Direct spinning of polyamide 6 (PA 6) fibers, traditionally impeded by the presence of approximately 10% residual monomer and oligomers in the polymerized form, has been made feasible through our innovative approach. Current extraction methods predominantly employ hot water to extract monomer and oligomers. However, this approach is characterized by time-consuming procedures, high energy consumption, and substantial water usage. Therefore, in this study, a straightforward falling-film devolatilization method is proposed to synchronize the liquid-phase viscosity enhancement and oligomer removal of PA 6. PA 6 industrial yarns were successfully produced using devolatilized PA 6 (D-PA 6) obtained by this method. The viscosities of D-PA 6 samples were increased from 2.5 and 2.8 to 2.8 and 3.4, their monomer contents were reduced to 0.26%, and their dimer and residual oligomer contents were reduced to 0.54 and 2.54%, respectively, with a lower removal of dimer and trimer. The process led to a wider molecular weight distribution, consistent with that typical of PA 6 spinning. The obtained PA 6 industrial yarn exhibited a high degree of crystallinity, and its orientation, thermal properties, and mechanical properties were comparable to those of conventional yarn. Although its dyeing ability was slightly compromised, this did not hinder the practical application of the PA 6 industrial yarn. The falling-film devolatilization process enables simultaneous viscosity enhancement and devolatilization without the need for hot-water extraction (24 h) and drying (24 h), drastically shortening the production time from more than 48 h to less than 10 h, thereby greatly reducing energy consumption and wastewater discharge. This study provides technical guidance for the sustainable industrial production of PA 6 industrial yarn by direct melt-spinning, which significantly reduces energy and environmental impacts while improving production efficiency.
