The effect of polydispersity on the conversion kinetics of starch oxidation and depolymerisation

Biobased feedstocks offer a potent source of building blocks for biobased products. However, these feedstocks (e.g. starch, cellulose) are generally highly polydisperse in molecular weight. To study the effect of polydispersity on conversion kinetics, the influence of molecular size on the oxidation and depolymerisation rates of starch was investigated. Kinetic experiments for the homogeneous TEMPO/hypochlorite catalysed oxidation of amylopectins with different molecular sizes showed that large starch molecules oxidise and depolymerise at a higher rate than small molecules. In addition, increasing degrees of oxidation inhibit the rate of further oxidation exponentially. These results demonstrate that polydispersity is an important factor in the conversion of these feedstocks. A model was formulated that assigns individual kinetic parameters to starch fractions of different molecular weight and degree of oxidation. The model predicts 2-D product distributions over molecular weight and degree of oxidation, and predicts asymmetrical distribution shifts as a result of substrate polydispersity.

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