Biodegradation of PHBV-based biocomposites in two different marine environments of the Mediterranean Sea

Plastic pollution has become one of the most pressing environmental issues worldwide, with large amounts of conventional plastics accumulating in terrestrial and marine ecosystems due to their persistence and ineffective waste management. Developing and understanding the biodegradation behavior of environmentally friendly alternatives, such as bioplastics, is therefore crucial to mitigate this problem. In this context, the degradation of PHBV-based biocomposites containing purified cellulose (TC), wood flour (WF), and almond shell (AS) fibers have been investigated and compared with neat PHBV in two Mediterranean marine locations-a port and the open sea, within the same geographic region. Changes in weight, surface morphology, surface roughness, surface chemistry, and mechanical properties were monitored and periodically evaluated over 18 months of seawater exposure at the two sites. After 18 months of immersion, PHBV/AS showed the highest disintegration degree (88% for 150 µm films and 33% for 500 µm sheets), with the port environment promoting up to a two- to three-fold higher biodegradation rate compared to the open sea. Additionally, mineralization was studied in lab-simulated marine conditions by tracking CO₂ release in order to study the actual effect of the fibers on the biodegradation rate of the PHBV. The research highlighted the significant influence of habitat-specific factors on biodegradation, with the port environment exhibiting a more pronounced impact on bacterial adhesion, weight loss, and the deterioration of mechanical properties compared to the open sea. Lignocellulosic fillers, regardless of type, promoted PHBV biodegradation in both conditions. In particular, PHBV/AS exhibited the highest disintegration degree, followed by PHBV/TC and PHBV/WF. Fiber characteristics such as size, shape, and porosity predominantly governed biocomposite disintegrability. Almond shell was revealed as the most favorable fiber for PHBV biodegradation during mineralization test. Under laboratory-simulated marine conditions, the composites reached 50% mineralization between 55 and 70% faster than neat PHBV, confirming the accelerating effect of the fibers on the biodegradation kinetics. This study aims to shed light on the understanding of the biodegradation mechanism of biodegradable polymers and the effect of cellulosic fillers on this natural process. Additionally, the study includes tests and measurements of biodegradation under real conditions, which will provide further insights into the kinetics of this process. This knowledge is of interest for designing biodegradable products and predicting their biodegradation time.