Sustainable Production of Polyamide 6 Fibers: Direct Melt Spinning and Efficient Reuse of Residual Oligomers during Polymerization

Abstract

Direct melt spinning of PA6 from a polymerization reactor is currently unachievable in the industrial production of polyamide 6 (PA6) fibers because the hydrolysis polymerization of its monomer (caprolactam) is a reversible reaction which requires a boiling water extraction of oligomers from the polymer before melt spinning. Here, we proposed a polymerization method where the content of the cyclic dimer is controlled by reducing the temperature at the monomer ring-opening stage and the content of oligomers is monitored by rapid devolatilization through the polycondensation stage. As a result, the content of oligomers in PA6 is less than 1.5 wt % and the cyclic dimer is at 0.1–0.3 wt %, which are 80 and 48% lower than the values for the conventional PA6 production process. This allows for direct melt spinning of PA6 fibers at the industrial scale (spinning speed: 4000 m/min and a continuous production line of 10 kg/h), which reduces the production time from over 40 h to within 10 h, and the resource consumption reduces by over 30%. The resulting PA6 fibers show comparable mechanical and dyeing properties to those spun with the conventional multistep spinning method. In addition, the unreacted oligomers extracted during the polymerization stage can be directly reused in the polymerization, with no further treatment. This work provides an effective route to the sustainable production of PA6 fibers at the industrial scale, which significantly decreases the consumption of resources and the generation of chemical wastes while improving the production efficiency.

Ring Opening of N-Acyl Lactams Using Nickel-Catalyzed Transamidation

“…According to the general procedure, the reaction of aniline (93 mg, 1.0 mmol) and 1-([1,1′-biphenyl]-4-carbonyl)pyrrolidin-2-one (530.6 mg, 2.0 mmol) afforded N-[4-oxo-4-(phenylamino)butyl]-[1,1′-biphenyl]-4-carboxamide (3fa) (240.2 mg, 0.67 mmol, 67%) as a pale brown solid after column chromatography eluting with hexane/ EtOAc (1:1): mp 195−198 °C; 1 H NMR [500 MHz, (CD 3 ) 2 SO] δ 9.92 (s, 1H), 8.57 (t, J = 5.6 Hz, 1H), 7.97−7.95 (m, 2H), 7.77−7.75 (m, 2H), 7.73−7.72 (m, 2H), 7.61−7.59 (m, 2H), 7.49 (t, J = 7.4 Hz, 2H), 7.42−7.39 (m, 1H), 7.30−7.26 (m, 2H), 7.02 (t, J = 7.3 Hz, 1H), 3.35 (q, J = 6.6 Hz, 2H), 2.39 (t, J = 7.5 Hz, 2H), 1.88 (quint, J = 7.3 Hz, 2H); 13 C{ 1 H} NMR [126 MHz, (CD 3 ) 2 SO] δ 170.9, 165. 9,142.6,139.3,139.2,133.4,129.0,128.6,128.0,127.9,126.8,126.4,122.9,119.0,38.9,33.9,25.1; 358.1676358. , found 358.1680butyl]benzamide (3ga).…”

“…5 Recently, our group published various synthetic methodologies that involve the use of amides as pivotal starting materials amenable to conversion into other amides, 6 acyl azides, 7 ketones, 8 and esters. 9 Notably, our particular interest was directed toward elucidating the ring-opening reaction of lactams and exemplifying the synthesis of primary amides from activated amides using ammonium carbonate. The findings provided valuable insights for further field exploration.…”

Kinetics Comparison of Solid-State Polycondensation and Melt Postpolycondensation for Polyamide 6 with Controllable Extractive Content

“…Polyamide 6 stands out in the engineering world for its remarkable mechanical and thermal stability, alongside impressive optical and dimensional properties. − It is widely used in electronic and electrical, automotive, construction, optics, pharmaceutical, and packaging industries. − The predominant industrial method for synthesizing polyamide 6 involves the hydrolysis of caprolactam (CPL). This reversible reaction requires rigorous control to achieve high yield and superior product quality. − Affected by the reaction balance, polyamide 6 melt, formed through ring-opening hydrolysis, contains roughly 8–10% extractable small molecules (75% caprolactam monomer and 25% other oligomers). − The caprolactam monomer’s volatility is a known issue, often causing bubble formation during fiber spinning, leading to breakage . At typical industrial temperatures (250–270 °C), the ring dimer does not ring-open and remains undissolved in fresh caprolactam, forming sediment. − The presence of other oligomers also prevents further growth of the polymer molecular chain .…”

Electrospun PA6 Nanofibers Bearing the CeO2 Dephosphorylation Catalyst

“…Nevertheless, functionalization of nanofibers may significantly extend their area of applications. Nylon 6 (PA6) is a synthetic polymer with high strength, good chemical resistance, and water tolerance, and PA6 fibers are currently the second most produced synthetic fibers in the world . PA6 nanofibers are therefore an excellent candidate for further modification/functionalization by various materials and techniques, either for improving nanofiber properties , or for specific applications such as sensing, antiviral mask filters, batteries, or bone regeneration …”

“…Nylon 6 (PA6) is a synthetic polymer with high strength, good chemical resistance, and water tolerance, and PA6 fibers are currently the second most produced synthetic fibers in the world. 29 PA6 nanofibers are therefore an excellent candidate for further modification/functionalization by various materials and techniques, either for improving nanofiber properties 30,31 or for specific applications such as sensing, 32 antiviral mask filters, 33 batteries, 34 or bone regeneration. 35 Anchoring enzymes onto the fibers may improve enzyme operational stability, reusability, and product separation making 1D fibrous materials one of the most desirable supports for enzyme immobilization, as elaborated in several review articles.…”