A nylon 66 resin with low gel content and its preparation method and application

Abstract

The application provides a nylon 66 resin with low gel content and a preparation method and application thereof, and the preparation method of the nylon 66 resin with low gel content comprises the following steps: heating and melting nylon 66 monomers, an end-capping agent, a catalyst, a lubricant and a stabilizer to form a melt; and the melt is heated to polymerize, so that the nylon 66 resin with low gel content is obtained. The nylon 66 resin with low gel content is synthesized by using a direct melt polymerization method and by adding the lubricant and the stabilizer with synergistic effect, and has the characteristics of good melt fluidity, good thermal stability, high impact strength and excellent mechanical properties, and therefore can be applied to the field of high-speed spinning.

Description

Technical Field

[0001] This invention relates to the field of nylon 66 resin preparation technology, and in particular to a method for preparing nylon 66 resin with low gel content, the nylon 66 resin with low gel content obtained therefrom, and its application in high-speed spinning. Background Technology

[0002] The production of nylon 66 resin typically follows a salt-prepolymerization-final polymerization process. First, adipic acid is neutralized with hexamethylenediamine to form a salt, then a condensation reaction is carried out using a nylon 66 salt solution. During the reaction, evaporated water is removed to ensure the forward reaction proceeds. To maintain the fluidity of nylon 66 in the reactor, the temperature of the material transport pipelines and the inner walls of the equipment is generally above 280°C. Under these temperature conditions, even in an oxygen-free environment, nylon 66 will undergo thermal degradation and cross-linking reactions, generating insoluble and infusible gels, with the amount of gel increasing with reaction time. Besides the gel entering the material, prolonged material residence during nylon 66 resin production can also lead to scaling and carbonization into black particles. These gels and black particles in the granules can cause spinneret blockage during spinning, resulting in fiber breakage and affecting production. This limits the spinning speed, production efficiency, and fiber fineness of nylon 66 resin, making it difficult to widely apply in the apparel fiber field requiring high-speed spinning. Therefore, it is essential to invent a new method for producing nylon 66 resin with low gel content.

[0003] Some studies have attempted to reduce gel content by adding antioxidants and heat stabilizers to improve the thermal stability of nylon 66 resin. For example, CN104327494A uses various organic acids, and CN1252183C uses various copper salts, phosphorus-containing compounds, and hindered amines as antioxidants to improve the stability of nylon 66 resin, but none of them mention any improvement in gel formation.

[0004] Some studies have also optimized production equipment and processes to obtain nylon 66 with low gel content. CN114106319A discloses a real-time online titration system that controls the molecular weight and gel content of nylon 66 by controlling the acid-amine ratio during polymerization in real time, achieving a gel content as low as 0.2% in the obtained nylon 66. CN108602227A increases the molecular weight of nylon 66 while reducing gel formation by adding a vacuum process in the post-polymerization stage and using a twin-screw extruder to remove volatile components, resulting in nylon 66 with a gel content of less than 50 ppm. However, it only measures gels larger than 10 micrometers, and the vacuum devolatilization twin-screw extruder has problems such as high liquid holdup, inconsistent material residence time, and wide molecular weight distribution when the material viscosity is high. Furthermore, the die temperature also has a significant impact on gel formation. CN116120542A and CN108602227A disclose a solid-phase polymerization method for thickening nylon polymers to avoid black spots and discoloration, but the reaction time is long, the production efficiency is low, and the yellow index of nylon is still high. CN102746509A describes a polycondensation reactor that uses falling film or drop strip methods to accelerate the evaporation of condensation water, lower the reaction temperature, shorten the reaction time, reduce gelation, and avoid scaling on the reactor wall, but it does not provide a clear measurement of the gel content of the polymer.

[0005] The formation of gel and black spots in nylon 66 resin is due to factors beyond just liquid level fluctuations and prolonged material adhesion caused by high equipment friction; it is also caused by cross-linking from side reactions. While the methods described above yielded nylon 66 resin with relatively low gel content, and some methods optimized the polymerization equipment, the control methods are relatively simple, attempting to reduce gel content from a single perspective, and they have high technical requirements, increasing production costs. Therefore, it is still necessary to explore a more energy-efficient, easier-to-implement, and adaptable method for reducing gel formation that can be adapted to existing equipment. Summary of the Invention

[0006] One of the objectives of this invention is to provide a method for preparing nylon 66 resin with low gel content.

[0007] The second objective of this invention is to provide a nylon 66 resin with low gel content.

[0008] The third objective of this invention is to provide an application of nylon 66 resin with low gel content in high-speed spinning.

[0009] In a first aspect, the present invention provides a method for preparing nylon 66 resin with low gel content, comprising the following steps:

[0010] S1. Nylon 66 monomer, end-capping agent, catalyst, lubricant and stabilizer are heated and melted to form a melt;

[0011] The nylon 66 monomers mentioned above include adipic acid and hexamethylenediamine;

[0012] The lubricant is selected from one or more of polypropylene wax, polyethylene wax, oxidized polyethylene wax, erucamide, dendritic polyamide, butyl stearate, glyceryl monostearate, and calcium stearate.

[0013] The stabilizer is selected from one or more of copper acetate, manganese acetate, cuprous iodide, potassium iodide, potassium chloride, and potassium phosphate.

[0014] S2. The melt is heated to polymerize, resulting in nylon 66 resin with low gel content.

[0015] The following is a detailed explanation:

[0016] In this invention, there are no particular restrictions on the method and order of heating and melting in step S1. Adipic acid can be mixed with hexamethylenediamine, capping agent, catalyst, lubricant and stabilizer and then heated and melted together. Alternatively, hexamethylenediamine can be heated and melted first, and then capping agent, catalyst, lubricant and stabilizer can be added and mixed and heated and melted. Alternatively, adipic acid and hexamethylenediamine can be heated and melted separately, and then the two melts can be mixed, and then capping agent, catalyst, lubricant and stabilizer can be added and mixed and heated and melted.

[0017] In step S1, in some embodiments, the molar ratio of adipic acid to hexamethylenediamine is 1:1.001-1.01;

[0018] In step S1, in some embodiments, based on the total mass of nylon 66 monomers, the amount of end-capping agent added is 0.02-0.2 wt%, such as 0.05%, 0.1%, or 0.15%, but not limited thereto, preferably 0.1-0.2 wt%; the amount of catalyst added is 0.1-0.3 wt%, such as 0.12%, 0.15%, 0.18%, 0.2%, or 0.3%, but not limited thereto, preferably 0.15-0.3 wt%. The lubricant is added at 0.02-0.15 wt%, such as 0.05%, 0.06%, 0.08%, 0.1%, but not limited thereto, preferably 0.02-0.1 wt%; the stabilizer is added at 0.001-0.01 wt%, such as 0.001%, 0.0025%, 0.005%, 0.0075%, 0.01%, but not limited thereto, preferably 0.0025-0.01 wt%.

[0019] In some embodiments, the capping agent is one or more selected from acetic acid, butyric acid, propionic acid, and adipic acid, preferably one or two selected from acetic acid and adipic acid;

[0020] In some embodiments, the catalyst is one or more selected from potassium phosphite, sodium phosphite, magnesium phosphite, calcium phosphite, zinc phosphite, potassium hypophosphite, sodium hypophosphite, magnesium hypophosphite, calcium hypophosphite, and zinc hypophosphite, preferably one or more selected from potassium hypophosphite, sodium hypophosphite, zinc hypophosphite, and magnesium hypophosphite.

[0021] In some embodiments, the lubricant is one or more selected from polypropylene wax, polyethylene wax, oxidized polyethylene wax, calcium stearate, and dendritic polyamide;

[0022] In some embodiments, the stabilizer is one or more selected from copper acetate, cuprous iodide, and potassium iodide;

[0023] In step S1, in some embodiments, the heating and melting temperature is 160-220°C, preferably 160-190°C, and more preferably 160-180°C.

[0024] In this invention, the polymerization in step S2 may include prepolymerization and final polymerization.

[0025] In step S2, in some embodiments, the prepolymerization temperature is 220-250℃, preferably 230-240℃, more preferably 230-235℃; the prepolymerization pressure is 1.2-1.8MPa, preferably 1.4-1.6MPa, more preferably 1.4-1.5MPa; and the prepolymerization time is 1-2h, preferably 1-1.5h, more preferably 1.2-1.5h.

[0026] In step S2, in some embodiments, the final polymerization includes a two-stage polymerization. In the first stage polymerization, the temperature is first raised to 250-265°C, preferably 250-255°C, and the pressure inside the reactor is maintained at 1.2-1.8 MPa, preferably 1.4-1.6 MPa, by venting water vapor. In the second stage polymerization, the temperature is further raised to 265-285°C, preferably 270-280°C, more preferably 275-280°C, and the pressure is released to atmospheric pressure within 0.5-2 hours, preferably 0.5-1 hour, more preferably 0.6-1 hour. Then, a vacuum is drawn for 5-30 minutes, preferably 10-20 minutes, more preferably 10-15 minutes, with a vacuum degree of 0.08-0.1 MPa, preferably 0.09-0.1 MPa.

[0027] In some embodiments, a method for preparing a nylon 66 resin with low gel content includes the following steps:

[0028] (1) Add adipic acid in a molar ratio of 1:1.001-1.01, along with 0.02-0.2 wt% end-capping agent, 0.001-0.01 wt% stabilizer, 0.02-0.15 wt% lubricant, and 0.1-0.3 wt% catalyst to the reactor, purge with nitrogen to remove air and maintain a certain positive pressure, seal and heat to 160-220℃, and start stirring;

[0029] (2) Continue heating to 220-250℃, and the pressure reaches 1.2-1.8MPa. Maintain the pressure and temperature, and continue the reaction for 1-2 hours.

[0030] (3) The temperature is then raised to 250-265℃, and the pressure inside the reactor is maintained at 1.2-1.8MPa by venting the water vapor inside the reactor.

[0031] (4) Continue to heat to 265-285℃, and release the pressure to normal pressure within 0.5-2h, then evacuate for 5-30min, with a vacuum degree of 0.08-0.1MPa;

[0032] (5) The material is pulled out, granulated, and dried to obtain nylon 66 resin chips.

[0033] In a second aspect, the present invention provides a nylon 66 resin with low gel content, prepared by the preparation method described above, wherein the gel content in the nylon 66 resin with low gel content is 0.1 wt‰ to 1 wt‰.

[0034] In some embodiments, the low-gel-content nylon 66 resin has the following structure:

[0035]

[0036] Wherein, n = 45-130, preferably n = 65-110, and the weight-average molecular weight of nylon 66 is 10000-30000; preferably 15000-25000.

[0037] Thirdly, the present invention provides the application of the low gel content nylon 66 resin in high-speed spinning.

[0038] Beneficial effects:

[0039] This invention utilizes direct melt polymerization and synthesizes nylon 66 resin with low gel content by adding lubricants and stabilizers with synergistic effects. It has the characteristics of good melt flowability, good thermal stability, high impact strength and excellent mechanical properties, and therefore can be applied in the field of high-speed spinning.

[0040] In addition, the method of the present invention has the advantages of simple process, flexible operation, easy control, high production efficiency and low cost.

[0041] The present invention has been described in detail above; however, the above embodiments are merely illustrative in nature and are not intended to limit the invention. Furthermore, this document is not limited to the foregoing prior art or the invention itself, or to any theory described in the following embodiments.

[0042] Unless otherwise expressly stated, numerical ranges throughout the application include any subranges therein and any numerical values ​​incremented by the smallest subunit of a given value. Unless otherwise expressly stated, numerical values ​​throughout the application represent approximate measures or limitations on the range of embodiments including minor deviations from a given value and having approximately the mentioned value as well as having the mentioned precise value. Except in the detailed description of the working embodiments provided at the end, all numerical values ​​of parameters (e.g., quantities or conditions) in this application (including the appended claims) should in all cases be understood to be modified by the term “approximately,” regardless of whether “approximately” actually precedes the numerical value. “Approximately” indicates that the stated numerical value allows for slight inaccuracies (some close to precision at that value; approximately or reasonably close to the value; approximate). If the inaccuracy provided by “approximately” is not understood in this common sense in the art, then “approximately” as used herein at least indicates a variation that can be produced by common methods of measuring and using these parameters. For example, “approximately” can include variations less than or equal to 10%, less than or equal to 5%, less than or equal to 4%, less than or equal to 3%, less than or equal to 2%, less than or equal to 1%, or less than or equal to 0.5%. Detailed Implementation

[0043] The present invention will be further described below with reference to the embodiments. It should be noted that the following embodiments are provided for illustrative purposes only and do not constitute a limitation on the scope of protection of the present invention.

[0044] Unless otherwise specified, the raw materials, reagents, and methods used in the embodiments are all conventional raw materials, reagents, and methods in the art.

[0045] raw material:

[0046] All raw materials used in the experiment were readily available to those skilled in the art through conventional means. Specifically, polypropylene wax, polyethylene wax, oxidized polyethylene wax, and calcium stearate were sourced from Qingdao Sainuo New Materials Co., Ltd., and dendritic polyamide was sourced from Weihai Chenyuan Molecular New Materials Co., Ltd.

[0047] Example 1

[0048] (1) Add 1114.13g of adipic acid, 886.08g of hexamethylenediamine, 2.0g of acetic acid, 6.0g of sodium hypophosphite, 0.05g of cuprous iodide, 0.1g of potassium iodide, and 0.4g of polyethylene wax to the reactor. After adding all the raw materials, purge the reactor with nitrogen to remove air and pressurize it to 0.1MPa. Seal the reactor and heat it. When the temperature reaches 180℃, start stirring.

[0049] (2) Continue to heat up and gradually increase the pressure. When the temperature reaches 220℃, the pressure reaches 1.2MPa. Maintain the pressure and temperature for 1.5h.

[0050] (3) The temperature is raised to 250℃, and the pressure inside the reactor is maintained at 1.2MPa by venting the water vapor inside the reactor.

[0051] (4) Continue heating to 265℃, and after releasing the pressure to normal pressure, evacuate to -0.1MPa.

[0052] (5) The material is pulled out, granulated, and dried to obtain nylon 66 resin chips.

[0053] Example 2

[0054] (1) Add 1114.13g of adipic acid, 889.76g of hexamethylenediamine, 2.0g of acetic acid, 4.0g of sodium hypophosphite, 0.03g of cuprous iodide, 0.1g of potassium iodide, and 1.0g of polyethylene wax to the reactor. After adding all the raw materials, purge the reactor with nitrogen to remove air and pressurize it to 0.1MPa. Seal the reactor and heat it. When the temperature reaches 200℃, start stirring.

[0055] (2) Continue to heat up and gradually increase the pressure. When the temperature reaches 240℃, the pressure reaches 1.6MPa. Maintain the pressure and temperature for 1.5h.

[0056] (3) The temperature is raised to 265°C, and the pressure inside the reactor is maintained at 1.6 MPa by venting water vapor inside the reactor.

[0057] (4) Continue heating to 285℃, and after releasing the pressure to normal pressure, evacuate to -0.1MPa.

[0058] (5) The material is pulled out, granulated, and dried to obtain nylon 66 resin chips.

[0059] Example 3

[0060] (1) Add 1114.13g of adipic acid, 894.76g of hexamethylenediamine, 0.4g of acetic acid, 4.0g of sodium hypophosphite, 0.1g of cuprous iodide, 0.1g of potassium iodide, and 2.0g of polyethylene wax to the reactor. After adding all the raw materials, purge the reactor with nitrogen to remove air and pressurize it to 0.1MPa. Seal the reactor and heat it. When the temperature reaches 220℃, start stirring.

[0061] (2) Continue to heat up and gradually increase the pressure. When the temperature reaches 250℃, the pressure reaches 1.8MPa. Maintain the pressure and temperature for 1.5h.

[0062] (3) Heat up to 265℃, and release pressure appropriately during the process to maintain a pressure of 1.8MPa.

[0063] (4) Continue heating to 285℃, release the pressure to normal pressure, and then evacuate to -0.1MPa.

[0064] (5) The material is pulled out, granulated, and dried to obtain nylon 66 resin chips.

[0065] Example 4

[0066] (1) Add 1114.13g of adipic acid, 886.76g of hexamethylenediamine, 4.0g of acetic acid, 4.0g of sodium hypophosphite, 0.05g of cuprous iodide, 0.1g of potassium iodide, and 1.0g of polypropylene wax to the reactor. After adding all the raw materials, purge the reactor with nitrogen to remove air and pressurize it to 0.1MPa. Seal the reactor and heat it. When the temperature reaches 160℃, start stirring.

[0067] (2) Continue to heat up and gradually increase the pressure. When the temperature reaches 230℃, the pressure reaches 1.4MPa. Maintain the pressure and temperature for 1.5h.

[0068] (3) Heat up to 250℃, and release pressure appropriately during the process to maintain a pressure of 1.4MPa.

[0069] (4) Continue heating to 280℃, release the pressure to normal pressure, and then evacuate to -0.1MPa.

[0070] (5) The material is pulled out, granulated, and dried to obtain nylon 66 resin chips.

[0071] Example 5

[0072] (1) Add 1114.13g of adipic acid, 886.76g of hexamethylenediamine, 4.0g of acetic acid, 4.0g of magnesium hypophosphite, 0.05g of cuprous iodide, 0.1g of potassium iodide, and 1.0g of oxidized polyethylene wax to the reactor. After adding all the raw materials, purge the reactor with nitrogen to remove air and pressurize it to 0.1MPa. Seal the reactor and heat it. When the temperature reaches 160℃, start stirring.

[0073] (2) Continue to heat up and gradually increase the pressure. When the temperature reaches 230℃, the pressure reaches 1.4MPa. Maintain the pressure and temperature for 1 hour.

[0074] (3) Heat up to 250℃, and release pressure appropriately during the process to maintain a pressure of 1.4MPa.

[0075] (4) Continue heating to 275℃, release the pressure to normal pressure, and then evacuate to -0.1MPa.

[0076] (5) The material is pulled out, granulated, and dried to obtain nylon 66 resin chips.

[0077] Example 6

[0078] (1) Add 1114.13g of adipic acid, 886.76g of hexamethylenediamine, 4.0g of acetic acid, 4.0g of potassium hypophosphite, 0.05g of cuprous iodide, 0.1g of potassium iodide, and 1.0g of calcium stearate to the reactor. After adding all the raw materials, purge the reactor with nitrogen to remove air and pressurize it to 0.1MPa. Seal the reactor and heat it. When the temperature reaches 160℃, start stirring.

[0079] (2) Continue to heat up and gradually increase the pressure. When the temperature reaches 230℃, the pressure reaches 1.4MPa. Maintain the pressure and temperature for 2 hours.

[0080] (3) Heat up to 250℃, and release pressure appropriately during the process to maintain a pressure of 1.4MPa.

[0081] (4) Continue heating to 280℃, release the pressure to normal pressure, and then evacuate to -0.1MPa.

[0082] (5) The material is pulled out, granulated, and dried to obtain nylon 66 resin chips.

[0083] Example 7

[0084] (1) Add 1114.13g of adipic acid, 886.76g of hexamethylenediamine, 4.0g of adipic acid, 4.0g of sodium hypophosphite, 0.05g of copper acetate, and 1.0g of dendritic polyamide to the reactor. After adding all the raw materials, purge the reactor with nitrogen to remove air and pressurize it to 0.1MPa. Seal the reactor and heat it. When the temperature reaches 160℃, start stirring.

[0085] (2) Continue to heat up and gradually increase the pressure. When the temperature reaches 230℃, the pressure reaches 1.4MPa. Maintain the pressure and temperature for 1.5h.

[0086] (3) Heat up to 250℃, and release pressure appropriately during the process to maintain a pressure of 1.4MPa.

[0087] (4) Continue heating to 280℃, release the pressure to normal pressure, and then evacuate to -0.1MPa.

[0088] (5) The material is pulled out, granulated, and dried to obtain nylon 66 resin chips.

[0089] Comparative Example 1

[0090] (1) Add 1114.13g of adipic acid, 886.76g of hexamethylenediamine, 4.0g of acetic acid, 4.0g of sodium hypophosphite, and 1000g of deionized water to the reactor. After adding all the raw materials, purge the reactor with nitrogen to remove air and pressurize it to 0.1MPa. Seal the reactor and heat it. When the temperature reaches 160℃, start stirring.

[0091] (2) Continue to heat up and gradually increase the pressure. During the process of the temperature rising from room temperature to 230℃, the pressure is controlled by the exhaust valve. When the temperature reaches 230℃, the pressure is maintained at 1.4MPa for 1.5h.

[0092] (3) Heat up to 250℃, and release pressure appropriately during the process to maintain a pressure of 1.4MPa.

[0093] (4) Continue heating to 280℃, release the pressure to normal pressure, and then evacuate to -0.1MPa.

[0094] (5) The material is pulled out, granulated, and dried to obtain nylon 66 resin chips.

[0095] Comparative Example 2

[0096] (1) Add 1114.13g of adipic acid, 886.76g of hexamethylenediamine, 4.0g of acetic acid, and 4.0g of sodium hypophosphite to the reactor. After adding all the raw materials, purge the reactor with nitrogen to remove air and pressurize it to 0.1MPa. Seal the reactor and heat it. When the temperature reaches 160℃, start stirring.

[0097] (2) Continue to heat up and gradually increase the pressure. During the process of the temperature rising from room temperature to 230℃, the pressure is controlled by the exhaust valve. When the temperature reaches 230℃, the pressure is maintained at 1.4MPa for 1.5h.

[0098] (3) Heat up to 250℃, and release pressure appropriately during the process to maintain a pressure of 1.4MPa.

[0099] (4) Continue heating to 280℃, release the pressure to normal pressure, and then evacuate to -0.1MPa.

[0100] (5) The material is pulled out, granulated, and dried to obtain nylon 66 resin chips.

[0101] Comparative Example 3

[0102] (1) Add 1114.13g of adipic acid, 886.76g of hexamethylenediamine, 4.0g of acetic acid, 4.0g of sodium hypophosphite, 0.05g of cuprous iodide, and 0.05g of potassium iodide to the reactor. After adding all the raw materials, purge the reactor with nitrogen to remove air and pressurize it to 0.1MPa. Seal the reactor and heat it. When the temperature reaches 160℃, start stirring.

[0103] (2) Continue to heat up and gradually increase the pressure. During the process of the temperature rising from room temperature to 230℃, the pressure is controlled by the exhaust valve. When the temperature reaches 230℃, the pressure is maintained at 1.4MPa for 1.5h.

[0104] (3) Heat up to 250℃, and release pressure appropriately during the process to maintain a pressure of 1.4MPa.

[0105] (4) Continue heating to 280℃, release the pressure to normal pressure, and then evacuate to -0.1MPa.

[0106] (5) The material is pulled out, granulated, and dried to obtain nylon 66 resin chips.

[0107] Comparative Example 4

[0108] (1) Add 1114.13g of adipic acid, 886.76g of hexamethylenediamine, 4.0g of acetic acid, 4.0g of sodium hypophosphite and 1.0g of polyethylene wax to the reactor. After adding all the raw materials, purge the reactor with nitrogen to remove air and pressurize it to 0.1MPa. Seal the reactor and heat it. When the temperature reaches 160℃, start stirring.

[0109] (2) Continue to heat up and gradually increase the pressure. When the temperature reaches 230℃, the pressure reaches 1.4MPa. Maintain the pressure and temperature for 1.5h.

[0110] (3) The temperature is raised to 250°C, and the pressure inside the reactor is maintained at 1.4 MPa by venting the water vapor inside the reactor.

[0111] (4) Continue heating to 280℃, and after releasing the pressure to normal pressure, evacuate to -0.1MPa.

[0112] (5) The material is pulled out, granulated, and dried to obtain nylon 66 resin chips.

[0113] Performance Evaluation

[0114] The gel content and mechanical properties of the products obtained in the examples and comparative examples were tested, and the specific test methods are as follows:

[0115] 1. Gel content test

[0116] (1) Take a certain mass of M0 nylon 66 resin slices to be tested and dissolve them in 98% anhydrous formic acid for 24 hours.

[0117] (2) Select a microporous filter membrane of appropriate specifications with a minimum pore size of 0.22 μm. Soak it in formic acid solution until the mass is constant. The mass of the filter membrane is recorded as M1.

[0118] (3) Install a sand core filter and a circulating water vacuum pump. During the filtration process, it is necessary to prevent contamination by foreign matter, and when the filtrate level is low, add a certain amount of formic acid and repeat several times.

[0119] (4) After filtration, rinse with a certain amount of deionized water and anhydrous ethanol, remove the filter membrane and dry it to constant weight. Its mass is recorded as M2.

[0120] The amount of gel G in Nylon 66 is calculated using the following formula:

[0121] G = (M2 - M1) / M0 × 100%.

[0122] 2. Mechanical property testing

[0123] Tests were conducted according to the standards GB / T1042-92 for tensile strength, GB / T9341-88 for bending, and GB / T1843-1996 for impact.

[0124] 3. Thermodynamic property testing

[0125] The thermodynamic properties of nylon 66 resin were analyzed and tested using differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA).

[0126] The results are shown in Table 1.

[0127] Table 1. Performance test results of nylon 66 resin in the examples and comparative examples.

[0128]

[0129] As shown in Table 1, the thermodynamic properties of the nylon 66 resins prepared in Examples 1-7 and Comparative Examples 1-4 are not significantly different. Regarding mechanical properties, the nylon 66 resins prepared in Examples 1-8 exhibit superior mechanical properties compared to Comparative Examples 1-4, particularly with a significant improvement in impact strength. According to the gel test data, the gel content of the nylon 66 resins prepared in Examples 1-7 is significantly lower than that in Comparative Examples 1-4, demonstrating that this invention has a significant effect on reducing the gel content in nylon 66 resin. Further comparison reveals that the addition of lubricants and stabilizers has a significant synergistic effect, achieving results not possible with the addition of a single component, thereby further reducing the gel content and enabling high-speed spinning of this type of nylon 66 resin.

[0130] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing nylon 66 resin with low gel content, characterized in that, Includes the following steps: S1. Nylon 66 monomer, end-capping agent, catalyst, lubricant, and stabilizer are heated and melted to form a melt; wherein, based on the total mass of nylon 66 monomer, the amount of end-capping agent added is 0.02-0.2wt%; the amount of catalyst added is 0.1-0.3wt%; the amount of lubricant added is 0.02-0.15wt%; the amount of stabilizer added is 0.001-0.01wt%; the heating and melting temperature is 160-220℃; The nylon 66 monomer comprises adipic acid and hexamethylenediamine, wherein the molar ratio of adipic acid to hexamethylenediamine is 1:1.001-1.01; The capping agent is selected from one or more of acetic acid, butyric acid, propionic acid, and adipic acid; The catalyst is selected from one or more of potassium phosphite, sodium phosphite, magnesium phosphite, calcium phosphite, zinc phosphite, potassium hypophosphite, sodium hypophosphite, magnesium hypophosphite, calcium hypophosphite, and zinc hypophosphite. The lubricant is selected from one or more of polypropylene wax, polyethylene wax, oxidized polyethylene wax, erucamide, dendritic polyamide, butyl stearate, glyceryl monostearate, and calcium stearate. The stabilizer is selected from one or more of copper acetate, manganese acetate, cuprous iodide, potassium iodide, potassium chloride, and potassium phosphate. S2. The melt is heated to carry out polymerization, resulting in nylon 66 resin with low gel content. The polymerization includes prepolymerization and final polymerization; The prepolymerization temperature is 220-250℃; the prepolymerization pressure is 1.2-1.8MPa; and the prepolymerization time is 1-2h. The final polymerization consists of two stages. In the first stage, the temperature is raised to 250-265℃, and the pressure inside the reactor is maintained at 1.2-1.8MPa by venting water vapor. In the second stage, the temperature is raised to 265-285℃, and the pressure is reduced to atmospheric pressure within 0.5-2 hours. Then, a vacuum is drawn for 5-30 minutes, with a vacuum degree of 0.08-0.1MPa.

2. The preparation method according to claim 1, characterized in that, In step S1, based on the total mass of nylon 66 monomers, the amount of end-capping agent added is 0.1-0.2 wt%; the amount of catalyst added is 0.15-0.3 wt%; the amount of lubricant added is 0.02-0.1 wt%; and the amount of stabilizer added is 0.0025-0.01 wt%.

3. The preparation method according to claim 1, characterized in that, In step S1, the capping agent is one or both selected from acetic acid and adipic acid; and / or The catalyst is selected from one or more of potassium hypophosphite, sodium hypophosphite, zinc hypophosphite, and magnesium hypophosphite; and / or The lubricant is selected from one or more of polypropylene wax, polyethylene wax, oxidized polyethylene wax, calcium stearate, and dendritic polyamide; and / or The stabilizer is selected from one or more of copper acetate, cuprous iodide, and potassium iodide.

4. The preparation method according to claim 1, characterized in that, In step S1, the heating and melting temperature is 160-190℃.

5. The preparation method according to claim 1, characterized in that, In step S1, the heating and melting temperature is 160-180℃.

6. The preparation method according to claim 1, characterized in that, The prepolymerization temperature is 230-240℃; the prepolymerization pressure is 1.4-1.6MPa; and the prepolymerization time is 1-1.5h.

7. The preparation method according to claim 1, characterized in that, The prepolymerization temperature is 230-235℃; the prepolymerization pressure is 1.4-1.5MPa; and the prepolymerization time is 1.2-1.5h.

8. The preparation method according to claim 1, characterized in that, The first stage of final polymerization involves heating to 250-255℃, maintaining the pressure inside the reactor at 1.4-1.6 MPa by venting water vapor. The second stage of polymerization involves heating to 270-280℃, releasing the pressure to atmospheric pressure within 0.5-1 hour, and then evacuating for 10-20 minutes to a vacuum level of 0.09-0.1 MPa.

9. The preparation method according to claim 8, characterized in that, The first stage of final polymerization involves heating to 250-255℃, maintaining the pressure inside the reactor at 1.4-1.6 MPa by venting water vapor. The second stage of polymerization involves heating to 275-280℃, releasing the pressure to atmospheric pressure within 0.6-1 hour, and then evacuating for 10-15 minutes to a vacuum level of 0.09-0.1 MPa.

10. The preparation method according to claim 1, characterized in that, Includes the following steps: (1) Add adipic acid and hexamethylenediamine in a molar ratio of 1:1.001-1.01, 0.02-0.2wt% end-capping agent, 0.001-0.01wt% stabilizer, 0.02-0.15wt% lubricant and 0.1-0.3wt% catalyst to the reactor, purge with nitrogen to remove air and maintain a certain positive pressure, seal and heat to 160-220℃, and start stirring; (2) Continue heating to 220-250℃, and the pressure reaches 1.2-1.8MPa. Maintain the pressure and temperature, and continue the reaction for 1-2 hours. (3) The temperature is then raised to 250-265℃, and the pressure inside the reactor is maintained at 1.2-1.8MPa by venting the water vapor inside the reactor. (4) Continue to heat up to 265-285℃, and release the pressure to normal pressure within 0.5-2h, then evacuate for 5-30min, with a vacuum degree of 0.08-0.1MPa; (5) The material is pulled out, granulated, and dried to obtain nylon 66 resin chips.

11. A nylon 66 resin with low gel content, characterized in that, The nylon 66 resin with low gel content is prepared by the preparation method according to any one of claims 1-10, wherein the gel content is 0.1 wt‰ to 1 wt‰.

12. The low gel content nylon 66 resin according to claim 11, characterized in that, The low-gel-content nylon 66 resin has the following structure: Where n=45-130, the weight-average molecular weight of Nylon 66 is 10000-30000.

13. The low gel content nylon 66 resin according to claim 12, characterized in that, n=65-110, the weight-average molecular weight of nylon 66 is 15000-25000.

14. The application of the low gel content nylon 66 resin as described in any one of claims 11-13 in high-speed spinning.

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