Investigation of the mechanical properties of posidonia-reinforced thermoplastic composites for eco-friendly applications

In the context of the development of sustainable materials with reduced environmental impact, this study investigates the mechanical performance of biocomposites reinforced with Posidonia oceanica, a marine plant abundantly present on the Mediterranean coast. Two matrices were used: conventional polypropylene (PP) and a biodegradable polypropylene-based hybrid resin (PP-Bio). The composites were reinforced with different mass fractions (20%, 30%, and 40%) of Posidonia fibers or leaves and were manufactured by a thermocompression molding process. The mechanical behavior was evaluated by tensile and three-point bending tests, complemented by digital image correlation (DIC) to analyze the strain distribution and Poisson’s ratio. The results showed that Posidonia fibers significantly improved the tensile and bending properties of both matrices, with optimal reinforcement observed at 30 wt% fibers. The maximum tensile strength reached 31.77 MPa for PP composites and 33.86 MPa for PP-Bio, while the flexural strength increased up to 65 MPa for fibre-reinforced PP-Bio composites. The Poisson’s ratio decreased from 0.37 to 0.23 as the fibre content increased, confirming enhanced stiffness and reduced transverse deformation. In contrast, sheet-based reinforcements failed to provide substantial mechanical improvements due to poor matrix adhesion and poor fiber morphology. Scanning electron microscopy (SEM) revealed structural defects, including porosities and poor fiber dispersion, especially at higher fiber contents. These findings highlight the potential of Posidonia oceanica as a valuable natural reinforcement for environmentally friendly composites, particularly for lightweight interior automotive applications, while emphasizing the need for improved fiber processing and treatments to maximize performance.