A Simple Acid Soak Turns Food Waste Into Plastics

Researchers report a simple method to convert food waste into cellulose-based plastics of varying thermal and mechanical properties (Macromolecules 2014, DOI: 10.1021/ma5008557).

Most synthetic plastics have environmental concerns: They’re petroleum-based; they can’t biodegrade; or they potentially contain toxic compounds such as phthalates. Ilker S. Bayer, Athanassia Athanassiou, and their colleagues at the Italian Institute of Technology have sought ways to make plastics from biomass so that the materials are renewable, biodegradable, and possibly less toxic. One potential feedstock is cellulose, which, as a component of plant cell walls, is nature’s most abundant renewable polymer.

In their new plastic-making method, the researchers turned to a technique that’s normally used to break down cellulose into simpler sugars for biofuel production: soaking the material in acid. Because the researchers only wanted to break apart the cellulose’s crystalline structure—and not convert it into simple sugars—the team used trifluoroacetic acid (TFA), which isn’t as strong as acids used in biofuel applications.

The team used TFA to soak inedible waste from four food crops: spinach, rice, cocoa beans, and parsley. After several days of soaking, the researchers removed the volatile acid, yielding plastic coatings and films with a variety of mechanical properties. These materials have tensile strengths similar to synthetic polymers such as polyethylene terephthalate and polyethylene, the researchers say. The plant-waste plastics start to thermally degrade at temperatures between 150 and 300 ºC, which is similar to the range for synthetic polymers.