Acetylated and native corn starch blend films produced by blown extrusion

Thermoplastic starch (TPS) materials were developed from mixtures of native and acetylated corn starches with glycerol. To optimize the formulations an experimental design for multicomponent mixtures was used and the assayed formulations were determined by statistical software. Blends and pellets humidity content increased with glycerol concentration. Starch destructuration during the extrusion process was studied by thermal analysis. Films presented homogenous structure, rough surfaces and certain stickiness. They presented different properties, related mainly to the differential characteristics of native and acetylated starches and to hydrophilic character of glycerol. Their mechanical behavior indicated that they are a good option as a food packaging materials since TPS films resulted enough resistant to protect the product and flexible to resist moderate deformations. Besides, the use of acetylated starch in the formulations enhanced film resistance and reduced their WVP, despite of its low modification degree. The storage of the films under controlled conditions increased their stiffness, while their flexibility and WVP were reduced. Plasticizer migration towards the matrix surface was observed in stored films. Films resulted stable till aw = 0.7 and due to their selective gaseous permeability they are useful to package products susceptible to oxidation or to control vegetable respiration and senescence.

► TPS were developed by optimizing blending mixtures and extrusion conditions.
► Blowing technique allows obtaining TPS films from statistical designed formulation.
► Films presented homogenous structure, rough surfaces and certain stickiness.
► Acetylated starch enhanced film resistance and reduced their WVP.
► Storage increased film stiffness and reduce their flexibility and WVP.