Separation and Chemo-Enzymatic Depolymerization to Monomers of Nylon from Composite Textiles

Nylon is a petroleum-derived synthetic polyamide that exhibits excellent strength, flexibility, and durability; however, it is highly resistant to both chemical and biological degradation, which leads to its long-term persistence in the environment and imposes a significant environmental burden. Although nylon is widely used as a fiber in clothing and various other applications, it is frequently blended with other types of fibers. Practical and widely applicable technologies for selectively separating such composite materials have not yet been established. Because recycling is not feasible in their mixed state, these materials have conventionally been disposed of as waste. Therefore, the development of effective separation technologies is essential to enable the recycling of nylon-containing products. In this study, we targeted composite textiles composed of nylon blended with polyester, wool, or cotton and aimed to establish a process for the separation and depolymerization of nylon. First, high-molecular-weight nylon was selectively extracted from the composites using nylon-specific solvents, namely formic acid and 2,2,2-trifluoroethanol (TFE). The isolated nylon was then subjected to a biological monomer recycling (BMR) process that combines chemical conversion into water-soluble oligomers via hydrochloric acid treatment with subsequent enzymatic monomerization using a previously developed series of nylon-hydrolyzing enzymes (Nyl series). Each step was successfully achieved, enabling efficient conversion of nylon into its monomeric products. This method was applicable to all three types of composite textiles examined. Furthermore, to reduce the number of processing steps, we investigated direct heating of the composite materials in hydrochloric acid without prior separation. Although this approach was applicable only to polyester–nylon composites, it enabled single-step selective separation and conversion of nylon into water-soluble oligomers. This study provides a process-oriented framework for designing selective and efficient chemo-enzymatic recycling routes for nylon-containing composite materials.