Fabrication processes film casting

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. 

Due to its high melting point, P30 cannot be processed by injection molding or extrusion teehniques. However, P30 ean be fabricated by solution casting techniques into films or by wet spin techniques into fibers. On orientation or heat treatment, these materials beeome insoluble. 

Although there are several SEEP formulations described in literature (Table 12.2), the most described and widely used is SELP-47K. Besides the ability to produce hydrogels, self-assembled structures and electrospun fibres, it is also possible to fabricate thin films by solvent evaporation at room temperature [65,66]. The major difference between hydrogels and thin films resides in the fabrication process and the resulting microstructure. Thin films of SELP-47K were made by dissolving the lyophilized powder in water and letting the solvent evaporate from the casting moulds [65-67]. Film thickness is controlled by the solution concentration and the volume used to cast. 

Cast embossing n. A process of casting films against an embossed temporary carrier. Vinyl plastisols, organosols, solutions, or lattices are used as film formers, which may be backed up with layers of foam or fabric. The temporary carrier is often paper, embossed with the desired pattern and treated so as to be easily stripped from the fused film or laminate. 

Recently, the thermal and mechanical properties of MWCNT/PMMA or SWCNT/PMMA nanocomposites have been thoroughly investigated [145, 146]. For instance, Lee et al. [146] reported the fabrication and characterization of MWCNT/PMMA by using both injection molding and film-casting processes. The tensile strength of the MWCNT/PMMA nanocomposite increased by more than 15% and tensile stiffness also increased by about 17.5%, compared to pure PMMA. It was confirmed that a combined fabrication process efficiently dispersed MWCNTs in the PMMA matrix and also maintained the well-dispersed state more effectively [146]. 

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