CONFORMATION-DEPENDENT DEPOLYMERIZATION KINETICS OF POLYSACCHARIDES STUDIED BY VISCOSITY MEASUREMENTS

Degradation of single- and multiple-stranded polysaccharides by acid h ydrolysis or free radical depolymerisation with H2O2/Fe2+ was monitore d by viscosity measurements. Single-stranded polysaccharides (alginate , hydroxyethyl cellulose, carboxymethyl cellulose and kappa-carrageena n in its disordered conformation) gave the expected linear relationshi p between 1/eta(sp)((1/a)) and the degradation time, where a is the Ma rk-Houwink-Sakurada exponent. Double-stranded xanthan and triple-stran ded scleroglucan showed a different pattern. Following an initial peri od with apparently slow degradation, a second regime was entered where the apparent degradation rate was much higher, and where eta(sp) foll owed the power law, eta(sp) similar to t(-vu). However, the estimated values of the parameter nu differed from those calculated by a Monte C arte method for double- (xanthan) and triple- (scleroglucan) stranded polymers. kappa-Carrageenan in its iodide-induced ordered conformation was very stable in acid as compared to the disordered conformation. I n the ordered state the apparent degradation rate was initially consta nt, but increased in later stages. However, the double-logarithmic plo t of eta(sp), versus time showed that there was neither a pronounced s table regime nor a regime following the power law. The degradation of gellan resulted in a rapid and linear increase in 1/eta(sp), With degr adation time, both in the ordered and disordered conformation. The sam e type of degradation kinetics was obtained for welan.