From cracks to secondary microplastics - surface characterization of polyethylene terephthalate (PET) during weathering.

Secondary microplastics are a product of the fragmentation of plastic debris. Despite concerns regarding the omnipresence of microplastics in the environment, knowledge about the mechanics of their actual formation is still limited. Fragmentation is usually linked to weathering, which alters the properties of the plastic and allows fragmentation to occur. Therefore, in this study, polyethylene terephthalate (PET) samples were exposed to artificial UV light or a combination of UV light and water for a total of three months to simulate natural weathering. The samples included three forms of PET with different production histories: pellets, yarns, and films. The surface alterations to the samples during weathering were characterized using scanning electron microscopy and Raman spectroscopy. Results indicated that the three different types of PET developed markedly different surface defects and also exhibited signs of weathering within different time frames. Differences were also found between samples exposed only to UV and those exposed to UV and submerged in water. In water, the first surface changes were spotted within 30 days of initial submersion and later developed into an organized crack network. Upon the introduction of mild mechanical forces, pieces of the weathered surface started to delaminate. The fragments from films had an elongated shape with a median size of 16.1 × 2.1 × 1.8 µm, resembling a fibre. If the weathered surface of a film were to detach completely, it could create 1.4-7.9 million microplastic fragments/cm2. For pellets, this number would range between 0.4 and 2.2 million microplastics/cm2. In addition to particle formation by surface delamination, particles also emerged on the weathered surfaces of all studied samples, presenting another possible source of micro-sized particles during weathering. Overall, the results of this work show that the weathering of plastics and the formation of microplastics are heavily influenced not only by the weathering mechanism but also by the type and production history of the polymers.

Characterization of fiber fragments released from polyester textiles during UV weathering.

Synthetic textiles are considered a prime source of microplastics fibers which are a prevalent shape of microplastic pollution. Whilst the release mechanisms and formation of such microplastic fibers have been so far mainly studied in connection with laundry washing, there are some studies emerging that describe also other release pathways for microplastic fibers such as abrasion during wearing. The aim of this study was to consider weathering as another process contributing to the formation of microplastic fibers and their presence in the environment. Four types of polyester fabrics were selected and exposed to artificial weathering by UV-light for two months. The fabrics were extracted every 15 days to quantify and characterize the formed microplastics. Microplastic fibers with the diameter matching the size of the fibers in the textiles were observed. However, additional microplastic fibers of different shapes were also formed. These included partially broken fibers, thin fibers with a diameter below the size of the fiber in the fabrics, fibers flattened into a ribbon, and non-fibrous microplastics. The released microplastics evinced physical alterations on their surface in the form of pits and cracks. The released microplastics exhibited a steep increase in number with progressing weathering; from hundreds of fibers per gram of textile from unaged fabrics, to hundred thousands fibers (150,000-450,000 MPF/g) after 2 months of weathering. Additional 10,000-52,000 unfibrous microplastics/g were released from the weathered fabrics. While plain fabrics showed higher releases than interlock and fleece, further research is needed to evaluate the importance of the textile architecture on the weathering process in comparison with the production history of the fabrics. Based on a comparison with washing studies with the same textiles, we can estimate that the potential of weathered fabrics to be a source of microplastic fibers can be 20-40 times larger than washing only.