Characterisation of the Substituent Distribution in Starch and Cellulose Derivatives

Sammanfattning: Starch and cellulose can be chemically modified to produce derivatives with specific properties. Knowledge of correlations between the modification reaction, substituent distribution and properties is important in order to design modification processes so as to produce derivatives with the desired properties. This thesis describes research on analytical methods for the determination of the distribution of substituents along the polymer chain in starch and cellulose derivatives. The methods are based on enzymic degradation of the polymer followed by separation and/or identification of the hydrolysis products. The enzyme action is hindered by the presence of substitution groups, resulting in a product spectrum different from that obtained with unmodified polymers. Substituted hydrolysis products, for which no standard compounds are available, are difficult to identify. Thus, various analytical techniques are needed to characterise the hydrolysates. The use of different enzymes enables different kinds of information to be obtained on the substituent distribution. Microdialysis coupled on-line to high-performance anion-exchange chromatography (HPAEC) was employed for sampling and sample clean-up of starch hydrolysates. The hydrolysis products obtained from enzymic degradation of cationic potato amylopectin starch were characterised using MALDI-TOF-MS and ESI-MS. Furthermore, HPAEC was coupled on-line to ESI-MS for the separation and identification of substituted mono- and oligomers released from the enzymic hydrolysis of hydroxypropylated potato amylopectin starch and ethyl(hydroxyethyl) cellulose. For correct interpretation of the results the degradation of the polymer must be defined, which requires knowledge of the enzyme action on the derivatives. Information on the hydrolytic properties of the enzymes used was provided by MALDI-TOF-MS and ESI-MS analysis of the enzymic hydrolysates. Starch modified under homogeneous and heterogeneous conditions was studied. The results obtained from analysis of the substituent distribution were evaluated with respect to the modification reaction. Heterogeneously modified starch was shown to have a more heterogeneous substituent distribution than starch modified in a homogeneous reaction phase.