Big Chemical Encyclopedia

Chemical substances, components, reactions, process design ...

Articles Figures Tables About

Poly critical flocculation temperature

FIG. 13.14 Critical flocculation temperature of aqueous poly(vinyl acetate) dispersion stabilized by poly(oxyethylene) indicated by a sharp change in absorbance with temperature. (Redrawn with permission from D. H. Napper, in Colloid and Interface Science (M. Kerker, R. L. Rowell, and A. C. Zettlemoyer, Eds.), Academic Press, New York, 1977.)... [Pg.610]

Filler particles can be modified to decrease flocculation. Kaolin particles modified by a graft of poly(ethylene oxide) showed an increase in the upper critical flocculation temperature. Stabilization of particle dispersion was due to an enhanced steric stabilization." ... [Pg.262]

This can be achieved for stericaUy stabihsed suspensions, when the medium for the chains becomes a 0-solvent This occurs, for example, on heating an aqueous suspension stabilised with PEO or poly(vinyl alcohol) chains. Above a certain temperature (the 0-temperature), which depends on the electrolyte concentration, flocculation of the suspension will occur, and the temperature at which this occurs is defined as the critical flocculation temperature (CFT). [Pg.419]

Neville and Hunter [6] studied the flocculation of poly(methylmethacrylate) (PMMA) latex stabilised with poly(ethylene oxide) (PEO). Flocculation was induced by the addition of electrolyte and/or an increase in temperature. Figure 21.12 shows the variation of with increase of temperature at constant electrolyte concentration. In the figure, it can be seen that increased with increases of temperature, reaching a maximum at the critical flocculation temperature (CFT), and then decreased with further increase in temperature. The initial increase was due to the flocculation of the latex with increase of temperature, as the result of a reduction in solvency of the PEO chains with the increase in temperature. The... [Pg.457]

Experimental observation of selective flocculation. Croucher and Hair (1980a) have demonstrated the phenomenon of selective flocculation in mixtures of heterosterically stabilized dispersions. They prepared particles of poly(vinyl acetate) stabilized by polystyrene and polyacrylonitrile particles stabilized by polyisobutylene, both in cyclopentane. The value of X23 for polystyrene and polyisobutylene is known to be positive (Hyde and Tanner, 1968), corresponding to mutually incompatible polymers. The poly(vinyl acetate) particles stabilized by polystyrene exhibited both upper and lower critical flocculation temperatures whereas the polyisobutylene stabilized particles only flocculated on heating. [Pg.318]

When a mixture of the two different types of particles dispersed in cyclopentane was cooled to the lower critical flocculation temperature (280 K) of the poly(vinyl acetate) particles stabilized by polystyrene, those... [Pg.318]

For sterically stabilized suspensions, one can measure the incipient flocculation when the medium for the chains becomes a 0-solvent. This occurs, for example, on heating an aqueous suspension stabilized with poly(ethylene oxide) (PEO) or poly(vinyl alcohol) chains. Above a certain temperature (the 0-temperature) that depends on electrolyte concentration, flocculation of the suspension occurs. The temperature at which this occurs is defined as the critical flocculation temperature (CFT). This process of incipient flocculation can be followed by measuring the turbidity of the suspension as a function of temperature. Above the CFT, the turbidity of the suspension rises very sharply. For this purpose, the cell in the spectrophotometer that is used to measure the turbidity is placed in a metal block that is connected to a temperature programming unit (which allows one to increase the temperature raise at a controlled rate). [Pg.246]

Note that, as reported in Table 6.2, latices stabilized either by poly(a-methyl styrene) in -butyl chloride or by polystyrene in cyclopentane flocculated both on heating and on cooling. Moreover, the UCFT in nonaqueous systems tends to occur as the critical temperature of-the dispersion medium is approached. In aqueous systems, the UCFT can occur well below the critical temperature. [Pg.115]

The effect of molecular weight of the free polymer. Figure 16.5 presents the characteristic dependence of the critical volume fraction of free polymer required to induce flocculation as a function of the molecular weight of the added polymer. For the particles stabilized by poly(oxyethylene) 750, two different temperatures (25 °C and 45 °C) are shown. [Pg.362]


See other pages where Poly critical flocculation temperature is mentioned: [Pg.45]    [Pg.387]    [Pg.136]    [Pg.319]    [Pg.235]    [Pg.101]    [Pg.302]    [Pg.585]    [Pg.223]    [Pg.179]    [Pg.3717]    [Pg.7717]    [Pg.40]    [Pg.551]    [Pg.364]    [Pg.150]    [Pg.159]    [Pg.155]    [Pg.243]    [Pg.76]   
See also in sourсe #XX -- [ Pg.456 ]




SEARCH



Critical flocculation temperature

Critical temperatur

Flocculation temperature

Poly temperature

Temperature critical

© 2024 chempedia.info