Preparation method of branched polyamide 6 fiber

Abstract

The invention belongs to the technical field of preparation of high polymer materials, and relates to a preparation method of branched polyamide 6 fibers, which is characterized in that branched polyamide 6 is subjected to melt spinning to prepare the branched polyamide 6 fibers. According to the invention, the structure of branched polyamide 6 is designed, a plurality of anchoring points arranged at intervals are generated on a molecular chain, and the non-fusible cyclic dimer is anchored on the branched polyamide 6 molecular chain by using hydrogen bonds and Van der Waals force, so that uniform dispersion of the non-fusible cyclic dimer is realized, and the problem of aggregation and agglomeration of the non-fusible cyclic dimer in the processing process is avoided; the influence of residual oligomers (especially infusible cyclic dimers) in the melt on the spinning process is fundamentally solved.

Description

Technical Field

[0001] The invention belongs to the technical field of polymer material preparation, and relates to a method for preparing branched polyamide 6 fiber. 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 performance. In recent years, with the rapid development of the polyamide 6 industry, its supply and demand have shown an upward trend. However, in the production and processing of polyamide 6, the presence of oligomers has always been a problem that needs to be solved.

[0003] Polyamide 6 is mainly produced from caprolactam by hydrolysis polymerization. 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, are easy to volatilize or agglomerate during the spinning process, resulting in fiber defects, hard ends, uneven strands, etc., which ultimately affect the fiber's breaking strength and overall performance.

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

[0005] As for the method of removing the infusible cyclic dimer, although it can be attempted to remove it by hot water extraction or negative pressure devolatilization in the polycondensation stage, the effect is limited. Patents CN105669969B and CN104480561B both attempted to remove oligomers by kinetic means, however, the infusible cyclic dimer is a product of thermodynamic equilibrium and will continue to be generated through reverse reaction after removal, and it is difficult to completely remove it by kinetic means. Therefore, the method of removing the infusible cyclic dimer in the prior art has limited effect in practical applications.

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

[0007] In summary, how to fundamentally solve the impact of residual oligomers in the melt, reduce the generation of oligomers and avoid oligomer agglomeration in the matrix, especially how to effectively deal with 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 purpose of the present invention is to solve the problems existing in the prior art and provide a method for preparing branched polyamide 6 fiber.

[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 fiber, comprising melt spinning branched polyamide 6 to prepare branched polyamide 6 fiber, wherein the structural formula of the branched polyamide 6 is one of the following formulas:

[0011] , ;

[0012] In the formula, Represents the polyamide 6 molecular chain, and the value range of x, y, and z is 1~2.

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

[0014] The existing technology solves this problem by removing the infusible cyclic dimer or inhibiting the generation of the infusible cyclic dimer, but the effect is not ideal.

[0015] The present invention takes a different approach. By designing the structure of branched polyamide 6, a plurality of anchoring points arranged at intervals are generated on the molecular chain of branched polyamide 6. The infusible cyclic dimer is then anchored on the molecular chain of branched polyamide 6 by hydrogen bonds and van der Waals forces, thereby evenly dispersing the infusible cyclic dimer and preventing the infusible cyclic dimer from aggregating during processing. In addition to the covalent bonds on 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 paired stable hydrogen bonds are formed within the molecule. There will also be hydrogen bonds and van der Waals forces in the polyamide 6 molecular chain. However, in the case of no branching, the movement of the molecular chain is enhanced at high temperature, and the distance between the molecular chains is large. In fact, it is difficult to form intermolecular anchoring with small molecules such as infusible cyclic dimers through this secondary chemical bond. However, after branching, the branching points will form fixed molecular chain entanglement points, which can aggregate adjacent molecular chains with small molecules such as infusible cyclic dimers to form more hydrogen bonds and van der Waals forces, thereby achieving anchoring and dispersion, and avoiding the movement of infusible cyclic dimers in a hot environment, which will lead to the formation of hydrogen bonds between each other, thereby agglomerating and affecting processing.

[0016] In addition, in the present invention, since the infusible cyclic dimer is not removed from the matrix, according to thermodynamic equilibrium, the infusible cyclic dimer will be in 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 oligomers, thereby reducing the oligomers in the melt.

[0017] As the preferred technical solution:

[0018] According to the method for preparing branched polyamide 6 fiber, 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] The preparation method of branched polyamide 6 fiber as described above comprises the following steps: caprolactam, water and a polycarboxyl branching agent are mixed, and then ring-opening reaction and polycondensation reaction are sequentially performed to obtain branched polyamide 6, wherein the polycarboxyl branching agent is trimesic acid, trimesic acid or pyromellitic acid.

[0020] When the polycarboxyl branching agent is pyromellitic acid, the carboxyl groups of pyromellitic acid will successively react with the terminal amino groups of the polyamide 6 segments during the ring opening-polycondensation stage. 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 segments. Because in the polymerization system, only the infusible cyclic dimer cannot open the ring again to participate in the reaction, so in this process, even if it forms a force with other short molecular chains, the short chain will continue to intensify and polycondense at high temperature. Finally, only the infusible cyclic dimer can be stably combined in the small molecule. Because all reactions are reversible, the carboxyl groups of the branched structure in the actual polymerization will not react completely. Only the branched long chain structure will form an additional anchoring effect on the infusible cyclic dimer. The same applies when the polycarboxyl branching agent is trimesic acid or trimesic acid.

[0021] In the method for preparing branched polyamide 6 fiber as described above, 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.

[0022] In the preparation method of branched polyamide 6 fiber as described above, 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. The polycondensation reaction is carried out under negative pressure conditions to reduce the oligomer content.

[0023] In the preparation method of the branched polyamide 6 fiber as described above, 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%.

[0024] The method for preparing a branched polyamide 6 fiber as described above has a single fiber fineness of 0.5-10 dtex, an oligomer content of <0.45wt%, a non-melting cyclic dimer content of 0.1-0.15wt%, a breaking strength of 2.0-4.0 cN / dtex, a saturated water absorption rate of 4-6%, and a dyeing rate of 85-95%.

[0025] Beneficial effects:

[0026] (1) The present invention designs the structure of branched polyamide 6 to generate multiple anchor points arranged at intervals on the molecular chain, and uses hydrogen bonds and van der Waals forces to anchor the infusible cyclic dimer on the branched polyamide 6 molecular chain, thereby achieving uniform dispersion of the infusible cyclic dimer and avoiding the problem of aggregation during processing. This fundamentally solves the influence of residual oligomers (especially infusible cyclic dimers) in the melt on the spinning process, thereby improving the quality and stability of polyamide 6 fibers.

[0027] (2) Compared with the conventional method 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 This is the synthesis process of branched polyamide 6 and the capture and dispersion mechanism of free infusible cyclic dimers in the spinning melt of Example 1 of the present invention. DETAILED DESCRIPTION

[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 are not intended 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 fall within the scope limited by the appended claims of the application equally.

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

[0031] Relative viscosity: Referring to the test method of China Textile Industry Standard FZ / T 51004-2011, the branched polyamide 6 sample was dissolved in a 96wt% sulfuric acid aqueous solution to prepare a test solution with a concentration of 0.01g / ml. The test was carried out using an Ubbelohde viscometer (capillary diameter of 1.03mm) in a constant temperature water bath at a water temperature of 25±0.1℃. The average value was obtained by repeating 5 parallel tests. The relative viscosity of branched polyamide 6 The calculation is performed according to the following formula:

[0032]

[0033] Wherein, t is the outflow time (s) of the test solution with a concentration of 0.01 g / ml, and t0 is the outflow time (s) of the sulfuric acid aqueous solution with a concentration of 96 wt%.

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

[0035] Number average molecular weight: first dry the branched polyamide 6 sample and then dissolve it in hexafluoroisopropanol to prepare a solution with a concentration of 1.0 mg / mL. Then use the GPC-50 gel permeation chromatograph of PL Company of Britain to test the number average molecular weight of the sample. During the test, use 1,1,1,3,3,3-hexafluoro-2-propanol as the eluent and set its flow rate to 1 mL / min. When the temperature of the chromatographic column is stabilized at 40±1℃, inject the prepared solution into the chromatograph for testing and record the data.

[0036] Denier: The branched polyamide 6 fiber was wound using a yarn length measuring instrument, and the mass of each 100 meters of fiber was weighed.

[0037] Oligomer content (indirectly reflected by testing the hot water extractable content): Referring to the test method of China 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 hours until constant weight, then a certain mass (recorded 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 hours. After taking out, the sample was placed in a vacuum oven at 105°C and dried for 24 hours and then weighed (the mass was recorded as m1, unit g). Subsequently, the hot water extractable content E (wt%) was calculated by the following formula:

[0038] E=(m0-m1) / m0×100%.

[0039] Infusible cyclic dimer content: The infusible cyclic dimer content in the branched polyamide 6 fiber sample was determined using a Shimadzu LC-16 high performance liquid chromatograph (HPLC) equipped with a WondaSil C18-WR column (200 mm, filled with 5 μm particle size) and a UV detector; the detection wavelength was 210 nm and the detection temperature was 40°C; mobile phase: a binary gradient test method was used, with mobile phase A being methanol and mobile phase B being 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 hours, the tensile performance of the sample was tested using an A0-3000cN multifilament strength meter; wherein the stretching speed was 200mm / min, the pre-tension was 5cN, and the test interval was 200±0.5mm; 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±0.5g) in a vacuum oven to constant weight (the mass at this time is recorded as m3, unit g), take out the sample and immerse it in deionized water for 48h. Then wipe the water on the surface of the sample with a dry paper towel and weigh the sample mass (recorded as m4, unit g). Then, calculate the saturated water absorption rate A0 of the sample by the following formula:

[0042] A0=(m4-m3) / m3×100%;

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

[0044] Dye uptake: Acid Scarlet GR was added into water to form a dye solution with a concentration of 1% owf. The pH value of the dye solution was adjusted to 4 by using a 0.2M sodium acetate aqueous solution. The bath ratio was controlled to be 200:1. The branched polyamide 6 fiber was placed in boiling water with a temperature of ≥95°C and dyed at normal pressure (standard atmospheric pressure) for 90 minutes. After dyeing, the absorbance of the residual liquid was tested and the dye uptake was calculated by the following formula:

[0045] ;

[0046] Where: is the absorbance of the residual solution after staining, is the absorbance of the dye solution before staining, is the dilution factor of the residual solution after staining, It is the dilution factor of the dye solution before staining.

[0047] The structural formula of branched polyamide 6 in the following embodiments 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 range of x, y, and z is 1~2.

[0051] Example 1

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

[0053] (1) Preparation of raw materials;

[0054] Caprolactam;

[0055] water;

[0056] Polycarboxyl branching agent: pyromellitic acid;

[0057] (2) Preparation of branched polyamide 6. The synthesis process is as follows: Figure 1 As shown;

[0058] After caprolactam, water and polycarboxyl branching agent are mixed, the mixture is first subjected to ring-opening reaction at a temperature of 220°C and a pressure of 0.5 MPa for 4 hours, and then subjected to polycondensation reaction at a temperature of 270°C and a vacuum degree of 500 Pa for 5 hours; wherein the mass of the polycarboxyl branching agent is 0.3wt% of the mass of caprolactam, and the mass of water is 2wt% 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 fibers;

[0061] The branched polyamide 6 is melt-spun (eg Figure 1 As shown, in this process, the branching points on the branched polyamide 6 will form fixed molecular chain entanglement points, and form hydrogen bonds with the adjacent free infusible cyclic dimers, thereby avoiding the aggregation of the infusible cyclic dimers), and thus the branched polyamide 6 fibers are obtained; wherein, the process parameters of melt spinning are: spinning temperature 280°C, spinning speed 1000m / min, stretching multiple 1.5 times, cooling air temperature 25°C, cooling air speed 0.5m / s, cooling air relative humidity 60%.

[0062] The final branched polyamide 6 fiber has a single fiber fineness of 10 dtex, an oligomer content of 0.45 wt%, a non-melting cyclic dimer content of 0.15 wt%, a breaking strength of 2 cN / dtex, a saturated water absorption of 6%, and a dyeing rate of 95%.

[0063] Example 2

[0064] A method for preparing branched polyamide 6 fiber, 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 caprolactam, water and polycarboxyl branching agent are mixed, a ring-opening reaction is first carried out at a temperature of 240°C and a pressure of 0.3 MPa for 3 hours, and then a polycondensation reaction is carried out at a temperature of 260°C and a vacuum degree of 400 Pa for 4 hours to obtain branched polyamide 6; wherein the mass of the polycarboxyl branching agent is 0.6wt% of the mass of caprolactam, and the mass of water is 3wt% 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) Preparation of branched polyamide 6 fibers;

[0073] The branched polyamide 6 is melt-spinned to obtain branched polyamide 6 fibers; wherein the process parameters of the melt spinning are: spinning temperature 275°C, spinning speed 2000m / min, stretching multiple 1.5 times, cooling air temperature 25°C, cooling air speed 0.6m / s, and cooling air relative humidity 70%.

[0074] The final branched polyamide 6 fiber has a single fiber fineness of 6 dtex, an oligomer content of 0.4 wt%, a non-melting cyclic dimer content of 0.13 wt%, a breaking strength of 2.7 cN / dtex, a saturated water absorption of 5.5%, and a dyeing rate of 94%.

[0075] Example 3

[0076] A method for preparing branched polyamide 6 fiber, the specific steps are as follows:

[0077] (1) Preparation of raw materials;

[0078] Caprolactam;

[0079] water;

[0080] Polycarboxyl branching agent: pyromellitic acid;

[0081] (2) Preparation of branched polyamide 6;

[0082] After caprolactam, water and a polycarboxyl branching agent are mixed, a ring-opening reaction is first carried out at a temperature of 235°C and a pressure of 0.4 MPa for 3 hours, and then a polycondensation reaction is carried out at a temperature of 255°C and a vacuum degree of 100 Pa for 4 hours to obtain branched polyamide 6; wherein the mass of the polycarboxyl branching agent is 0.8wt% of the mass of caprolactam, and the mass of water is 2wt% 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) Preparation of branched polyamide 6 fibers;

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

[0086] The final branched polyamide 6 fiber has a single fiber fineness of 0.5 dtex, an oligomer content of 0.2 wt%, a non-melting cyclic dimer content of 0.1 wt%, a breaking strength of 4 cN / dtex, a saturated water absorption of 4%, and a dyeing rate of 85%.

[0087] Example 4

[0088] A method for preparing branched polyamide 6 fiber, the specific steps are as follows:

[0089] (1) Preparation of raw materials;

[0090] Caprolactam;

[0091] water;

[0092] Polycarboxyl branching agent: trimesic acid;

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

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

[0095] The relative viscosity of the obtained branched polyamide 6 is 2.6, the melting point is 223°C, the number average molecular weight is 18500 g / mol, and the structural formula is formula (II), wherein 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-spinned to obtain branched polyamide 6 fibers; wherein the process parameters of the melt spinning are: spinning temperature 265°C, spinning speed 2500m / min, stretching multiple 1.4 times, cooling air temperature 25°C, cooling air speed 0.7m / s, and cooling air relative humidity 75%.

[0098] The final branched polyamide 6 fiber has a single fiber fineness of 3 dtex, an oligomer content of 0.3wt%, a non-melting cyclic dimer content of 0.11wt%, a breaking strength of 3.0 cN / dtex, a saturated water absorption of 5.5%, and a dyeing rate of 92%.

[0099] Example 5

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

[0101] (1) Preparation of raw materials;

[0102] Caprolactam;

[0103] water;

[0104] Polycarboxyl branching agent: trimesic acid;

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

[0106] After caprolactam, water and polycarboxyl branching agent are mixed, a ring-opening reaction is first carried out at a temperature of 245°C and a pressure of 0.3MPa for 2h, and then a polycondensation reaction is carried out at a temperature of 255°C and a vacuum degree of 300Pa for 4h to obtain branched polyamide 6; wherein the mass of the polycarboxyl branching agent is 0.8wt% of the mass of caprolactam, and the mass of water is 3wt% 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, and the structural formula is formula (II), wherein x, y, and z are 2, 2, and 2 respectively;

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

[0109] The branched polyamide 6 is melt-spinned to obtain branched polyamide 6 fibers; wherein the process parameters of the melt spinning are: spinning temperature 270°C, spinning speed 3000m / min, stretching multiple 1.3 times, cooling air temperature 20°C, cooling air speed 0.8m / s, and cooling air relative humidity 80%.

[0110] The final branched polyamide 6 fiber has a single fiber fineness of 2 dtex, an oligomer content of 0.3 wt%, a non-melting cyclic dimer content of 0.12 wt%, a breaking strength of 3.4 cN / dtex, a saturated water absorption of 4.5%, and a dyeing rate of 90%.

[0111] Example 6

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

[0113] (1) Preparation of raw materials;

[0114] Caprolactam;

[0115] water;

[0116] Polycarboxyl branching agent: trimesic acid;

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

[0118] After caprolactam, water and a polycarboxyl branching agent are mixed, a ring-opening reaction is first carried out at a temperature of 250°C and a pressure of 0.2 MPa for 2 hours, and then a polycondensation reaction is carried out at a temperature of 250°C and a vacuum degree of 60 Pa for 3 hours to obtain branched polyamide 6; wherein the mass of the polycarboxyl branching agent is 1wt% of the mass of caprolactam, and the mass of water is 3wt% of the mass of caprolactam;

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

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

[0121] The branched polyamide 6 is melt-spinned to obtain branched polyamide 6 fibers; wherein the process parameters of the melt spinning are: spinning temperature 260°C, spinning speed 3500m / min, stretching multiple 1.2 times, cooling air temperature 20°C, cooling air speed 0.9m / s, and cooling air relative humidity 85%.

[0122] The final branched polyamide 6 fiber has a single fiber fineness of 1 dtex, an oligomer content of 0.2wt%, a non-melting cyclic dimer content of 0.1wt%, a breaking strength of 3.7 cN / dtex, a saturated water absorption of 4.5%, and a dyeing rate of 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 1~2.

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

3. The method for preparing branched polyamide 6 fiber according to claim 2, characterized in that: 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.

4. The method for preparing branched polyamide 6 fiber according to claim 3, characterized in that: The mass of the polycarboxyl 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.

5. The method for preparing branched polyamide 6 fiber according to claim 3, characterized in that: The temperature of the ring-opening reaction is 220~250℃, the pressure is 0.2~0.5MPa, and the time is 2~4h; the temperature of the polycondensation reaction is 250~270℃, the vacuum degree is 60~500Pa, and the time is 3~5h.

6. 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℃, spinning speed 1000~4000m / min, stretching multiple 1.1~1.5 times, cooling air temperature 15~25℃, cooling air speed 0.5~1m / s, cooling air relative humidity 60%~90%.

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

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