Rheological Properties of Thermoplastic Starch and Starch/Poly(ethylene-co-vinyl alcohol) Blends

M.A. VILLAR; E.L. THOMAS; R.C. ARMSTRONG

POLYMER

ELSEVIER SCI LTD

Lugar: Amsterdam; Año: 1995 vol. 36 p. 1869 - 1876

0032-3861

Blends consisting of a systematic compositional series of starch/poly(ethylene-co-vinyl alcohol) were studied by using capillary viscometry. Three different types of starches were used: waxy maize, a starch containing essentially 100% amylopectin; native corn, possessing approximately 70% amylopectin and 30% amylose; and a treated, high-amylose starch, consisting of approximately 30% amylopectin and 70% amylose. Poly(ethylene-co-vinyl alcohol) with 44 mol% ethylene was blended in varying proportions with the starches, and glycerine and water were added as plasticizers. The viscosity of the blends was measured over the shear-rate range l-1000 s-l. Samples unconditioned (as stored) as well as conditioned at 65% relative humidity and 23°C were measured at temperatures between 140 and 170°C. All viscosity results fall in the power-law regime, and there is no indication of approach to a zero-shear-rate viscosity in any of the starch blend systems. As in starch-based food materials, the viscosity has an Arrhenius dependence on temperature, an exponential dependence on moisture content and a power-law dependence on shear rate. The power-law exponents from the starch blends are less than unity, indicating that the melts are shear thinning. Results on the starch/poly(ethylene-co-vinyl alcohol) blends indicate that the viscosity decreases with decreasing amylose content or increasing poly(ethylene-co-vinyl alcohol) content. The shear-rate dependence increases with an increase in the amylose content of the blends.