Comprehensive assessment of fragmented fiber shedding from recycled cotton textiles part II image-based methodology for assessment of contaminants shed from yarns

As the second part of a three-part investigation into fiber release from recycled cotton, this study presents an adapted image-analysis workflow for the qualitative and semi-quantitative characterization of fibers, fragments, and particulate contaminants shed from yarn hanks during laundering. This yarn-level approach overcomes critical gravimetric limitations caused by cotton hygroscopicity and small sample filter mass uncertainty. The validated workflow classifies released material into particles, individual fibers, and aggregates, quantifying their count, size, and morphology. Skeleton-based analysis measures fragment lengths and structural complexity, complemented by binary area fraction analysis to evaluate clustering behavior. Results demonstrate that the method effectively differentiates release behaviors between recycled rotor-spun and compact warp yarns, as well as gray and dyed variants. Fragment lengths show strongly right-skewed distributions, while particulates predominantly fall into the respirable size range. Although significant differences exist between yarn types, partial distribution overlaps and experimental constraints limit direct generalization. Nevertheless, this controlled dataset establishes an essential baseline for hierarchical scaling and subsequent fabric-level evaluations.