Stress growth function in shear and dynamic viscoelastic properties of blends of corn starch with ethylene-co-vinyl acetate, EVA, and maleic anhydride modified ethylene-co-vinyl acetates, EVAMA, containing 28% and 18% vinyl acetate were studied at 180°C with different starch contents. Shear stress growth function data could be obtained at low shear rates only (0.005 to 0.5 s-1). The transient data at 0.1 s-1 indicated that the viscosity-composition curve of these blends goes through a maximum. The transition behavior of the blends was studied with dynamic mechanical analysis and the melting behavior was investigated using a differential scanning calorimeter. The dynamic data indicated that the storage and loss modulus increased with increased starch content. The relaxation processes of the blends were analyzed with a weighted relaxation spectrum computed from the dynamic data. The emulsion model of Choi and Schowalter with the modifications introduced by Gramespacher and Meissner was applied to the blends. Assuming the validity of the model to a relatively dilute composition blend (starch (20)/EVA(80)), dynamic data for corn starch were determined. The emulsion model predicted the dynamic properties of incompatible blends well. The dynamic data for corn starch computed from the emulsion model was used to predict the viscoelastic behavior for the reactive compatibilized blends (i.e., with EVAMA) and were compared with the experimental data.
|Original language||English (US)|
|Number of pages||11|
|Journal||Polymer Networks and Blends|
|State||Published - 1997|