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.