The impact of functional additives on biodegradable plastic biodegradation in natural terrestrial and composting environments

Biodegradable plastics show promise in addressing traditional plastic waste issues. However, most commercially available biodegradable plastic products are blended/composite materials, combining biodegradable polymers with other polymers, fillers and additives. Non-reactive functional additives, such as plasticizers and stabilizers, raise concerns due to potential leaching as well as release on degradation. Thus, understanding how these additives affect biodegradation rates and processes is crucial, and a comprehensive overview is missing in the literature. This review highlights that the localized additive concentration levels adjacent to the plastic materials could, at least for a time, exceed the threshold concentrations for substantial impacts on microbial activities, especially in slow transport media such as soil and compost. Of the available literature, it is concerning that only a small fraction reported continuous quantitative biodegradation data with sampling frequency and duration adequate for comprehensive data synthesis. In those studies, the presence of additives resulted in an extended lag time for biodegradation compared to virgin polymer. Interestingly, additives also typically increased the biodegradation rate following this initial lag time. Overall, variation was observed in the half-life of biodegradable polymer/additive blends when considering both lag time and biodegradation rate. The likely key controlling factors dictating how additives impact biodegradable plastics biodegradation include the rate of additive leaching, alterations in polymer properties induced by additives and their leaching, and the intrinsic characteristics of the additives themselves. Future life cycle analysis and environmental impact assessments of new bioplastic products must consider the influence of additives.