H. Iyer, P. Grandgeorge, A.M. Jimenez, I.R. Campbell, M. Parker, M. Holden, M. Venkatesh, C. Quiroz-Arita, E. Roumeli
University of Washington,
Keywords: algae, bioplastics, biodegradable, recyclable, mechanical properties
Summary:Since the mid-1900s, 8.3 billion tonnes (Bt) of virgin plastics have been produced, of which around 5 Bt have accumulated as waste in oceans and other natural environments, posing severe threats to ecosystems and habitats. The need for sustainable bio-based alternatives to traditional petroleum-derived plastics is evident, but bioplastics produced from unprocessed biological materials have thus far suffered from weak mechanical properties due to non-cohesive morphologies. This, combined with a lack of processability, hinders the industrial integration of biological materials without intensive processing methods. Here, a simple and scalable process is presented to transform raw microalgal cells into a self-bonded bioplastic with mechanical properties comparable to those of traditional commodity plastics (e.g., polypropylene or polystyrene), with the added properties of recyclability and backyard-compostability. Upon hot-pressing, the abundant and photosynthetic algae spirulina forms cohesive bioplastics with flexural modulus and strength in the range 3-5 GPa and 25.5-57 MPa, respectively, depending on pre-processing conditions and the addition of nanofillers. The resulting bioplastics are machinable and self-extinguishing in flame, making them promising candidates for consumer plastics. These bioplastics can also be mechanically recycled through grinding and re-pressing, and they degrade quickly in soil, presenting two end-of-life options for products made from spirulina cells. Finally, the benefits to the environment of using a carbon-negative feedstock such as spirulina to fabricate plastics is highlighted, using global warming potential to characterize the environmental impacts.