Influence of alkali and temperature on glucomannan gels at high concentration

The effect of type and concentration of alkali on 5 g/100 mL of glucomannan gels was examined in depth by mechanical and thermo-rheological analysis. Four KGM gels were made from aqueous glucomannan solutions deacetylated with 0.6 mol/L and 1 mol/L of KOH (A(0) and A(1)) and NaOH (B-0 and B-1), respectively. At 25 degrees C all physical networks were too tight and dense due to the large number of extended junction zones, as indicated by the high breaking force (BF), complex modulus (G*) and low strain amplitude (gamma(max)). The influence of alkali concentration was noticeable only in KOH gels, of which A(0) was significantly more elastic and time stable than A(1) over both short and longer-time scales. 0.6 mol/L KOH was the most suitable alkali, producing the most stable and homogeneous gel, with the highest level of connectivity, the lowest relaxation exponent (n) and the highest gel strength (S). Increasing temperature resulted in loss of elasticity in A(0), where gamma(max), G* and S decreased, and the loss factor (tan delta), creep and recovery compliances (J) and n increased. Thus, the networks become less flexible and more unstable at high temperatures, especially between 25 and 50 degrees C. (C) 2012 Elsevier Ltd. All rights reserved.