Microporous layers fabrication processes

Another important point regarding the fabrication process of MPLs is that, typically, when carbon fiber paper is used as the DL, the MPL is coated on only one surface of the CFP. However, when a carbon cloth DL is used, it is normally coated on both sides with MPLs. Section 4.3.S.4 will discuss these DLs with multiple microporous layers in more detail. 

Lower-density E-plastomers have found alternate use in cast film processes to make elastic film laminates with good breathability which contain laminates of liquid impermeable extensible polymeric films with extensible-thermoplastic-polymer-fiber nonwovens and nonwoven webs of polyethylene-elastomer fibers as the intermediate layers. The development relates to a breathable film including an E-plastomer and filler that contributes to pore formation after fabrication and distension of the film. The method and extent of distension is designed to produce a breathable film by stretching the film to form micropores by separation of the film of the E-plastomer from the particulate solids. This film is useful for manufacture of absorbent personal-care articles, such as disposable diapers and sanitary napkins and medical garments. In detail, these constructions comprise a liquid impermeable extensible film comprising polyolefins. The outer layer contains extensible-thermoplastic-polymer-fiber nonwovens, and an elastic intermediate layer contains nonwoven webs of fiber E-plastomers. The intermediate layer is bonded to the film layer and the outer... 

Fabrication of a thin film composite membrane is typically a more expensive route to reverse osmosis membranes because it involves a two-step process versus the one-step nature of the phase inversion film casting method. However, it offers the possibility of each individual layer being tailor-made for maximum performance. The semipermeable coating can be optimized for water flux and solute rejection characteristics. The microporous sublayer can be optimized for porosity, compression resistance and strength. Both layers can be optimized for chemical resistance. In nearly all thin film composite reverse osmosis membranes, the chemical composition of the surface barrier layer is radically different from the chemical composition of the microporous sublayer. This is a common result of the thin film composite approach. 

Microporous membranes are often used in many processes to remove impurities or contaminants through size-selective filtration. The breath figures method also finds application in this field, specially the approaches that facilitate the easy transfer to other supports. Another prerequisite is the formation of through pores that penetrate from the top of the layer to the bottom and the use of ice support favors this fact. For example, highly uniform membranes of PS-h-PDMAEMA have been prepared with pores on the micrometer scale for size-selective separation. The films were prepared by casting at an air-ice interface and easily transferred onto other supports [219]. Miktoarm star copolymers with proper water wettability and mechanical stability have been used to fabricate separation membranes also using ice substrate [131]. Moreover, the breath figures approach has been employed to build polymer membranes on structured substrates in order to obtain hierarchically structured microsieves [208]. 

Instead of the PA precursors, Hayashi et al. deposited a polyimide film on the outer surface of a porous alumina tube by dip-coating three times. After imidization and pyrolyzation at 973-1073 K, the carbon membranes were fabricated on porous alumina tube. The enhancement of the volume of micropores accessible to smaller molecules has been observed. Hayashi et al. obtained an optimal pyrolysis temperature of 973 K and maximum permeance was achieved. In order to improve selectivity, a carbon layer was further deposited on the resultant supported carbon membrane by chemical vapor deposition (CVD) of propylene at 923 K.The CVD process favors the deposition of carbon in micropores, which explains the increase of the selectivity of CO2/N2 from 47 to 73. 

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