Microplastic Formation and Surface Crack Patterns: A Method for Waste Plastic Identification

Accumulation of plastic debris in marine environments has become a critical global issue, with microplastics (MPs) posing persistent ecological risks. This review synthesizes current knowledge on the formation mechanisms of MPs from polyolefins such as polypropylene (PP) and polyethylene (PE), emphasizing the influence of marine conditions on degradation pathways. Autoxidation is identified as the dominant mechanism; however, salinity and chloride ions significantly retard radical formation, altering photodegradation kinetics and crack propagation. These effects lead to distinctive surface morphologies-such as rectangular and trapezoidal crack patterns in PP-which can serve as reliable indicators for polymer identification. This review further explores the role of polymer chain orientation and spherulite structures in crack development and discusses how these features can be leveraged for cost-effective sorting and recycling strategies. Finally, emerging approaches using AI-based image recognition for automated identification of weathered plastics are highlighted as promising tools to enhance resource recovery and mitigate marine plastic pollution.