Thermoplastic starch (TPS) films are considered one of the most promising alternatives for replacing synthetic polymers in the packaging field due to the starch biodegradability, low cost, and abundant availability. However, starch granule composition, expressed in terms of amylose content and phosphate monoesters, and molecular weight of starch clearly affects some film properties. In this contribution, biodegradable TPS films made from potato, corn, wheat, and rice starch were prepared using the casting technique. The effect of the grain structure of each starch on microstructure, transparency, hydration properties, crystallinity, and mechanical properties of the films, was evaluated. Potato starch films were the most transparent and corn starch films the most opaque. All the films had homogeneous internal structures—highly amorphous and with no pores, both of which point to a good starch gelatinization process. The maximum tensile strength (4.48–8.14 MPa), elongation at break (35.41–100.34%), and Young’s modulus (116.42–294.98 MPa) of the TPS films were clearly influenced by the amylose content, molecular weight, and crystallinity of the film. In this respect, wheat and corn starch films, are the most resistant and least stretchable, while rice starch films are the most extensible but least resistant. These findings show that all the studied starches can be considered suitable for manufacturing resistant and flexible films with similar properties to those of synthetic low-density polyethylene (LDPE), by a simple and environmentally-friendly process.

Highlights: -Biodegradable potato starch/PVA/rosin blends were developed.  -Addition of rosin to the blends improves mechanical properties substantially.  -Mechanical properties are comparable to those offered by polymers such as LDPE.  -Starch/PVA/rosin blends could be interesting materials for packaging applications. AbstractBiodegradable potato starch/PVA samples containing different concentrations of rosin were prepared by melt-mixing in order to study the enhancement of the properties of native starch films. Glycerol and polyvinyl alcohol (PVA) are commonly used as plasticizers of starch. Their relatively low molecular weight (compared with starch) contributes to a good processability. Rosin is a renewable product whose incorporation in the starch/PVA matrix induces processing aid and reinforcing effects. Its relatively high molecular weight might prevent its migration to the surface of the final product.Water content, solubility in water, mechanical properties, microstructure and dynamic mechanical analysis of the samples were studied. The addition of 8% rosin to starch/PVA blends led to tensile strength values higher than 10 MPa and elongation at break values close to 2000%, values comparable to those offered by conventional polymers used in food packaging, for example LDPE. Furthermore, starch compounds have low cost and high biodegradability.

Starch films are gaining attention as substitutes of synthetic polymers due to their biodegradability and low cost. Some ionic liquids have been postulated as alternatives to glycerol, one of the best starch plasticizers, due to their great capacity to form hydrogen bonds with starch and hence great ability of preventing starch retrogradation and increasing film stability. In this work, [emim + ][Ac-]-plasticized starch films were prepared from potato, corn and wheat starch. The effect of starch molecular structure in terms of granular composition (amylose and phosphate monoester contents) and molecular weight (Mw) on film properties was evaluated. Potato starch films were the most amorphous because of the higher Mw and phosphate monoester content of potato starch, both contributing to a lower rearrangement of the starch chains difficulting the crystallization process. In contrast, corn and wheat starches lead to more crystalline films because of their lower Mw, which may imply higher mobility and crystal growth rate, and lower phosphate monoester content. This more crystalline structure could be the responsible of their better mechanical properties. [emim + ][Ac-] can be considered suitable for manufacturing starch films showing corn and wheat starch films similar properties to synthetic low-density polyethylene, but involving a simple and environmentally-friendly process.

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