Aerobic Biodegradation at a Seawater-Sediment Interface of a New Bioplastic 100% Based on Natural Polymers

Bioplastics are a family of sustainable materials, trying to substitute for fossil-based plastic. Despite their growing expansion over the past decade, there are many scientific concerns about their biodegradability, especially if they are accidentally released into the environment. This is because biomass-based bioplastics are in general composed of blended polymers in which the blending material can come from fossil sources or cannot be biodegradable. Furthermore, the production of bioplastics (BPs) is generally made from first generation raw materials that represent food crops. This may generate critical ethical and environmental issues. To avoid these issues, in the last 20 years, many new materials have been developed starting from many different byproducts to valorize biomass. However, in most cases, the percentage of waste in the final BP formulation is very low since they are only added as additives to other BPs. Proteins are a family of natural polymers that have intrinsic plastic properties, so they can be produced without blending with other fossil-based polymers. In this work, a protein-based BP produced from milk (SP Milk®), already tested for biodegradability in soil and compostability in a home composter, was tested for biodegradability at the natural seawater-sediment interface according to ISO 19679:2020 measuring evolved CO2. The aim of this work is to acquire general and preliminary results regarding how much biodegradable a BP 100% based on natural polymers would be in a simulated marine ecosystem. This is very important in view of the recent EU directive in single-use plastics, which admits to this aim only materials based on natural polymers not chemically modified. Our results show that a hypothetical transient anoxia occurred at the beginning of the experiment and that an 83% biodegradation was achieved in 52 days. This adds fundamental information on the aquatic behavior of BPs based only on natural polymers, in particular proteins, which is totally lacking, and encourages the development of those kinds of materials.