This study aimed at the influence of native starch blend composition on the functional properties of thermoplastic starch (TPS) films processed by extrusion, using maize (MS), cassava (CS), and potato (PS) starches as components. A simplex-centroid mixture design was applied to systematically evaluate the effects of starch proportions on the physicochemical, thermal, and mechanical behavior of the films. The blends were processed by single-screw extrusion using water (10 phr) and glycerol (35 phr) as plasticizers. The materials were characterized by X-ray diffraction, thermogravimetric analysis, moisture uptake measurements, and tensile testing. The results showed that crystallinity ranged from 8.7 to 14.4%, tensile strength from 1.78 to 5.82 MPa, and elongation at break from 21.61 to 111.67%, depending on the composition of the blend. Potato starch improves the crystallinity, rigidity, and thermal stability of TPS, while cassava starch improves elasticity and increases moisture absorption capacity (up to 53.31%). Statistical modeling showed that the results exhibit non-linear responses and that synergistic and antagonistic effects occur among the starches. The results indicate that the system does not follow a linear rule of mixtures. The results show that differences in molecular architecture, such as the amylose/amylopectin ratio, contribute to differences in molecular rearrangement during extrusion. The results provide new insights into structure-property relationships for thermoplastic starch (TPS) systems and show that blending native starch is a successful method for improving properties for biodegradable films.
Milfont et al. (Fri,) studied this question.