The main components of textile materials include polyethylene terephthalate (PET), cotton, and nylon (polyamides, PA) fibers. Currently, the technology for recycling PET is more mature compared to nylon. Nylon recycling is primarily through incineration, which emits a significant amount of carbon dioxide and accelerates global warming. If waste textile fibers can be effectively converted into value-added monomers, it would not only address the issue of carbon dioxide emissions from waste textile fibers but also obtain monomers with economic value. These monomers can be further used to synthesize regenerated fibers, achieving a higher value. To address the pollution and recycling issues associated with waste textile fibers, hydrothermal liquefaction technology can be applied to upgrade and recycle these waste fibers. Typically, this process is conducted at high temperatures (280-450 °C) and high pressures (7-30 MPa). Through the changes in water properties during this process, organic waste can be rapidly converted into liquid products. This research aims to develop a hydrothermal liquefaction system to convert nylon textiles into a recycled-monomer caprolactam (r-CPL), which can be subsequent use in synthesizing regenerated elastic fibers. First, nylon pellets or greige will be pulverized into powder form using a grinder and then dried and sieved. Subsequently, hydrothermal liquefaction will be employed to convert the nylon powder into CPL monomer. The present study focused on investigating the influence of different reaction conditions, such as reaction temperature, pressure, and reaction time, on the conversion of nylon into monomers, including yield and the physicochemical properties of the monomers. The results indicated that under controlled hydrothermal liquefaction conditions at a temperature of 280 oC, pressure of 900 psi, and reaction time of 1 hr, nylon fibers can be effectively converted into liquid products. Further using GC-MS confirms that the main liquid product is CPL monomers (accounted for 54.95% in terms of peak area). This demonstrates the feasibility of using hydrothermal liquefaction technology to convert nylon into CPL monomer. Subsequently, the CPL monomer, r-CPL, and water are subjected to a ring-opening reaction for the synthesis of nylon elastomers. Polyether amine, adipic acid, and cross-linking agents are added for copolymerization to obtain nylon elastic copolymers. These copolymers are then processed into nylon elastic fibers. Identification through NMR and FT-IR confirmed the successful synthesis of nylon copolymers with different crosslinking agent ratios. Thermogravimetric (TGA) results demonstrated excellent heat resistance of the nylon copolymer (decomposition temperature exceeding 350 °C), ensuring thermal stability during the filament extraction process and its successful melting and spinning.

Hydrothermal liquefaction、Nylon、Waste textile fibers、Regenerated fibre、Caprolactam (CPL) monomer