Patent attributes
A biodegradable packaging film is provided. The film is formed from a blend that contains a thermoplastic starch and polylactic acid. Starch is a relatively inexpensive natural polymer that is also renewable and biodegradable. Polylactic acid is likewise an inexpensive synthetic polymer that is biodegradable and renewable, yet also capable of providing increased tensile strength to the film. Although providing a good combination of biodegradability/renewability and increased tensile strength, the polylactic acid is also relatively rigid and can result in films having a relatively high stiffness (e.g., high modulus of elasticity) and low ductility. While more ductile than polylactic acid, the thermoplastic starch is often difficult to melt process in film forming processes and very sensitive to moisture and water vapor, reducing its ability to be used as a stand alone packaging film. In an effort to counteract the effect of such polymers, an aliphatic-aromatic copolyester is also employed in the blend of the present invention. While such copolyesters are biodegradable, they also possess the melt properties and ductility that lend them well to the formation of films. Although the combination of these polymers may achieve a good balance between biodegradability/renewability, high tensile strength, and good ductility (e.g., high peak elongation), it is still often difficult to achieve a precise set of mechanical properties as desired for packaging films. In this regard, the blend also contains a filler. Due to its rigid nature, the amount of the filler may be readily adjusted to fine tune the blend to the desired degree of ductility (e.g., peak elongation) and stiffness (e.g., modulus of elasticity).
