Xanthan temperature, effect

The effect of water soluble polymers on the phase behavior of the anionic mlcroemulslon system was studied as a function of surfactant H/L properties. The cloud point temperatures for the neat mlcroemulslons and those containing 1500 ppm HPAM, partially hydrolyzed polyacrylamide, and 1000 ppm Xanthan gum are given In figure 4. The addition of either xanthan blopolymer or HPAM results In an Increase In the cloud point temperature of the mlcreomulslon. Both polymers have similar Interactions with the mlcroemulslon. Again one observes a lipophilic shift of the mlcroemulslon system Indicative of a repulsive interaction between the polymer and these anionic surfactants. 

Rochefort, W. E. and Middleman, S. 1987. Rheology of xanthan gum salt, temperature and strain effects in oscillatory and steady shear experiments. J. Rheol. 31 337-369. 

Walkenstrom, P., Panighetti, N., Wrndhab, E., and Hermansson, A. M. 1998. Effects of fluid shear and temperature on whey protein gels, pure or mixed with xanthan. Food Hydrocolloids 12 469-479. 

Exposure to temperatures as high as 80 C for extended periods has little effect on the viscosity of xanthan gum solutions. This resistance to thermal degradation is enhanced by the presence of... 

The formation of a weak bond between the metal and xanthan molecule is not expected to increase the thermal stability of the gel beyond that of xanthan. Since thermal stability of xanthan gum limits its application to temperatures below 80°C (176°F) , the effectiveness of this gelling system at temperatures above 80 C, is questionable. ... 

A few studies considered the effect of pH on the viscosity of xanthan solutions. Jeanes et al. observed a rapid increase in the viscosity of xanthan solution at pH 9-11 [28]. Whitcomb and Macosko [29] and Philips et al. [30] found the viscosity of xanthan to be independent of pH. Szabo examined the stability of various EOR polymers in caustic solutions at room temperature, including Kelzan MF (a biopolymer) [6]. He found a fast initial drop in the viscosity of a xanthan solution containing 2 wt% sodium chloride and 5 wt% sodium hydroxide, at 12.5 s", which virtually stopped after 10 days. Krumrine and Falcone found that the effect of alkali (sodium silicates) on the viscosity of xanthan solution depended on the concentration of sodium and calcium ions present [31]. Ryles examined the thermal stability of bio-polymers in alkaline conditions [16]. He found that xanthan was totally degraded (in anaerobic conditions) upon the addition of 0.8 wt% sodium hydroxide at temperatures from 50 to 90°C (in a 1 wt% sodium chloride brine). Seright and Henrici observed total biopolymer degradation at pH > 8 and a temperature of 120°C [26]. 

Rochefort, W. E. and S. Middleman, Rheology of Xanthan Gum Salt, Temperature, and Strain Effects in Oscillatory and Steady Shear Experiments J. Rheol. 31, 337-369 (1987). 

As well as the physical mechanism which may affect the degradation of biopolymer at elevated temperatures. Ash et al. (1983) discuss a number of other mechanisms including hydrolytic, free-radical and enzymatic mechanisms. With reference to the hydrolytic stability of xanthan. Ash et al. (1983) noted that the acetate group in xanthan is removed very readily at pH 12 even at room temperature. They also noted that a lower acetate content of xanthan has the effect of lowering the transition temperature. It has previously been reported that the viscosity of xanthan solutions is either increased (Jeanes et al, 1961) or is almost unaffected (Nisbet et al, 1982) by this loss of acetate groups. Ash et al (1983) concluded that the effect on solution viscosity of the loss of acetate may indeed be small but the... 

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