Low-temperature hydrolytic polymerization of caprolactam. synthesis and processing of experimental batches of polymer into filament yarns

Abstract

Using different methods to study the properties of polycaproamide obtained by low-temperature hydrolytic polymerization of caprolactam and by commercial production (GrodnoKhimvolokno OAO), we have shown that the experimental samples have higher degree of oxidation and content of caprolactam and low molecular weight compounds. Since we previously established a correlation between these indices of the polymer and the strength characteristics of the fi lament made from it, despite the greater drawability of polycaproamide fi laments obtained by low-temperature hydrolytic polymerization of caprolactam, the strength indices of the fi laments formed from polycaproamide proved to be lower over the entire range of draw ratios.Systematic studies in the area of hydrolytic polymerization of caprolactam (CL) that have been conducted at Ivanovo State Chemical Engineering University in recent years [1-10] provide a basis for assuming that further substantial progress in production of technical fi laments from PA-6 is impossible without going away from the traditional high-temperature process to low-temperature hydrolytic polymerization of caprolactam.Such technology for synthesis of PA-6 is also economically profi table, since it allows us to appreciably reduce the cost of the process, particularly as a result of replacing the energy-intensive and materials-intensive step of demonomerization of the polymer by aqueous extraction followed by regeneration of the caprolactam from the extraction water with the process of demonomerization by sublimation of the residual monomer from the granulate under vacuum or under a stream of inert gas, as was proposed back at the beginning of the 1950s [11].However, due to the high residual monomer and cyclic oligomer content in the polymer obtained by high-temperature hydrolytic polymerization of caprolactam, such a process could not be effi ciently realized. The level of the residual monomer and oligomer content in the granulate attainable with low-temperature hydrolytic polymerization of caprolactam will allow us to do this.Fabrication and assembly of an experimental pilot line for low-temperature synthesis of PA-6 is currently in progress according to the working design documentation developed, including the following technical steps: 1) synthesis of the prepolymer by hydrolytic polymerization of caprolactam in the supercooled melt state (<220°C) in a vertical reactor, with "plug" fl ow of the melt from bottom to top;2) dehydration of the supercooled prepolymer melt in a pre-polycondensation reactor with controllable steam pressure above the melt, ensuring that we obtain a polymer with degree of polyamidation P n  130 and content of low molecular weight (LMW) compounds ~ 8 wt.%;3) solid-phase pre-polyamidation of the polymer granulate in an atmosphere of superheated steam until P = 200-220 is achieved along with an LMW content of 3-4 wt.%; 81 4) combination drying/demonomerization of the polymer granulate in a stream of inert gas, obtaining a residual caprolactam and oligomer content at th...

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

“…As the reaction time increases, the molecular weight of prePA6 gradually rises, while the end-amino content decreases (Figure S1). The rate of the ring-opening reaction and addition reaction of cyclic oligomers is greater than the rate of the ring-formation reaction which is reflected in the rapid decrease of monomer and cyclic oligomer content . When the reaction time reaches 240 min, the oligomers in the prePA6-210, prePA6-230, and prePA6-250 samples are 12.02, 8.78, and 7.88 wt %, respectively.…”

“…The rate of the ring-opening reaction and addition reaction of cyclic oligomers is greater than the rate of the ringformation reaction which is reflected in the rapid decrease of monomer and cyclic oligomer content. 22 When the reaction time reaches 240 min, the oligomers in the prePA6-210, prePA6-230, and prePA6-250 samples are 12.02, 8.78, and 7.88 wt %, respectively. The reaction at 230 and 250 °C for 4 h has reached the equilibrium state.…”

“…Solid-phase polymerization is another way to achieve low-temperature polymerization. It allows the establishment of a new reflective equilibrium at low temperatures, thus reducing the content of oligomers. , However, it is difficult to maintain the homogeneity and stability of the melt. In our previous work, ,, a series of PA6-based polyamides were prepared by molecular design based on the hydrolytic polymerization of CPL.…”

Unveiling the Mechanisms of Hydrolytic Ring-Opening Polymerization of Caprolactam and Amino-Assisted Ring Opening of Cyclic Dimers: A DFT Study

“…Bazarov et al opened caprolactam at 210 °C for 8–12 h to obtain the PA6 prepolymer with 6.5–7.0 wt % oligomer and then reduced the monomer and water content by a vacuum method so that the polymerization degree of PA6 reaches 120, and the oligomer content can be reduced to the spinning requirements. Isaeva et al first prepared the PA6 prepolymer from caprolactam, then removed the water in the prepolymer by controlling the pressure, and then placed it in a superheated steam environment for solid-phase polymerization so that the degree of polymerization of the polymer can reach 200, and the oligomer mass fraction is 3.0–4.0%. Finally, the water and a large amount of monomers in the polymer are removed using an inert gas flow and PA6 chips that meet the spinning requirements were obtained.…”