A COMPARATIVE-STUDY OF THE POLYMERIZATION OF ACRYLIC-ACID WITH NATIVEAND HYDROLYZED MAIZE STARCHES USING A POTASSIUM BROMATE THIOUREA DIOXIDE REDOX INITIATION SYSTEM

Polymerization of acrylic acid (AA) with native and hydrolyzed maize s tarches was carried out via a potassium bromate-thiourea dioxide redox initiation system. The factors affecting the efficiency of the redox system and, in turn, the polymerization process were studied. These fa ctors included the concentrations of AA, KBrO3, thiourea dioxide (TUD) (and equimolar ratio of the latter two), polymerization temperature a nd the extent of starch hydrolysis. The behaviour of the apparent visc osity of the cooked poly(AA)-starch composite paste, obtained under di fferent polymerization conditions, was also studied. The polymerizatio n reaction was monitored via the determination of the total percentage conversion (% TC) of AA. The poly(AA)-starch composite was evaluated by calculating the polymer yield, namely the graft yield (% GY), the g rafting efficiency (% GE), the percentage homopolymer (% HP) and the t otal conversion. Results obtained indicated that the optimum condition s, expressed as percent of total conversion are: (a) with native starc h (NS): (KBrO3), 6 mmol/100 g NS; (TUD), 7.4 mmol/100 g NS; (AA), 30% of weight of starch; polymerization temperature, 50 degrees C; and pol ymerization time 30 min. (b) With hydrolyzed starch (HS): (KBrO3), 4 m mol/100 g HS; (TUD), 4 mmol/100 g HS; (AA), 30%; polymerization temper ature, 40 degrees C; and polymerization time, 30 min. The results also indicated that, for a given rate of shear, while the apparent paste v iscosity of the poly(AA)-NS decreases with increasing concentration of KBrO3, TUD, and AA (within the studied range), it increases with incr easing polymerization temperature from 30 to 50 degrees C. Regardless of the polymerization conditions used, the apparent viscosity of NS is higher than that of the poly(AA)-NS composite. On the other hand, the apparent viscosity of the poly(AA)-HS (hydrolyzed starch) composite d epends upon the extent of hydrolysis of the starch used as well as the polymerization conditions.