PHASE SEPARATION IN XANTHAN SOLUTIONS

The effect of ethanol (Et), isopropanol (IP) and NaCl addition on xanthan gum (XG) separation from aqueous solution was investigated by turbidimetry at 25 degrees C. The turbidity started to increase in the presence of alcohols (above 10% Et and 5% IP), independently of the XG concentration in the initial aqueous solution. In contrast, the NaCl content, which determines an increase of the turbidity, was dependent on the XG quantity according to an established relationship. Upon addition of the alcohols, phase separation into a polymer-poor phase and a polymer-rich one (with gel-like behaviour) was observed for both XG/water/Et and XG/water/NaCl/IP systems. After one week at rest, the gel-like phase of XG/water/Et system was more structured compared to that of XG/water/NaCl/IP system, in which XG precipitate was observed. NaCl addition reduced the alcohol quantity required to determine the separation of XG due to the enhancement of the polymer-polymer interactions in the presence of salt. The reduced viscosity of XG/water/Et system, higher than those of XG/water/NaCl/IP (at a constant XG/NaCl ratio), has also confirmed that the XG chains present a more compact conformation in the presence of salt.