Dry phase Inversion process

When solvents are removed solely by evaporation, the membrane formation is known as a dry phase inversion process [Resting, 1985]. When the phase separation and structure forma-... 

When solvents are removed solely by evaporation, the membrane formation is known as a dry phase inversion process (Resting 1985). When the phase separation and structure formation are achieved by immersion of a cast membrane in a quench medium, the process is known as a wet phase inversion process (Heffelfinger 1978). The latter process is used to prepare asymmetric membranes for either microfiltration (Roesink 1989), ultrafiltration (Michaels 1971), reverse... 

Recently, an in-depth review on molecular imprinted membranes has been published by Piletsky et al. [4]. Four preparation strategies for MIP membranes can be distinguished (i) in-situ polymerization by bulk crosslinking (ii) preparation by dry phase inversion with a casting/solvent evaporation process [45-51] (iii) preparation by wet phase inversion with a casting/immersion precipitation [52-54] and (iv) surface imprinting. 

In an alternative approach, MIP membranes can be obtained by generating molec-ularly imprinted sites in a non-specific matrix of a synthetic or natural polymer material during polymer solidification. The recognition cavities are formed by the fixation of a polymer conformation adopted upon interaction with the template molecule. Phase inversion methods have used either the evaporation of polymer solvent (dry phase separation) or the precipitation of the pre-synthesised polymer (wet phase inversion process). The major difficulties of this method lay both in the appropriate process conditions allowing the formation of porous materials and recognition sites and in the stability of these sites after template removal due to the lack of chemical cross-linking. 

Sol 2 is present either when one phase separates into two phases or when two phases are prevented from recombining into a single phase. It is expedient to entitle this factor inoompatibilityt and to discuss the various phase inversion processes in terms of the reasons for incompatibility. In the sections to follow four phase inversion processes are discussed a dry process, a wet process, a thermal process and a polymer assisted phase inversion process. 

The dry or complete evaporation phase inversion process is the oldest and easiest to understand. It can be illustrated by a typical cellulose nitrate (CN) casting solution (see Table I). This system can be used to exemplify the various macroscopically observable stages involved in the formation of membranes by the dry process ... 

For many years polymeric membranes have been utilized widely for material separation without detailed characterization of the pore size and the pore size distribution. Most of the commercially available membranes are prepared by either a dry or a wet phase-inversion process. These membranes are formed by the phase separation of multicomponent polymer-solvent systems, the underlying principle being phase separation of the polymer solution. 

Phase-Inversion Process. Most tortuous-pore membranes are made by a casting process known as "phase inversion." Figure 2.2 is a simplified schematic of a casting machine which makes cellulose ester membranes. Typically, a casting solution made up of the polymer and a multicomponent solvent system is metered onto a stainless steel belt or web. The belt passes through a series of environmental chambers usually containing water vapor at elevated temperatures. The more volatile solvents evaporate and the water vapor precipitates the polymer around the less volatile solvent which becomes the "pore-former." Subsequently, (not shown in Figure 2.2), after the membrane is formed, the residual solvents are washed out of the pores, surfactants are added, and the membrane is dried. 

Membrane structures can also be formed by a microphase separation process in which the outermost region of the cast membrane undergoes phase separation induced by solvent evaporation, while the bulk of the structure is formed by sol vent/non-sol vent exchange during a quench step. This type of structure formation is defined as a dry/wet phase inversion process [Pinneau et al., 1990]. 

Membranes are prepared from polymer(s) dissolved in a solvent using either a dry process or a wet process. In the dry process, a volatile solvent is used for dissolving the polymer(s) and the extruded polymer solution is transferred into an evaporation chamber to yield a porous, isotropic or anisotropic membrane. In the wet process, on the other hand, the extruded mixture is coagulated by exposing the mixture to a nonsolvent in the form of vapor or liquid. The latter process is often referred to as the phase inversion process. 

In addition, PEEK-WC membranes have been prepared by using a phase inversion process with supercritical fluids. The supercritical fluid acts as a non-solvent. In comparison to the dry/wet phase inversion method, the supercritical fluid allows the cell size and the membrane morphology to modulate by changing the experimental conditions, such as polymer concentration, temperature, and pressure. A dry membrane can be obtained rapidly and without additional post-treatments. ... 

The phase-inversion process consists of the induction of phase separation in a previously homogeneous jx)lymer solution either by temperature change, by immersing the solution in a nonsolvent bath (wet process) or exposing it to a nonsolvent atmosphere (dry process). 

Data in this report are generated from both commercial and developmental flat-sheet CA membranes. CA manbranes are prepared by dissolving commercial grades of CA polymers into a solvenl/non-solvent mixture to give a highly viscous dope solution. After microfiltration a knife blade is used to spread the dope onto a woven nylon substrate. The commercial equipment utilized allows for a 1-m width to be cast. The thin dope film is quenched into a water bath to form the microporous structure by the phase inversion process. Membrane is washed with water and post-treated to give finished product in dry state as roll stock. 

Hollow fiber spinning is usually based on the dry-wet phase inversion process that involves the following four steps ... 

Hou et al. (2010) applied the DCMD process to remove F from brackish groundwater. They used PVDF hollow fibers that were self-prepared by a dry/wet phase inversion process and assembled into a polyester tube. The main membrane properties and the module characteristics are reported in the Tables 13.15 and 13.16. 

The term phase inversion refers to the process by which a polymer solution inverts into a three-dimensional network. Initially, the solvent system is the continuous phase, and after phase inversion the polymer is the continuous phase." Four phase inversion processes exist (1) the dry process, in which a volatile solvent is lost and phase inversion occurs, (2) the wet process, in which solvent is exchanged for non-solvent and precipitation occurs, (3) the thermal process, where a latent solvent (a substance which is only a solvent at elevated temperatures) is used, involving the cooling of the polymer solution which... 

Phase inversion is a process in which a polymer is transformed from a liquid to a solid state. There are a number of methods to achieve phase inversion. Among others, the dry-wet phase inversion technique and the temperature induced phase separation (TIPS) are most commonly used in the industrial membrane manufacturing. The dry-wet phase inversion technique was applied by Loeb and Sourirajan in their development... 

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