Abstract:

A DHR-1 rheometer was used to determine the steady-state and dynamic rheological properties of oxidized
hydroxypropyl tapioca starch. The results showed the oxidized hydroxypropyl tapioca starch paste was a pseudoplastic
non-Newtonian fluid (n < 1) and the experimental data were fitted with Herschel-Bulkley model (R2 > 0.98). Increasing
carboxyl contents and hydroxypropyl molar substitution degree (molar substitution, MS) resulted in a decreased consistency
coefficient k and weakened non-Newtonian characteristics and the system tended to turn into a Newtonian fluid. Samples
exhibited a dominant elastic behavior over the entire amplitude range (1 × 10-4-1 rad). The storage and loss modulus of
samples varied slightly when the amplitude was increased. Increasing carboxyl contents and MS resulted in decreased
storage and loss modulus of samples and increased tanδ. The storage and loss modulus of samples increased and tanδ varied
slightly when the angular frequency was increased over the entire frequency range (0.1–12.5 rad). Increasing carboxyl
contents and MS resulted in decreased storage and loss modulus and increased tanδ of samples.

Key words: oxidized hydroxypropyl tapioca starch, rheological properties, Herschel-Bulkley model