Films for food packaging are usually made from petroleum-based polymers. Biodegradable starch-based materials could be a more sustainable and environmentally friendly alternative. However, starch is hydrophilic, which causes problems such as moisture uptake and a lack of mechanical strength. Adding rigid materials as a filler can improve the mechanical properties, but synthetic fillers can be harmful to human health and the environment.

Long Yu, South China University of Technology and Sino-Singapore International Joint Research Institute, both Guangzhou, China, and colleagues have developed biodegradable starch-based film reinforced with corn hulls (pictured right) or wheat hulls. The team prepared a starch solution and added 5 % of filler, i.e., granulated particles of either corn or wheat hulls. The resulting suspensions were cast into a dish and dried for six to eight hours at 37 °C to give the finished films with a thickness of about 0.15 mm (microscopic image of the corn-hull variant pictured left).

Compared to non-reinforced starch films, the addition of hulls improved the mechanical properties of the material. Additionally, the films were better at keeping out water vapor and showed improved protection against UV light. According to the researchers, the films are safe for food packing and might also be used for medicinal capsules.

• Preparation and characterization of starch-based composite films reinforced by corn and wheat hulls,
  Amjad Ali, Long Yu, Hongsheng Liu, Saud Khalid, Linghan Meng, Ling Chen,
  J. Appl. Polym. Sci. 2017.
  DOI: 10.1002/app.45159