Method for preparing high-quality polyamide 6 material through combination of anionic polymerization and graded devolatilization

Abstract

The invention provides a method for preparing a high-quality polyamide 6 material by combining anionic polymerization with graded devolatilization. Caprolactam and a catalyst are added into a drying device A to remove system moisture and then placed into a storage tank A. Caprolactam is added into a drying device B to remove moisture and then placed into a storage tank B together with an initiator. Then continuously injecting the caprolactam liquid in the storage tank A and the storage tank B into a screw extruder, carrying out anionic ring-opening polymerization reaction to prepare a polyamide 6 basic melt, and further conveying the basic melt into a tandem devolatilization reaction system to remove monomers and part of cyclic oligomers so as to obtain a polyamide 6 final polymer; finally, spinning, injection molding or film blowing can be directly carried out to obtain polyamide 6 fibers, engineering plastics or films.

Description

Technical Field

[0001] The present invention belongs to the field of polyamide material preparation, and particularly relates to a method for preparing high-quality polyamide 6 material by anionic polymerization combined with staged devolatilization. Background Art

[0002] Polyamide 6 (PA6), as an important engineering plastic, is widely used in the fields of textiles, automobiles, electronics, etc. Its traditional preparation process is mainly achieved through the hydrolysis ring-opening polymerization of caprolactam. However, in actual industrial production, about 10% of residual caprolactam monomers and small molecules such as cyclic oligomers (also known as hot water extractables) need to be removed by a continuous hot water extraction process for dozens of hours.

[0003] The monomer conversion rate of preparing polyamide 6 by anionic polymerization can reach about 95%, and about 5% of hot water extractables remain. Anionic polymerization has the advantages of fast and efficient reaction, low pollution and low energy consumption, etc., but there are still many problems. For example, residual monomers and oligomers still need to be removed to meet the application requirements in the fields of fibers, films, high-end engineering plastics, etc. At present, the industrial production has not realized the preparation of polyamide 6 by anionic polymerization of caprolactam for fibers, films, etc.

[0004] Part of the monomers and oligomers can be removed by vacuum devolatilization. Hyoungsan Kye et al. (Journal of Applied Polymer Science 1994, 52(9), 1249 - 1262) used vacuum devolatilization to remove monomers and oligomers in anionic polyamide 6, and then directly carried out melt spinning by adding a spinneret at the outlet of the screw extruder. However, due to the large amount of residual oligomers, the fibers produced by them are in the millimeter scale and do not meet the usage requirements of daily fibers. By designing an efficient devolatilization method, it is expected to remove the residual monomers and oligomers in anionic polymerization polyamide 6, reduce production energy consumption, and promote the more green and low-carbon development of the polyamide 6 material industry. Summary of the Invention

[0005] The purpose of the present invention is to provide a method for preparing high-quality polyamide 6 material by anionic polymerization combined with staged devolatilization. Polyamide 6 basic melt is prepared by anionic reaction extrusion and then two series-connected devolatilization reactors are used to efficiently remove monomers and cyclic oligomers, so as to realize the preparation of high-quality polyamide 6 material.

[0006] Among the small molecules remaining in polyamide 6, caprolactam monomer accounts for the vast majority. Although caprolactam has a low boiling point and is easy to remove by devolatilization, it is difficult to remove cyclic oligomers at the same time, and the accumulation of cyclic oligomers (especially cyclic dimers) will affect the processing stability and product quality of polyamide 6. According to the relationship between the physical properties of caprolactam monomer and cyclic oligomers in polyamide 6 and the temperature and pressure of the devolatilization reactor, the present invention proposes a series devolatilization reaction system in which a first devolatilization reactor and a second devolatilization reactor are used in series. Since the boiling point of caprolactam monomer is relatively low, the reaction temperature of the first devolatilization reactor of the series devolatilization reaction system is set to 240-280 °C and the reaction pressure is 200-4000 Pa. Under this condition, more than 90% of the caprolactam monomer can be selectively removed, effectively reducing the influence of high-content monomers on the next-stage devolatilization reaction while reducing the energy consumption required for vacuum power. After a large amount of caprolactam monomer is removed, according to the physical property parameters of the cyclic oligomers, the reaction temperature of the second devolatilization reactor of the series devolatilization reaction system is set to 240-280 °C and the reaction pressure is 20-600 Pa, which can achieve the enhanced removal of the remaining small amount of caprolactam monomer and cyclic oligomers, so that the monomer residue in the end polymer is less than 0.1 wt%, the content of cyclic oligomers is less than 1.5 wt% (where the content of cyclic dimers in the cyclic oligomers is less than 0.1 wt%), and the content of hot water extractables is less than 0.5 wt%. This method omits steps such as cooling and pelletizing, hot water extraction, drying and re-melting compared with the traditional hot water extraction method, saving a large amount of time and energy.

[0007] Based on the above series devolatilization reaction system, the present technical solution provides a method for preparing high-quality polyamide 6 materials by anionic polymerization combined with fractional devolatilization, comprising the following steps: (1) Prepare basic active material A: Mix a catalyst and caprolactam to obtain a first mixture, subject the first mixture to vacuum distillation and store it in storage tank A, where storage tank A is protected by an inert atmosphere and kept at a constant temperature of 80-150 °C; (2) Prepare basic active material B: Heat and melt caprolactam monomer and then perform vacuum distillation, mix the water-removed caprolactam monomer and an initiator evenly to obtain a second mixture, and store the second mixture in storage tank B, where it is protected by an inert atmosphere and kept at a constant temperature of 80-150 °C; (3) Inject basic active material A and basic active material B components into a screw extruder in a volume ratio of 1-10:10 for anionic polymerization, and react and extrude to obtain a polyamide 6 basic melt; (4) Feed the polyamide 6 base melt to the first devolatilization reactor to remove caprolactam monomer to obtain polyamide 6 intermediate, and input the polyamide 6 intermediate into the second devolatilization reactor to remove a small amount of caprolactam monomer, cyclic dimer, partial cyclic trimer and partial cyclic tetramer to obtain the polyamide 6 end polymer, wherein the reaction temperature of the first devolatilization reactor is set at 240-280 °C, the reaction pressure is 200-4000 Pa, the reaction temperature of the second devolatilization reactor is 240-280 °C, and the reaction pressure is 20-600 Pa.

[0008] In step (1), the catalyst is one or more of sodium caprolactamate, sodium ethoxide, LiH, NaH, KH, LiOH, NaOH, KOH.

[0009] In step (1), subject the first mixture to vacuum distillation to fully remove moisture, and the conditions of vacuum distillation are a temperature of 80-150 °C and an absolute reaction pressure of 5-95 kPa.

[0010] In step (1), the inert atmosphere is one or more of N2, CO2, He, Ne, Ar.

[0011] In step (1), by mass, mix 0.3-1.2 parts of catalyst and 10-100 parts of caprolactam to obtain the first mixture.

[0012] In step (2), the initiator is one or more of N-acetylcaprolactam (AcCL), bis-acylated lactam-1,6-hexanamine, terephthaloyl bis-caprolactam (TBCL), isophthaloyl bis-caprolactam, toluene diisocyanate (TDI), diphenylmethane diisocyanate (MDI), 1,6-hexane diisocyanate (HMDI).

[0013] In step (2), subject the caprolactam monomer to vacuum distillation, and the conditions of vacuum distillation are a temperature of 80-150 °C and an absolute reaction pressure of 5-95 kPa.

[0014] In step (2), the inert atmosphere is one or more of N2, CO2, He, Ne, Ar.

[0015] In step (2), mix 100 parts of the moisture-removed caprolactam monomer and 1.0-2.4 parts of initiator to obtain the second mixture.

[0016] In step (3), set the feeding temperature of the screw extruder at 90-160 °C, the discharging port temperature at 220-240 °C, the temperature of the middle section of the screw to increase gradually from the feeding port temperature to the discharging port temperature, with no less than 1 heating section, and the rotation speed at 20-300 rpm.

[0017] In step (3), the relative viscosity of the polyamide 6 base melt is 2.0-4.5, the monomer content is less than 4.2 wt%, the cyclic oligomer content is less than 2.6 wt% (wherein the cyclic dimer content in the cyclic oligomer is less than 0.8 wt%), and the hot water extractable content is less than 5.5 wt%.

[0018] In step (4), the reaction temperatures of the first devolatilization reactor and the second devolatilization reactor can be independently controlled, and both are connected to a vacuum system, and the vacuum system is used to control the reaction pressures of the first devolatilization reactor and the second devolatilization reactor, wherein the first devolatilization reactor is selected from a horizontal squirrel cage reactor, a horizontal disc reactor, a falling strip devolatilizer, and a vertical falling film devolatilization reactor; the second devolatilization reactor is a vertical falling film devolatilization reactor or a horizontal biaxial devolatilization reactor; the reaction pressure of the first devolatilization reactor is controlled by the vacuum system to be 200~4000 Pa, and the reaction temperature is set to 240~280 °C; the reaction pressure of the second devolatilization reactor is controlled by the vacuum system to be 20~600 Pa, and the reaction temperature is set to 240~280 °C.

[0019] In step (4), the relative viscosity of the polyamide 6 final polymer is 2.0-4.5, the monomer content is less than 0.1 wt%, the cyclic oligomer content is less than 1.5 wt% (wherein the cyclic dimer content in the cyclic oligomer is less than 0.1 wt%), and the hot water extractable content is less than 0.5 wt%.

[0020] In some embodiments, the present technical solution provides a method for preparing high-quality polyamide 6 material by anionic polymerization combined with fractional devolatilization, comprising the following steps: Furthermore, the method for preparing polyamide 6 material by anionic polymerization of the present scheme further comprises the steps of: (5) Directly spinning the polyamide 6 final polymer to obtain polyamide 6 civil yarn or industrial yarn, or directly blowing the polyamide 6 film to obtain polyamide 6 film; or adding fiber reinforcement material to the polyamide 6 final polymer for injection molding to obtain a polyamide 6 composite material.

[0021] When polyamide 6 final polymer is directly spun to obtain polyamide 6 civil yarn or industrial yarn, the spinning temperature is 245~300 °C and the spinning speed is 2500~6000 m / min.

[0022] When fiber reinforcement material is added to polyamide 6 final polymer for injection molding, a polyamide 6 composite material is obtained, wherein the fiber reinforcement material is one or more of glass fiber, carbon fiber, aramid fiber, silicon carbide fiber, natural fiber, and basalt fiber, and the added amount of the fiber reinforcement material is not more than 50wt%.

[0023] Figure 1 , Figure 2 andFigure 3 Three schematic structural diagrams of preparing high-quality polyamide 6 materials by anionic polymerization combined with staged devolatilization are provided, as Figure 1 , Figure 2 and Figure 3 shown. After caprolactam and a catalyst are mixed, they are added to drying device A for vacuum distillation and then stored in storage tank A; after caprolactam is heated and melted, it is placed in drying device B for vacuum distillation. After the water-removed caprolactam is mixed evenly with an initiator, a second mixture is obtained and stored in storage tank B; basic reactive material A and basic reactive material B are injected into a screw extruder according to a volume ratio of 1-10:10 for anionic polymerization, and a polyamide 6 basic melt is prepared by reactive extrusion; the polyamide 6 basic melt is transported to devolatilization reactor 1 to selectively remove more than 90% of the caprolactam monomer. After a large amount of caprolactam monomer is removed, it enters devolatilization reactor 2 to intensively remove the remaining small amount of caprolactam monomer and cyclic oligomers to obtain a polyamide 6 final polymer. The differences are as follows: Figure 1 In , devolatilization reactor 1 adopts a vertical falling film devolatilization reactor, and devolatilization reactor 2 also adopts a vertical falling film devolatilization reactor; Figure 2 In , devolatilization reactor 1 adopts a horizontal devolatilization reactor, and devolatilization reactor 2 adopts a vertical falling film devolatilization reactor, Figure 3 In , devolatilization reactor 1 adopts a horizontal devolatilization reactor, and devolatilization reactor 2 adopts a horizontal double-shaft devolatilization reactor.

[0024] By adopting the technical solution of the present invention, the following beneficial effects can be achieved: The present invention provides a method for preparing high-quality polyamide 6 by anionic polymerization combined with a series of devolatilization reactions. The two devolatilization reactors can respectively control the reaction temperature and pressure according to the physical property differences of the monomer and cyclic oligomers. The first devolatilization reactor can selectively remove more than 90% of the caprolactam monomer, effectively reducing the influence of the high-content monomer on the next-stage devolatilization reaction. After a large amount of the monomer is removed, according to the physical property characteristics of the cyclic oligomers, the reaction temperature and reaction pressure of the second devolatilization reactor are set, and the intensive removal of the remaining small amount of caprolactam monomer and cyclic oligomers can be realized.

[0025] In the polyamide 6 final polymer obtained by applying the series of devolatilization reaction system provided by the present invention to the devolatilization of polyamide 6, the monomer content is lower than 0.1 wt%, the cyclic oligomer content is lower than 1.5 wt% (where the cyclic dimer content is lower than 0.1 wt%), and the hot water extractable content is lower than 0.5 wt%. It can be directly used for spinning, injection molding or blow molding, omitting steps such as cooling and pelletizing, hot water extraction, drying and remelting compared with the traditional hot water extraction process, saving a large amount of water and energy, and significantly improving production efficiency. Description of the Drawings

[0026] Figure 1 , Figure 2 and Figure 3 are the schematic structural diagrams of the preparation of high-quality polyamide 6 materials by anionic polymerization combined with staged devolatilization provided by the present invention. Detailed Embodiments

[0027] The present invention will be further described below in conjunction with specific embodiments. It should be understood that these embodiments are only used to illustrate the present invention and not to limit the scope of the present invention. In addition, it should be understood that after reading the content taught by the present invention, those skilled in the art can make various changes or modifications to the present invention, and these equivalent forms also fall within the scope defined by the appended claims of this application.

[0028] To further illustrate the present invention, a method for preparing high-quality polyamide 6 fibers provided by the present invention will be described in detail below in conjunction with embodiments, but they should not be construed as limiting the protection scope of the present invention.

[0029] The present invention measures the contents of monomers and cyclic oligomers in the polyamide 6 base melt and the final polymer using an ultra-high performance liquid chromatograph, and the specific condition parameters are as follows: - Chromatographic column: T3 column, 100 mm × 2.1 mm (inner diameter) × 1.7 μm, or equivalent; - Column temperature: 30 °C; - Flow rate: 0.3 mL / min; - Detection wavelength: 200 nm; - Injection volume: 2 μL; - Elution program (as shown in the following table): Mobile phase A is water, and mobile phase B is acetonitrile.

[0030]

[0031] Comparative Example (1) Preparation of basic active material A: By mass, 0.8 parts of NaOH are added to 100 parts of caprolactam and mixed evenly. The water is removed by vacuum distillation at 100 °C and 5 kPa, and then stored in a storage tank A protected by N2 and kept at a constant temperature of 110 °C; (2) Preparation of basic active material B: By mass, 100 parts of monomer caprolactam are heated and melted. The water is removed by vacuum distillation at 100 °C and 5 kPa, and then 2.0 parts of N-acetylcaprolactam (AcCL) are added and mixed evenly, and then stored in a storage tank B protected by N2 and kept at a constant temperature of 110 °C; (3) Inject the basic reactive materials A and B into a screw extruder in a volume ratio of 1:1 for anionic polymerization. The feeding temperature of the screw extruder is set at 90 °C, the discharging temperature is set at 230 °C, the temperature in the middle section of the screw is set to gradually increase from 90 °C to 230 °C, there are 3 heating zones, the rotation speed is 30 rpm, and the reaction extrusion is carried out to obtain a polyamide 6 basic melt with a relative viscosity of 2.65, a monomer content of 4.09 wt%, a cyclic oligomer content of 2.51 wt% (where the cyclic dimer content is 0.78 wt%), and a hot water extractable content of 5.32 wt%. (4) Transport the polyamide 6 basic melt to a spinning machine for direct spinning. During spinning, there is a large amount of caprolactam gas on the spinneret plate, making it impossible to spin.

[0032] Example 1 A method for preparing high-quality polyamide 6 materials by combining anionic polymerization and fractional devolatilization, the specific steps are as follows: (1) Preparation of basic reactive material A: By mass, add 0.8 parts of NaOH to 100 parts of caprolactam and mix evenly. Remove moisture by vacuum distillation at 100 °C and 5 kPa, and then store it in storage tank A protected by N2 and kept at a constant temperature of 110 °C. (2) Preparation of basic reactive material B: By mass, heat 100 parts of monomer caprolactam to melt, remove moisture by vacuum distillation at 100 °C and 5 kPa, then add 2.0 parts of N-acetylcaprolactam (AcCL) and mix evenly, and then store it in storage tank B protected by N2 and kept at a constant temperature of 110 °C. (3) Inject the basic reactive materials A and B into a screw extruder in a volume ratio of 1:1 for anionic polymerization. The feeding temperature of the screw extruder is set at 90 °C, the discharging temperature is set at 230 °C, the temperature in the middle section of the screw is set to gradually increase from 90 °C to 230 °C, there are 3 heating zones, the rotation speed is 30 rpm, and the reaction extrusion is carried out to obtain a polyamide 6 basic melt with a relative viscosity of 2.63, a monomer content of 4.12 wt%, a cyclic oligomer content of 2.55 wt% (where the cyclic dimer content is 0.75 wt%), and a hot water extractable content of 5.37 wt%. (4) Feed the polyamide 6 base melt into two series-connected devolatilization reactors. The first devolatilization reactor is a horizontal cage reactor, and the second devolatilization reactor is a vertical falling film devolatilization reactor. Each of the two devolatilization reactors is connected to a vacuum pump. The temperature of the first devolatilization reactor is 260 °C, and the reaction pressure is 1000 Pa. The temperature of the second devolatilization reactor is 270 °C, and the reaction pressure is 50 Pa. Finally, a high-quality polyamide 6 melt with a relative viscosity of 2.66, a monomer content of 0.02 wt%, a cyclic oligomer content of 1.34 wt% (where the cyclic dimer content is 0.02 wt%), and a hot water extractable content of 0.35 wt% is obtained; (5) Feed the high-quality polyamide 6 melt into a spinning machine for direct spinning. The spinning temperature is 270 °C, and the winding speed is 4200 m / min to obtain high-quality polyamide 6 fibers with a fiber breaking strength of 5.2 cN / dtex and an elongation at break of 23%.

[0033] Example 2 A method for preparing high-quality polyamide 6 materials by anionic polymerization combined with fractional devolatilization, the specific steps are as follows: (1) Preparation of basic active material A: By mass, add 1.0 part of NaOH to 10 parts of caprolactam and mix evenly. Distill off water under reduced pressure at 80 °C and 5 kPa, and then store it in storage tank A protected by Ar and kept at a constant temperature of 150 °C; (2) Preparation of basic active material B: By mass, heat 100 parts of monomer caprolactam to melt, distill off water under reduced pressure at 80 °C and 5 kPa, then add 1.2 parts of isophthaloyl biscaprolactam and mix evenly, and then store it in storage tank B protected by Ar and kept at a constant temperature of 150 °C; (3) Inject the basic active materials A and B into a screw extruder in a volume ratio of 1:10 for anionic polymerization. The feeding temperature of the screw extruder is set at 110 °C, the discharging temperature of the screw extruder is set at 220 °C, the temperature of the middle section of the screw is set to gradually increase from 110 °C to 220 °C with 3 heating zones, the rotation speed is 30 rpm, and a polyamide 6 base melt with a relative viscosity of 3.50, a monomer content of 4.05 wt%, a cyclic oligomer content of 2.46 wt% (where the cyclic dimer content is 0.72 wt%), and a hot water extractable content of 5.21 wt% is prepared by reactive extrusion; (4) Feed the polyamide 6 base melt into two series-connected devolatilization reactors. The first devolatilization reactor is a horizontal disk reactor, and the second devolatilization reactor is a vertical falling film devolatilization reactor. Each of the two devolatilization reactors is connected to a vacuum pump. The temperature of the first devolatilization reactor is 240 °C, and the reaction pressure is 1000 Pa. The temperature of the second devolatilization reactor is 250 °C, and the reaction pressure is 40 Pa. Finally, a high-quality polyamide 6 melt with a relative viscosity of 3.52, a monomer content of 0.04 wt%, a cyclic oligomer content of 1.36 wt% (where the cyclic dimer content is 0.03 wt%), and a hot water extractable content of 0.40 wt% is obtained; (5) Feed the high-quality polyamide 6 melt into a spinning machine for direct spinning. The spinning temperature is 290 °C, and the winding speed is 3100 m / min to obtain polyamide 6 industrial yarn with a fiber breaking strength of 8.5 cN / dtex and an elongation at break of 23%.

[0034] Example 3 A method for preparing high-quality polyamide 6 materials by anionic polymerization combined with fractional devolatilization, the specific steps are as follows: (1) Preparation of basic active material A: By mass, add 1.1 parts of NaH to 100 parts of caprolactam and mix evenly. Distill off water under reduced pressure at 130 °C and 95 kPa, and then store it in a storage tank A protected by Ar and kept at a constant temperature of 130 °C; (2) Preparation of basic active material B: By mass, heat 100 parts of monomer caprolactam to melt, distill off water under reduced pressure at 130 °C and 95 kPa, then add 1.6 parts of terephthaloyl biscaprolactam (TBCL) and mix evenly, and then store it in a storage tank B protected by Ar and kept at a constant temperature of 130 °C; (3) Inject the basic active materials A and B into a screw extruder in a volume ratio of 1:1 for anionic polymerization. The feeding temperature of the screw extruder is set at 140 °C, the discharging temperature of the screw extruder is set at 240 °C, the temperature in the middle section of the screw is set to gradually increase from 140 °C to 240 °C, there are 3 heating zones, the rotation speed is 30 rpm, and a polyamide 6 base melt with a relative viscosity of 3.2, a monomer content of 3.96 wt%, a cyclic oligomer content of 2.49 wt% (where the cyclic dimer content is 0.71 wt%), and a hot water extractable content of 5.29 wt% is prepared by reactive extrusion; (4) Feed the polyamide 6 base melt into two series-connected devolatilization reactors. The first devolatilization reactor is a falling-strip devolatilizer, and the second devolatilization reactor is a horizontal twin-shaft devolatilization reactor. Each of the two devolatilization reactors is connected to a vacuum pump. The temperature of the first devolatilization reactor is 250 °C, and the reaction pressure is 1500 Pa. The temperature of the second devolatilization reactor is 260 °C, and the reaction pressure is 60 Pa. Finally, a high-quality polyamide 6 melt with a relative viscosity of 3.2, a monomer content of 0.03 wt%, a cyclic oligomer content of 1.25 wt% (where the cyclic dimer content is 0.04 wt%), and a hot water extractable content of 0.35 wt% is obtained; (5) Mix the high-quality polyamide 6 melt with 10% glass fiber reinforcing material and melt-extrude to obtain a glass fiber reinforced polyamide 6 composite material.

[0035] Example 4 A method for preparing high-quality polyamide 6 material by anionic polymerization combined with fractional devolatilization, the specific steps are as follows: (1) Preparation of basic active material A: By mass, add 0.5 parts of sodium ethoxide to 100 parts of caprolactam and mix evenly. Distill off water under reduced pressure at 120 °C and 50 kPa, and then store it in a storage tank A protected by Ar and kept at a constant temperature of 130 °C; (2) Preparation of basic active material B: By mass, heat 100 parts of monomer caprolactam to melt, distill off water under reduced pressure at 120 °C and 50 kPa, then add 1.5 parts of bisacylated lactam-1,6-caprolactam and mix evenly, and then store it in a storage tank B protected by Ar and kept at a constant temperature of 130 °C; (3) Inject the basic active materials A and B into a screw extruder in a volume ratio of 1:1 for anionic polymerization. The feeding temperature of the screw extruder is set at 120 °C, the discharging temperature of the screw extruder is set at 240 °C, the temperature of the middle section of the screw is set to gradually increase from 120 °C to 240 °C with 5 heating zones, the rotation speed is 30 rpm, and a polyamide 6 base melt with a relative viscosity of 2.81, a monomer content of 3.84 wt%, a cyclic oligomer content of 2.52 wt% (where the cyclic dimer content is 0.78 wt%), and a hot water extractable content of 4.96 wt% is obtained by reactive extrusion; (4) The polyamide 6 base melt is fed into two series-connected devolatilization reactors. The first devolatilization reactor is a vertical falling film devolatilization reactor, and the second devolatilization reactor is also a vertical falling film devolatilization reactor. Each of the two devolatilization reactors is connected to a vacuum pump. The temperature of the first devolatilization reactor is 265 °C, and the reaction pressure is 2000 Pa. The temperature of the second devolatilization reactor is 270 °C, and the reaction pressure is 50 Pa. Finally, a high-quality polyamide 6 melt with a relative viscosity of 2.83, a monomer content of 0.02 wt%, a cyclic oligomer content of 1.39 wt% (where the cyclic dimer content is 0.07 wt%), and a hot water extractable content of 0.37 wt% is obtained. (5) The high-quality polyamide 6 melt is fed into a spinning machine for direct spinning. The spinning temperature is 275 °C, and the winding speed is 4000 m / min to obtain high-quality polyamide 6 fibers with a fiber breaking strength of 5.5 cN / dtex and an elongation at break of 20%.

[0036] Example 5 A method for preparing high-quality polyamide 6 materials by anionic polymerization combined with fractional devolatilization, the specific steps are as follows: (1) Preparation of basic active material A: By mass, 0.7 parts of NaOH are added to 100 parts of caprolactam and mixed evenly. Water is removed by vacuum distillation at 120 °C and 90 kPa, and then it is stored in a storage tank A protected by Ar and kept at a constant temperature of 120 °C. (2) Preparation of basic active material B: By mass, 100 parts of monomer caprolactam are heated and melted. Water is removed by vacuum distillation at 120 °C and 90 kPa, and then 1.1 parts of N-acetylcaprolactam (AcCL) are added and mixed evenly. Then it is stored in a storage tank B protected by Ar and kept at a constant temperature of 120 °C. (3) The components of basic active materials A and B are injected into a screw extruder in a volume ratio of 1:1 for anionic polymerization. The feeding temperature of the screw extruder is set at 150 °C, the discharging temperature of the screw extruder is set at 210 °C, the temperature of the middle section of the screw is gradually increased from 150 °C to 210 °C, there are 5 heating sections, the rotation speed is 30 rpm, and a polyamide 6 base melt with a relative viscosity of 3.4, a monomer content of 3.87 wt%, a cyclic oligomer content of 2.54 wt% (where the cyclic dimer content is 0.76 wt%), and a hot water extractable content of 5.19 wt% is prepared by reactive extrusion. (4) The polyamide 6 base melt is transported to two series-connected devolatilization reactors. The first devolatilization reactor is a vertical falling film devolatilization reactor, and the second devolatilization reactor is also a vertical falling film devolatilization reactor. Each of the two devolatilization reactors is connected to a vacuum pump. The temperature of the first devolatilization reactor is 270 °C and the reaction pressure is 900 Pa. The temperature of the second devolatilization reactor is 260 °C and the reaction pressure is 60 Pa. Finally, a high-quality polyamide 6 melt with a relative viscosity of 3.4, a monomer content of 0.02 wt%, a cyclic oligomer content of 1.35 wt% (where the cyclic dimer content is 0.08 wt%), and a hot water extractable content of 0.45 wt% is obtained. (5) The high-quality polyamide 6 melt is transported to a spinning machine for direct spinning. The spinning temperature is 290 °C and the winding speed is 3000 m / min, obtaining high-quality polyamide 6 fibers with a fiber breaking strength of 8.4 cN / dtex and an elongation at break of 22%.

[0037] Table 1 Performance characterization table of the polyamide 6 base melt and polyamide 6 end polymers in the comparative examples and Examples 1 to 5

[0038] Those skilled in the art should understand that the technical features of the above embodiments can be combined arbitrarily. For the sake of brevity of description, not all possible combinations of the technical features in the above embodiments are described. However, as long as these combinations of technical features do not conflict, they should be considered as falling within the scope described in this specification.

[0039] The above embodiments only represent several implementation manners of the present application, and their descriptions are relatively specific and detailed, but should not be construed as limiting the scope of the present application. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present application, several modifications and improvements can still be made, and these all belong to the protection scope of the present application. Therefore, the protection scope of the present application should be subject to the appended claims.

Claims

1. A method for preparing high-quality polyamide 6 materials by anionic polymerization combined with fractional devolatilization, characterized in that, Including: (1) Prepare the basic active material A: Mix the catalyst and caprolactam to obtain the first mixture, subject the first mixture to vacuum distillation and then store it in the storage tank A, where the storage tank A is protected by an inert atmosphere and kept at a constant temperature of 80-150 °C; (2) Prepare the basic active material B: Heat and melt the caprolactam monomer and then perform vacuum distillation, mix the caprolactam monomer with the water removed and the initiator evenly to obtain the second mixture, and store the second mixture in the storage tank B, where it is protected by an inert atmosphere and kept at a constant temperature of 80-150 °C; (3) Inject the basic active material A and the basic active material B components into a screw extruder according to a volume ratio of 1-10:10 for anionic polymerization, and react and extrude to obtain the polyamide 6 basic melt; (4) Transport the polyamide 6 basic melt to the first devolatilization reactor to remove the caprolactam monomer to obtain the polyamide 6 intermediate, and input the polyamide 6 intermediate into the second devolatilization reactor to remove a small amount of caprolactam monomer, cyclic dimer, part of cyclic trimer and part of cyclic tetramer to obtain the polyamide 6 end polymer, where the reaction temperature of the first devolatilization reactor is set at 240-280 °C and the reaction pressure is 200-4000 Pa, and the reaction temperature of the second devolatilization reactor is 240-280 °C and the reaction pressure is 20-600 Pa.

2. The method for preparing a high-quality polyamide 6 material by anionic polymerization combined with staged devolatilization according to claim 1, characterized in that, Directly spin the polyamide 6 end polymer to obtain polyamide 6 civil yarn or industrial yarn; or directly blow film to obtain polyamide 6 film; or add fiber reinforcing material to the polyamide 6 end polymer for injection molding to obtain polyamide 6 composite material.

3. A method for preparing high-quality polyamide 6 material by anionic polymerization combined with fractional devolatilization according to claim 1, characterized in that, In step (1), the catalyst is one or more of sodium caprolactam, sodium ethoxide, LiH, NaH, KH, LiOH, NaOH, KOH.

4. A method for preparing a high-quality polyamide 6 material by anionic polymerization combined with fractional devolatilization according to claim 1, characterized in that, The conditions for vacuum distillation in steps (1) and (2) are a temperature of 80-150 °C and an absolute reaction pressure of 5-95 kPa.

5. A method for preparing a high-quality polyamide 6 material by anionic polymerization combined with fractional devolatilization according to claim 1, characterized in that In step (2), the initiator is one or more of N-acetyl caprolactam, bisacylated lactam-1,6-caprolactam, terephthaloyl biscaprolactam, isophthaloyl biscaprolactam, toluene diisocyanate, diphenylmethane diisocyanate, 1,6-hexane diisocyanate.

6. The method for preparing a high-quality polyamide 6 material by anionic polymerization combined with fractional devolatilization according to claim 1, characterized in that, In step (3), the feeding temperature of the screw extruder is set at 90-160 °C, the discharging port temperature is set at 220-240 °C, the temperature of the middle section of the screw is set to gradually increase from the feeding port temperature to the discharging port temperature, the number of heating sections is not less than 1, and the rotation speed is 20-300 rpm.

7. A method for preparing a high-quality polyamide 6 material by anionic polymerization combined with fractional devolatilization according to claim 1, characterized in that, In step (3), the relative viscosity of the polyamide 6 basic melt is 2.0-4.5, the monomer content is less than 4.2 wt%, the content of cyclic oligomers is less than 2.6 wt%, where the content of cyclic dimer in the cyclic oligomers is less than 0.8 wt% and the content of hot water extractables is less than 5.5 wt%.

8. A method for preparing a high-quality polyamide 6 material by anionic polymerization combined with fractional devolatilization according to claim 1, characterized in that In step (4), the reaction temperatures of the first devolatilization reactor and the second devolatilization reactor can be independently controlled, and both are connected to a vacuum system, and the vacuum system is used to control the reaction pressures of the first devolatilization reactor and the second devolatilization reactor.

9. A method for preparing a high-quality polyamide 6 material by anionic polymerization combined with fractional devolatilization according to claim 1, characterized in that The first devolatilization reactor is selected from one of a horizontal squirrel-cage reactor, a horizontal disk reactor, a falling-strip devolatilizer, and a vertical falling-film devolatilization reactor; the second devolatilization reactor is selected from a vertical falling-film devolatilization reactor or a horizontal twin-shaft devolatilization reactor.

10. A method for preparing a high-quality polyamide 6 material by anionic polymerization combined with fractional devolatilization according to claim 1, characterized in that In step (4), the relative viscosity of the polyamide 6 end-polymer is 2.0 to 4.5, the monomer content is less than 0.1 wt%, the cyclic oligomer content is less than 1.5 wt%, wherein the cyclic dimer content in the cyclic oligomer is less than 0.1 wt%, and the hot water extractable content is less than 0.5 wt%.

Images