High-strength modified nylon 66 material and preparation method

Abstract

This invention relates to the field of functional nylon material research and development technology, and discloses a high-strength modified nylon 66 material and its preparation method. Specifically, it involves synthesizing a flame-retardant epoxy crosslinking agent I containing disulfide bonds and a flame-retardant epoxy crosslinking agent II containing multiple hydrogen bonds; utilizing the flame-retardant epoxy crosslinking agent I and the flame-retardant epoxy crosslinking agent II to undergo a ring-opening crosslinking reaction with the terminal amino / carboxyl groups of nylon 66 through epoxy groups, introducing a dual dynamic crosslinking network between the nylon 66 molecular chains to obtain a high-strength modified nylon 66 material. This invention significantly improves the mechanical strength, intrinsic flame-retardant properties, and damage self-healing ability of nylon 66 material through the synergistic effect of the dual dynamic crosslinking mechanism, while retaining its original thermoplastic processing characteristics. It can replace traditional fiber-reinforced nylon 66 composite materials or metal structural parts, and can be used in high-precision, high-reliability lightweight structural components in the fields of automotive parts, electronics and electrical engineering, aerospace, or machinery manufacturing.

Description

Technical Field

[0001] This invention relates to the field of functional nylon material research and development technology, specifically to a high-strength modified nylon 66 material and its preparation method. Background Technology

[0002] Nylon 66, as an important engineering plastic, possesses excellent mechanical properties, wear resistance, chemical corrosion resistance, self-lubricating properties, and good heat resistance, and is widely used in automotive parts, electronics, aerospace, and machinery manufacturing. However, with the development trend of lightweighting and high performance in modern industry, engineering plastics are gradually replacing some metal materials, which places higher demands on the strength, rigidity, and overall performance of nylon 66 materials.

[0003] However, unmodified pure nylon 66 materials have many limitations in practical applications: (1) The absolute strength and modulus of pure PA66 are not enough to withstand high loads under extreme working conditions, making it difficult to meet the demand for plastic to replace steel in high-end structural parts; (2) PA66 molecular chains contain a large number of polar amide groups, resulting in a high water absorption rate. After absorbing water, it will not only cause size changes, but also lead to a significant decrease in mechanical properties; (3) Pure PA66 has poor impact toughness at low temperature and in dry state.

[0004] In existing technologies, PA66 is typically physically reinforced and modified by adding fillers such as glass fibers and carbon fibers. For example, patent CN114907690A discloses a composite material of aramid fiber and glass fiber reinforced nylon 66 and its preparation method. The resulting nylon 66 material exhibits strong stability, high wear resistance, and high strength, high modulus, and high impact resistance. However, fiber-reinforced systems may suffer from problems such as weak interfacial bonding (high chemical inertness of the fiber surface, resulting in poor compatibility with the nylon 66 matrix resin), uneven filler dispersion, easy fiber floating (leading to fiber exposure on the product surface), and increased weight. These issues limit the improvement in the overall performance of the material, resulting in poor processing stability and product appearance, thus restricting its application in high-precision, high-reliability, and lightweight structural components.

[0005] Cross-linking chemical modification of nylon 66 materials can change the molecular structure and achieve the technical goal of enhancing its performance. However, nylon 66 materials cross-linked by conventional covalent bonds often form a rigid three-dimensional network structure, which severely restricts the movement of molecular chains. This results in a sharp decrease in elongation at break and impact strength, even though the modulus of the material is improved. The material exhibits strong but brittle characteristics, and the melt viscosity increases significantly, making it difficult to process and form.

[0006] Research has found that dynamic chemical bonds (reversible sacrificial bonds) are considered an important structural feature of natural materials that combine high strength and high toughness (such as spider silk, mussel byssal silk, and bones). During the deformation process of the material under stress, dynamic chemical bonds break preferentially before the polymer backbone is destroyed. The breaking of sacrificial bonds can not only dissipate mechanical energy, but also release hidden chain segments at the same time, promote local molecular chain orientation, thereby achieving significant reinforcement and toughening.

[0007] Furthermore, the presence of dynamic covalent bonds can also endow materials with self-healing capabilities. That is, when a material is damaged by external factors (such as scratches, cracks, or fractures), the dynamic covalent bonds at the damaged interface can undergo a reversible break-reorganization process under mild conditions, allowing the molecular chains to reconnect and thus autonomously restore the original structure and properties of the material, extending its service life and improving its reliability.

[0008] Besides the bottleneck of mechanical properties, the flammability of nylon 66 itself is also a significant factor restricting its diversified product development. PA66 is extremely flammable, producing molten droplets and releasing large amounts of smoke during combustion, severely limiting its application in more fields. However, traditional physically blended flame retardant additives are prone to problems such as poor interfacial compatibility, deterioration of mechanical properties, and migration and precipitation of flame retardants, making it difficult to achieve a synergistic improvement in both mechanical and flame retardant properties. Summary of the Invention

[0009] This invention addresses the technical problems of existing nylon 66 materials, such as difficulty in achieving a balance between strength and toughness and insufficient flame retardancy, by providing a high-strength modified nylon 66 material and its preparation method. Through molecular structure design, it achieves a synergistic improvement in mechanical properties, flame retardancy, and self-healing function.

[0010] First, two multifunctional epoxy crosslinking agents containing both dynamic chemical bonds (disulfide bonds or multiple hydrogen bonds) and phosphorus / nitrogen flame-retardant structural units were designed and synthesized. Then, these crosslinking agents were used to introduce a dual dynamic crosslinking network between the nylon 66 molecular chains through ring-opening crosslinking reactions between the epoxy groups and the terminal amino / carboxyl groups of nylon 66: the disulfide bonds, as dynamic covalent bonds, preferentially break and recombine when the material is subjected to stress, dissipating mechanical energy and releasing hidden chain segments; the multiple hydrogen bonds, as physical crosslinking points, provide reversible sacrificial bonding. The synergistic effect of the two dynamic bonds endows the material with strong and tough properties.

[0011] Furthermore, the phosphorus / nitrogen flame retardant elements integrated in the independently developed crosslinking agent molecule play a dual role in gas phase flame retardancy (releasing non-combustible gases to dilute oxygen) and condensed phase flame retardancy (promoting char formation and isolating heat transfer) during combustion. Moreover, the flame retardant structure is chemically bonded to the polymer network, effectively avoiding the migration and precipitation and interfacial compatibility problems of traditional physically added flame retardants.

[0012] A high-strength modified nylon 66 material is prepared by crosslinking modification of nylon 66 resin, flame-retardant epoxy crosslinking agent I containing disulfide bonds and flame-retardant epoxy crosslinking agent II containing multiple hydrogen bonds;

[0013] The epoxy functional groups in the flame-retardant epoxy crosslinking agent undergo ring-opening reactions with the terminal amino or carboxyl functional groups on the main chain of nylon 66 resin molecules, forming a disulfide / hydrogen bond dual dynamic crosslinking network between nylon 66 molecular chains.

[0014] The nylon 66 resin is 100 parts by weight, the flame-retardant epoxy crosslinking agent I is 1-3 parts by weight, and the flame-retardant epoxy crosslinking agent II is 1-3 parts by weight.

[0015] Preferably, the nylon 66 resin has a terminal amino group content of 43-50 mmol / kg and a terminal carboxyl group content of 45-55 mmol / kg.

[0016] A method for preparing a high-strength modified nylon 66 material includes the following steps:

[0017] Step 1: Synthesize flame-retardant epoxy crosslinking agent I and flame-retardant epoxy crosslinking agent II;

[0018] Step 2: Under nitrogen protection, add 100 parts by weight of nylon 66 resin to 500-800 parts by weight of anhydrous N-methylpyrrolidone, heat to 105-115℃ and stir to dissolve for 3-5 hours, then cool to 75-85℃, and add 30-50 parts by weight of anhydrous N-methylpyrrolidone solution containing 1-3 parts by weight of flame-retardant epoxy crosslinking agent I and 1-3 parts by weight of flame-retardant epoxy crosslinking agent II, and 1-2 parts by weight of BDMA catalyst. Maintain the temperature at 75-85℃ and stir for 4-6 hours. After the reaction is complete, pour in 8-12 times the volume of vigorously stirred deionized water to precipitate, filter, extract with acetone using a Soxhlet extractor for 10-15 hours, and dry to obtain high-strength modified nylon 66 material.

[0019] Preferably, the preparation method of the flame-retardant epoxy crosslinking agent I is as follows:

[0020] Using 1 molar equivalent of allyl diphenylphosphine and 1 molar equivalent of 3-mercaptopropionic acid as raw materials, a carboxylated diphenylphosphine intermediate was prepared by a mercapto-allyl click reaction in the presence of a photoinitiator.

[0021] A diphenylphosphine intermediate containing a disulfide bond is prepared by esterification of 2.01-2.05 molar equivalents of acyl chloride-treated carboxylated diphenylphosphine intermediate with 1 molar equivalent of 2-hydroxyethyl disulfide via acyl chloride functional groups and hydroxyl functional groups at 50-60°C.

[0022] By utilizing a nucleophilic substitution reaction mechanism, a flame-retardant epoxy crosslinking agent I containing disulfide bonds was prepared by reacting 1 molar equivalent of a diphenylphosphine intermediate containing disulfide bonds with 2.1-2.3 molar equivalents of epichlorohydrin at 50-55°C through a quaternization reaction.

[0023] Preferably, the preparation method of the flame-retardant epoxy crosslinking agent II is as follows:

[0024] Triethylamine catalyzes the amidation reaction of 2.01-2.05 molar equivalents of acyl chloride-treated carboxylated diphenylphosphine intermediate with 1 molar equivalent of 2,4-diamino-6-hydroxypyrimidine via acyl chloride functional groups and amino functional groups at 60-70°C to obtain a diphenylphosphine intermediate containing multiple hydrogen bonds.

[0025] By utilizing a nucleophilic substitution reaction mechanism, a flame-retardant epoxy crosslinking agent II containing multiple hydrogen bonds was prepared by reacting 1 molar equivalent of a diphenylphosphine intermediate containing multiple hydrogen bonds with 2.1-2.3 molar equivalents of epichlorohydrin at 50-55°C through a quaternization reaction.

[0026] Preferably, the photoinitiator is one of 2,2-dimethoxy-2-phenylacetophenone, 2-hydroxy-2-methyl-1-phenylpropanone, and 2,2-diethoxyacetophenone.

[0027] Beneficial effects:

[0028] This invention is based on molecular design principles. First, allyl diphenylphosphine is used as the starting material. A carboxyl functional group is introduced through a click reaction with 3-mercaptopropionic acid to obtain a carboxyl diphenylphosphine intermediate. Then, 2-hydroxyethyl disulfide or 2,4-diamino-6-hydroxypyrimidine is used as the extended molecular backbone, and the intermediate undergoes esterification or amidation reactions with the acylated carboxyl diphenylphosphine intermediate to obtain a diphenylphosphine intermediate containing dynamic chemical bonds (disulfide bonds or multiple hydrogen bonds). Finally, a flame-retardant epoxy crosslinking agent containing dynamic chemical bonds (disulfide bonds or multiple hydrogen bonds) is synthesized through a quaternization reaction between the diphenylphosphine structure and epichlorohydrin.

[0029] Nylon 66 was crosslinked using the aforementioned crosslinking agent to obtain a disulfide / hydrogen bond dual dynamic crosslinked nylon 66 material. This material exhibits a tensile strength of 138-141 MPa and an impact strength of 15-16 kJ / m. 2 With a self-healing efficiency of >75%, a limiting oxygen index close to or reaching 30%, and achieving V-0 flame retardancy, it realizes the technical goal of high strength-high toughness synergy, intrinsic flame retardancy, and self-healing function integration of nylon 66 material. It can replace traditional fiber-reinforced nylon 66 composite materials or metal structural parts and be used in high-precision, high-reliability, lightweight structural components in the fields of automotive parts, electronics and electrical, aerospace, or machinery manufacturing. Detailed Implementation

[0030] Example 1:

[0031] The preparation method of flame-retardant epoxy crosslinking agent I containing disulfide bonds is as follows:

[0032] Using 1 molar equivalent of allyl diphenylphosphine (CAS No. 2741-38-0) and 1 molar equivalent of 3-mercaptopropionic acid (CAS No. 107-96-0) as raw materials, a carboxyl diphenylphosphine intermediate was prepared via a mercapto-allyl click reaction in the presence of a photoinitiator (2,2-dimethoxy-2-phenylacetophenone). The chemical structural formula of the intermediate is as follows:

[0033] ;

[0034] A triethylamine-catalyzed esterification reaction was carried out with 1 molar equivalent of 2-hydroxyethyl disulfide (CAS No. 1892-29-1) via acyl chloride and hydroxyl functional groups at 50℃-60℃ (to protect the disulfide bonds from breaking) to obtain a diphenylphosphine intermediate containing disulfide bonds. The chemical structural formula of this intermediate is as follows:

[0035] ;

[0036] By utilizing a nucleophilic substitution reaction mechanism, a flame-retardant epoxy crosslinking agent I containing disulfide bonds was prepared by reacting 1 molar equivalent of a diphenylphosphine intermediate containing disulfide bonds with 2.2 molar equivalents of epichlorohydrin (CAS No. 106-89-8) at 50℃-55℃ (to protect the disulfide bonds from breaking and to avoid epoxy ring opening). Its chemical structural formula is as follows:

[0037] ;

[0038] The specific preparation steps of flame-retardant epoxy crosslinking agent I containing disulfide bonds are as follows:

[0039] Under nitrogen protection, 6.8 g of allyl diphenylphosphine, 0.1 g of 2,2-dimethoxy-2-phenylacetophenone, and 50 mL of anhydrous N,N-dimethylformamide were added to a three-necked flask and stirred at room temperature until completely dissolved. Then, under UV irradiation (360 nm, 10 cm), 10 mL of anhydrous N,N-dimethylformamide solution containing 3.2 g of 3-mercaptopropionic acid was added dropwise to the three-necked flask. After the addition was complete, the reaction was stirred under UV irradiation for 30 min. The solvent was removed by rotary evaporation under reduced pressure, and the product was dried to obtain the carboxydiphenylphosphine intermediate.

[0040] 2.1 mL of oxaloyl chloride and 0.2 mL of anhydrous N,N-dimethylformamide were added dropwise to 50 mL of anhydrous dichloromethane containing 6.6 g of the carboxydiphenylphosphine intermediate. The mixture was heated to 60 °C and stirred for 5 h. After cooling to room temperature, the solvent and residual oxaloyl chloride were removed by rotary evaporation under reduced pressure to obtain the acylated carboxydiphenylphosphine intermediate. This intermediate and 50 mL of anhydrous N,N-dimethylformamide were added to a three-necked flask, and the mixture was stirred at room temperature under nitrogen protection until completely dissolved. 20 mL of anhydrous N,N-dimethylformamide solution containing 1.5 g of 2-hydroxyethyl disulfide and 2.5 mL of triethylamine were added dropwise to a three-necked flask. The mixture was stirred at room temperature for 30 min, heated to 55 °C and stirred for 6 h. After cooling to room temperature, the solvent was removed by rotary evaporation under reduced pressure. Dichloromethane was added to the residue and stirred to dissolve the product. The insoluble triethylamine hydrochloride solid was removed by filtration. The filtrate was then subjected to rotary evaporation under reduced pressure to remove the solvent and dried to obtain a diphenylphosphine intermediate containing disulfide bonds.

[0041] Under nitrogen protection, 3.9 g of diphenylphosphine intermediate containing disulfide bonds and 40 mL of anhydrous N,N-dimethylformamide were added to a three-necked flask and stirred at room temperature until completely dissolved. Then, 0.9 mL of epichlorohydrin was added dropwise to the three-necked flask, the temperature was raised to 50 °C and stirred for 6 h, and then cooled to room temperature. The solvent and residual epichlorohydrin were removed by rotary evaporation. The crude product was purified by neutral alumina column chromatography (elution with ethyl acetate / petroleum ether = 1:8 to 1:4 gradient), the eluent was removed by rotary evaporation, and the product was dried to obtain flame-retardant epoxy crosslinking agent I containing disulfide bonds.

[0042] The 1H NMR characterization of flame-retardant epoxy crosslinking agent I containing disulfide bonds is as follows: 1 H NMR (DMSO-d6, 400MHz) δ: 1.77-1.83 (m, 4H), 2.67-2.69 (t, 4H), 2.75-2.78 (t, 4H), 2.91-3.00 (m, 8H), 3.71-3. 79(m, 6H), 3.83-3.89(m, 4H), 3.97-4.01(m, 4H), 4.24-4.26(t, 4H), 7.41-7.59(m, 20H);

[0043] The molecular formula of flame-retardant epoxy crosslinking agent I containing disulfide bonds is C 46 H 58 O6Cl2P2S4 was tested using a Vario EL Ⅲ elemental analyzer. The experimental values ​​(theoretical values, %) were: C 57.14 (57.07), H 6.01 (6.04), S 13.20 (13.25).

[0044] Therefore, the error range between the actual and theoretical values ​​of C, H and S elements is within 0.3%. Combined with the hydrogen spectrum results, this indicates that the structure of flame-retardant epoxy crosslinking agent I is consistent with the expected design.

[0045] Example 2:

[0046] The preparation method of flame-retardant epoxy crosslinking agent II containing multiple hydrogen bonds is as follows:

[0047] A triethylamine-catalyzed amidation reaction was carried out on 2.02 molar equivalents of acylated carboxylated diphenylphosphine intermediate and 1 molar equivalent of 2,4-diamino-6-hydroxypyrimidine (CAS No. 56-06-4) at 60-70°C via an amidation reaction between the acylation group and the amino group (-NH2). The resulting diphenylphosphine intermediate contained multiple hydrogen bonds has the following chemical structure:

[0048] ;

[0049] By utilizing a nucleophilic substitution reaction mechanism, a flame-retardant epoxy crosslinking agent II containing multiple hydrogen bonds was prepared by reacting 1 molar equivalent of a diphenylphosphine intermediate containing multiple hydrogen bonds with 2.2 molar equivalents of epichlorohydrin at 50℃-55℃ (avoiding epoxy ring opening). Its chemical structural formula is as follows:

[0050] ;

[0051] The specific preparation steps for flame-retardant epoxy crosslinking agent II containing multiple hydrogen bonds are as follows:

[0052] 2.1 mL of oxaloyl chloride and 0.2 mL of anhydrous N,N-dimethylformamide were added dropwise to 50 mL of anhydrous dichloromethane containing 6.6 g of the carboxydiphenylphosphine intermediate. The mixture was heated to 60 °C and stirred for 5 h. After cooling to room temperature, the solvent and residual oxaloyl chloride were removed by rotary evaporation under reduced pressure to obtain the acylated carboxydiphenylphosphine intermediate. This intermediate and 50 mL of anhydrous N,N-dimethylformamide were added to a three-necked flask. Under nitrogen protection, the mixture was stirred at room temperature until completely dissolved. Then, the solution was added to the three-necked flask... 10 mL of anhydrous N,N-dimethylformamide solution containing 1.2 g of 2,4-diamino-6-hydroxypyrimidine and 2.5 mL of triethylamine were added dropwise to a bottle. The mixture was stirred at room temperature for 30 min, heated to 65 °C and stirred for 5 h. After cooling to room temperature, the solvent was removed by rotary evaporation under reduced pressure. Dichloromethane was added to the residue and stirred to dissolve the product. The insoluble triethylamine hydrochloride solid was removed by filtration. The filtrate was then subjected to rotary evaporation under reduced pressure to remove the solvent and dried to obtain a diphenylphosphine intermediate containing multiple hydrogen bonds.

[0053] Under nitrogen protection, 3.8 g of diphenylphosphine intermediate containing multiple hydrogen bonds and 40 mL of anhydrous N,N-dimethylformamide were added to a three-necked flask and stirred at room temperature until completely dissolved. Then, 0.9 mL of epichlorohydrin was added dropwise to the three-necked flask, the temperature was raised to 50 °C and stirred for 6 h, and then cooled to room temperature. The solvent and residual epichlorohydrin were removed by rotary evaporation. The crude product was purified by neutral alumina column chromatography (elution with ethyl acetate / petroleum ether = 0:100 to 15:85 gradient), the eluent was removed by rotary evaporation, and the product was dried to obtain flame-retardant epoxy crosslinking agent II containing multiple hydrogen bonds.

[0054] The 1H NMR spectrum characterization of flame-retardant epoxy crosslinking agent II containing multiple hydrogen bonds is as follows: 1 H NMR (DMSO-d6, 400MHz) δ: 1.75-1.84 (m, 4H), 2.56-2.59 (t, 4H), 2.70-2.80 (m, 4H), 3.07-3.10 (t, 4H), 3.73-3.79 (m, 6H), 3.83- 3.89(m, 4H), 3.97-4.01(m, 4H), 5.62(s, 1H), 7.40-7.59(m, 20H), 8.65(s, 1H), 9.28(s, 1H), 9.56(s, 1H);

[0055] The molecular formula of flame-retardant epoxy crosslinking agent II containing multiple hydrogen bonds is C 46 H 54 O5Cl2N4P2S2 was tested using a Vario ELⅢ elemental analyzer. The experimental values ​​(theoretical values, %) were: C 58.89 (58.78), H 5.70 (5.79), N 5.92 (5.96), S 6.76 (6.82).

[0056] Accordingly, the error range between the actual and theoretical values ​​of C, H, N and S elements is within 0.3%. Combined with the hydrogen spectrum results, this indicates that the structure of the flame-retardant epoxy crosslinking agent II is consistent with the expected design.

[0057] Example 3:

[0058] A high-strength modified nylon 66 material I (i.e., disulfide / hydrogen bond dual dynamic crosslinked nylon 66 material I) was prepared. The formulation was as follows: 100 parts by weight of nylon 66 resin (model EPR27, terminal amino content of 45.3 mmol / kg, terminal carboxyl content of 50.8 mmol / kg), 2 parts by weight of flame-retardant epoxy crosslinking agent I containing disulfide bonds, and 2 parts by weight of flame-retardant epoxy crosslinking agent II containing multiple hydrogen bonds. The preparation method was as follows: the epoxy functional groups in the flame-retardant epoxy crosslinking agent reacted with the terminal amino functional groups or terminal carboxyl functional groups on the molecular backbone of nylon 66 resin through a ring-opening reaction, thereby achieving crosslinking modification of nylon 66 resin and obtaining disulfide / hydrogen bond dual dynamic crosslinked nylon 66 material I.

[0059] The specific preparation steps of disulfide / hydrogen bond dual dynamic crosslinked nylon 66 material I are as follows: Under nitrogen protection, 100 parts by weight of nylon 66 resin and 600 parts by weight of anhydrous N-methylpyrrolidone were added to a three-necked flask, heated to 110℃ and stirred for 4 hours to dissolve, then cooled to 80℃. 40 parts by weight of anhydrous N-methylpyrrolidone solution containing 2 parts by weight of flame-retardant epoxy crosslinking agent I and 2 parts by weight of flame-retardant epoxy crosslinking agent II, and 1.5 parts by weight of BDMA catalyst (N,N-dimethylbenzylamine) were added sequentially to the three-necked flask. The mixture was stirred at 80℃ for 5 hours. After the reaction, the reaction solution was poured into 10 times its volume of vigorously stirred deionized water to precipitate, filtered, and extracted with acetone using a Soxhlet extractor for 12 hours. After drying, disulfide / hydrogen bond dual dynamic crosslinked nylon 66 material I was obtained.

[0060] Example 4:

[0061] The preparation method of high-strength modified nylon 66 material II (i.e., disulfide bond / hydrogen bond dual dynamic crosslinked nylon 66 material II) differs from that of disulfide bond / hydrogen bond dual dynamic crosslinked nylon 66 material I only in that the amount of flame-retardant epoxy crosslinking agent I containing disulfide bonds is adjusted from 2 parts by weight to 3 parts by weight, and the amount of flame-retardant epoxy crosslinking agent II containing multiple hydrogen bonds is adjusted from 2 parts by weight to 1 part by weight.

[0062] Example 5:

[0063] The preparation method of high-strength modified nylon 66 material III (disulfide bond / hydrogen bond dual dynamic crosslinked nylon 66 material III) differs from that of disulfide bond / hydrogen bond dual dynamic crosslinked nylon 66 material I only in that the amount of flame-retardant epoxy crosslinking agent I containing disulfide bonds is adjusted from 2 parts by weight to 1 part by weight, and the amount of flame-retardant epoxy crosslinking agent II containing multiple hydrogen bonds is adjusted from 2 parts by weight to 3 parts by weight.

[0064] Comparative Example 1:

[0065] The preparation method of disulfide bond monodynamic crosslinked nylon 66 material differs from that of disulfide bond / hydrogen bond double dynamic crosslinked nylon 66 material I only in that the amount of flame-retardant epoxy crosslinking agent I containing disulfide bonds is adjusted from 2 parts by weight to 4 parts by weight, and the amount of flame-retardant epoxy crosslinking agent II containing multiple hydrogen bonds is adjusted from 2 parts by weight to 0 parts by weight (i.e., the formulation does not contain flame-retardant epoxy crosslinking agent II).

[0066] Comparative Example 2:

[0067] The preparation method of hydrogen-bonded single dynamic crosslinked nylon 66 material differs from that of disulfide / hydrogen-bonded double dynamic crosslinked nylon 66 material I only in that the amount of flame-retardant epoxy crosslinking agent I containing disulfide bonds is adjusted from 2 parts by weight to 0 parts by weight, and the amount of flame-retardant epoxy crosslinking agent II containing multiple hydrogen bonds is adjusted from 2 parts by weight to 4 parts by weight (i.e., the formulation does not contain flame-retardant epoxy crosslinking agent I).

[0068] Performance testing:

[0069] The nylon 66 material and the original nylon 66 resin from the examples and comparative examples were dissolved in hexafluoroisopropanol to form a 20wt% solution. The solution was poured into a polytetrafluoroethylene mold, and air bubbles were removed under reduced pressure of 30 mmHg. The mold was then placed in a vacuum oven at 50°C for 24 hours to dry completely. After curing at room temperature (25°C) for 12 hours, performance tests were conducted, as follows:

[0070] I. Mechanical property testing:

[0071] (1) Tensile strength test: In accordance with GB / T 1040.3-2006 "Determination of tensile properties of plastics - Part 3: Test conditions for films and sheets", a 150mm×20mm×1mm (length×width×height) type 2 specimen was fixed on a universal testing machine and a tensile test was performed at a tensile rate of 10mm / min. The tensile strength of the specimen was recorded.

[0072] (2) Impact strength (toughness) test: According to GB / T 1843-2008 "Determination of impact strength of plastic cantilever beam", an 80mm×10mm×4mm (length×width×height) type A notch specimen (notch bottom radius 0.25mm, notch width 8mm, notch depth 2mm) was fixed on a cantilever beam impact testing machine for impact performance testing. The pendulum energy was 2.75J and the impact speed was 3.5m / s. The impact strength of the sample was recorded.

[0073] II. Self-healing performance test: A 150mm×20mm×1mm (length×width×height) Type 2 specimen was cut in half, the cuts were aligned, and the specimen was placed in an 80℃ oven for 2 hours for repair. Afterwards, it was removed and cured at room temperature (25℃) for 12 hours. Then, it was fixed on a universal testing machine and subjected to a tensile test at a tensile rate of 10mm / min. The tensile strength of the sample after self-healing was recorded, and the self-healing efficiency was calculated. The specific calculation method is as follows:

[0074] Self-repair efficiency (%) = σ1 / σ0 × 100%;

[0075] Wherein, σ1 is the tensile strength after repair at 80℃ / 2h, and σ0 is the initial tensile strength, that is, the tensile strength value measured in performance test one (1);

[0076] III. Flame retardant performance test:

[0077] (1) LOI (Limiting Oxygen Index) test: The test was conducted using an oxygen index meter in accordance with GB / T 2406.2-2009 "Determination of Combustion Behavior by Oxygen Index Method for Plastics - Part 2: Room Temperature Test". The sample size was 125mm × 10mm × 4mm.

[0078] (2) UL-94 test: According to GB / T 2408-2021 "Determination of the flammability of plastics by horizontal and vertical methods", the test method B-vertical flammability test was used. The sample size was 125mm×13mm×3mm.

[0079] The results of the above performance experiments are shown in Table 1.

[0080] Table 1. Experimental results of the performance of disulfide / hydrogen bond dual dynamic crosslinked nylon 66 materials.

[0081]

[0082] A comprehensive analysis of the above experimental results leads to the following conclusions:

[0083] Conclusion 1: The disulfide / hydrogen bond dual dynamic crosslinked nylon 66 material developed in this invention, compared with single dynamic crosslinked nylon 66 materials (disulfide bonds or hydrogen bonds) and conventional nylon 66 resin, exhibits improved tensile strength (to 138.7-141.5 MPa, an increase of 15.1%-17.4% compared with conventional nylon 66 resin, and an increase of 6.4%-11.1% compared with single dynamic crosslinked systems) and impact strength (to 15.0-15.9 kJ / m²). 2 It has achieved significant synergistic improvement in terms of strength (63.0%-72.8% higher than conventional nylon 66 resin, and 30.4%-48.6% higher than single dynamic crosslinking system), and belongs to high-strength modified nylon 66 material;

[0084] Conclusion 2: The disulfide / hydrogen bond dual dynamic crosslinked nylon 66 material developed in this invention exhibits excellent self-healing and flame-retardant properties.

Claims

1. A high-strength modified nylon 66 material, characterized in that, The high-strength modified nylon 66 material is obtained by crosslinking modification of nylon 66 resin, flame-retardant epoxy crosslinking agent I containing disulfide bonds, and flame-retardant epoxy crosslinking agent II containing multiple hydrogen bonds; The epoxy functional groups in the flame-retardant epoxy crosslinking agent undergo ring-opening reactions with the terminal amino or carboxyl functional groups on the main chain of nylon 66 resin molecules, forming a disulfide / hydrogen bond dual dynamic crosslinking network between nylon 66 molecular chains. The nylon 66 resin is 100 parts by weight, the flame-retardant epoxy crosslinking agent I is 1-3 parts by weight, and the flame-retardant epoxy crosslinking agent II is 1-3 parts by weight; The chemical structural formula of the flame-retardant epoxy crosslinking agent I is: 。 The chemical structural formula of the flame-retardant epoxy crosslinking agent II is: 。 2. The high-strength modified nylon 66 material according to claim 1, characterized in that, The nylon 66 resin has an end-amino group content of 43-50 mmol / kg and an end-carboxyl group content of 45-55 mmol / kg.

3. The method for preparing a high-strength modified nylon 66 material according to claim 1, characterized in that, Includes the following steps: Step 1: Synthesize flame-retardant epoxy crosslinking agent I and flame-retardant epoxy crosslinking agent II; Step 2: Under nitrogen protection, add 100 parts by weight of nylon 66 resin to 500-800 parts by weight of anhydrous N-methylpyrrolidone, heat to 105-115℃ and stir to dissolve for 3-5 hours, then cool to 75-85℃, and add 30-50 parts by weight of anhydrous N-methylpyrrolidone solution containing 1-3 parts by weight of flame-retardant epoxy crosslinking agent I and 1-3 parts by weight of flame-retardant epoxy crosslinking agent II, and 1-2 parts by weight of BDMA catalyst. Maintain the temperature at 75-85℃ and stir for 4-6 hours. After the reaction is complete, pour in 8-12 times the volume of vigorously stirred deionized water to precipitate, filter, extract with acetone using a Soxhlet extractor for 10-15 hours, and dry to obtain high-strength modified nylon 66 material.

4. The method for preparing a high-strength modified nylon 66 material according to claim 3, characterized in that, The preparation method of the flame-retardant epoxy crosslinking agent I is as follows: Using 1 molar equivalent of allyl diphenylphosphine and 1 molar equivalent of 3-mercaptopropionic acid as raw materials, a carboxylated diphenylphosphine intermediate was prepared by a mercapto-allyl click reaction in the presence of a photoinitiator. A diphenylphosphine intermediate containing a disulfide bond is prepared by esterification of 2.01-2.05 molar equivalents of acyl chloride-treated carboxylated diphenylphosphine intermediate with 1 molar equivalent of 2-hydroxyethyl disulfide via acyl chloride functional groups and hydroxyl functional groups at 50-60°C. By utilizing a nucleophilic substitution reaction mechanism, a flame-retardant epoxy crosslinking agent I containing disulfide bonds was prepared by reacting 1 molar equivalent of a diphenylphosphine intermediate containing disulfide bonds with 2.1-2.3 molar equivalents of epichlorohydrin at 50-55°C through a quaternization reaction.

5. The method for preparing a high-strength modified nylon 66 material according to claim 4, characterized in that, The preparation method of the flame-retardant epoxy crosslinking agent II is as follows: Triethylamine catalyzes the amidation reaction of 2.01-2.05 molar equivalents of acyl chloride-treated carboxylated diphenylphosphine intermediate with 1 molar equivalent of 2,4-diamino-6-hydroxypyrimidine via acyl chloride functional groups and amino functional groups at 60-70°C to obtain a diphenylphosphine intermediate containing multiple hydrogen bonds. By utilizing a nucleophilic substitution reaction mechanism, a flame-retardant epoxy crosslinking agent II containing multiple hydrogen bonds was prepared by reacting 1 molar equivalent of a diphenylphosphine intermediate containing multiple hydrogen bonds with 2.1-2.3 molar equivalents of epichlorohydrin at 50-55°C through a quaternization reaction.

6. The method for preparing a high-strength modified nylon 66 material according to claim 4, characterized in that, The photoinitiator is one of 2,2-dimethoxy-2-phenylacetophenone, 2-hydroxy-2-methyl-1-phenylpropanone, and 2,2-diethoxyacetophenone.

7. The application of the high-strength modified nylon 66 material according to claim 1 in high-precision, high-reliability lightweight structural components in the fields of automotive parts, electronics and electrical engineering, aerospace, or machinery manufacturing, characterized in that... The material simultaneously meets the requirements of high strength, high toughness, intrinsic flame retardancy, and self-healing function, and can replace traditional fiber-reinforced nylon 66 composite materials or metal structural parts.

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