain values of surface porosity and pore size. The conclusions of those studies were that CSLM gave some characteristics on membrane morphology that SEM, which views only surfaces, cannot provide. However, as also mentioned previously in this chapter, they pointed out low resolution for membrane characterization as the main drawback of CSLM. This restricts the use of CSLM to the characterization of microfiltration membranes if measurements on pore size and surface porosity have to be performed. 

Polymers commonly used to make such microfiltration membranes are polyvinylidene fluoride (PVDF), Nylon 66, polytetrafluoroethylene (PTFE), polysuUbne, cellulose, cellulose acetate/cellulose nitrate, polypropylene (PP), polyester, polycarbonate, etc. Ceramic microfiltration membranes are not uncommon. Polymeric membranes may have the following stmctures. 

The thermal phase inversion process is also employed for ultra- and microfiltration membranes. Crystalline polymers such as polyethylene and polypropylene are generally preferred as solutions these can be prepared at temperatures above the melting point, but cooling below the melting point will yield rapid crystallization and phase separation. These membranes are often employed in microfiltration and dialysis applications. 

Yu, S., Zheng, Y, Zhou, Q., Shuai, S., Lu, Z., and Gao, C. 2012b. Facile modification of polypropylene hollow fiber microfiltration membranes for nanofiltration. Desalination 298 49-58. 

Polysulfone and Polypropylene-based polymers are presently being commercially used for ultrafiltration and microfiltration (polysulfone supported on a PP backing) applications such as extraction of insulin, polymer synthesis, effluent water recovery etc. ... 

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