Quality assessment of upcycled waste/cotton blend rotor yarn and optimization modeling using Taguchi design of experiment

Textile industry generates huge finishing waste, including brush fiber (BF) from sueding/emerizing processes. Although BF is often discarded, it is already available in loose fibrous form and can provide pre-colored feedstock when collected from dyed fabrics. Unlike previous studies primarily exploring BF-integrated ring-spun yarns or mechanically recycled BFs, this study investigates the direct use of unrecycled, pre-colored BF waste in rotor-spun yarn production without intermediate steps. Droppings-1 (D1) waste and 100% virgin cotton rotor yarn were used as comparative benchmarks. A full-factorial design, Taguchi optimization, and regression modeling were applied to evaluate effects of yarn count, waste type, and blend ratio on yarn unevenness (coefficient of mass variation (CVm%)), imperfection index (IPI), hairiness, tensile strength, elongation, and reisskilometer (RKM). The results showed that 100% virgin cotton yarns had the best overall performance. D1 blends showed good evenness and mechanical properties with limited quality loss, whereas BF blends produced acceptable rotor yarns with moderately higher CVm%, IPI, hairiness, and slightly lower tensile properties due to their shorter fiber length. However, BF provided a distinct pre-colored mélange appearance, reducing the need for additional dyeing. Regression models described the main yarn responses well, with adjusted R 2 values ranging from 0.326 to 0.862; the models for IPI and breaking force showed only moderate fit. Taguchi analysis identified waste type as the most influential factor affecting yarn quality. Direct use of pre-colored BF waste can avoid additional mechanical recycling and dyeing steps, with indicative, literature-based estimates of approximately 1559 L water, 4.8 kWh energy and 2.2 kg CO₂-eq per kg of virgin cotton replaced.. These findings establish a simplified textile-to-textile recycling route that produced value-added rotor-spun mélange yarns.