Comprehensive Analysis of the Preparation of Regenerated ε‑Caprolactam Based on Solvent-Free Alkali-Catalyzed Depolymerization of Colored Waste Polyamide 6/Polyurethane Blended Textiles

The deficiency in efficient and cost-effective methodologies for the dissociation of dyes from polymers and the segregation of fibers within blended textiles impedes the widespread recycling of textile materials on a grand scale. We specialize in the direct, clean, economically viable, and ecologically sound interfiber recycling of colored waste polyamide 6/polyurethane (PU) (CPA6/PU) blended textiles. In this research, a commercially available and cost-effective alkali catalyst were utilized to illustrate a unique methodology for recovering CPA6/PU blended textiles containing a variety of dyes. The product evolution of solvent-free alkali-catalyzed closed depolymerization (SACD) of CPA6/PU blended textiles was monitored in real time at 320 °C using pyrolysis gas chromatography–mass spectrometry (Py-GC/MS). The solvent-free alkali-catalyzed depolymerization (SAD) of CPA6/PU blended textiles with different compositions was systematically investigated by combining various analytical tools such as liquid chromatography–MS and GC–MS. This holistic approach mitigates the ambiguity induced by a solitary testing method and elucidates the authentic depolymerization product. Additionally, preliminary verification was conducted on the factors that influence the production rate of regenerated ε-caprolactam (rCPL). The depolymerization process is distinguished by its straightforward operation, environmental friendliness, efficiency, convenient product packaging, high yield (approximately 80.2%), high purity (around 97.85%), automated decolorization, and automatic separation of PU constituents. To date, no economically sustainable and environmentally conscientious method has been demonstrated for the direct extraction of rCPL monomer from CPA6/PU blended textiles, encompassing a variety of dyes, without segregating the PU while concurrently achieving decolorization.