Lightweight high-strength low-water-absorption bio-based copolyamide and preparation method and application thereof

Abstract

The present application relates to the technical fields of high polymer engineering plastic synthesis, in particular to a lightweight high-strength low-water-absorption bio-based copolyamide, and a preparation method and application thereof.The lightweight high-strength low-water-absorption bio-based copolyamide is a compound as shown in formula (I) and its racemate, stereoisomer or tautomer, wherein x is 15-25, y is 50-70, and z is 15-25.The preparation method of the lightweight high-strength low-water-absorption bio-based copolyamide comprises the following steps: taking hexanediamine and mixed dibasic acid as raw materials, mixing them in a solvent, and performing a mixed salt formation reaction to obtain a mixed nylon salt aqueous solution; performing a pre-polycondensation reaction on the mixed nylon salt aqueous solution under inert gas protection to obtain an oligomer; and performing a final polycondensation reaction on the oligomer under the condition of reduced pressure and temperature to obtain the lightweight high-strength low-water-absorption bio-based copolyamide.The main use of the present application is to provide a new selection for polyamide materials.

Description

Technical Field

[0001] This invention relates to the field of polymer engineering plastics synthesis technology, specifically to a lightweight, high-strength, low-water-absorption bio-based copolyamide, its preparation method, and its applications. Background Technology

[0002] Polyamides (such as PA6 and PA66) are widely used in industrial manufacturing as engineering plastics with excellent comprehensive properties. However, traditional polyamides have two inherent limitations that are difficult to overcome: First, their density is high. Due to the dense hydrogen bonding between amide bonds, the molecular chains are arranged extremely closely, and the intrinsic density of pure PA66 is approximately 1.14 g / cm³. 3 To achieve the required rigidity for engineering structural components, it is typically necessary to fill with more than 30% glass fiber, causing the density of the composite material to soar to 1.35 g / cm³. 3 This contradicts the current trend of lightweighting in fields such as new energy vehicles. Secondly, it is extremely hygroscopic. The strong hydrophilicity of amide bonds causes traditional nylon to easily absorb water and swell in humid and hot environments, leading to dimensional deformation of the product and a sharp decline in mechanical properties (especially tensile strength and modulus).

[0003] In existing technologies, PA610 and PA612 are typically prepared by copolymerizing long-chain dicarboxylic acids (such as sebacic acid and dodecanoic acid). However, this not only has a limited effect on reducing density but also causes a significant decrease in the material's rigidity and heat resistance (glass transition temperature). Therefore, developing a novel polyamide material that combines low intrinsic density and low water absorption without sacrificing engineering-grade strength has extremely high commercial and research value. Summary of the Invention

[0004] To address the problems existing in the prior art, the present invention aims to provide a lightweight, high-strength, low-water-absorption bio-based copolymer polyamide, its preparation method, and its application, in order to solve the problems of high intrinsic density and high saturation water absorption rate caused by the extreme water absorption of existing polyamide materials.

[0005] The technical solution of the present invention is as follows: This invention provides a lightweight, high-strength, low-water-absorption bio-based copolyamide, the structural formula of which is shown in formula (I) and its racemic, stereoisomer, or tautomer: (I); In formula (I), x takes values ​​of 15 to 25, y takes values ​​of 50 to 70, and z takes values ​​of 15 to 25.

[0006] The lightweight, high-strength, and low-water-absorption bio-based copolyamide provided by this invention has an ingenious structural design: the macromolecular backbone not only contains a highly hydrophobic long carbon chain branched network, but also blocks an asymmetric rigid aromatic heterocyclic skeleton, resulting in a significantly reduced intrinsic density and saturated water absorption rate. This solves the problems of high intrinsic density and high saturated water absorption rate caused by the high water absorption of existing polyamide materials.

[0007] Furthermore, the intrinsic density of the lightweight, high-strength, low-water-absorption bio-based copolyamide is 1.04~1.08 g / cm³. 3 .

[0008] Furthermore, the saturated water absorption rate of the lightweight, high-strength, low-water-absorption bio-based copolyamide is 1.5% to 2.1%.

[0009] Furthermore, the relative viscosity of the lightweight, high-strength, low-water-absorption bio-based copolyamide in a 96% sulfuric acid system is 2.3~3.2.

[0010] Furthermore, the lightweight, high-strength, low-water-absorption bio-based copolyamide has a tensile strength of 68 MPa to 75 MPa, a tensile modulus of 2.5 to 2.8 GPa, and a notched impact strength of 12.5 kJ / m. 2 ~15.2kJ / m 2 The bottom radius of the notch is 0.25 mm.

[0011] This invention also provides a method for preparing the above-mentioned lightweight, high-strength, low-water-absorption bio-based copolyamide, and the reaction equations in the preparation process are shown in formulas (II), (III), (IV) and (V): (II); (III); (IV); (V); In formula (V), x takes values ​​of 15 to 25, y takes values ​​of 50 to 70, and z takes values ​​of 15 to 25.

[0012] This invention ingeniously combines the massive hydrophobic side chains of dimer acid with the rigid asymmetric aromatic heterocycles of 2,5-furandicarboxylic acid, thereby breaking the tight packing of nylon molecular chains to achieve a significant reduction in density, while endowing the material with extremely low water absorption and excellent mechanical modulus.

[0013] Furthermore, the preparation method includes the following steps: S1. Using hexamethylenediamine and mixed dicarboxylic acids as raw materials, they are mixed in a solvent to carry out a mixed salt formation reaction to obtain a mixed nylon salt aqueous solution; S2. Under the protection of an inert gas, the mixed nylon salt aqueous solution is subjected to a pre-condensation reaction to obtain oligomers; S3. Under reduced pressure and increased temperature, the oligomer is subjected to a final polycondensation reaction to obtain a lightweight, high-strength, low-water-absorption bio-based copolymer polyamide.

[0014] This invention provides a lightweight, high-strength, low-water-absorption bio-based copolyamide with a mature synthesis process and ingenious structural design. It uses plant oil-based dimer acid to provide a large steric hindrance and hydrophobic barrier, and 2,5-furandicarboxylic acid structure to provide rigid support, thus achieving a "combination of rigidity and flexibility" at the molecular level to reduce density. In the preparation method of lightweight, high-strength, and low-water-absorption bio-based copolyamide: hexamethylenediamine and mixed dicarboxylic acids (adipic acid, hydrogenated dimer acid, and 2,5-furandicarboxylic acid) are dispersed in deionized water in a specific ratio, and a uniform and stable mixed nylon salt solution is formed through acid-base neutralization reaction; in a closed high-pressure reactor, the nylon salt is dissociated and undergoes a preliminary amidation condensation reaction by utilizing the high temperature and the pressure of the generated water vapor, forming oligomers with well-closed end groups; by depressurizing and removing the by-product water, a vacuum system is introduced, and the condensation chemical equilibrium is forcibly shifted to the right at a temperature higher than the polymer melting point, rapidly increasing the molecular weight and melt viscosity of the polymer, and finally obtaining lightweight, high-strength, and low-water-absorption bio-based copolyamide.

[0015] Furthermore, the mixed dicarboxylic acid includes adipic acid, hydrogenated dimer acid, and 2,5-furandicarboxylic acid; The solvent is selected from deionized water; The temperature for the salt-forming reaction is 60℃~90℃, and the time is 1.5h~2.5h. The pH value of the mixed nylon salt aqueous solution is 7.5~8.5.

[0016] Furthermore, the hydrogenated dimer acid is a hydrogenated derivative of a vegetable oil-based dimer acid.

[0017] Vegetable oil-based dimer acid is a hydrogenated dimer acid containing 36 carbon atoms and their side chains, which can ensure the color stability of the material during high-temperature processing.

[0018] Furthermore, the inert gas is selected from nitrogen or argon; The conditions for the pre-condensation reaction include: a reaction temperature of 210℃~230℃, a reaction pressure of 1.5 MPa~2.5 MPa, and a reaction time of 1h~2h.

[0019] Furthermore, the conditions for the final polycondensation reaction include: a reaction temperature of 260℃~280℃, a reaction pressure of -0.05 MPa~-0.09 MPa, and a reaction time of 0.5h~1.5h.

[0020] Furthermore, the equimolar ratio of the hexamethylenediamine and the mixed dicarboxylic acid is 1 to 1.02:1.

[0021] Furthermore, in the mixed dicarboxylic acids, the proportion of adipic acid is 40 mol% to 80 mol%, the proportion of hydrogenated dimer acid is 5 mol% to 30 mol%, and the proportion of 2,5-furandicarboxylic acid is 5 mol% to 30 mol.

[0022] This invention also provides the application of the lightweight, high-strength, low-water-absorption bio-based copolyamide prepared by the above-mentioned method in the preparation of lightweight copolyamide resin, characterized in that the preparation method of the lightweight copolyamide resin includes the following steps: Under normal pressure conditions, the lightweight, high-strength, low-water-absorption bio-based copolyamide is melted, cooled, and pelletized and dried to obtain a lightweight copolyamide resin.

[0023] The present invention also provides the application of the lightweight, high-strength, low-water-absorption bio-based copolymer polyamide prepared by the above preparation method in the preparation of reinforced bio-based copolymer polyamide composite materials, characterized in that the raw materials of the reinforced bio-based copolymer polyamide composite material include: lightweight, high-strength, low-water-absorption bio-based copolymer polyamide and reinforcing filler; the reinforcing filler is selected from chopped glass fibers.

[0024] This invention also provides the application of the lightweight, high-strength, low-water-absorption bio-based copolyamide prepared by the above-mentioned preparation method in the preparation of lightweight engineering plastic products, including non-load-bearing structural components for new energy vehicles and non-load-bearing structural components for aircraft.

[0025] Furthermore, the non-load-bearing structural components of the new energy vehicle include trim panels, decorative shells, headlight bases, covers, air ducts, storage shells, and covers.

[0026] Furthermore, the non-load-bearing structural components of the aircraft include cabin interior panels, outer shell decorative skin, fairings, equipment housings, cable fasteners, and air duct housings.

[0027] The beneficial effects of this invention are: This invention discloses a lightweight, high-strength, and low-water-absorption bio-based copolyamide with an ingenious structural design: the macromolecular backbone not only contains a highly hydrophobic long carbon chain branched network but also blocks an asymmetric rigid aromatic heterocyclic skeleton, resulting in significantly reduced intrinsic density and saturated water absorption. This invention cleverly combines the massive hydrophobic branches of dimer acid with the rigid asymmetric aromatic heterocycle of 2,5-furandicarboxylic acid, breaking the tight packing of nylon molecular chains to achieve significant density reduction while endowing the material with extremely low water absorption and excellent mechanical modulus.

[0028] This invention provides a lightweight, high-strength, low-water-absorption bio-based copolyamide with a mature synthesis process and ingenious structural design. It uses plant oil-based dimer acid to provide a large steric hindrance and hydrophobic barrier, and 2,5-furandicarboxylic acid structure to provide rigid support, thus achieving a "combination of rigidity and flexibility" at the molecular level to reduce density. In the preparation method of lightweight, high-strength, and low-water-absorption bio-based copolyamide: hexamethylenediamine and mixed dicarboxylic acids (adipic acid, hydrogenated dimer acid, and 2,5-furandicarboxylic acid) are dispersed in deionized water in a specific ratio, and a uniform and stable mixed nylon salt solution is formed through acid-base neutralization reaction; in a closed high-pressure reactor, the nylon salt is dissociated and undergoes a preliminary amidation condensation reaction by utilizing the high temperature and the pressure of the generated water vapor, forming oligomers with well-closed end groups; by depressurizing and removing the by-product water, a vacuum system is introduced, and the condensation chemical equilibrium is forcibly shifted to the right at a temperature higher than the polymer melting point, rapidly increasing the molecular weight and melt viscosity of the polymer, and finally obtaining lightweight, high-strength, and low-water-absorption bio-based copolyamide.

[0029] This invention discloses a lightweight, high-strength, low-water-absorption bio-based copolyamide, its preparation method, and its application. Its beneficial effects are as follows: (1) Significant lightweight breakthrough: The massive long carbon chain support of dimer acid and the "micro-bending" conformation of the asymmetric five-membered ring of 2,5-furandicarboxylic acid form a "double-destructive crystallization" effect, forcibly increasing the molecular chain spacing. The intrinsic density of the lightweight, high-strength, low-water-absorption bio-based copolyamide of this invention is 1.04~1.08 g / cm³. 3 Therefore, the intrinsic density of the material can be calculated from 1.14 g / cm³. 3 Reduced to 1.04~1.08 g / cm³ 3 This achieves an essential weight reduction for nylon materials; (2) Dramatic reduction in water absorption rate: The super-hydrophobic hydrocarbon skeleton of dimer acid with up to 36 carbon atoms forms a natural water barrier inside the material. The saturated water absorption rate of the lightweight, high-strength, and low-water-absorption bio-based copolymer polyamide drops sharply from 8.5% of traditional PA66 to 1.5%~2.5%, completely solving the problems of nylon's dimensional instability and softening due to water absorption; (3) Mechanical balance of “rigidity and flexibility”: The rigid furan ring of 2,5-furandicarboxylic acid serves as a “hard skeleton”, which perfectly compensates for the modulus loss caused by the introduction of aliphatic dimer acid, so that the material can maintain excellent tensile strength and extremely high impact toughness at very low density. (4) Green and sustainable: The large-scale introduction of plant oil-based dimer acid and fructosyl 2,5-furandicarboxylic acid monomers has significantly reduced the dependence on traditional petrochemical resources.

[0030] In summary, the lightweight, high-strength, low-water-absorption bio-based copolyamide of the present invention and its preparation method have broad application prospects. Detailed Implementation

[0031] The present invention will be further described in detail below through embodiments, but in no way is the invention limited.

[0032] The hydrogenated dimer acid used in the following examples is a hydrogenated derivative of vegetable oil-based dimer acid.

[0033] The structural formula of hexamethylenediamine used in the following examples is as follows: The structural formula of adipic acid is: The structural formula of vegetable oil-based dimer acid is: The structural formula of 2,5-furandicarboxylic acid is: .

[0034] In the lightweight, high-strength, and low-water-absorption bio-based copolymer polyamides prepared in the following examples, "bio-based" refers to the introduction of dimer acids and 2,5-furandicarboxylic acid monomers derived from renewable plant resources into the copolymer macromolecular backbone. In specific implementations, the overall bio-based carbon content of the material can be further increased by using bio-based hexamethylenediamine or bio-based adipic acid. Example 1

[0035] A method for preparing a lightweight, high-strength, low-water-absorption bio-based copolyamide and a lightweight copolyamide resin: S1, Mixed salt formation reaction Add 500 mL of deionized water to a dissolving tank equipped with a mechanical stirrer, then add 118.5 g (1.02 mol, slightly excess to compensate for evaporation) of hexamethylenediamine, followed by the slow addition of 102.3 g (0.7 mol) of adipic acid, 84.8 g (0.15 mol) of hydrogenated dimer acid (molecular weight approximately 565), and 23.4 g (0.15 mol) of 2,5-furandicarboxylic acid. Stir continuously at 80 °C for 2 hours to fully neutralize until the solution is clear. Adjust the pH to 7.8 to obtain a mixed nylon salt aqueous solution with a mass concentration of approximately 40%. In the salt formation reaction: The reaction equation for the formation of hexamethylenediamine salt from hexamethylenediamine and adipic acid is shown in equation (II): (II); The reaction equation for the formation of hexamethylenediamine salt from hexamethylenediamine and vegetable oil-based dimer acid is shown in equation (III): (III); The reaction equation for the formation of hexamethylenediamine salt of 2,5-furandicarboxylic acid by mixing hexamethylenediamine and 2,5-furandicarboxylic acid is shown in equation (IV): (IV).

[0036] S2, High-pressure precondensation reaction The mixed nylon salt aqueous solution obtained in S1 was transferred to a 2L stainless steel high-pressure reactor, and the air inside the reactor was purged three times with high-purity nitrogen. The vent valve was closed, and the temperature was raised to 220°C. As the water evaporated, the pressure inside the reactor gradually increased to 1.8MPa. The reactor was maintained at this pressure and temperature with stirring for 1.5 hours to dehydrate the nylon salt and form oligomers.

[0037] S3, Atmospheric pressure dehydration and final condensation reaction After S2, the vent valve was slightly opened to slowly depressurize to atmospheric pressure at a rate of 0.05 MPa / min, while the reactor temperature was gradually increased to 270℃. After the water in the reactor was basically drained, the vacuum pump was started to bring the vacuum level in the reactor to -0.08 MPa, and high vacuum melt polycondensation was continued for 1 hour to obtain a lightweight, high-strength, low-water-absorption bio-based copolyamide.

[0038] In the pre-condensation reaction of S2 and the final condensation reaction of S3: The reaction equation for the dehydration of vegetable oil-based hexamethylene diamine salt, hexamethylene diamine salt of adipic acid, and hexamethylene diamine salt of 2,5-furandicarboxylic acid to form poly(dimeric acid-adipic acid-furandicarboxylic acid) amide alternating copolymers is shown in equation (VI): (VI).

[0039] In formula (VI), x is 15, y is 70, and z is 15. The poly(dimer acid-adipic acid-furandicarboxylic acid) amide alternating copolymer is a lightweight, high-strength, low-water-absorption bio-based copolymer polyamide.

[0040] S4, Discharge Granulation The high-viscosity melt (a lightweight, high-strength, low-water-absorption bio-based copolyamide in its molten state is a high-viscosity melt) is extruded and rapidly cooled and solidified, then pelletized to obtain the final lightweight copolyamide resin product. The specific steps are as follows: After S3, observe the torque of the stirring motor and stop the machine when the set viscosity is reached. Pour nitrogen into the reactor and restore atmospheric pressure. Open the bottom valve to extrude the molten polymer (the polymer in Example 1 refers to a lightweight, high-strength, low-water-absorption bio-based copolyamide) into a water tank for fiber drawing and water cooling. Use a pelletizer to cut it into cylindrical white semi-transparent granules to obtain lightweight copolyamide resin, which is then placed in an 80°C vacuum oven for drying and later use. Example 2

[0041] A method for preparing a lightweight, high-strength, low-water-absorption bio-based copolyamide and a lightweight copolyamide resin: S1, Mixed salt formation reaction Add 500 mL of deionized water to a dissolving vessel equipped with a mechanical stirrer, then add 118.5 g (1.02 mol, slightly excess to compensate for evaporation) of hexamethylenediamine, followed by the slow addition of 73.1 g (0.5 mol) of adipic acid, 141.3 g (0.25 mol) of hydrogenated dimer acid (molecular weight approximately 565), and 39.0 g (0.25 mol) of 2,5-furandicarboxylic acid. Stir continuously at 80 °C for 2 hours to fully neutralize until the solution is clear. Adjust the pH to 7.8 to obtain a mixed nylon salt aqueous solution with a mass concentration of approximately 40%. In the salt formation reaction: The reaction equation for the formation of hexamethylenediamine salt from hexamethylenediamine and adipic acid is shown in equation (II): (II); The reaction equation for the formation of hexamethylenediamine salt from hexamethylenediamine and vegetable oil-based dimer acid is shown in equation (III): (III); The reaction equation for the formation of hexamethylenediamine salt of 2,5-furandicarboxylic acid by mixing hexamethylenediamine and 2,5-furandicarboxylic acid is shown in equation (IV): (IV).

[0042] S2, High-pressure precondensation reaction The mixed nylon salt aqueous solution obtained in S1 was transferred to a 2L stainless steel high-pressure reactor, and the air inside the reactor was purged three times with high-purity nitrogen. The vent valve was closed, and the temperature was raised to 225°C. As the water evaporated, the pressure inside the reactor gradually increased to 1.8MPa. The reactor was maintained at this pressure and temperature with stirring for 2 hours to dehydrate the nylon salt and form oligomers.

[0043] S3, Atmospheric pressure dehydration and final condensation reaction After S2, the vent valve was slightly opened to slowly depressurize to atmospheric pressure at a rate of 0.05 MPa / min, while the reactor temperature was gradually increased to 265℃. After the water in the reactor was basically drained, the vacuum pump was started to bring the vacuum level in the reactor to -0.08 MPa, and high vacuum melt polycondensation was continued for 1.5 hours to obtain a lightweight, high-strength, low-water-absorption bio-based copolyamide.

[0044] In the pre-condensation reaction of S2 and the final condensation reaction of S3: The reaction equation for the dehydration of vegetable oil-based hexamethylene diamine salt, hexamethylene diamine salt of adipic acid and hexamethylene diamine salt of 2,5-furandicarboxylic acid to form poly(dimeric acid-adipic acid-furandicarboxylic acid) amide alternating copolymers is shown in equation (VII): (VII).

[0045] In formula (VII), x is 25, y is 50, and z is 25. The poly(dimer acid-adipic acid-furandicarboxylic acid) amide alternating copolymer is a lightweight, high-strength, low-water-absorption bio-based copolymer polyamide.

[0046] S4, Discharge Granulation After S3, observe the torque of the stirring motor and stop the machine when the set viscosity is reached. Pour nitrogen into the reactor and restore atmospheric pressure. Open the bottom valve to extrude the molten polymer (the polymer in Example 2 refers to a lightweight, high-strength, low-water-absorption bio-based copolyamide) into a water tank for fiber drawing and water cooling. Use a pelletizer to cut it into cylindrical white semi-transparent granules to obtain lightweight copolyamide resin, which is then placed in an 80°C vacuum oven for drying and later use.

[0047] Comparative Example 1 A method for synthesizing a bio-based copolyamide and pure PA66 resin: S1, Mixed salt formation reaction Add 500 mL of deionized water to a dissolving vessel equipped with a mechanical stirrer, then add 118.5 g (1.02 mol, slightly excess to compensate for evaporation) of hexamethylenediamine, followed by slowly adding 146.1 g (1.0 mol) of pure adipic acid. Stir continuously at 80 °C for 2 hours to fully neutralize until the solution is clear. Adjust the pH to 7.8 to obtain a mixed nylon salt aqueous solution with a mass concentration of approximately 40%.

[0048] S2, High-pressure precondensation reaction The mixed nylon salt aqueous solution obtained in S1 was transferred to a 2L stainless steel high-pressure reactor, and the air inside the reactor was purged three times with high-purity nitrogen. The vent valve was closed, and the temperature was raised to 220°C. As the water evaporated, the pressure inside the reactor gradually increased to 1.8MPa. The reactor was maintained at this pressure and temperature with stirring for 1.5 hours to dehydrate the nylon salt and form oligomers.

[0049] S3, Atmospheric pressure dehydration and final condensation reaction After S2, the vent valve was slightly opened to slowly depressurize to atmospheric pressure at a rate of 0.05 MPa / min, while the reactor temperature was gradually increased to 270°C. After the water in the reactor was basically drained, the vacuum pump was started to bring the vacuum level in the reactor to -0.08 MPa, and high vacuum melt polycondensation was continued for 1 hour to obtain bio-based copolyamide.

[0050] S4, Discharge Granulation After S3, observe the torque of the stirring motor and stop the machine when the set viscosity is reached. Introduce nitrogen into the reactor and restore atmospheric pressure. Open the bottom valve to extrude the molten polymer (the polymer in Comparative Example 1 refers to bio-based copolyamide) into a water tank for fiber drawing and water cooling. Use a pelletizer to cut it into cylindrical white semi-transparent granules to obtain pure PA66 resin. Place it in an 80℃ vacuum oven to dry for later use.

[0051] Detection and Analysis I. The following performance tests were performed on the lightweight copolyamide resin prepared in Example 1 (named Sample 1), the lightweight copolyamide resin prepared in Example 2 (named Sample 2), and the pure PA66 resin prepared in Comparative Example 1 (named Sample 3): Sample 1, Sample 2 and Sample 3 are collectively referred to as samples.

[0052] Performance testing methods: 1. Density test: According to ISO1183-1:2019 standard, deionized water is used as the impregnation liquid during the test. The mass of the sample in air and the apparent mass in the liquid are measured in a standard constant temperature environment of 23℃, so as to accurately calculate the relative density of the sample.

[0053] 2. Relative viscosity test (RV determination): According to ISO 307 standard, the dried sample is dissolved in 96% concentrated sulfuric acid to prepare a solution of 0.01 g / mL. The RV is measured at 25°C using an Ubbelohde viscometer to characterize the relative molecular mass of the polymer.

[0054] 3. Water Absorption Test: The sample is prepared into a standard specimen as specified in ISO 62 (usually a square specimen with dimensions of 50 mm × 50 mm × 3 mm, or a circular specimen with a diameter of 50 mm and a thickness of 3 mm) by injection molding machine according to ISO 294-1 standard. The injection-molded standard specimen is then vacuum-dried at 80℃ for 24 hours and weighed. It is then immersed in deionized water at 23℃ and weighed periodically until it reaches saturation water absorption, and the percentage increase in weight is calculated.

[0055] 4. Mechanical performance testing: The samples were prepared into Type 1A multipurpose specimens (or Type 1B) using an injection molding machine according to ISO 294-1 standard. Tensile properties were then tested on the aforementioned Type 1A multipurpose specimens (or Type 1B) using a universal testing machine, strictly according to ISO 527-1 / -2:2012 standard: the testing speed for tensile modulus was set to 1 mm / min, and the testing speed for tensile strength was typically set to 5 mm / min.

[0056] The sample was injection molded according to ISO 294-1 standard using an injection molding machine to obtain a standard strip specimen without notches (typically 80 mm × 10 mm × 4 mm). Then, a standard strip with an A-type notch (notch bottom radius r = 0.25 mm) was prepared by mechanical cutting using a dedicated notch-making machine. The cantilever beam impact performance was determined according to ISO 180:2019 standard: using the aforementioned standard strip with the A-type notch (notch bottom radius r = 0.25 mm), an impact test was conducted on the notched side of the standard strip at room temperature using a pendulum impact testing machine, and the material's impact resistance was recorded.

[0057] 5. Thermal performance test (DSC): The melting point (Tm) and glass transition temperature (Tg) of the sample were determined using a differential scanning calorimeter.

[0058] Performance test results: 1. Performance test results of the lightweight copolyamide resin obtained in Example 1: (1) Density test: The intrinsic density of this copolynylon (lightweight copolyamide resin) is 1.08 g / cm³. 3 (significantly lower than the 1.14 g / cm³ of pure PA66) 3 ).

[0059] (2) RV determination: The RV of the lightweight copolyamide resin was determined to be 2.68, indicating that the system achieved efficient melt polycondensation during the vacuum stage and obtained the target product with high molecular weight, which laid the structural foundation for its excellent mechanical properties.

[0060] (3) Water absorption rate test: The saturated water absorption rate in deionized water at 23℃ is 2.1% (significantly lower than the 8.5% of pure PA66).

[0061] (4) Mechanical properties: tensile strength is 75 MPa, tensile modulus is 2.8 GPa, and notched impact strength is as high as 12.5 kJ / m. 2 (Exhibiting excellent resilience).

[0062] (5) Thermal properties: T m The temperature is 245℃, T g The temperature was 58℃. The data shows that despite the introduction of a large amount of flexible dimer acid, thanks to the synergistic support of the rigid furan ring, the glass transition temperature of the material only fluctuated slightly, and the phenomenon of a cliff-like drop in heat resistance as seen in traditional modifications did not occur. The processing window is wide and it also has excellent thermal dimensional stability.

[0063] 2. Performance test results of the lightweight copolyamide resin obtained in Example 2: (1) Density test: The intrinsic density decreased to 1.045 g / cm³. 3 .

[0064] (2) RV measurement: 2.48.

[0065] (3) Water absorption rate test: The saturated water absorption rate in deionized water at 23℃ is only 1.5%, and the dimensional stability is extremely excellent.

[0066] (4) Mechanical properties: tensile strength is 68 MPa, tensile modulus is 2.5 GPa, and notched impact strength is increased to 15.2 kJ / m. 2 .

[0067] (5) Thermal properties: T m The temperature is 232℃, T g The glass transition temperature is 53℃. Even with a very high proportion of fatty acid substitution, the material still maintains an excellent glass transition temperature above 50℃, fully meeting the high-temperature environment requirements of conventional engineering structural components.

[0068] 3. Performance test results of pure PA66 resin prepared in Comparative Example 1: (1) Density test: 1.141 g / cm³ 3 .

[0069] (2) RV measurement: 2.75.

[0070] (3) Water absorption rate test: The saturated water absorption rate in deionized water at 23℃ is 8.5%.

[0071] (4) Mechanical properties: The tensile strength in the dry state is 82 MPa, the tensile modulus is 3.1 GPa, and the notched impact strength is 5.5 kJ / m. 2 (It exhibits typical characteristics of high stiffness and low toughness).

[0072] (5) Thermal properties: T m The temperature is 262℃, T g The temperature is 60℃.

[0073] II. To verify the advantages of the lightweight, high-strength, low-water-absorption bio-based copolyamide of the present invention in practical engineering structural components, the lightweight copolyamide resin prepared in Example 1 and the pure PA66 resin prepared in Comparative Example 1 were respectively blended, extruded, and granulated with 30 wt% chopped glass fiber (CGF) in a twin-screw extruder, and then injection molded into standard test strips. The standard test strips were then tested, and the specific steps are as follows: Step 1, Specimen Preparation: The lightweight copolyamide resin prepared in Example 1 and the pure PA66 resin prepared in Comparative Example 1 were melt-blended and extruded with 30 wt% chopped glass fiber (CGF) in a twin-screw extruder to obtain the composite material of Example 1 (reinforced bio-based copolyamide composite material) and the composite material of Comparative Example 1, respectively. Subsequently, the composite material of Example 1 and the composite material of Comparative Example 1 were injection molded into multi-purpose test specimens (standard test specimens) conforming to ISO527 and ISO180 standards, respectively. Step 2, “Drying” treatment: Place the injection-molded standard test strip in an 80℃ vacuum drying oven for 24 hours to completely remove residual moisture from the sample. After removal, place it in a desiccator to cool to 23℃ room temperature for later use.

[0074] Step 3, "Water Saturation" Treatment: Completely immerse another set of dried standard test samples in a constant-temperature water bath containing deionized water, and continuously boil them at 100℃ for 72 hours to force the material to reach water saturation. After removal, quickly transfer them to 23℃ deionized water for 1 hour to cool. Wipe off any surface water and immediately conduct mechanical and density tests.

[0075] Step 4, Test Standards: Density is determined according to ISO 1183-1 standard; tensile strength and tensile modulus of elasticity are determined according to ISO 527 standard; notched impact strength of cantilever beam is determined according to ISO 180 standard.

[0076] The test results are shown in Table 1: Table 1. Test results of the composite material of Example 1 and the composite material of Comparative Example 1. As shown in Table 1, under dry conditions, the density of the composite material in Example 1 is significantly lower than that of the composite material in Comparative Example 1, with a decrease of 0.08 g / cm³. 3 This achieved effective weight reduction. More importantly, after 72 hours of extreme boiling in water, the tensile strength of the composite material in Comparative Example 1 decreased by 40% (down to 105 MPa), while the tensile strength of the composite material in Example 1 remained at 152 MPa, with a strength retention rate of over 90%. This fully demonstrates that the material exhibits overwhelming dimensional stability and mechanical retention advantages in humid and hot environments, completely overcoming the industry-level pain point of traditional nylon materials "weakening when exposed to water."

[0077] In conclusion: This invention discloses a lightweight, high-strength, and low-water-absorption bio-based copolyamide with an ingenious structural design: the macromolecular backbone not only contains a highly hydrophobic long carbon chain branched network but also blocks an asymmetric rigid aromatic heterocyclic skeleton, resulting in significantly reduced intrinsic density and saturated water absorption. This invention cleverly combines the massive hydrophobic branches of dimer acid with the rigid asymmetric aromatic heterocycle of 2,5-furandicarboxylic acid, breaking the tight packing of nylon molecular chains to achieve significant density reduction while endowing the material with extremely low water absorption and excellent mechanical modulus.

[0078] This invention provides a lightweight, high-strength, low-water-absorption bio-based copolyamide with a mature synthesis process and ingenious structural design. It uses plant oil-based dimer acid to provide a large steric hindrance and hydrophobic barrier, and 2,5-furandicarboxylic acid structure to provide rigid support, thus achieving a "combination of rigidity and flexibility" at the molecular level to reduce density. In the preparation method of lightweight, high-strength, and low-water-absorption bio-based copolyamide: hexamethylenediamine and mixed dicarboxylic acids (adipic acid, hydrogenated dimer acid, and 2,5-furandicarboxylic acid) are dispersed in deionized water in a specific ratio, and a uniform and stable mixed nylon salt solution is formed through acid-base neutralization reaction; in a closed high-pressure reactor, the nylon salt is dissociated and undergoes a preliminary amidation condensation reaction by utilizing the high temperature and the pressure of the generated water vapor, forming oligomers with well-closed end groups; by depressurizing and removing the by-product water, a vacuum system is introduced, and the condensation chemical equilibrium is forcibly shifted to the right at a temperature higher than the polymer melting point, rapidly increasing the molecular weight and melt viscosity of the polymer, and finally obtaining lightweight, high-strength, and low-water-absorption bio-based copolyamide.

[0079] This invention discloses a lightweight, high-strength, low-water-absorption bio-based copolyamide, its preparation method, and its application. Its beneficial effects are as follows: (1) Significant lightweight breakthrough: The massive long carbon chain support of dimer acid and the "micro-bending" conformation of the asymmetric five-membered ring of 2,5-furandicarboxylic acid form a "double-destructive crystallization" effect, forcibly increasing the molecular chain spacing. The intrinsic density of the lightweight, high-strength, low-water-absorption bio-based copolyamide of this invention is 1.04~1.08 g / cm³. 3 Therefore, the intrinsic density of the material can be calculated from 1.14 g / cm³. 3 Reduced to 1.04~1.08 g / cm³ 3 This achieves an essential weight reduction for nylon materials; (2) Dramatic reduction in water absorption rate: The super-hydrophobic hydrocarbon skeleton of dimer acid with up to 36 carbon atoms forms a natural water barrier inside the material. The saturated water absorption rate of the lightweight, high-strength, and low-water-absorption bio-based copolymer polyamide drops sharply from 8.5% of traditional PA66 to 1.5%~2.5%, completely solving the problems of nylon's dimensional instability and softening due to water absorption; (3) Mechanical balance of “rigidity and flexibility”: The rigid furan ring of 2,5-furandicarboxylic acid serves as a “hard skeleton”, which perfectly compensates for the modulus loss caused by the introduction of aliphatic dimer acid, so that the material can maintain excellent tensile strength and extremely high impact toughness at very low density. (4) Green and sustainable: The large-scale introduction of plant oil-based dimer acid and fructosyl 2,5-furandicarboxylic acid monomers has significantly reduced the dependence on traditional petrochemical resources.

[0080] In summary, the lightweight, high-strength, low-water-absorption bio-based copolyamide of the present invention and its preparation method have broad application prospects.

Claims

1. A lightweight, high-strength, low-water-absorption bio-based copolyamide, characterized in that, Compounds with structural formulas as shown in formula (I) and their racemates, stereoisomers, or tautomers: （I）； In formula (I), x takes values ​​of 15 to 25, y takes values ​​of 50 to 70, and z takes values ​​of 15 to 25.

2. The lightweight, high-strength, low-water-absorption bio-based copolyamide according to claim 1, characterized in that, The intrinsic density of the lightweight, high-strength, low-water-absorption bio-based copolyamide is 1.04~1.08 g / cm³. 3 ; And / or, the saturated water absorption rate of the lightweight, high-strength, low-water-absorption bio-based copolyamide is 1.5%~2.1%; And / or, the relative viscosity of the lightweight, high-strength, low-water-absorption bio-based copolyamide in a 96% sulfuric acid system is 2.3~3.2; And / or, the lightweight, high-strength, low-water-absorption bio-based copolyamide has a tensile strength of 68 MPa~75 MPa, a tensile modulus of 2.5~2.8 GPa, and a notched impact strength of 12.5 kJ / m. 2 ~15.2kJ / m 2 The bottom radius of the notch is 0.25 mm.

3. The method for preparing the lightweight, high-strength, low-water-absorption bio-based copolyamide as described in claim 1 or 2, characterized in that, The reaction equations for the preparation process are shown in equations (II), (III), (IV), and (V): (II); (III); (IV); （V）； In formula (V), x takes values ​​of 15 to 25, y takes values ​​of 50 to 70, and z takes values ​​of 15 to 25.

4. The preparation method according to claim 3, characterized in that, Includes the following steps: S1. Using hexamethylenediamine and mixed dicarboxylic acids as raw materials, they are mixed in a solvent to carry out a mixed salt formation reaction to obtain a mixed nylon salt aqueous solution; S2. Under the protection of an inert gas, the mixed nylon salt aqueous solution is subjected to a pre-condensation reaction to obtain oligomers; S3. Under reduced pressure and increased temperature, the oligomer is subjected to a final polycondensation reaction to obtain a lightweight, high-strength, low-water-absorption bio-based copolymer polyamide.

5. The preparation method according to claim 4, characterized in that, The mixed dicarboxylic acid includes adipic acid, hydrogenated dimer acid, and 2,5-furandicarboxylic acid; The solvent is selected from deionized water; The temperature for the salt-forming reaction is 60℃~90℃, and the time is 1.5h~2.5h. The pH value of the mixed nylon salt aqueous solution is 7.5~8.

5.

6. The preparation method according to claim 4, characterized in that, The inert gas is selected from nitrogen or argon; The conditions for the pre-condensation reaction include: a reaction temperature of 210℃~230℃, a reaction pressure of 1.5 MPa~2.5 MPa, and a reaction time of 1h~2h; And / or, the conditions for the final polycondensation reaction include: a reaction temperature of 260℃~280℃, a reaction pressure of -0.05 MPa~-0.09 MPa, and a reaction time of 0.5h~1.5h.

7. The preparation method according to claim 4, characterized in that, The equimolar ratio of hexamethylenediamine and the mixed dicarboxylic acid is 1~1.02:1; And / or, in the mixed dicarboxylic acids, the adipic acid accounts for 40 mol% to 80 mol%, the hydrogenated dimer acid accounts for 5 mol% to 30 mol%, and the 2,5-furandicarboxylic acid accounts for 5 mol% to 30 mol% by molar amount.

8. The application of a lightweight, high-strength, low-water-absorption bio-based copolyamide prepared by the preparation method according to any one of claims 3 to 7 in the preparation of lightweight copolyamide resins, characterized in that, The preparation method of the lightweight copolyamide resin includes the following steps: Under normal pressure conditions, the lightweight, high-strength, low-water-absorption bio-based copolyamide is melted, cooled, and pelletized and dried to obtain a lightweight copolyamide resin.

9. The application of a lightweight, high-strength, low-water-absorption bio-based copolyamide prepared by the preparation method according to any one of claims 3 to 7 in the preparation of reinforced bio-based copolyamide composite materials, characterized in that, The raw materials for the reinforced bio-based copolyamide composite material include: lightweight, high-strength, low-water-absorption bio-based copolyamide and reinforcing filler; the reinforcing filler is selected from chopped glass fibers.

10. The application of a lightweight, high-strength, low-water-absorption bio-based copolyamide prepared by the preparation method according to any one of claims 3 to 7 in the preparation of lightweight engineering plastic products, characterized in that, The lightweight engineering plastic products include non-load-bearing structural components for new energy vehicles and non-load-bearing structural components for aircraft.

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