A preparation method of branched polyamide 6 fiber

Abstract

The present invention belongs to the technical field of polymer material preparation, and relates to a method for preparing branched polyamide 6 fibers. The branched polyamide 6 is melt-spun to obtain branched polyamide 6 fibers. By designing the structure of the branched polyamide 6, multiple spaced anchoring points are generated on the molecular chain, and the infusible cyclic dimer is anchored on the branched polyamide 6 molecular chain by hydrogen bonds and van der Waals forces, thereby realizing the uniform dispersion of the infusible cyclic dimer and avoiding the problem of aggregation during processing. Fundamentally, the influence of residual oligomers (especially infusible cyclic dimers) in the melt on the spinning process is solved.

Description

Technical Field

[0001] The present invention belongs to the technical field of polymer material preparation, and relates to a method for preparing branched polyamide 6 fibers. Background Art

[0002] Polyamide 6 (PA6) has been widely used in the field of plastic fibers due to its excellent physical and mechanical properties and textile processing properties. In recent years, with the rapid development of the polyamide 6 industry, both its supply and demand have shown an increasing trend. However, in the production and processing of polyamide 6, the existence of oligomers has always been an urgent problem to be solved.

[0003] Polyamide 6 is mainly prepared by hydrolysis polymerization of caprolactam. However, due to the limitation of thermodynamic equilibrium, the conversion rate of caprolactam is generally only about 90%, which means that about 10% of caprolactam monomers and oligomers will remain in the polymer. These oligomers, especially the infusible cyclic dimers among them, are prone to volatilization or agglomeration during the spinning process, resulting in problems such as fiber defects, hard head filaments, and uneven yarn evenness, ultimately affecting the breaking strength and overall performance of the fibers.

[0004] In the prior art, in order to reduce the influence of infusible cyclic dimers on the spinning process, two main strategies have been adopted: one is to remove the infusible cyclic dimers, and the other is to inhibit the formation of infusible cyclic dimers. However, the effects of these two methods are not ideal.

[0005] For the method of removing infusible cyclic dimers, although it can be attempted to remove them by hot water extraction or negative pressure devolatilization in the polycondensation stage, the effect is limited. Patents CN105669969B and CN104480561B have both attempted to remove oligomers by kinetic means. However, infusible cyclic dimers are products of thermodynamic equilibrium and will continuously generate through reverse reactions after being removed, and it is difficult to completely remove them by kinetic means. Therefore, the methods for removing infusible cyclic dimers in the prior art have limited effects in practical applications.

[0006] On the other hand, for the method of inhibiting the formation of infusible cyclic dimers, theoretically, it can be achieved by adjusting and reducing the polymerization temperature or adding end group inhibitors. However, adjusting the polymerization conditions may affect the polymerization efficiency of polyamide 6, prolong the reaction time, and may cause thermal degradation and yellowing. Adding inhibitors may introduce new impurities due to incomplete reactions and even affect the stability of the spinning process. Therefore, the methods for inhibiting the formation of infusible cyclic dimers in the prior art also have certain drawbacks.

[0007] In summary, how to fundamentally solve the influence of residual oligomers in the melt, reduce the generation of oligomers and avoid the aggregation of oligomers in the matrix, especially how to effectively address the spinning problems caused by infusible cyclic dimers, has become the key to achieving stable production and improving the quality of polyamide 6 fibers. Summary of the Invention

[0008] The object of the present invention is to solve the problems existing in the prior art and provide a method for preparing branched polyamide 6 fibers.

[0009] To achieve the above object, the technical solution adopted by the present invention is as follows:

[0010] A method for preparing branched polyamide 6 fibers, wherein the branched polyamide 6 is melt-spun to obtain branched polyamide 6 fibers, and the structural formula of the branched polyamide 6 is one of the following formulas:

[0011] 、 ;

[0012] In the formula, represents a polyamide 6 molecular chain, and the value ranges of x, y, and z are all 1 to 2.

[0013] In the process of preparing polyamide 6 fibers, if the polyamide 6 melt contains infusible cyclic dimers, during the spinning process, through the high shear and high winding traction of the spinneret, the infusible cyclic dimers will aggregate and cause production problems such as hard head filaments, floating filaments, and hairy filaments.

[0014] The prior art solves this problem by removing infusible cyclic dimers or inhibiting the generation of infusible cyclic dimers, but the effect is not ideal.

[0015] The present invention takes a new approach. By designing the structure of branched polyamide 6, multiple spaced anchoring points are generated on the molecular chain of branched polyamide 6. Then, through hydrogen bonds and van der Waals forces, the infusible cyclic dimer is anchored on the molecular chain of branched polyamide 6, thereby uniformly dispersing the infusible cyclic dimer and avoiding the aggregation of the infusible cyclic dimer during processing. In addition to the covalent bonds in the main chain of the molecular chain, hydrogen bonds and van der Waals forces are both "secondary chemical bonds" in polymers. The reason why the infusible cyclic dimer is stable is that stable hydrogen bonds are formed within the molecule. Similarly, there will also be hydrogen bond and van der Waals force interactions in the molecular chain of polyamide 6. However, in the case of non-branched, the molecular chain motion is enhanced at high temperatures, and the molecular chain spacing is large. In fact, it is difficult to form intermolecular anchoring with small molecules such as the infusible cyclic dimer through this secondary chemical bond. But after branching, the branching points will form fixed molecular chain entanglement points, which can aggregate adjacent molecular chains to form more hydrogen bonds and van der Waals forces with small molecules such as the infusible cyclic dimer, thereby achieving anchoring and dispersion and avoiding the aggregation of the infusible cyclic dimer due to the movement of the infusible cyclic dimer under heat conditions, which affects processing.

[0016] In addition, since the infusible cyclic dimer is not removed from the matrix in the present invention, according to the thermodynamic equilibrium, the infusible cyclic dimer will be in a dynamic equilibrium, so no new infusible cyclic dimer will be formed during processing. In addition, the unreacted carboxyl groups in the branched polyamide 6 can further react with the terminal amino groups of the linear oligomer, thereby reducing the oligomer in the melt.

[0017] As a preferred technical solution:

[0018] For the preparation method of a branched polyamide 6 fiber as described above, the relative viscosity of the branched polyamide 6 is 2.4 - 3.6, the melting point is 220 - 230 °C, and the number average molecular weight is 16000 - 30000 g / mol.

[0019] For the preparation method of a branched polyamide 6 fiber as described above, the preparation process of the branched polyamide 6 is: caprolactam, water, and a polycarboxyl branching agent are mixed, and then ring-opening reaction and polycondensation reaction are carried out in sequence to obtain the branched polyamide 6, where the polycarboxyl branching agent is trimellitic acid, trimesic acid, or pyromellitic acid.

[0020] When the polycarboxylic acid branching agent is pyromellitic acid, during the ring-opening - polycondensation stage, the carboxylic acid groups of pyromellitic acid will successively react with the terminal amino groups of the polyamide 6 chain segments. Due to the steric hindrance effect, the diagonal groups of pyromellitic acid will react first, and then as the reaction proceeds, the other two carboxyl groups will also react with the polyamide 6 chain segments. Since only the infusible cyclic dimer in the polymerization system cannot undergo ring-opening again to participate in the reaction, even if it forms an interaction with other molecular short chains during this process, the short chains will continue to undergo intensification and polycondensation reactions at high temperatures. Finally, only the infusible cyclic dimer remains stably bound in the small molecules. Because all reactions are reversible, in actual polymerization, the carboxyl groups in the branched structure do not all completely react. Only those that form a branched long-chain structure will form an additional anchoring effect on the infusible cyclic dimer. The same applies when the polycarboxylic acid branching agent is trimellitic acid or trimesic acid.

[0021] For the preparation method of a branched polyamide 6 fiber as described above, the mass of the polycarboxylic acid branching agent is 0.3 - 1 wt% of the mass of caprolactam, and the mass of water is 2 - 3 wt% of the mass of caprolactam.

[0022] For the preparation method of a branched polyamide 6 fiber as described above, the temperature of the ring-opening reaction is 220 - 250 °C, the pressure is 0.2 - 0.5 MPa, and the time is 2 - 4 h; the temperature of the polycondensation reaction is 250 - 270 °C, the vacuum degree is 60 - 500 Pa, and the time is 3 - 5 h. Conducting the polycondensation reaction under negative pressure conditions can reduce the content of oligomers.

[0023] For the preparation method of a branched polyamide 6 fiber as described above, the process parameters of melt spinning include: spinning temperature 260 - 280 °C, spinning speed 1000 - 4000 m / min, draw ratio 1.1 - 1.5 times, cooling air temperature 15 - 25 °C, cooling air speed 0.5 - 1 m / s, and relative humidity of cooling air 60% - 90%.

[0024] For the preparation method of a branched polyamide 6 fiber as described above, the denier per filament of the branched polyamide 6 fiber is 0.5 - 10 dtex, the oligomer content is < 0.45 wt%, the content of infusible cyclic dimer is 0.1 - 0.15 wt%, the breaking strength is 2.0 - 4.0 cN / dtex, the saturated water absorption rate is 4 - 6%, and the dye uptake rate is 85 - 95%.

[0025] Beneficial effects:

[0026] (1) By designing the structure of branched polyamide 6, multiple spaced anchoring points are generated on the molecular chain. The infusible cyclic dimer is anchored on the branched polyamide 6 molecular chain by hydrogen bonds and van der Waals forces, thereby achieving the uniform dispersion of the infusible cyclic dimer and avoiding its aggregation problem during the processing. Fundamentally, the influence of the remaining oligomers (especially the infusible cyclic dimer) in the melt on the spinning process is solved, and the quality and stability of polyamide 6 fibers are improved.

[0027] (2) Compared with the traditional methods for removing or inhibiting the infusible cyclic dimer, the method of the present invention is more effective and easier to implement, and will not introduce new impurities or affect the stability of the spinning process. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 It is the synthesis process of branched polyamide 6 in Example 1 of the present invention and the capture and dispersion mechanism of free infusible cyclic dimer in the spinning melt. DETAILED DESCRIPTION OF THE INVENTION

[0029] 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.

[0030] The following are the test methods for relevant performance indicators in each embodiment:

[0031] Relative viscosity: Referring to the test method of China's textile industry standard FZ / T 51004-2011, the branched polyamide 6 sample is dissolved in a sulfuric acid aqueous solution with a concentration of 96 wt% to prepare a test solution with a concentration of 0.01 g / ml, and a Ubbelohde viscometer (capillary diameter of 1.03 mm) is used to conduct the test in a constant temperature water bath at a water temperature of 25 ± 0.1 °C. Five parallel tests are repeated and the average value is taken; the relative viscosity of branched polyamide 6 is calculated according to the following formula:

[0032]

[0033] In the formula, t is the outflow time (s) of the test solution with a concentration of 0.01 g / ml, and t 0 is the outflow time (s) of the sulfuric acid aqueous solution with a concentration of 96 wt%.

[0034] Melting point: The crystallization and melting behaviors of the branched polyamide 6 sample were tested using a TA-Q20 differential scanning calorimeter. 5 mg of the dried sample was heated and cooled at a rate of 10 °C / min under a nitrogen atmosphere, and the scanning results of the first cooling and the second heating were selected.

[0035] Number-average molecular weight: First, the branched polyamide 6 sample was dried and then dissolved in hexafluoroisopropanol to prepare a solution with a concentration of 1.0 mg / mL. Then, the number-average molecular weight of the sample was tested using a GPC-50 gel permeation chromatograph from Polymer Laboratories Ltd. of the UK. During the test, 1,1,1,3,3,3-hexafluoro-2-propanol was used as the eluent and its flow rate was set at 1 mL / min. When the temperature of the chromatographic column was stable at 40 ± 1 °C, the prepared solution was injected into the chromatograph for testing and data recording.

[0036] Fineness: The branched polyamide 6 fiber was wound using a yarn winding and length measuring instrument, and the mass of every 100-meter fiber was weighed.

[0037] Oligomer content (indirectly reflected by testing the content of hot water extractables): Referring to the test method of China's textile industry standard FZ / T 51004-2011, the branched polyamide 6 fiber sample was placed in a vacuum oven at 105 °C and dried for 24 h until constant weight. Subsequently, a certain mass (denoted as m0, unit: g) of the sample was weighed, deionized water was added at a bath ratio of 20:1, and the sample was extracted in boiling water (water bath temperature ≥ 98 °C) using a Soxhlet extractor for 8 h. After taking out, the sample was placed in a vacuum oven at 105 °C and dried for 24 h and then weighed (the mass was denoted as m1, unit: g). Subsequently, the content of hot water extractables E (wt%) was calculated by the following formula:

[0038] E = (m0 - m1) / m0 × 100%.

[0039] Content of infusible cyclic dimer: The content of infusible cyclic dimer in the branched polyamide 6 fiber sample was determined using an LC-16 high-performance liquid chromatograph (HPLC) from Shimadzu Corporation, equipped with a WondaSil C18-WR chromatographic column (200 mm, packing particle size 5 μm) and an ultraviolet detector. Among them, the detection wavelength was 210 nm and the detection temperature was 40 °C; mobile phase: The binary gradient test method was used, mobile phase A was methanol, and mobile phase B was water.

[0040] Breaking strength: After the branched polyamide 6 fiber sample was placed in a constant temperature and humidity chamber at a temperature of 20 °C and a humidity of 65% for 48 h, the tensile properties of the sample were tested using an A0-3000cN multifilament strength tester. Among them, the tensile speed was 200 mm / min, the pre-tension was 5 cN, and the test spacing was 200 ± 0.5 mm; each sample was tested 10 times and the average value was taken.

[0041] Saturated water absorption rate: After drying the branched polyamide 6 fiber sample (20 ± 0.5 g) to a constant weight in a vacuum oven (the mass at this time is denoted as m3, unit: g), take out the sample, immerse it in deionized water for 48 h, then dry the water on the surface of the sample with a dry paper towel, weigh the sample mass (denoted as m4, unit: g). Subsequently, calculate the saturated water absorption rate A0 of the sample through the following formula:

[0042] A0 = (m4 - m3) / m3 × 100%;

[0043] Each sample is tested in parallel for 4 groups and the average value is taken.

[0044] Dye uptake rate: Add Acid Red GR to water to form a dye solution with a concentration of 1% owf, adjust the pH value of the dye solution to 4 with an aqueous solution of sodium acetate with a concentration of 0.2 M, control the bath ratio to 200:1, place the branched polyamide 6 fiber in boiling water at a temperature ≥ 95 °C and dye it at normal pressure (standard atmospheric pressure) for 90 min. After the dyeing is completed, measure the absorbance of the residual liquid, and calculate the dye uptake rate through the following formula:

[0045] ;

[0046] In the formula: is the absorbance of the residual liquid after dyeing, is the absorbance of the dye solution before dyeing, is the dilution factor of the residual liquid after dyeing, is the dilution factor of the dye solution before dyeing.

[0047] In the following examples, the structural formula of the branched polyamide 6 is formula (Ⅰ) or formula (Ⅱ):

[0048] 、 ;

[0049] Formula (Ⅰ) Formula (Ⅱ)

[0050] In the formula, represents the polyamide 6 molecular chain, and the value ranges of x, y, and z are all 1 - 2.

[0051] Example 1

[0052] A preparation method of branched polyamide 6 fiber, the specific steps are as follows:

[0053] (1) Preparation of raw materials;

[0054] Caprolactam;

[0055] Water;

[0056] Multi - carboxyl branching agent: Pyromellitic acid;

[0057] (2) Preparation of branched polyamide 6, and the synthesis process is as follows Figure 1 shown;

[0058] After mixing caprolactam, water and polycarboxyl branching agent, first carry out ring-opening reaction at a temperature of 220 °C and a pressure of 0.5 MPa for 4 h, and then carry out polycondensation reaction at a temperature of 270 °C and a vacuum degree of 500 Pa for 5 h; among them, the mass of the polycarboxyl branching agent is 0.3 wt% of the mass of caprolactam, and the mass of water is 2 wt% of the mass of caprolactam;

[0059] The relative viscosity of the obtained branched polyamide 6 is 3.6, the melting point is 230 °C, the number-average molecular weight is 30000 g / mol, and the structural formula is formula (Ⅰ);

[0060] (3) Preparation of branched polyamide 6 fiber;

[0061] Melt-spin the branched polyamide 6 (as Figure 1 shown. During this process, the branching points on the branched polyamide 6 will form fixed molecular chain entanglement points and form hydrogen bonds with adjacent free infusible cyclic dimers, avoiding the aggregation of infusible cyclic dimers), and then the branched polyamide 6 fiber is obtained; among them, the process parameters of melt spinning are: spinning temperature 280 °C, spinning speed 1000 m / min, drawing ratio 1.5 times, cooling air temperature 25 °C, cooling air speed 0.5 m / s, and relative humidity of cooling air 60%.

[0062] The fineness of the single filament of the finally obtained branched polyamide 6 fiber is 10 dtex, the content of oligomers is 0.45 wt%, the content of infusible cyclic dimers is 0.15 wt%, the breaking strength is 2 cN / dtex, the saturated water absorption rate is 6%, and the dye uptake rate is 95%.

[0063] Example 2

[0064] A preparation method of branched polyamide 6 fiber, and the specific steps are as follows:

[0065] (1) Preparation of raw materials;

[0066] Caprolactam;

[0067] Water;

[0068] Polycarboxyl branching agent: pyromellitic acid;

[0069] (2) Preparation of branched polyamide 6;

[0070] After mixing caprolactam, water, and a polycarboxylic acid branching agent, first conduct a ring-opening reaction at a temperature of 240 °C and a pressure of 0.3 MPa for 3 h, and then conduct a polycondensation reaction at a temperature of 260 °C and a vacuum degree of 400 Pa for 4 h to obtain branched polyamide 6; among them, the mass of the polycarboxylic acid branching agent is 0.6 wt% of the mass of caprolactam, and the mass of water is 3 wt% of the mass of caprolactam;

[0071] The relative viscosity of the obtained branched polyamide 6 is 3.2, the melting point is 227 °C, the number-average molecular weight is 25000 g / mol, and the structural formula is formula (I);

[0072] (3)Prepare branched polyamide 6 fiber;

[0073] Melt-spin the branched polyamide 6 to obtain the branched polyamide 6 fiber; among them, the process parameters of melt spinning are: spinning temperature 275 °C, spinning speed 2000 m / min, draw ratio 1.5 times, cooling air temperature 25 °C, cooling air speed 0.6 m / s, and relative humidity of cooling air 70%.

[0074] The fineness of the single filament of the finally obtained branched polyamide 6 fiber is 6 dtex, the content of oligomers is 0.4 wt%, the content of infusible cyclic dimers is 0.13 wt%, the breaking strength is 2.7 cN / dtex, the saturated water absorption rate is 5.5%, and the dye uptake rate is 94%.

[0075] Example 3

[0076] A preparation method of a branched polyamide 6 fiber, the specific steps are as follows:

[0077] (1)Preparation of raw materials;

[0078] Caprolactam;

[0079] Water;

[0080] Polycarboxylic acid branching agent: pyromellitic acid;

[0081] (2)Prepare branched polyamide 6;

[0082] After mixing caprolactam, water, and a polycarboxylic acid branching agent, first conduct a ring-opening reaction at a temperature of 235 °C and a pressure of 0.4 MPa for 3 h, and then conduct a polycondensation reaction at a temperature of 255 °C and a vacuum degree of 100 Pa for 4 h to obtain branched polyamide 6; among them, the mass of the polycarboxylic acid branching agent is 0.8 wt% of the mass of caprolactam, and the mass of water is 2 wt% of the mass of caprolactam;

[0083] The relative viscosity of the obtained branched polyamide 6 is 3, the melting point is 225 °C, the number-average molecular weight is 23000 g / mol, and the structural formula is formula (I);

[0084] (3)Prepare branched polyamide 6 fiber;

[0085] The branched polyamide 6 is melt-spun to obtain branched polyamide 6 fibers; among them, the process parameters of melt spinning are: spinning temperature 270 °C, spinning speed 4000 m / min, draw ratio 1.1 times, cooling air temperature 15 °C, cooling air speed 1 m / s, and relative humidity of cooling air 90%.

[0086] The fineness of the single filament of the finally obtained branched polyamide 6 fiber is 0.5 dtex, the oligomer content is 0.2 wt%, the content of infusible cyclic dimer is 0.1 wt%, the breaking strength is 4 cN / dtex, the saturated water absorption rate is 4%, and the dye uptake rate is 85%.

[0087] Example 4

[0088] A preparation method of branched polyamide 6 fibers, the specific steps are as follows:

[0089] (1) Preparation of raw materials;

[0090] Caprolactam;

[0091] Water;

[0092] Multi-carboxyl branching agent: trimellitic acid;

[0093] (2) Preparation of branched polyamide 6;

[0094] After mixing caprolactam, water, and the multi-carboxyl branching agent, first carry out a ring-opening reaction at a temperature of 230 °C and a pressure of 0.4 MPa for 3 h, and then carry out a polycondensation reaction at a temperature of 265 °C and a vacuum degree of 200 Pa for 3 h to obtain branched polyamide 6; among them, the mass of the multi-carboxyl branching agent is 0.8 wt% of the mass of caprolactam, and the mass of water is 3 wt% of the mass of caprolactam;

[0095] The relative viscosity of the prepared branched polyamide 6 is 2.6, the melting point is 223 °C, the number-average molecular weight is 18500 g / mol, the structural formula is formula (II), and x, y, and z are 1, 1, and 1 respectively;

[0096] (3) Preparation of branched polyamide 6 fibers;

[0097] The branched polyamide 6 is melt-spun to obtain branched polyamide 6 fibers; among them, the process parameters of melt spinning are: spinning temperature 265 °C, spinning speed 2500 m / min, draw ratio 1.4 times, cooling air temperature 25 °C, cooling air speed 0.7 m / s, and relative humidity of cooling air 75%.

[0098] The fineness of the single filament of the finally obtained branched polyamide 6 fiber is 3 dtex, the oligomer content is 0.3 wt%, the content of infusible cyclic dimer is 0.11 wt%, the breaking strength is 3.0 cN / dtex, the saturated water absorption rate is 5.5%, and the dye uptake rate is 92%.

[0099] Example 5

[0100] A preparation method of branched polyamide 6 fiber, the specific steps are as follows:

[0101] (1) Preparation of raw materials;

[0102] Caprolactam;

[0103] Water;

[0104] Multi-carboxyl branching agent: benzene-1,3,5-tricarboxylic acid;

[0105] (2) Preparation of branched polyamide 6;

[0106] After mixing caprolactam, water and the multi-carboxyl branching agent, first carry out a ring-opening reaction at a temperature of 245 °C and a pressure of 0.3 MPa for 2 h, and then carry out a polycondensation reaction at a temperature of 255 °C and a vacuum degree of 300 Pa for 4 h to obtain branched polyamide 6; among them, the mass of the multi-carboxyl branching agent is 0.8 wt% of the mass of caprolactam, and the mass of water is 3 wt% of the mass of caprolactam;

[0107] The relative viscosity of the obtained branched polyamide 6 is 2.8, the melting point is 225 °C, the number-average molecular weight is 20500 g / mol, the structural formula is formula (Ⅱ), and x, y, and z are 2, 2, and 2 respectively;

[0108] (3) Preparation of branched polyamide 6 fiber;

[0109] Melt-spin the branched polyamide 6 to obtain branched polyamide 6 fiber; among them, the process parameters of melt spinning are: spinning temperature 270 °C, spinning speed 3000 m / min, draw ratio 1.3 times, cooling air temperature 20 °C, cooling air speed 0.8 m / s, and relative humidity of cooling air 80%.

[0110] The fineness of the single filament of the finally obtained branched polyamide 6 fiber is 2 dtex, the oligomer content is 0.3 wt%, the content of infusible cyclic dimer is 0.12 wt%, the breaking strength is 3.4 cN / dtex, the saturated water absorption rate is 4.5%, and the dye uptake rate is 90%.

[0111] Example 6

[0112] A preparation method of branched polyamide 6 fiber, the specific steps are as follows:

[0113] (1) Preparation of raw materials;

[0114] Caprolactam;

[0115] Water;

[0116] Polycarboxylic acid branching agent: benzene - 1,3,5 - tricarboxylic acid;

[0117] (2) Preparation of branched polyamide 6;

[0118] After mixing caprolactam, water and the polycarboxylic acid branching agent, first carry out a ring - opening reaction at a temperature of 250 °C and a pressure of 0.2 MPa for 2 h, and then carry out a polycondensation reaction at a temperature of 250 °C and a vacuum degree of 60 Pa for 3 h to obtain branched polyamide 6; among them, the mass of the polycarboxylic acid branching agent is 1 wt% of the mass of caprolactam, and the mass of water is 3 wt% of the mass of caprolactam;

[0119] The relative viscosity of the prepared branched polyamide 6 is 2.4, the melting point is 220 °C, the number - average molecular weight is 16000 g / mol, the structural formula is formula (Ⅱ), and x, y, and z are 2, 2, and 2 respectively;

[0120] (3) Preparation of branched polyamide 6 fibers;

[0121] Carry out melt spinning on the branched polyamide 6 to obtain branched polyamide 6 fibers; among them, the process parameters of melt spinning are: spinning temperature 260 °C, spinning speed 3500 m / min, draw ratio 1.2 times, cooling air temperature 20 °C, cooling air speed 0.9 m / s, and relative humidity of cooling air 85%.

[0122] The fineness of the single filament of the finally prepared branched polyamide 6 fiber is 1 dtex, the oligomer content is 0.2 wt%, the content of infusible cyclic dimer is 0.1 wt%, the breaking strength is 3.7 cN / dtex, the saturated water absorption rate is 4.5%, and the dyeing rate is 87%.

Claims

1. A method for preparing branched polyamide 6 fiber, characterized in that: The branched polyamide 6 is melt-spun to obtain branched polyamide 6 fibers, wherein the structural formula of the branched polyamide 6 is one of the following formulas: In the formula, Represents the polyamide 6 molecular chain, and the value range of x, y, and z is 1 to 2 The preparation process of branched polyamide 6 is as follows: caprolactam, water and a polycarboxyl branching agent are mixed, and then ring-opening reaction and polycondensation reaction are carried out in sequence to obtain branched polyamide 6, wherein the polycarboxyl branching agent is trimesic acid, trimesic acid or pyromellitic acid, the mass of the polycarboxyl branching agent is 0.3-1wt% of the mass of caprolactam, and the mass of water is 2-3wt% of the mass of caprolactam; the temperature of the ring-opening reaction is 220-250° C., the pressure is 0.2-0.5MPa, and the time is 2-4h; the temperature of the polycondensation reaction is 250-270° C., the vacuum degree is 60-500Pa, and the time is 3-5h.

2. The method for preparing branched polyamide 6 fiber according to claim 1, characterized in that: The relative viscosity of the branched polyamide 6 is 2.4-3.6, the melting point is 220-230° C., and the number average molecular weight is 16000-30000 g / mol.

3. The method for preparing branched polyamide 6 fiber according to claim 1, characterized in that: The process parameters of melt spinning include: spinning temperature 260-280°C, spinning speed 1000-4000m / min, stretching multiple 1.1-1.5 times, cooling air temperature 15-25°C, cooling air speed 0.5-1m / s, cooling air relative humidity 60%-90%.

4. The method for preparing branched polyamide 6 fiber according to claim 1, characterized in that: The monofilament fineness of the branched polyamide 6 fiber is 0.5-10 dtex, the oligomer content is less than 0.45wt%, the infusible cyclic dimer content is 0.1-0.15wt%, the breaking strength is 2.0-4.0 cN / dtex, the saturated water absorption is 4-6%, and the dyeing rate is 85-95%.

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