Environmentally friendly, biodegradable biopolymers can be prepared via the chemical modification of starch. These biopolymers are able to partially or totally substitute synthetic additives used today in the chemical or environmental technologies. Through the building of ionic function groups into polymeric chains of the starch ion exchangers, flocculants or dispersants can be produced. In this paper, we examine water-soluble ionic derivatives called polyelectrolytes. By phosphorylating starch while preserving or maybe increasing the molecular weight of the native starch polymers, anionic flocculating agents can be prepared. If the polymer chains degrade during the reaction, the products will act as dispersing agents in aqueous suspensions. It is apparent that, during the phosphorylation reaction, the changes in the molecular weight distribution and the ionic charge of the polymers have crucial importance. In our experiments, we investigated the solid-phase reactions by following the change in the molecular weight distributions, using size exclusion chromatography, and the change in the charge densities, using a particle charge detector. The efficiency of the products was tested in the laboratory, and the results were evaluated by means of severity parameters.

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Experiments were carried out to produce biodegradable flocculants by phophorylation and heat treatment of corn starch at elevated temperatures in the dry state. The temporal change of molecular weight distribution was measured by HPSEC/MALLS/RI. To elucidate the mechanism and kinetics of degradation during this treatment a Markov-chain stochastic model was used. For this, five molecular weight intervals were defined between >32 × 10 6 and 2 × 10 6 Da with exponentially decreasing spans. The probabilities of mass fraction transitions among these intervals at different processing temperatures were determined by fitting the calculated molecular weight distributions to the experimental data. Examining the transition probabilities between various MW intervals, it was concluded that degradation took place gradually by multiple splits of molecules, resulting in stepwise transition of fragments from higher intervals to lower ones. From the values of the transition probabilities between different molecular weight intervals, and considering the evolution of molecular weight distributions during the process, it was concluded that an end-scission mechanism did not play a role in the studied system under the applied conditions. The degradation probability of starch molecules diminished with decreasing molecular weight and increased with the temperature of treatment. These dependences were described by an exponential relationship.