Polypropylene marine waste degradation study and recyclability prospects

Marine plastic pollution is a critical environmental concern due to the slow degradation rate of polypropylene (PP) in marine conditions. This investigation focuses on the degradation potential of marine PP debris using optical inspection, ultraviolet (UV) spectrophotometry, and tensile testing as well as recyclability aspects by involving specific mechanical recycling and different mixing ratios. Initially the debris were categorized into three damage tiers, i.e. light, moderate, and high, based on deterioration in ultimate tensile strength (σ_UTS) and Young's modulus. To restore functionality, recycled blends were produced by incorporating virgin PP (VPP) at varying ratios. Results indicate that 100 % debris utilization is unviable, leading to losses in σ_UTS and Young's modulus exceeding 50 %. However, two optimal blends were identified: (a) the blend with 50 % lightly damaged debris (and 50 % VPP) and the blend with 30 % moderately damaged debris (and 70 % VPP), they both exhibited an extremely short (10 %) σ_uts decrease of the virgin (reference) material while providing substantial environmental benefits. A comparative Life Cycle Assessment (LCA) using an integrated cradle-to-gate boundary quantified these gains, where it was shown that against a VPP baseline of 270.25 kg CO_2,eq, the 50/50 and 30/70 blends achieved carbon footprint reductions of 39 % and 23 %, respectively. While the scenario of 100 % debris recycling offers a 77 % emission reduction, associated mechanical properties necessitate significant VPP incorporation to maintain the baseline structural integrity. This contribution suggests that valorising marine plastic through targeted blending represents a potentially mechanically viable and environmentally beneficial strategy to help address marine plastic pollution.