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CONFORMATION-DEPENDENT DEPOLYMERIZATION KINETICS OF POLYSACCHARIDES STUDIED BY VISCOSITY MEASUREMENTS

, , , , and . Carbohydr. Polym. 24 (4): 265 -- 275 (1994)

Abstract

Degradation of single- and multiple-stranded polysaccharides by acid hydrolysis or free radical depolymerisation with H2O2/Fe2+ was monitored by viscosity measurements. Single-stranded polysaccharides (alginate, hydroxyethyl cellulose, carboxymethyl cellulose and kappa-carrageenan in its disordered conformation) gave the expected linear relationship between 1/eta(sp)((1/a)) and the degradation time, where a is the Mark-Houwink-Sakurada exponent. Double-stranded xanthan and triple-stranded scleroglucan showed a different pattern. Following an initial period with apparently slow degradation, a second regime was entered where the apparent degradation rate was much higher, and where eta(sp) followed the power law, eta(sp) similar to t(-vu). However, the estimated values of the parameter nu differed from those calculated by a Monte Carte 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. In the ordered state the apparent degradation rate was initially constant, but increased in later stages. However, the double-logarithmic plot of eta(sp), versus time showed that there was neither a pronounced stable regime nor a regime following the power law. The degradation of gellan resulted in a rapid and linear increase in 1/eta(sp), With degradation time, both in the ordered and disordered conformation. The same type of degradation kinetics was obtained for welan.

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HJERDE1994
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