Role of entanglement concentration in dynamic viscoelasticity and film-forming property of cereal starches.

Entanglement concentration (c, w/v) means the onset of overlap and interpenetration of random-coil chains in a macromolecule solution. The effects of c on the dynamic viscoelasticity and film-forming property of cereal starches were investigated. The results showed that c affected significantly the ratio of crystalline to amorphous regions of normal rice starch, waxy rice starch, normal maize starch and wheat starch because the absorbance ratio (1047cm/1022cm) increased more obviously at concentrations increasing from 0.1% to c. Storage modulus increased faster than loss modulus with increasing frequency. The presence of lower entanglement density and stronger mobility of the chain segments in normal rice starch due to the highest crossover, whereas the contrary is the case for waxy rice starch. But, no crossover point occurred in four cereal starch dispersions at concentrations <c. The normal maize and wheat starch dispersions at concentrations around c showed a Newtonian behaviour at low angular frequency, whereas it exhibited a shear-thinning behaviour at higher frequency. The normal rice and waxy rice starch dispersions exhibited a shear-thinning behaviour throughout the entire frequency. Four cereal starch films could only develop at concentrations ≥c. Comparatively, wheat and normal rice starches had good filming properties.