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Nonsolvent addition

A pair of polysaccharide molecules approaching each other in water exerts an interaction potential ( ) that is the algebraic sum of the competing attractive and repulsive forces. integrated over all pairs of molecules, is . This principle is embodied in the Deijaguin-Verwey-Landau-Overbeek (DLVO) theory of colloidal stability (Ross and Morrison, 1988). The equilibrium distance between the molecules is related to c, the volume of the hydrated particles, ionic strength, cosolute, nonsolvent additions, temperature, and shearing. [Pg.42]

If the poorer solvent is less volatile than the initial solvent, distillation may be combined with nonsolvent addition to accomplish solvent exchange or at least minimize the volume change on addition. Since the relative volatilities change with composition in the crystallizing solution, reflux ratio and distillate take-off rate must be controlled separately to follow the desired time-solubility profile. If the solubility of the solute has a suitable sensitivity to temperature, jacket cooling may be combined with the nonsolvent addition. The temperature of the nonsolvent should also be considered, and adequate control provided to prevent operation outside the expected temperature-dependent metastable zone. [Pg.219]

Khayet et al. prepared a number of poly(vinyhdene fluoride) hollow fiber membranes for ultrafiltration using the solution spinning method. N,N-dimethylaceta-mide (DMAc) was the solvent, and ethylene glycol was the nonsolvent additive [37]. The effect of the concentration of ethylene glycol in the PVDF spinning solution, as well as the effect of the concentration of ethanol either in the bore liquid or in the coagulation bath, on the morphology of the hollow fiber membrane was stud-... [Pg.125]

Xu et al. [11] studied the effects of both N,N-dimethylacetamide (DMAc) as a solvent additive in an internal coagulant (water) and acetic acid as a nonsolvent additive in a dope solution (PEI in DMAc) on the morphology and performance of poly(etherimide) (PEI) hollow fiber membranes for UF. Cross-sectional pictures were taken by SEM. The authors observed nodular structures on the inner and outer edges of the cross section when the amount of the acetic acid in the dope solution was increased. Pure water permeation flux increased when the nodules appeared. [Pg.144]

Fig. 8.6. Pure O2/N2 permeance ratio of asymmetric poly(phenylene oxide) membranes as a function of surface tension of chloroform/nonsolvent additives mixtures. Nonsolvent additives include 2-ethyl-l-hexanol (1m), 1-octanol (2m), 2-propanol (3d), 2-decanol (4m), 3,5,5-trimethyl-1-hexanol (5m), 2,4-dimethyl-3-pentanol (6d), 2,4,4-trimethyl-1-pentanol (7d), 2-methyl-3-hexanol (lOd), 3-ethyl-3-pentanol (12m), and 2-methyl-2-hexanol (13d). Merged is indicated by m discrete is indicated by d. Reprinted from [22], with kind permission from J.Tan... Fig. 8.6. Pure O2/N2 permeance ratio of asymmetric poly(phenylene oxide) membranes as a function of surface tension of chloroform/nonsolvent additives mixtures. Nonsolvent additives include 2-ethyl-l-hexanol (1m), 1-octanol (2m), 2-propanol (3d), 2-decanol (4m), 3,5,5-trimethyl-1-hexanol (5m), 2,4-dimethyl-3-pentanol (6d), 2,4,4-trimethyl-1-pentanol (7d), 2-methyl-3-hexanol (lOd), 3-ethyl-3-pentanol (12m), and 2-methyl-2-hexanol (13d). Merged is indicated by m discrete is indicated by d. Reprinted from [22], with kind permission from J.Tan...
Khayet and Matsuura (2004) studied the separation of chloroform-water mixture via PVDF flat membrane by using both PV and VMD techniques. Both PV and VMD membranes were prepared using the phase inversion method and the same polymer material. VMD membranes with different pore sizes were prepared using pure water as a pore-forming additive in the PVDF/dimethylacetamide (DMAC) casting solution, whereas PV membranes were obtained with higher polymer concentration, without nonsolvent additives (water) and with solvent evaporation before gelation. A comparative study was made between both. [Pg.280]

Formation of physical gels from aqueous PVA solutions may also occur by impairing the thermodynamic quality of the solvent as a result of the introduction of nonsolvent additives [4, 5, 45]. However, in all cases, the so-obtained thermore-versible PVA gels possess low melting temperatures (T < 30-40 °C), low mechanical strength, and they are not able to retain their size and dimensions for a long time. [Pg.174]

Methods are also available for rapidly estimating polymer molecular weight distribution. These methods include swelling, in which the amount of polymer precipitated vs nonsolvent added gives a cumulative distribution curve (i.e., higher molecular weights first precipitate out with nonsolvent addition) and tur-bidimetric titration, which uses turbidity induced by nonsolvent addition as a measure of molecular weight distribution. These methods are described in detail in Ref. 28. [Pg.24]

As can be seen from the above description, there are many variables involved in the phase-inversion technique. Among others the composition of the polymer solution, the solvent evaporation temperature and evaporation period, the nature and the temperature of the gelation media, and the heat treatment temperature are the primary factors affecting the reverse osmosis performance of the membrane. When polymers other than cellulose acetate are used, solvents and nonsolvent additives appropriate to prepare membranes from the particular polymer must be found. Depending on the combination of variables, membranes of different polymeric materials with different pore sizes can be prepared. [Pg.50]

Modification of polymeric membrane materials through incorporation of hydrophi-licity results in membranes with low fouling behavior and high flux. Thus, literature presents sulfonated polysulfone/cellulose acetate blends applied in various compositions for obtaining ultrafiltration membranes, where their performance is improved by the inclusion of polyethyleneglycol into the casting solution as a nonsolvent additive in various concentrations. In this way, total polymer concentration, cellulose acetate, sulfonated polysulfone polymer blend composition, additive concentration, and their compatibility with polymer blends are optimized [133]. [Pg.376]

Tomaszewska (1996) studied the variation of the LEP of the laboratory-made PVDF membranes with the LiCl concentration in the polymer casting solution. As can be seen in Figure 12.12, the PVDF membranes prepared with higher amounts of FiCl exhibited lower values of FEP due to their larger pore size. Similar results were obtained by Khayet and Matsuura (2001) for the supported and unsupported PVDF membranes prepared with the same solvent (DMAC) and water as a nonsolvent additive. [Pg.323]

Khayet et al. (2004c) were the first to characterize MD membranes by AFM. The mean pore size, pore size distribution, surface porosity, pore density, and roughness parameters of the prepared PVDF membranes for MD with the phase inversion method were determined. The membranes were prepared with different amounts of nonsolvent additive... [Pg.329]

Khayet, M., Feng, C. Y., Khulbe, K. C., and Matsuura, T. (2002b). Study on the effect of a nonsolvent additive on the morphology and performance of ultrafiltration hoUow-iiber membranes. Desalination 148, 321. [Pg.364]

Even with negative values of AGm, negative values of eqn [2] will yield an area of the phase diagram where the polymer-solvent mixture will separate into a polymer-rich phase and a solvent-rich phase. Temperature changes can result in phase separation as well as nonsolvent addition. Although polymer-polymer blends often exhibit lest (lower aitical solution temperature) behavior, polymer-solvent systems usually exhibit ucst (upper critical solution temperature) behavior. [Pg.328]

Although there are many types of membranes employed in various gas separation and water purification processes, similar membrane formation processes are often employed. The phase inversion process promoted by nonsolvent addition and the thermal phase separation process based on the fundamentals discussed above are the most prevalent processes to produce membranes. In addition to References 20-22,References 25-31 " also discuss these processes, and therein applications are covered in more detail than will be attempted in this chapter. [Pg.329]

PVDF hollow-fiber membranes were prepared through TIPS from dopes containing GTA as diluent and glycerol or PEG as nonsolvent additives [130,131]. The prepared PVDF hollow-fiber membranes were tested as gas-liquid MCs for CO2... [Pg.29]

FIGURE 7.10 Shear and elongation viscosities as a function of shear and elongation rates for PVDF/NMP solutions with different nonsolvent additives. (Data from P. Sukitpaneenit and T.S. Chung, J. Memb. ScL, 340, 192-205, 2009.)... [Pg.231]

Ceramic hollow-fiber support can be fabricated by a phase inversion-based extrusion/sintering technique [3], which allows a more flexible control over the membrane macro/microstructures by adjusting fabricating parameters such as air-gap, extrusion rate, internal coagulant composition, and the amount of nonsolvent additive in the spinning suspensions [4]. Such unique structural diversity delivers... [Pg.349]

Cloud point of a polymer dope is simply a temperature or composition where the dope becomes no longer homogeneous and turns cloudy due to phase separation. In NIPS, cloud points are usually determined by a titrimetric method that examines the amount of nonsolvent required to make the dope cloudy [166,167]. In this method, the droplets of nonsolvent are slowly added into a polymer dope until permanent turbidity is visually observed in the dope. Frequently, repeating cycles of heating and cooling are involved due to the occurrence of local gelation upon nonsolvent addition. [Pg.552]

It should be however kept in mind that the membrane preparation procedure could influence its structure and gas transport properties. Thus, casting of the integrally skinned asymmetric membranes from p-DMePO solution using different nonsolvent additives produced the nodule structures in the surface skin layer of the membranes, which affected the permeance ratios for O2/N2 and CO2/CH4 [72]. In the homogeneous films of polyphenylene oxides considered in this chapter such structures apparently do not exist. [Pg.44]

Effect of nonsolvent additives in the membrane casting solutions on the performances of PPO asymmetric membranes... [Pg.125]


See other pages where Nonsolvent addition is mentioned: [Pg.199]    [Pg.220]    [Pg.1127]    [Pg.107]    [Pg.98]    [Pg.108]    [Pg.781]    [Pg.168]    [Pg.3353]    [Pg.371]    [Pg.147]    [Pg.200]    [Pg.312]    [Pg.313]    [Pg.215]    [Pg.223]    [Pg.223]    [Pg.224]    [Pg.230]    [Pg.231]    [Pg.240]    [Pg.296]    [Pg.296]    [Pg.549]    [Pg.732]    [Pg.8]    [Pg.125]   
See also in sourсe #XX -- [ Pg.15 , Pg.17 ]




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