A method for inhibiting the formation of polyamide 6 oligomers during melt conveying

Abstract

The present invention belongs to the technical field of polymer material preparation, and relates to a method for inhibiting the generation of polyamide 6 oligomers during melt delivery. By adding a functional masterbatch containing a specific small molecule acid during the delivery of the polyamide 6 melt, under the premise of strictly controlling the amount of small molecule acid added, the terminal amino group on the polyamide 6 molecular chain is shielded, the terminal amino group ring-forming reaction is reduced, and the generation of oligomers such as infusible cyclic dimers is effectively inhibited. The method of the present invention does not need to add additional production steps and costs, and is conducive to the green and efficient preparation of polyamide 6 fibers.

Description

Technical Field

[0001] The invention belongs to the technical field of polymer material preparation, and relates to a method for inhibiting the generation of polyamide 6 oligomers during melt conveying. Background Art

[0002] As a synthetic fiber material with excellent performance, polyamide 6 (PA6) is widely used in many fields such as clothing fibers, engineering plastics, industrial yarns, and military and aerospace. In recent years, with the continuous growth of PA6 production capacity and demand, the problem of oligomer control in its production process has become increasingly prominent. Especially in the production process of PA6 fibers, the presence of oligomers will not only lead to a decline in fiber quality, but may also cause production problems such as equipment blockage.

[0003] At present, the industry generally uses hot water continuous extraction process to remove monomers and oligomers from PA6 chips to meet the requirements of high-speed spinning. However, this process not only consumes a lot of energy, but also greatly increases the production cost of PA6 fibers. In order to reduce production costs and improve production efficiency, melt direct spinning technology has gradually become a research hotspot in the field of PA6 fiber preparation. However, during the melt transport process from the polymerization end to the spinning end, due to the high temperature and long time, the PA6 molecular segments are prone to reverse reactions and generate oligomers again, thus affecting the spinning quality. In addition, oligomers (especially infusible cyclic dimers) are easy to volatilize, sublimate and accumulate at processing components such as spinnerets, which not only increases the difficulty and frequency of cleaning the processing equipment, but also seriously affects the stable processing of PA6 melt.

[0004] In order to solve the above problems, the literature (A Novel Synthetic Strategy for Preparing Polyamide 6 (PA6)-Based Polymer with Transesterification [J]. Polymers, 2019, 11 (6): 978.) uses a dibasic acid end-capping method to inhibit the formation of oligomers. However, this method has obvious shortcomings: both ends of the PA6 molecular chain after end-capping are carboxyl groups, and chain growth cannot be achieved directly. Further esterification or amidation reaction is required to prepare high molecular weight polymers, which not only increases the production steps and costs, but may also have an adverse effect on the molecular chain structure and performance of PA6.

[0005] Therefore, a more effective and simple method is urgently needed to inhibit the formation of oligomers during the PA6 melt conveying process to achieve green and efficient preparation of PA6 fibers. Summary of the invention

[0006] The purpose of the present invention is to solve the problems existing in the prior art and provide a method for inhibiting the generation of polyamide 6 oligomers during melt conveying.

[0007] To achieve the above object, the technical solution adopted by the present invention is as follows:

[0008] A method for inhibiting the generation of polyamide 6 oligomers during melt conveying, wherein a functional masterbatch is added during the conveying of the polyamide 6 melt, wherein the matrix of the functional masterbatch is branched polyamide 6, and the functional masterbatch contains a small molecule acid, and the structural formula of the small molecule acid is , , or , where n<10, r<10, m<10, and the mass of the small molecule acid is 2~4wt% of the total mass of the functional masterbatch and polyamide 6 melt;

[0009] The structural formula of branched polyamide 6 is one of the following:

[0010] , ;

[0011] In the formula, Represents the polyamide 6 molecular chain, and the value range of x, y, and z is 1~2.

[0012] As the preferred technical solution:

[0013] In the method for inhibiting the formation of polyamide 6 oligomers during melt conveying as described above, the content of small molecular acid in the functional masterbatch is 10-20wt%.

[0014] As described above, in a method for inhibiting the formation of polyamide 6 oligomers during melt conveying, the conveying temperature is 240-260° C., the conveying time is 20-80 min, and the conveying pressure is -0.1-1.0 MPa.

[0015] As described above, a method for inhibiting the formation of polyamide 6 oligomers during melt conveying, the relative viscosity of the polyamide 6 melt is 2.4-3.6, the melting point is 220-230° C., and the number average molecular weight is 16000-30000 g / mol.

[0016] In the method for suppressing the formation of polyamide 6 oligomers during melt conveying as described above, the relative viscosity of 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.

[0017] As described above, a method for inhibiting the formation of polyamide 6 oligomers during melt conveying, the preparation process of branched polyamide 6 is: after mixing caprolactam, water, and a polycarboxyl branching agent, 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.

[0018] As described above, a method for inhibiting the formation of polyamide 6 oligomers during melt conveying, the mass of the polycarboxyl branching agent is 0.3~1wt% of the mass of caprolactam, 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. The polycondensation reaction is carried out under negative pressure conditions to reduce the oligomer content.

[0019] In the method for suppressing the generation of polyamide 6 oligomers during melt conveying as described above, the functional masterbatch is added at the start of conveying.

[0020] The above method for inhibiting the formation of polyamide 6 oligomers during melt conveying is as follows: after the conveying is completed, the terminal amino group content of the conveyed product is 5×10 -4 ~2×10 -3 mol / kg, the oligomer content is 0.5~1wt%, the content of infusible cyclic dimer is 0.1~0.3wt%, and the molecular weight distribution index is 1.5~3.0; the number average molecular weight of the conveyed product is 80~90% of the number average molecular weight of the polyamide 6 melt. End-capping will hinder the reversible reaction and partially reduce the molecular weight.

[0021] Principle of the invention:

[0022] Hydrolysis of caprolactam ring-opening will generate an infusible cyclic dimer (the formation process is as follows Figure 1 As shown in the figure, the present invention adds a specific small molecule acid during the polyamide 6 melt conveying process, and the small molecule acid can shield the terminal amino groups on the polyamide 6 molecular chain, reduce the terminal amino group cyclization reaction, and inhibit the formation of infusible cyclic dimers (such as Figure 2 shown);

[0023] During the conveying process of the polyamide 6 melt, the polyamide 6 is already in the form of a macromolecular chain segment, and the small molecule acid only inhibits the reverse reaction during the conveying process, and has no effect on the molecular chain structure of the polyamide 6. The present invention has strict requirements on the amount of small molecule acid added. If the amount of small molecule acid added is too low, there will be no obvious inhibitory effect, and if the amount of small molecule acid added is too high, the polyamide 6 melt will be depolymerized during the conveying process, resulting in a significant decrease in the molecular weight of the polyamide 6 and failure to meet the spinning application requirements.

[0024] In order to make the small molecule acid uniformly mixed with the polyamide 6 melt after addition, the present invention adopts the method of adding masterbatch to effectively avoid the aggregation phenomenon that may be caused by directly adding the small molecule acid, thereby preventing the problem of local depolymerization of polyamide 6 caused by aggregation, and ensuring the uniformity of the molecular weight distribution of polyamide 6;

[0025] In addition, the present invention selects branched polyamide 6 as the matrix of the masterbatch. This is because the addition of a small molecule acid in a high proportion usually leads to a decrease in the melt fluidity of the matrix. Branched polyamide 6 has good melt fluidity due to its unique branched structure and can effectively overcome this defect. This makes the masterbatch based on branched polyamide 6 easier to prepare and more suitable for use in the preparation process of high-content masterbatches.

[0026] Beneficial effects:

[0027] The present invention adds a functional masterbatch based on branched polyamide 6 and containing a specific small molecule acid during the polyamide 6 melt conveying process, and under the premise of strictly controlling the amount of small molecule acid added, effectively inhibits the reverse reaction of polyamide 6 during the conveying process, reduces the generation of infusible cyclic dimers, and avoids adverse effects on the molecular chain structure of polyamide 6 and aggregation and depolymerization problems that may be caused by direct addition of small molecule acid, thereby ensuring the uniformity of the molecular weight distribution of polyamide 6, without adding additional production steps and costs, and is conducive to the green and efficient preparation of polyamide 6 fibers. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 The formation mechanism of infusible cyclic dimer;

[0029] Figure 2 This is the mechanism for inhibiting the formation of infusible cyclic dimers in the present invention. DETAILED DESCRIPTION

[0030] 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.

[0031] The following are the test methods for the relevant performance indicators in each embodiment and comparative example:

[0032] 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:

[0033]

[0034] 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%.

[0035] Melting point: The crystallization and melting behavior of the sample were tested using a TA-Q20 differential scanning calorimeter. About 5 mg of the 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.

[0036] Number average molecular weight and molecular weight distribution index: first dry the 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.

[0037] Terminal amino group content: The chemical titration method was used for testing. The test process of the experimental group was as follows: first, 0.25 g of the transport product was weighed and dissolved in 15 mL of a mixed solution of trifluoroethanol and ethanol with a volume ratio of 75:25 to obtain solution x. Then, solution x was titrated with 0.002 mol / L HCl aqueous solution, and methyl orange was added as an acid-base indicator. When the color of solution x changed from yellow to red, it was the titration end point. Finally, the terminal amino group content of the transport product was calculated according to the following formula (mol / kg):

[0038] ;

[0039] In the formula, is the volume of HCl aqueous solution consumed in titrating the sample, mL; The volume of HCl aqueous solution consumed by the blank control group (basically the same as the experimental group, except that no transport product was added, and only 0.002 mol / L HCl aqueous solution was used to titrate 15 mL of a mixed solution of trifluoroethanol and ethanol with a volume ratio of 75:25), mL; is the concentration of HCl aqueous solution, mol / L; is the mass of the transported product, g;

[0040] The experiment was repeated 5 times and the average value was taken.

[0041] 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 conveying product sample is placed in a vacuum oven at 105°C and dried for 24 hours to constant weight, then a certain mass of the sample (recorded as m0, unit g) is weighed, deionized water is added at a bath ratio of 20:1, and the sample is extracted in boiling water (water bath temperature ≥98°C) using a Soxhlet extractor for 8 hours. After taking out, the sample is placed in a vacuum oven at 105°C and dried for 24 hours and then weighed (the mass is recorded as m1, unit g). Subsequently, the hot water extractable content E (wt%) is calculated by the following formula:

[0042] E=(m0-m1) / m0×100%.

[0043] Content of infusible cyclic dimer: The content of infusible cyclic dimer in the transport product sample was determined using Shimadzu's LC-16 high performance liquid chromatograph (HPLC) equipped with a WondaSil C18-WR column (200 mm, filled particle size 5 μm) 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.

[0044] The structural formula of the branched polyamide 6 in the following Examples 1 to 6 is Formula (I) or Formula (II):

[0045] , ;

[0046] Formula (I) Formula (II)

[0047] In the formula, Represents the polyamide 6 molecular chain, and the value range of x, y, and z is 1~2.

[0048] Example 1

[0049] A method for preparing branched polyamide 6, the specific steps are as follows:

[0050] (1) Preparation of raw materials;

[0051] Caprolactam;

[0052] water;

[0053] Polycarboxyl branching agent: pyromellitic acid;

[0054] (2) Preparation of branched polyamide 6;

[0055] After caprolactam, water and a polycarboxyl branching agent are mixed, a ring-opening reaction is first carried out at a temperature of 220°C and a pressure of 0.5 MPa for 4 hours, and then a polycondensation reaction is carried out 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.

[0056] The relative viscosity of the finally obtained branched polyamide 6 is 3.6, the melting point is 230° C., the number average molecular weight is 30,000 g / mol, and the structural formula is formula (I).

[0057] Example 2

[0058] A method for preparing branched polyamide 6, the specific steps are as follows:

[0059] (1) Preparation of raw materials;

[0060] Caprolactam;

[0061] water;

[0062] Polycarboxyl branching agent: pyromellitic acid;

[0063] (2) Preparation of branched polyamide 6;

[0064] After caprolactam, water and a 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.

[0065] The relative viscosity of the finally 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).

[0066] Example 3

[0067] A method for preparing branched polyamide 6, the specific steps are as follows:

[0068] (1) Preparation of raw materials;

[0069] Caprolactam;

[0070] water;

[0071] Polycarboxyl branching agent: pyromellitic acid;

[0072] (2) Preparation of branched polyamide 6;

[0073] 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.

[0074] The relative viscosity of the finally 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).

[0075] Example 4

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

[0077] (1) Preparation of raw materials;

[0078] Caprolactam;

[0079] water;

[0080] Polycarboxyl branching agent: trimesic acid;

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

[0082] After mixing caprolactam, water and a polycarboxyl branching agent, they are first subjected to a ring-opening reaction at a temperature of 230°C and a pressure of 0.4 MPa for 3 hours, and then subjected to a condensation reaction at a temperature of 265°C and a vacuum degree of 200 Pa for 3 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 3wt% of the mass of caprolactam.

[0083] The final branched polyamide 6 has a relative viscosity of 2.6, a melting point of 223° C., a number average molecular weight of 18500 g / mol, and a structural formula of formula (II), wherein x, y, and z are 1, 1, and 1, respectively.

[0084] Example 5

[0085] A method for preparing branched polyamide 6, the specific steps are as follows:

[0086] (1) Preparation of raw materials;

[0087] Caprolactam;

[0088] water;

[0089] Polycarboxyl branching agent: trimesic acid;

[0090] (2) Preparation of branched polyamide 6;

[0091] After caprolactam, water and a polycarboxyl branching agent are mixed, a ring-opening reaction is first carried out at a temperature of 245°C and a pressure of 0.3 MPa for 2 hours, and then a polycondensation reaction is carried out at a temperature of 255°C and a vacuum degree of 300 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 3wt% of the mass of caprolactam.

[0092] The relative viscosity of the finally 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.

[0093] Example 6

[0094] A method for preparing branched polyamide 6, the specific steps are as follows:

[0095] (1) Preparation of raw materials;

[0096] Caprolactam;

[0097] water;

[0098] Polycarboxyl branching agent: trimesic acid;

[0099] (2) Preparation of branched polyamide 6;

[0100] 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.

[0101] The relative viscosity of the finally obtained 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.

[0102] Example 7

[0103] A method for inhibiting the generation of polyamide 6 oligomers during melt conveying, the specific steps are as follows:

[0104] (1) Preparation of raw materials;

[0105] Small molecule acid: nonanoic acid;

[0106] Branched polyamide 6: prepared from Example 1;

[0107] Polyamide 6 melt: relative viscosity 3.6, melting point 230°C, number average molecular weight 30,000 g / mol;

[0108] (2) Preparation of functional masterbatch;

[0109] The small molecule acid and branched polyamide 6 are melt-blended at 240° C. to obtain a functional masterbatch containing 10 wt % of the small molecule acid;

[0110] (3) During the conveying process of the polyamide 6 melt, the functional masterbatch is added to the polyamide 6 melt at the beginning of the conveying; wherein the conveying temperature is 240°C, the conveying time is 20 min, and the conveying pressure is 1 MPa; the mass of the small molecular acid in the functional masterbatch is 2 wt% of the total mass of the functional masterbatch and the polyamide 6 melt.

[0111] After the delivery, the terminal amino group content of the delivered product was 2×10 -3 mol / kg, the oligomer content is 0.9wt%, the content of infusible cyclic dimer is 0.25wt%, and the molecular weight distribution index is 3; the number average molecular weight of the transported product is 80% of the number average molecular weight of the polyamide 6 melt.

[0112] Comparative Example 1

[0113] A method for inhibiting the formation of polyamide 6 oligomers during melt conveying is basically the same as Example 7, except that: in step (3), the mass of the small molecule acid in the functional masterbatch is 1wt% of the total mass of the functional masterbatch and the polyamide 6 melt.

[0114] After the delivery, the oligomer content of the delivered product was 1.5 wt %, and the content of the infusible cyclic dimer was 0.38 wt %.

[0115] Compared with Example 7, the oligomer content and the infusible cyclic dimer content of the conveying product of Comparative Example 1 are significantly increased. This is because the amount of small molecular acid added in Comparative Example 1 is too low to fully and effectively shield the terminal amino groups on the polyamide 6 molecular chain, and the terminal amino group cyclization reaction cannot be effectively inhibited, resulting in the difficulty in curbing the formation of infusible cyclic dimers, thereby significantly increasing the amount of oligomers and infusible cyclic dimers generated.

[0116] Example 8

[0117] A method for inhibiting the generation of polyamide 6 oligomers during melt conveying, the specific steps are as follows:

[0118] (1) Preparation of raw materials;

[0119] Small molecule acid: decanoic acid;

[0120] Branched polyamide 6: prepared from Example 2;

[0121] Polyamide 6 melt: relative viscosity 2.4, melting point 220°C, number average molecular weight 16000 g / mol;

[0122] (2) Preparation of functional masterbatch;

[0123] The small molecule acid and branched polyamide 6 are melt-blended at 245° C. to obtain a functional masterbatch containing 15 wt % of the small molecule acid;

[0124] (3) During the conveying process of the polyamide 6 melt, the functional masterbatch is added to the polyamide 6 melt at the beginning of the conveying; wherein the conveying temperature is 245°C, the conveying time is 60 min, and the conveying pressure is 0.6 MPa; the mass of the small molecular acid in the functional masterbatch is 2 wt% of the total mass of the functional masterbatch and the polyamide 6 melt.

[0125] After the delivery, the terminal amino group content of the delivered product was 1×10 -3 mol / kg, the oligomer content is 0.9wt%, the content of infusible cyclic dimer is 0.25wt%, and the molecular weight distribution index is 2.8; the number average molecular weight of the transported product is 82% of the number average molecular weight of the polyamide 6 melt.

[0126] Example 9

[0127] A method for inhibiting the generation of polyamide 6 oligomers during melt conveying, the specific steps are as follows:

[0128] (1) Preparation of raw materials;

[0129] Small molecule acid: 3-phenylpropionic acid;

[0130] Branched polyamide 6: prepared from Example 3;

[0131] Polyamide 6 melt: relative viscosity 3.5, melting point 228°C, number average molecular weight 28800 g / mol;

[0132] (2) Preparation of functional masterbatch;

[0133] The small molecule acid and branched polyamide 6 are melt-blended at 245° C. to obtain a functional masterbatch containing 11 wt % of the small molecule acid;

[0134] (3) During the conveying process of the polyamide 6 melt, the functional masterbatch is added to the polyamide 6 melt at the beginning of the conveying; wherein, the conveying temperature is 245°C, the conveying time is 30 min, and the conveying pressure is 0.8 MPa; the mass of the small molecular acid in the functional masterbatch is 2 wt% of the total mass of the functional masterbatch and the polyamide 6 melt.

[0135] After the delivery, the terminal amino content of the delivered product was 9×10 -4mol / kg, the oligomer content is 1wt%, the content of infusible cyclic dimer is 0.3wt%, and the molecular weight distribution index is 2.9; the number average molecular weight of the transported product is 81% of the number average molecular weight of the polyamide 6 melt.

[0136] Example 10

[0137] A method for inhibiting the generation of polyamide 6 oligomers during melt conveying, the specific steps are as follows:

[0138] (1) Preparation of raw materials;

[0139] Small molecule acid: phenylhexanoic acid;

[0140] Branched polyamide 6: prepared from Example 3;

[0141] Polyamide 6 melt: relative viscosity 2.8, melting point 226°C, number average molecular weight 21000 g / mol;

[0142] (2) Preparation of functional masterbatch;

[0143] The small molecule acid and branched polyamide 6 are melt-blended at 250° C. to obtain a functional masterbatch containing 18 wt % of the small molecule acid;

[0144] (3) During the conveying process of the polyamide 6 melt, the functional masterbatch is added to the polyamide 6 melt at the beginning of the conveying; wherein the conveying temperature is 250°C, the conveying time is 70 min, and the conveying pressure is 0.4 MPa; the mass of the small molecular acid in the functional masterbatch is 3 wt% of the total mass of the functional masterbatch and the polyamide 6 melt.

[0145] After the delivery, the terminal amino content of the delivered product was 5×10 -4 mol / kg, the oligomer content is 0.6wt%, the content of infusible cyclic dimer is 0.1wt%, and the molecular weight distribution index is 2.6; the number average molecular weight of the transported product is 85% of the number average molecular weight of the polyamide 6 melt.

[0146] Embodiment 11

[0147] A method for inhibiting the generation of polyamide 6 oligomers during melt conveying, the specific steps are as follows:

[0148] (1) Preparation of raw materials;

[0149] Small molecule acid: glutaric acid;

[0150] Branched polyamide 6: prepared from Example 4;

[0151] Polyamide 6 melt: relative viscosity 3.3, melting point 228°C, number average molecular weight 26500 g / mol;

[0152] (2) Preparation of functional masterbatch;

[0153] The small molecule acid and branched polyamide 6 were melt blended at 255° C. to obtain a functional masterbatch containing 11 wt % of the small molecule acid;

[0154] (3) During the conveying process of the polyamide 6 melt, the functional masterbatch is added to the polyamide 6 melt at the beginning of the conveying; wherein, the conveying temperature is 255°C, the conveying time is 50 min, and the conveying pressure is 0.5 MPa; the mass of the small molecular acid in the functional masterbatch is 2 wt% of the total mass of the functional masterbatch and the polyamide 6 melt.

[0155] After the delivery, the terminal amino content of the delivered product was 9×10 -4 mol / kg, the oligomer content is 0.8wt%, the content of infusible cyclic dimer is 0.2wt%, and the molecular weight distribution index is 2; the number average molecular weight of the transported product is 80% of the number average molecular weight of the polyamide 6 melt.

[0156] Example 12

[0157] A method for inhibiting the generation of polyamide 6 oligomers during melt conveying, the specific steps are as follows:

[0158] (1) Preparation of raw materials;

[0159] Small molecular acid: undecanedioic acid;

[0160] Branched polyamide 6: prepared from Example 4;

[0161] Polyamide 6 melt: relative viscosity 2.5, melting point 221°C, number average molecular weight 17300 g / mol;

[0162] (2) Preparation of functional masterbatch;

[0163] The small molecule acid and branched polyamide 6 were melt blended at 255° C. to obtain a functional masterbatch containing 19 wt % of the small molecule acid;

[0164] (3) During the conveying process of the polyamide 6 melt, the functional masterbatch was added to the polyamide 6 melt at the beginning of the conveying; wherein the conveying temperature was 255°C, the conveying time was 50 min, and the conveying pressure was 0.7 MPa; the mass of the small molecular acid in the functional masterbatch was 3 wt% of the total mass of the functional masterbatch and the polyamide 6 melt.

[0165] After the delivery, the terminal amino content of the delivered product was 7×10 -4mol / kg, the oligomer content is 0.7wt%, the content of infusible cyclic dimer is 0.15wt%, and the molecular weight distribution index is 1.7; the number average molecular weight of the transported product is 89% of the number average molecular weight of the polyamide 6 melt.

[0166] Example 13

[0167] A method for inhibiting the generation of polyamide 6 oligomers during melt conveying, the specific steps are as follows:

[0168] (1) Preparation of raw materials;

[0169] Small molecule acid: terephthalic acid;

[0170] Branched polyamide 6: prepared from Example 5;

[0171] Polyamide 6 melt: relative viscosity 3.2, melting point 227°C, number average molecular weight 25300 g / mol;

[0172] (2) Preparation of functional masterbatch;

[0173] The small molecule acid and branched polyamide 6 are melt-blended at 260° C. to obtain a functional masterbatch containing 20 wt % of the small molecule acid;

[0174] (3) During the conveying process of the polyamide 6 melt, the functional masterbatch is added to the polyamide 6 melt at the beginning of the conveying; wherein, the conveying temperature is 260°C, the conveying time is 70 min, and the conveying pressure is 0.2 MPa; the mass of the small molecular acid in the functional masterbatch is 4 wt% of the total mass of the functional masterbatch and the polyamide 6 melt.

[0175] After the delivery, the terminal amino content of the delivered product was 5×10 -4 mol / kg, the oligomer content is 0.5wt%, the content of infusible cyclic dimer is 0.1wt%, and the molecular weight distribution index is 2.1; the number average molecular weight of the transported product is 82% of the number average molecular weight of the polyamide 6 melt.

[0176] Embodiment 14

[0177] A method for inhibiting the generation of polyamide 6 oligomers during melt conveying, the specific steps are as follows:

[0178] (1) Preparation of raw materials;

[0179] Small molecule acid: terephthalic acid;

[0180] Branched polyamide 6: prepared from Example 6;

[0181] Polyamide 6 melt: relative viscosity 2.9, melting point 228°C, number average molecular weight 21850 g / mol;

[0182] (2) Preparation of functional masterbatch;

[0183] The small molecule acid and branched polyamide 6 are melt-blended at 260° C. to obtain a functional masterbatch containing 16 wt % of the small molecule acid;

[0184] (3) During the conveying process of the polyamide 6 melt, the functional masterbatch is added to the polyamide 6 melt at the beginning of the conveying; wherein, the conveying temperature is 260°C, the conveying time is 80 min, and the conveying pressure is -0.1 MPa; the mass of the small molecular acid in the functional masterbatch is 3 wt% of the total mass of the functional masterbatch and the polyamide 6 melt.

[0185] After the delivery, the terminal amino content of the delivered product was 8×10 -4 mol / kg, the oligomer content is 0.7wt%, the content of infusible cyclic dimer is 0.2wt%, and the molecular weight distribution index is 1.5; the number average molecular weight of the transported product is 90% of the number average molecular weight of the polyamide 6 melt.

Claims

1. A method for inhibiting the formation of polyamide 6 oligomers during melt conveying, characterized in that: The functional masterbatch is added during the conveying process of the polyamide 6 melt, wherein the matrix of the functional masterbatch is branched polyamide 6, and the functional masterbatch contains a small molecule acid, and the structural formula of the small molecule acid is Wherein, n<10, r<10, m<10, the mass of the small molecule acid is 2-4wt% of the total mass of the functional masterbatch and the polyamide 6 melt; The structural formula of branched polyamide 6 is one of the following: 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.

2. A method for inhibiting the formation of polyamide 6 oligomers during melt conveying according to claim 1, characterized in that: The content of small molecular acid in the functional masterbatch is 10-20wt%.

3. The method for inhibiting the formation of polyamide 6 oligomers during melt conveying according to claim 1, characterized in that: The conveying temperature is 240-260°C, the conveying time is 20-80min, and the conveying pressure is -0.1-1.0MPa.

4. The method for inhibiting the formation of polyamide 6 oligomers during melt conveying according to claim 1, characterized in that: The relative viscosity of the polyamide 6 melt is 2.4-3.6, the melting point is 220-230° C., and the number average molecular weight is 16000-30000 g / mol.

5. The method for inhibiting the formation of polyamide 6 oligomers during melt conveying 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.

6. A method for inhibiting the formation of polyamide 6 oligomers during melt conveying according to claim 5, characterized in that: 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.

7. The method for inhibiting the formation of polyamide 6 oligomers during melt conveying according to claim 1, characterized in that: The timing of adding the functional masterbatch is the start of delivery.

8. A method for inhibiting the formation of polyamide 6 oligomers during melt conveying according to any one of claims 1 to 7, characterized in that: After the delivery, the terminal amino content of the delivered product was 5×10 -4 ~2×10 -3 mol / kg, the oligomer content is 0.5-1wt%, the infusible cyclic dimer content is 0.1-0.3wt%, and the molecular weight distribution index is 1.5-3.0; the number average molecular weight of the transported product is 80-90% of the number average molecular weight of the polyamide 6 melt.

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