Fiber-shaped microplastics, often referred to as fibrous microplastic, are plastic particles with a length higher than 300 nm and lower than 15 mm and with a diameter to length ratio higher than 3 [1]. It was found that recycled synthetic fibers release more fibrous microplastics than virgin fibers, because they are more prone to breakage due to their uneven surfaces and lower break and tensile strengths [2, 3]. These results started raising questions about whether recycled fibers are a more sustainable choice. However, the morphological differences in microplastics also play a significant role in their mitigation. In this paper, a simple methodology was used to collect, analyze and compare the quantity and the morphological differences between virgin and recycled polyester fibrous microplastics emitted into the water during washing.
Two black interlock knitted polyester fabrics with filament yarns used in women’s sportswear were selected: F1 composition – 100 % virgin polyester, mass per unit area – 120.0 ± 5 g/m², thickness – 0.600 ± 0.05 mm, course density – 19.0 ± 0.5 cm⁻¹, wale density – 23.0 ± 0.5 cm⁻¹; F2: composition – 100 % recycled polyester, mass per unit area – 100.0 ± 5 g/m², thickness – 0.490 ± 0.05 mm, course density – 24.0 ± 0.5 cm⁻¹, wale density – 33.0 ± 0.5 cm⁻¹. Three samples of each fabric were washed five times in water with liquid detergent. Wastewater was collected after each wash and filtered through filters. Filters were weighed before and after filtration. Image analysis was performed using light microscope Lumenera INFINITY and ImageJ software to assess fibrous microplastics number, length, and shape.
Results confirmed that amounts of fibrous microplastic after each wash from both fabrics were similar and differences were statistically insignificant, but fibrous microplastics from recycled polyester fabrics were longer than fibrous microplastics from the virgin polyester fabric. These findings suggest that assessing fibrous microplastic morphology is important when implementing microplastic mitigations strategies, because fewer but longer particles are easier to mitigate than higher amounts of shorter particles.