Ultraviolet Irradiation Affects Microplastic Properties and Removal from Water Using Agglomeration–Micro-Flotation

The exposure of microplastics (MPs) to ultraviolet (UV) light in the environment can affect their flotation behavior and removal efficiency. This study investigated the effects of UVC irradiation on the physical and surface characteristics of polypropylene (PP), polyethylene (PE), acrylonitrile butadiene styrene (ABS), polystyrene (PS), polyethylene terephthalate (PET), and polyvinyl chloride (PVC), and evaluated their removal using agglomeration–micro-flotation. MPs were irradiated with UVC for 7 days, and they were characterized using particle size distribution analysis, CIE L*a*b* color analysis, and contact angle measurements. Flotation experiments were conducted using kerosene as a hydrophobic bridging liquid. The results showed that UVC irradiation induced polymer-dependent changes, including fragmentation, apparent shape-related changes, and redistribution behavior, resulting in changes in particle size distribution. Surface discoloration and reduced contact angle were also observed after UV exposure, suggesting photooxidative surface modification and increased surface hydrophilicity. These surface modifications reduced flotation performance at low kerosene dosages, particularly for PET and PVC. However, increasing kerosene dosage improved removal efficiency by enhancing agglomeration and particle–bubble attachment. The results indicated that agglomeration–micro-flotation is a promising approach for removing UV-aged MPs and provided insights into the influence of UV-induced surface modifications on flotation behavior.