Evaluation of the entanglement molecular weights of maize starches from solution rheological measurements

The entanglement molecular weights of waxy maize (WM) and normal maize (NM) starches were calculated from solution rheological data. The viscoelastic behavior of both WM and NM starches were measured at several different concentrations and then shifted to produce a master curve for each of the materials. The theory of Doi and Edwards was used to calculate the plateau moduli from which values for the entanglement molecular weights for WM and NM starches were calculated. The entanglement molecular weights were 100 +/- 15 kg/mol for WM starch and 96 +/- 8 kg/mol for NM starch. These two values were within experimental error of one another and represent the entanglement molecular weight of amylopectin, the major component of WM and NM starches. The entanglement degrees of polymerization for WM and NM starch, using a value of 162 g/mol for the monomer molecular weight of amylopectin, were 617 +/- 92 and 592 +/- 49, respectively. The values for the entanglement molecular weight and the entanglement degrees of polymerization for WM and NM starch were markedly higher than those quoted for many commercial polymers. This finding indicates that molecular weights of >1 million are required to produce starch-based materials with consistent physical properties.