Influence of extrusion process conditions on starch film morphology

- The effect of screw speed on extruded thermoplastic starch materials were evaluated.
- The process at 80 rpm led to a material with the starch completely gelatinized.
- Materials processed at 40 rpm and 120 rpm showed broken grain starch.
- After pressing the thread made at 120 rpm, no broken grain starch is observed.
- TPS80 had the highest εb while TPS40 and TPS120 the best modulus and σb.

The conditions of extrusion process for food packaging are determinant on their morphology and, as consequence, on their functionality. The effect of the screw speed of a starch-glycerol system extruded at the same temperature profile was evaluated. The process at 80 rpm led to a material with the starch completely gelatinized, while the systems fabricated at 40 rpm and 120 rpm presented broken starch grains. The morphology and density of the broken grains depended on the screw speed. The material at 120 rpm showed broken grains with smaller size and lower concentration than that observed in the system at 40 rpm. After pressing at 120 rpm, the film formed (TPS120) resulted similar than that at 80 rpm (TPS80), while the film at 40 rpm (TPS40) kept some broken grains. TGA of the material obtained at 40 rpm showed more than one degradation process of the glycerol due to the inhomogeneous glycerol dispersion. DRX revealed more cristallinity in TPS40, being TPS120 the most amorphous. TPS80 had the highest strain at break while the others the higher modulus and stress at break. Water vapor permeability of TPS80 and TPS120 showed similar results and lower than TPS40.