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As rates of textile manufacturing and disposal escalate, the ramifications to health and the environment through water pollution, microplastic contaminant concentrations, and greenhouse gas emissions increases. Discarding over 15.4 million tons of textiles each year, the U.S. recycles less than 15%, sending the remainder to landfills and incinerators. Textile reuse is not sufficient to de-escalate the situation; recycling is necessary. Most textile recycling technologies from past decades are expensive, create low quality outputs, or are not industry scalable. For viability, textile recycling system designs must evolve with the rapid pace of a dynamic textile and fashion industry. For any design to be sustainable, it must also be flexible to adapt with technological, user, societal, and environmental condition advances. To this end flexible and sustainable design principles were compared: overlapping principles were combined and missing principles were added to create twelve overarching sustainable, flexible design principles (DfSFlex). The Fiber Shredder was designed and built with flexibility and sustainability as its goal and evaluated on how well it met DfSFlex principles. An evaluation of the Fiber Shredder's performance found that increased speed and processing time increases the generation of the desired output - fibers and yarns, manifesting the principles of Design for Separation in design and Facilitate Resource Recovery in processing. The development of this technology, with the application of sustainable and flexible design, fiber-to-fiber recycling using mechanical systems appears promising for maintaining value while repurposing textiles. 

Due to the increasing speed of production, sale, and discard of home and apparel products, recycling of textiles is important for supporting the UN’s Sustainable Development Goal of Responsible Consumption and Production. In 2020, textile production was estimated to be responsible for 35% of primary microplastics released into the environment, 20% of global clean water pollution, and 10% of global greenhouse gas emissions. In 2018 the US generated around 17 million tons of textile waste and only 14.7% was recycled. Drum-operated textile shredding, a commonly utilized mechanical textile recycling technique, is not yet fully characterized. Even though there are many shredding machines that perform this process, the parameters that influence high-quality fiber output have not been researched; discovering ways to improve reusable fiber output is still a challenge. This research investigates the theory behind carded (toothed) drum textile shredding including how to improve the process outcome in order to obtain more reusable fiber and fewer textile pieces and dust. The mechanics of the textiles and fibers under tensile and shear stresses from the drums and drum teeth respectively were described to relate the textile material failure behavior to shredding process fiber outputs. Focusing on the interactions of the feeding drums and shredding drum, the drum-textile and tooth-yarn failure mechanics were characterized. By decreasing the teeth size and increasing the relative speed between drums, it is expected to increase the shear failure ratio, thus improving the shredding system. With this, it is expected that manufacturing new and better materials from recycled fibers becomes a possibility.