Abstract:
Polyacrylic acid/gum arabic or polyacrylic acid/dextrin (PAA/GA or PAA/D) adducts were prepared by free radical polymerization of highly concentrated, partially neutralized AA using Na2S2O8/Na2S2O3 redox system in the presence of GA or D. Optimum reaction conditions, viz., AA, 6.76 mol/L; Na2S2O3, 26.87 X 10(-3) mol/L; Na2S2O8, 34.9 X 10(-3) mol/L; degree of neutralization, 20%; temperature, 90 degrees C; and time 30 min, were utilized in preparing two adducts of each substrate (GA or D) at two liquor ratios (LRs; 1.25/1 and 6.3/1 L/K). The four adducts formed, viz., PAA/GA,, PAA/GA, PAA/D,, and PAA/D-2 (where 1 and 2 refer to the low and high LR, respectively) were found to be water soluble at all proportions. IR spectrum of these adducts confirmed the introduction of the COOH group onto their structures. Rheological properties of 7%, aqueous solutions of these adducts, including Na-alginate (Alg), showed that all are characterized by a non-Newtonian, shear-thinning, thixotropic behavior. Within the range of shear rate studied, the apparent viscosities of these solutions followed the descending order: PAA/D2 > PAA/D-1 > Alg > GA(1) = PAA/GA(2). Completing neutralization (Na form) of adducts to 100% results in a remarkable enhancement of their apparent viscosities, so that they follow the descending order, depending on the shear rate:
At 2 s(-1) shear rate: PAA/D-2 > PAA/D-1 = PAA/GA(1) > PAA/GA(2) > Alg
At 18.89 s(-1) shear rate:PAA/D-2 > PAA/D-1 = PAA/GA(1) > Alg >= PAA/GA(2)
At 40 s(-1) shear rate:PAA/D-2 > PAA/D-1 = PAA/GA(1) > PAA/GA(2) = Alg
(c) 2006 Wiley Periodicals, hic.
